Hybrid Organic-Inorganic Dielectric Bragg Mirrors, and Methods of Use Thereof

RELATED APPLICATIONS This application claims the benefit of priority to United States Provisional Patent

Application serial number 60/994,350, filed September 19, 2007, which is hereby incorporated by reference in its entirety.

GOVERNMENT SUPPORT

The inventions were made with support provided by the US Army Research Office (Contract DAAD- 19-02-0002, Project No. 6897309) and DARPA (Grant No. FA-9550-05- 1-0056, Project No. 6898417). Therefore, the government has certain rights in the inventions.

BACKGROUND

A distributed Bragg reflector (DBR) is a periodic grating that can be formed from alternating layers of differing index of refraction. DBRs have applications in various optic devices, in part because DBRs can achieve a high reflectivity in a relatively compact space. The performance of DBRs (e.g., bandwidth and reflectivity) improves with the index contrast of the materials used to form the DBR; that is, the performance improves when one material has a high index of refraction, and the other material has a low index. However, losses also increase as a consequence of light diffraction in the low-index regions.

Conventional solutions for reducing losses are usually either reduction of index contrast, or an excessive shortening of the low-index region, both leading to a decrease in device performance. In order to provide high reflectivity in small sizes, diffraction losses must be reduced to a minimum. Examples of devices that have incorporated DBRs include tunable optic filters, tunable detectors, and surface emitting lasers including vertical cavity surface emitting lasers (VCSEL).

The reflectivity of a DBR is a function of both its geometry and the relative difference between the index of refraction of the layers. The relative difference in the index of refraction of two materials is referred to as the index contrast. Generally, the reflectivity increases as the index contrast between layers increases and as the number of layers of the DBR increases. Also, the stop band width of the DBR increases as the index contrast increases.

A DBR can be formed from layers of semiconductor or dielectric materials layered together using known semiconductor fabrication techniques. For example, indium gallium arsenide phosphide (InGaAsP) can be layered together with indium phosphide (InP) (InGaAsP/InP DBR). Because the index of contrast between InGaAsP and InP is relatively small, on the order of 0.18, the number of layers needed to achieve a given reflectivity is high. Also, the stopband width is relatively small. In another example, silicon dioxide (SiO ₂ ) and titanium dioxide (TiO ₂ ) can be layered together (SiO ₂ /TiO ₂ DBR). SiO ₂ and TiO ₂ have a high index of contrast, on the order of 0.77, so relatively fewer layers are needed to achieve the same reflectivity. In comparison to a InGaAsP/InP DBR, a SiO ₂ /TiO ₂ DBR can be more compact while achieving the same reflectivity. This combination also has a broader stopband width than an InGaAsP/InP DBR.

In addition, air/semiconductor DBRs can be formed where layers of a semiconductor material, such as InP, are spaced apart by air gaps. Air and InP have a high index contrast of 2.2. An air/semiconductor DBR can achieve a high reflectivity with a relatively small number of layers over a broad stopband width because the index contrast between most semiconductor materials and air is large. In comparison with a InGaAsP/InP DBR or a SiO ₂ /TiO ₂ DBR, the air/semiconductor DBR can be the most compact at a given reflectivity.

Bragg reflectors are also be found in nature. For example, fascinating structural coloration effects are observed in animals possessing iridophores, cells which contain stacks of thin platelets separated by gel-like cytoplasm. Parker, A. R. 515 million years of structural color. J. Opt. A: Pure Appl. Opt. 2, R15-R28, (2000); Mathger, L. M., Land, M. F., Siebeck, U. E., Marshall, N. J. Rapid color changes in multilayer reflecting stripes in the paradise whiptail, pentapudos paradiseus. J. Exp. Biol. 206, 3607-3613 (2003); Land, M. F. A multilayer interference reflector in the eye of the scallop. Pecten maximus. J. Exp. Biol. 45, 433-447 (1966); Mathger, L. M., Denton, E. J. Reflective properties of iridophores and fluorescent eyespots in the loliginid squid alloteuthis subulata and loligo vulgaris. J. Exp. Biol. 204, 2103-2118 (2001); Ltythgoe, J. N., Shand, J. The structural basis for iridescent color changes in dermal and corneal iridophores in fish. J. Exp. Biol. 141, 313-325 (1989); and Vukusic, P. in Optical Interference Coatings (eds. Kaiser, N. and Pulker, H.K.) 1-34, Springer, New York (2003). Ideally, the thickness of each platelet and the cytoplasm separating them is regulated such that the reflections from each interface interfere constructively, generating a well known one dimensional photonic structure, a Bragg

mirror. The eye of a scallop, Pecten maximus, contains 30-40 layers of high index material guanine (n = 1.83) separated by low index cytoplasm (n = 1.33). The distinctive reflective stripes of a tropical fish Paradise whiptail are also made up of guanine-cytoplasm based iridophores and rapid (about 0.25 s) and reversible color transitions are caused by swelling and shrinking of spaces between the guanine plates, induced by osmotic movements of water in cytoplasm. Natural photonic structures, such as those observed in butterfly scales can have highly selective vapor response to individual vapors and hence potential technological applications for sensing. Potyrailo, R. A., Ghiradella, H., Vertiatchikh, A., Dovidenko, J. R., Cournoyer, J. R., Olson, E. Morpho butterfly wing scales demonstrate highly selective vapour response. Nature Photonics 1, 123-128 (2007).

As mentioned above, Bragg reflectors and other specialized optical filters have been manufactured commercially using inorganic materials on rigid substrates. See, also, Friz, M., Waibel, F. in Optical Interference Coatings (eds. Kaiser, N. and Pulker, H.K.) 105-130, Springer, New York (2003). Typically, layer thicknesses are precisely controlled by vapor deposition, a synthesis method capable of giving high growth rates uniformity over large areas. Rancourt, J. D. Optical thin films 24-30, SPIE Opt. Eng. Press, Washington (1996).

Use of organic materials for the layers used to fabricate DBRs has allowed the creation of deformable and tunable photonic structures. Monch, W., Denhert, J., Prucker, O., Ruhe, J., Zappe, H. Tunable Bragg filters based on polymer swelling. Applied optics 45, 18, 4284-4290 (2006); Ho, P. K. H., Thomas, D. S., Friend, R. H., Tessler, N. All-polymer optoelectronic devices. Science 285, 233-236 (1991); and Convertino, A., Capobianchi, A., Valentini, A., Cirillo, E. N. M. A new approach to organic solvent detection: High reflectivity Bragg reflectors based on a gold nanoparticle/Teflon®-like composite material. Advanced Materials 15, 13, 1103-1105 (2003). However, the refractive index contrast in organic mirrors is often low, necessitating a large numbers of layers to achieve high reflectivity. Ho, P. K. H., Thomas, D. S., Friend, R. H., Tessler, N. All-polymer optoelectronic devices. Science 285, 233-236 (1991). Additionally, crosslinking of the adjacent polymer layers is necessary to prevent dissolution during the wet fabrication processes, which further decreases the index contrast. The resultant thick and highly crosslinked structures introduce diffusion limitations on the response time during swelling and shrinkage cycles. In a recent study, the duration required for a complete shift in an all- organic Bragg structure in the reflectance band in the presence of an organic solvent was several tens of hours. Monch, W., Denhert, J., Prucker, O., Ruhe, J., Zappe, H. Tunable

Bragg filters based on polymer swelling. Applied Optics 45, 18, 4284-4290 (2006). Convertino and co-workers showed the possibility of tunable hybrid Bragg reflectors made from Teflon® and gold as promising sensing elements. Convertino, A., Capobianchi, A., Valentini, A., Cirillo, E. N. M. A new approach to organic solvent detection: High reflectivity Bragg reflectors based on a gold nanoparticle/Teflon®-like composite material. Advanced Materials 15, 13, 1103-1105 (2003). The presence of metal clusters significantly improves the solvent absorbing power of the organic Teflon® part, which is normally inert and completely insoluble. The resultant hybrid structures showed much better optical performance compared to the all-organic structures. However, the time required for complete band shift was about 20 min, which is still far slower than observed in living species. Furthermore, the presence of the metal clusters renders these structures unusable in the visible range.

Alternatively, tunable Bragg diffractors in the form of micro or nanoarrays of spherical particles embedded within appropriate polymer have been presented previously by many researchers. Volume change of the embedded media, or the polymer matrix, with the use of an external effect, such as solvent swelling, pH, or temperature change allowed them to be used for various sensor applications. Blanford, C. F.; Schroden, R. C; Al-Daous, M.; Stein, A. Adv. Mater. 2001, 13, 26; Holtz, J. H.; Asher, S. A. Nature 1997, 389, 829; and Fudouzi, H.; Xia, Y. AdV. Mater. 2003, 15, 892. Asher and co-workers produced metal ion and glucose responsive sensors from crystalline colloidal array of polymer spheres polymerized within a hydrogel. Using a similar swelling-shrinkage mechanism, Fudouzi and Xia demonstrated the potential of color writing using totally colorless materials.

Thus, there is a need for an improved hybrid organic-inorganic dielectric Bragg mirrors, and method of fabricating and using the same. SUMMARY

One aspect of the invention relates to tunable Bragg structures, and methods of making them using chemical vapor deposition (CVD) methodologies. In certain embodiments, a Bragg structure of the invention comprises a plurality of alternating organic and inorganic layers on a substrate. For example, an exemplary hybrid organic-inorganic multilayer thin film in accordance with the invention includes one or more first layers interstitially spaced between two or more second layers. Compositions of the invention may also have more than two types of layers. In certain embodiments, the Bragg structures of the invention are flexible, tunable, and exhibit rapid switching. In certain embodiments,

the Bragg structures of the invention are comprised of alternating layers of titania and poly(2-hydroxyethyl methacrylate).

Remarkably, the methods disclosed herein allow hybrid organic-inorganic multilayer thin films to be produced at nanometer scale, on a wide range of substrates, via a single stage vapor deposition method. The flexibility and durability of hybrid organic- inorganic films disclosed herein may allow them to serve in many different areas, including, in certain embodiments, organic vapor detection systems. In addition, in certain embodiments, the easy and precise control of the layer thicknesses may allow the production of advanced filter designs. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 depicts a TEM image of a 9-layer stack of titania-pHEMA deposited on (100) P-type silicon wafer. Dark layers are titania and white layers are pHEMA.

Figure 2 depicts hybrid Bragg structures deposited on various substrates: (a) Microscope glass (2.5 x 5 cm); (b) Quartz (2 cm in diameter); (c) Polycarbonate (2 x 5 cm); and (d) Red paper (1.5 x 3 cm).

Figure 3 depicts (a) experimental and theoretical reflectivity responses of a seven- layer titania (H)-pHEMA (L) hybrid structure in dry (I) and in swollen phases (II and III, corresponding to 6.7 and 10 mol% water vapor, respectively; dashed lines near Curve I and Curve II correspond to the reversed states); and (b) the schematic multilayer structure with designed optical parameters (I), and experimentally observed optical parameters after swelling (n represents refractive index and d represents thickness; the colored boxes under columns I, II, and III are the actual images cropped from the quartz window photographs taken during dry and swollen states, respectively).

Figure 4 depicts photographs of (a) the color change of the coated window (see Figure 2b) in the swelling cell with corresponding occurrence times Green phase (dry, as- deposited); (b) red phase caused by 1 mol% water vapor in N ₂ ; and (c) recovered green phase (after N ₂ purging).

Figure 5 depicts one embodiment of an iCVD reactor.

Figure 6 depicts a customized flexibility testing apparatus. Figure 7 depicts Ti _2p and Oi _s high-resolution XPS scans of the titania film deposited from HFCVD.

Figure 8 depicts an atomic force micrograph of the HFCVD titania film deposited on a Si wafer.

Figure 9 depicts FTIR absorbance spectrum of PHEMA film deposited from HFCVD.

Figure 10 depicts a graphs showing shift in the position of high reflectivity peak versus water vapor mole fraction (X ₀ = 460 nm for the dry film, δλ is the difference between the wavelength of the high reflectivity peak after and before exposure to the water vapor).

DETAILED DESCRIPTION

Certain aspects of the present application are drawn to Bragg reflectors and methods for fabricating and using the same. In certain embodiments, the Bragg reflector comprises a plurality of alternating organic and inorganic layers on a substrate. An exemplary Bragg reflector in accordance with the invention includes one or more first layers interstitially spaced between two or more second layers. While Bragg reflectors may be made from alternating layers of the same inorganic and organic materials (i.e., each inorganic layer has roughly the same composition, and each organic layer has roughly the same composition), variation between the inorganic layers and organic layers can also be incorporated. Just as the composition of each layer can be varied, so can the thickness of each layer. In certain embodiments, the Bragg reflectors of the invention are flexible, tunable, and exhibit rapid switching. In certain embodiments, by selectively swelling at least one of the organic layers, the properties of the Bragg reflector can be modified. For example, the fabrication of a flexible dielectric mirror of the invention, exhibiting a rapid and reversible biomimetic response, was achieved by alternating organic (poly(2-hydroxyethyl methacrylate; pHEMA) and inorganic (titania) layers. Remarkably, in the flexible dielectric mirror thus produced, tunable reflectance bands in the visible range resulted from the swelling of the uncrosslinked pHEMA layers in the presence of solvent vapors. The larger refractive index contrast of organic/inorganic stacks, as compared to that of all organic mirrors, was essential for achieving the desired reflectivity with the fewest number of layers. Minimizing the number of layers, and hence the overall the thickness of the dielectric mirror, serves to enhance the rate of diffusion of solvent into the swellable layers and hence results in rapid color switching. By this approach Bragg reflectors can be fabricated that are both flexible and have optimal performance characteristics.

In certain embodiments, taking advantage of the large refractive index difference between the organic and inorganic pairs, the final material is necessarily an extremely thin deformable multilayer film. For example, as described below, amorphous titania layers can

be deposited onto room-temperature substrates and in the absence of energetic ions by employing hot-wire chemical vapor deposition (HWCVD), and thus maintaining precisely the same hardware configuration as required for deposition of swellable pHEMA. In this way, precise layering of organic and inorganic materials at nanometer scale thickness was achieved in a single deposition chamber over large areas with high uniformity. HWCVD process also allows for precise control of the layer thicknesses using real-time interferometry or quartz crystal microbalance (QCM) techniques.

In addition, titanium dioxide, when deposited as a thin film, is an excellent optical coating for dielectric mirror application due to its high transparency and refractive index. Martinet, C; Paillard, V.; Gagnaire, A.; Joseph, J. J. Non-Cryst. Solids 1997, 216, 11. The lower refractive index layer comprises pHEMA, an optically clear flexible polymer. Vapor deposited pHEMA films swell with water to form hydrogel and further lowering refractive index. Chan, K.; Gleason, K. K. Langmuir 2005, 21, 8930. Many organic solvents also result in swelling of pHEMA. Goustouridis, D.; Chatzandroulis, S.; Raptis, L; Valamontes, E. S. In Proceedings of IEEE Sensors 2004, Third International Conference on Sensors, Vienna, Austria, Oct 24-27, 2004; IEEE: Piscataway, NJ, 2004; Vol. 1, p 162. The strong physical interaction between the hydroxyl group of polymer and Ti-O group of the inorganic matrix through hydrogen bonding prevents the swelling parallel to the substrate and confines the volume change in the swelling to one dimension, normal to the surface. Hu, Q.; Marand, E. Polymer 1998, 40, 4833. Hence, it is possible to tune the thickness of the low index pHEMA layer by water swelling, without affecting the optical thickness of the high refractive index inorganic layer, in precise analogy to the mechanism employed by iridophores in nature. DISTRIBUTED BRAGG REFLECTORS (DBRs) One aspect of the invention relates to a distributed Bragg reflector comprising a plurality of layers on a substrate (i.e., a multilayer stack), wherein each layer is independently selected from the group consisting of inorganic layers and organic layers.

While not attempting to limit the pattern of the plurality of layers on the substrate, it is noted that various combinations of inorganic and organic layers may be employed, where the inorganic layer is "I" and the organic layer is "O", as exemplified by the following embodiments: I/O, I/O/I, O/I/O, O/O/I, I/I/O, O/I/I, I/O/O, O/O/O/I, O/O/I/O, I/I/O/O, i/o/i/o, i/o/o/i, o/o/i/i, o/i/o/i, o/i/i/o, o/o/o/i, i/i/i/o, o/i/i/i, von/1, won, i/o/o/o,

O/I/O/O, O/O/I/O; wherein each "I" or "O" can be the same as, of different from, another

"I" or "O" in the composition. In addition, each DBR can comprise one repeating pattern, or a combination of patterns (such as one or more of those presented above), or no repeating pattern at all. The Bragg reflectors (i.e., multilayer stacks) can have symmetry and/or periodicity. Another aspect of the invention relates to a distributed Bragg reflector comprising a plurality of layers on a substrate, wherein each layer is independently selected from the group consisting of inorganic layers and organic layers; provided that the plurality of layers comprises alternating inorganic layers and organic layers. For example: I/O/I/O; wherein each "I" or "O" can be the same as, of different from, another "I" or "O" in the composition.

The inorganic layers used in the invention can comprise a wide range of inorganic materials. Each inorganic layer is independently selected and need not be identical. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers comprises a metal oxide. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers comprises a metal oxide, a metal carbide or a metal nitride. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein said metal is selected from the group consisting of Si, Nb, Ge, Sn, Pb, V, W, Y, Al, Cr, Mo, Ta, Ti, Zr, Hf, Mn, Pt, Pd, Ir, Rh, Ru and Co. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers comprises a transition metal oxide, a transition metal carbide or a transition metal nitride. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers comprises a transition metal oxide. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers comprises TiO ₂ , Ta ₂ Os, Nb ₂ Os, ZrO ₂ , Y ₂ O ₃ , AlO ₃ , SiO ₂ , or a mixture thereof. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers comprises TiO ₂ . For certain applications, the inorganic material will have a high transparency and/or a high refractive index. For example, it is known that titanium dioxide, when deposited as a thin film, is an excellent optical coating for dielectric mirror application due to its high transparency and refractive index. Martinet, C, Paillard, V., Gagnaire, A., Joseph, J.

Deposition of SiO ₂ and TiO ₂ thin films by plasma enhanced chemical vapor deposition for antireflection coatings. J. Noncrystalline Solids 216, 77-82 (1997). In certain embodiments, at least one of the inorganic layers serve as barrier layers.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers has a transparency of greater than about 80%. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers has a transparency of greater than about 85%. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers has a transparency of greater than about 90%. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers has a transparency of greater than about 95%. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers has a transparency of greater than about 98%.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers has a refractive index of between about 1 and about 8. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers has a refractive index of between about 2 and about 8. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers has a refractive index of between about 3 and about 8.

In certain embodiments, at least one of the inorganic layers further comprises an additive. In certain embodiments, the additive can modify the physical properties of the inorganic layer. For example, in certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers further comprises a carbon-containing compound. The incorporation of carbon into an inorganic layer can occur as a result of the inorganic precursor used (e.g., titanium tetra isopropoxide) in the deposition of at least one of the inorganic layers. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers further comprises about 10 mol% carbon. In certain embodiments, the present invention relates to an aforementioned

distributed Bragg reflector, wherein at least one of the inorganic layers further comprises about 20 mol% carbon. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers further comprises about 30 mol% carbon. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers further comprises between about 10 mol% carbon to about 30 mol% carbon. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the inorganic layers further comprises between about 1 mol% carbon to about 50 mol% carbon. The organic layers used in the distributed Bragg reflectors of the invention can comprise a wide range of organic materials. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers comprises a polymer. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers comprises a homopolymer. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers comprises a copolymer.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the polymers, homopolymers or copolymers which make up at least one of the organic layers have pendant functionality which can non- covalently bind to a metal atom. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the pendant functionality is a hydroxyl group. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the hydroxyl group is connected to the backbone of the polymer, homopolymer or copolymer by an alkylene moiety.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the polymers, homopolymers or copolymers which make up at least one of the organic layers are esters. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers comprises poly(acrylates), poly(methacrylates), or combinations thereof.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers comprises

polymerized monomers selected from the group consisting of ; wherein

X is alkylene; B is alkyl, cycloalkyl, heterocycloalkyl, alkenyl, alkynyl, aryl, heteroaryl, polycyclyl, halogen, hydroxyl, nitro, cyano, amine, alkylamine, acylamino, amido, carboxyl, carbamoyl, oxime, sulfhydryl, alkylthiol, sulfonate, sulfate, sulfanamido, sulfamoyl, sulfonyl, or sulfoxido; or X and B, taken together, are aryl or heteroaryl; and R ¹ is hydrogen or alkyl.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers comprises

polymerized monomers selected from the group consisting of

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers comprises

polymerized R ¹ monomers. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein X is -(CH ₂ ) _n -; and n is an integer from 1 to 10 inclusive.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein X is -CH ₂ -, -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, - CH ₂ CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ - or -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ -.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein X is -CH ₂ -, -CH ₂ CH ₂ -, or -CH ₂ CH ₂ CH ₂ -.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein X is -CH ₂ CH ₂ -.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein B is hydroxy.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein B is an epoxide. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein B is alkyl or cycloalkyl.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein B is heteroaryl.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein B is furyl.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein X and B, taken together, are aryl or heteroaryl.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein X and B, taken together, are aryl. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein X and B, taken together, are pentafluorophenyl

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein R ¹ is hydrogen or alkyl.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein R ¹ is hydrogen.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein R ¹ is methyl.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein X is -CH ₂ -, -CH ₂ CH ₂ -, or -CH ₂ CH ₂ CH ₂ -; B is -OH; and R ¹ is hydrogen or alkyl.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein X is -CH ₂ CH ₂ -; B is -OH; and R ¹ is methyl. In other words, in certain embodiments, at least one of the organic layers comprises pHEMA, an optically clear flexible polymer. For certain applications, at least one of the organic layers will have a high transparency and a low refractive index.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers has a transparency of

greater than about 80%. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers has a transparency of greater than about 85%. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers has a transparency of greater than about 90%. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers has a transparency of greater than about 95%. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers has a transparency of greater than about 98%. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers has a refractive index of between about 1 and about 8. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers has a refractive index of between about 1 and about 4. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one of the organic layers has a refractive index of between about 1 and about 2.

In certain embodiments, the properties of at least one of the organic layers can be modified by exposure to solvents which cause the layer to swell. For example, vapor deposited pHEMA films can be swelled with water to form a hydrogel and thereby further lower the refractive index of at least one of the organic layers. Chan, K., Gleason, K. K. Initiated chemical vapor deposition of linear and cross-linked poly(2-hydroxyethyl methacrylate) for use as thin film hydrogels. Langmuir 21, 19, 8930-8939 (2005). In addition, many organic solvents also result in swelling of pHEMA. Goustouridis, D., Chatzandroulis, S, Raptis, L, Valamontes, E. S. Modification of polymer swelling by UV irradiation for use in chemical sensing. Sensors, 2004 IEEE Proceedings 1, 162-165 (2004).

Interestingly, in certain embodiments, the strong physical interaction between at least one of the organic layers and metal-oxygen group of the inorganic matrix, through hydrogen bonding, prevents the swelling parallel to the substrate and confines the volume change in the swelling to one dimension, normal to the surface. Hu, Q., Marand, E. In situ formation of nanosized TiO ₂ domains within poly (amide-imide) by a sol-gel process. Polymer 40, 4833-4843 (1998). Therefore, as shown herein, it is possible to tune the thickness of a low index organic material layer (e.g., pHEMA) via swelling (e.g., with

water) without affecting the optical thickness of a high refractive index inorganic layer; this is in precise analogy to the mechanism employed by iridophores in nature.

Depending on the organic layer used, the DBRs of the invention can be used as sensors, and they can be made to swell only in the presence of certain compounds. In addition, if at least one of the organic layers comprises reactive functionalities, such as furyl, these functionalities can be used to selectively swell at least one of the organic layers, such as through Diels- Alder reactions. In the reaction of the reactive functionalities is reversible, then the swelling is reversible.

As discussed herein, distributed Bragg reflectors are a fundamental component of optical devices requiring an optical gain, such as various types of semiconductor lasers. While conventional vertical DBR's are formed from lattice-matched alternating semiconductor layered materials, these materials may provide a small difference in index of refraction between adjacent layers (depending on the semiconducting material used). As a result, a high number of pairs are required in a conventionally formed DBR to obtain desired reflectivities, e.g., about 25 to 40 pairs to attain reflectivities as high as 99.9%, depending on the difference of the index of refraction in adjacent layers. In addition, while these compositions may have good contrast properties, often they are not flexible, tunable or transparent enough for certain applications. However, remarkably, the large refractive index difference between the organic and inorganic layers in the DBRs described herein allows high reflectivity values with a much lower number of pairs, hence the resulting highly reflective structures can be extremely thin. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector comprises less than about twenty inorganic layers; and the distributed Bragg reflector comprises less than about twenty organic layers. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector comprises less than about fifteen inorganic layers; and the distributed Bragg reflector comprises less than about fifteen organic layers. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector comprises less than about five inorganic layers; and the distributed Bragg reflector comprises less than about five organic layers. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector comprises between five and fifteen

inorganic layers; and the distributed Bragg reflector comprises between five and fifteen organic layers.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector is usable in the visible range or IR range. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector is usable between about 100 nm to about 900 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector is usable between about 100 nm to about 200 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector is usable between about 200 nm to about 300 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector is usable between about 300 nm to about 400 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector is usable between about 400 nm to about 500 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector is usable between about 500 nm to about 600 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector is usable between about 600 nm to about 700 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector is usable between about 700 nm to about 800 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector is usable between about 800 nm to about 900 nm.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector exhibits rapid color switching. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector has a time required for a complete band shift; and the time required for a complete band shift is less than about 30 minutes. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the time required for a complete band shift is less than about 25 minutes. In certain embodiments, the present invention relates to an

aforementioned distributed Bragg reflector, wherein the time required for a complete band shift is less than about 20 minutes. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the time required for a complete band shift is less than about 15 minutes. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the time required for a complete band shift is less than about 10 minutes. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the time required for a complete band shift is less than about 5 minutes. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the time required for a complete band shift is less than about 1 minute.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the inorganic and the organic layers are not cross- linked.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector has a stop band width of between about 10 db and 30 db. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein the distributed Bragg reflector has a stop band width of about 20 db.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one inorganic layer has a first thickness; wherein the first thickness between about 1 nm and 1,000 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one inorganic layer has a first thickness; wherein the first thickness between about 50 nm and 500 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one inorganic layer has a first thickness; wherein the first thickness between about 100 nm and 500 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one inorganic layer has a first thickness; wherein the first thickness between about 200 nm and 400 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one inorganic layer has a first thickness; wherein the first thickness about 300 nm.

In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one organic layer has a second thickness;

wherein the second thickness between about 1 nm and 1,000 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one organic layer has a second thickness; wherein the second thickness between about 50 nm and 500 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one organic layer has a second thickness; wherein the second thickness between about 100 nm and 500 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one organic layer has a second thickness; wherein the second thickness between about 200 nm and 400 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein at least one organic layer has a second thickness; wherein the second thickness about 300 nm. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein said plurality of layers comprises at least 4 layers. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein said plurality of layers comprises at least 6 layers. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein said plurality of layers comprises at least 8 layers. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein said plurality of layers comprises at least 10 layers. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein said plurality of layers comprises at least 20 layers. In certain embodiments, the present invention relates to an aforementioned distributed Bragg reflector, wherein said plurality of layers comprises at least 50 layers.

In certain embodiments, chemical vapor deposition (CVD) is used to deposit the organic and/or inorganic layers. Use of CVD gives the freedom to select almost any type of substrate because CVD is a one-step, vacuum process which involves no solvents or volatiles. In addition, because in CVD monomers are converted directly to desired polymeric films, there is often no need for purification, drying, or curing steps. As shown in Figure 2, the ability to produce the hybrid multilayer structures at room temperature and in a solvent-free, dry atmosphere allows many different types of substrates to be coated. For example, microscope glass, quartz, polymer (polycarbonate, poly vinyl chloride and poly(dimethylsiloxane) sheets) and paper substrates may be coated. Remarkably, no

change on the visual appearance or on the structural integrity of the structures deposited on flexible substrates was observed even after hundreds of deformation events.

In certain embodiments, the present invention relates to an aforementioned Bragg reflector, wherein the substrate comprises glass, paper, plastic or metal. In certain embodiments, the present invention related to an aforementioned Bragg reflector, wherein the substrate comprises microscope glass, quartz, poly(carbonate), poly(vinyl chloride), poly(dimethylsiloxane), or paper. METHODS OF FABRICATION OF DISTRIBUTED BRAGG REFLECTORS

One aspect of the invention relates to a method of fabricating a distributed Bragg reflector comprising the step of depositing a plurality of layers on a substrate; wherein the plurality of layers comprises alternating inorganic layers and organic layers.

In certain embodiments, the hybrid hetero structures disclosed herein (i.e., the plurality of alternating inorganic and organic layers) were grown within a single chemical vapor deposition (CVD) chamber, resulting in smooth and uniform nanoscale layers of high interfacial quality. The resultant reflectors produce reversible optical responses which quantitative match predictive models. Additionally, during fabrication, the substrates remained at room temperature and were not exposed to solvents, which allowed for deposition onto deformable substrates, such as paper and plastics. Further, the CVD method is scalable to large areas and is analogous to commercially employed in the manufacture of rigid inorganic photonic devices. See, for example, Pulker, H. in Optical Interference Coatings (eds Kaiser, N. & Pulker, H. K.) 131-150, Springer, New York (2003).

In certain embodiments, inorganic layers can be deposited onto room temperature substrates, in the absence of energetic ions, by employing hot wire chemical vapor deposition (HWCVD), and thus maintaining precisely the same hardware configuration as required for deposition of organic layers. In this way, precise layering of organic and inorganic materials at nanometer scale thickness can be achieved in a single deposition chamber over large areas with high uniformity. The HWCVD approach is capable of producing smooth and uniform surfaces within very short production times over large areas without any heat, radiation, or solvent damage on the substrate, which gives freedom to select almost any type of substrates including papers, plastics, glasses, etc.

In certain embodiments, at least one of the organic layers can be deposited onto room temperature substrates by employing initiated chemical vapor deposition (iCVD).

iCVD generally takes place in a reactor. In certain embodiments, the surface to be coated is placed on a stage in the reactor and gaseous precursor molecules are fed into the reactor; the stage may be the bottom of the reactor and not a separate entity (see, e.g., Figure 5).

The iCVD process can take place at a range of pressures from atmospheric pressure to low vacuum. In certain embodiment, a low operating pressure, typically in the range of about 10 Pa to about 100 Pa, can provide an ideal environment for the coating extremely fine objects. In certain embodiments, the pressure is less than about 1 torr; in yet other embodiments, the pressure is less than about 0.7 torr or less than about 0.4 torr. In other embodiments, the pressure is about 1 torr; or about 0.7 torr; or about 0.4 torr. The flow rate of the monomer into the reactor can be adjusted in the iCVD method.

In certain embodiments, the monomer flow rate is about 10 seem. In other embodiments, the flow rate is less than about 10 seem. In certain embodiments, the monomer flow rate is about 5 seem. In other embodiments, the flow rate is less than about 5 seem. In certain embodiments, the monomer flow rate is about 3 seem. In other embodiments, the flow rate is less than about 3 seem. In certain embodiments, the monomer flow rate is about 1.5 seem. In other embodiments, the flow rate is less than about 1.5 seem. In certain embodiments, the monomer flow rate is about 0.75 seem. In other embodiments, the flow rate is less than about 0.75 seem. When more than one monomer is used (i.e., to deposit copolymers), the flow rate of the additional monomers, in certain embodiments, may be the same as those presented above.

In certain embodiments, a gaseous initiator is used to start the polymerization of the monomer. As used herein, "gaseous" initiator encompasses initiators which may be liquids or solids at STP, but upon heating may be vaporized and fed into the chemical vapor deposition reactor. In certain embodiments, the gaseous initiator of the instant invention is selected from the group consisting of compounds of formula I: A^L-A ² , wherein, independently for each occurrence, A ¹ is hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, aralkyl or heteroaralkyl; L is -O-O- or -N=N-; and A ² is hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, aralkyl or heteroaralkyl. In certain embodiments, the gaseous initiator of the instant invention is a compound of formula I, wherein A ¹ is alkyl. In certain embodiments, the gaseous initiator of the instant invention is a compound of formula I, wherein A ¹ is hydrogen or alkyl. In certain embodiments, the gaseous initiator of the instant invention is a compound of formula I, wherein A ¹ is hydrogen. In certain embodiments, the gaseous

initiator of the instant invention is a compound of formula I, wherein A ² is alkyl. In certain embodiments, the gaseous initiator of the instant invention is a compound of formula I, wherein L is -0-0- . In certain embodiments, the gaseous initiator of the instant invention is a compound of formula I, wherein L is -N=N-. In certain embodiments, the gaseous initiator of the instant invention is a compound of formula I, wherein A ¹ is -C(CH ₃ ) ₃ ; and A ² is -C(CH ₃ ) ₃ . In certain embodiments, the gaseous initiator of the instant invention is a compound of formula I, wherein A ¹ is -C(CH ₃ ) ₃ ; L is -O-O-; and A ² is -C(CH ₃ ) ₃ . In certain embodiments, the gaseous initiator is selected from the group consisting of hydrogen peroxide, alkyl or aryl peroxides (e.g., tert-butyl peroxide), hydroperoxides, halogens and nonoxidizing initiators, such as azo compounds (e.g., bis(l,l-dimethyl)diazene).

The flow rate of the initiator can be adjusted in the iCVD method. In certain embodiments, the initiator flow rate is about 10 seem. In other embodiments, the flow rate is less than about 10 seem. In certain embodiments, the initiator flow rate is about 5 seem. In other embodiments, the flow rate is less than about 5 seem. In certain embodiments, the initiator flow rate is about 3 seem. In other embodiments, the flow rate is less than about 3 seem. In certain embodiments, the initiator flow rate is about 1.5 seem. In other embodiments, the flow rate is less than about 1.5 seem. In certain embodiments, the initiator flow rate is about 0.75 seem. In other embodiments, the flow rate is less than about 0.75 seem. The temperature of the filament can be adjusted in the iCVD method. In certain embodiments, the temperature of the filament is about 350 ⁰ C. In certain embodiments, the temperature of the filament is about 300 ⁰ C. In certain embodiments, the temperature of the filament is about 250 ⁰ C. In certain embodiments, the temperature of the filament is about 245 ⁰ C. In certain embodiments, the temperature of the filament is about 235 ⁰ C. In certain embodiments, the temperature of the filament is about 225 ⁰ C. In certain embodiments, the temperature of the filament is about 200 ⁰ C. In certain embodiments, the temperature of the filament is about 150 ⁰ C. In certain embodiments, the temperature of the filament is about 100 ⁰ C.

The iCVD coating process can take place at a range of temperatures. In certain embodiments, the temperature is ambient temperature. In certain embodiments, the temperature is about 25 ⁰ C; in yet other embodiments, the temperature is between about 25 ⁰ C and 100 ⁰ C, or between about 0 ⁰ C and 25 ⁰ C. In certain embodiments said temperature is controlled by a water bath.

In certain embodiments, the rate of polymer deposition is about 1 micron/minute. In certain embodiments, the rate of polymer deposition is between about 1 micron/minute and about 50 nm/minute. In certain embodiments, the rate of polymer deposition is between about 10 micron/minute and about 50 nm/minute. In certain embodiments, the rate of polymer deposition is between about 100 micron/minute and about 50 nm/minute. In certain embodiments, the rate of polymer deposition is between about 1 nm/minute and about 50 nm/minute. In certain embodiments, the rate of polymer deposition is between about 10 nm/minute and about 50 nm/minute. In certain embodiments, the rate of polymer deposition is between about 10 nm/minute and about 25 nm/minute. In certain embodiments, the present invention relates to an aforementioned method, further comprising the step of exposing the distributed Bragg reflector to a solvent vapor thereby causing at least one of the organic layers to swell.

In certain embodiments, the present invention relates to an aforementioned method, wherein upon exposure to solvent vapor at least one of the organic layers substantially swells in less than about 20 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein upon exposure to solvent vapor at least one of the organic layers substantially swells in less than about 15 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein upon exposure to solvent vapor at least one of the organic layers substantially swells in less than about 10 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein upon exposure to solvent vapor at least one of the organic layers substantially swells in less than about 5 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein upon exposure to solvent vapor at least one of the organic layers substantially swells in less than about 1 minute. In certain embodiments, the present invention relates to an aforementioned method, wherein upon exposure to solvent vapor at least one of the inorganic layers does not swell.

In certain embodiments, the present invention relates to an aforementioned method, wherein the response time between shrinkage and swelling is less than about 20 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein the response time between shrinkage and swelling is less than about 15 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein the response time between shrinkage and swelling is less than about 10 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein the

response time between shrinkage and swelling is less than about 5 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein the response time between shrinkage and swelling is less than about 1 minutes.

In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers comprises a metal oxide, a metal carbide or a metal nitride. In certain embodiments, the present invention relates to an aforementioned method, wherein said metal is selected from the group consisting of Si, Nb, Ge, Sn, Pb, V, W, Y, Al, Cr, Mo, Ta, Ti, Zr, Hf, Mn, Pt, Pd, Ir, Rh, Ru and Co. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers comprises a transition metal oxide, a transition metal carbide or a transition metal nitride. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers comprises a transition metal oxide. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers comprises TiO ₂ , Ta ₂ Os, Nb ₂ Os, ZrO ₂ , Y ₂ O ₃ , AlO ₃ , SiO ₂ , or a mixture thereof. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers comprises TiO ₂ .

In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers has a transparency of greater than about 80%. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers has a transparency of greater than about 85%. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers has a transparency of greater than about 90%. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers has a transparency of greater than about 95%. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers has a transparency of greater than about 98%.

In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers has a refractive index of between about 1 and about 8. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers has a refractive index of between about

2 and about 8. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers has a refractive index of between about

3 and about 8.

In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers further comprises about 10 mol% carbon. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers further comprises about 20 mol% carbon. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers further comprises about 30 mol% carbon. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers further comprises between about 10 mol% carbon to about 30 mol% carbon. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the inorganic layers further comprises between about 1 mol% carbon to about 50 mol% carbon.

In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers comprises a polymer. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers comprises a homopolymer. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers comprises a copolymer.

In certain embodiments, the present invention relates to an aforementioned method, wherein the polymers, homopolymers or copolymers which make up at least one of the organic layers have pendant functionality which can non-covalently bind to a metal atom. In certain embodiments, the present invention relates to an aforementioned method, wherein the pendant functionality is a hydroxyl group. In certain embodiments, the present invention relates to an aforementioned method, wherein the hydroxyl group is connected to the backbone of the polymer, homopolymer or copolymer by an alkylene moiety. In certain embodiments, the present invention relates to an aforementioned method, wherein the polymers, homopolymers or copolymers which make up at least one of the organic layers are esters. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers comprises poly(acrylates), poly(methacrylates), or combinations thereof. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers comprises polymerized monomers selected from

heterocycloalkyl, alkenyl, alkynyl, aryl, heteroaryl, polycyclyl, halogen, hydroxyl, nitro, cyano, amine, alkylamine, acylamino, amido, carboxyl, carbamoyl, oxime, sulfhydryl, alkylthiol, sulfonate, sulfate, sulfanamido, sulfamoyl, sulfonyl, or sulfoxido; or X and B, taken together, are aryl or heteroaryl; and R ¹ is hydrogen or alkyl.

In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers comprises polymerized monomers selected from

the group and

^B

R ¹

In certain embodiments, the present invention relates to an aforementioned method,

wherein at least one of the organic layers comprises polymerized monomers.

In certain embodiments, the present invention relates to an aforementioned method, wherein X is -(CH ₂ )D-; and n is an integer from 1 to 10 inclusive. In certain embodiments, the present invention relates to an aforementioned method, wherein X is -CH ₂ -, -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ - or -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ -.

In certain embodiments, the present invention relates to an aforementioned method, wherein X is -CH ₂ -, -CH ₂ CH ₂ -, or -CH ₂ CH ₂ CH ₂ -. In certain embodiments, the present invention relates to an aforementioned method, wherein X is -CH ₂ CH ₂ -.

In certain embodiments, the present invention relates to an aforementioned method, wherein B is hydroxy.

In certain embodiments, the present invention relates to an aforementioned method, wherein B is an epoxide.

In certain embodiments, the present invention relates to an aforementioned method, wherein B is alkyl or cycloalkyl.

In certain embodiments, the present invention relates to an aforementioned method, wherein B is heteroaryl. In certain embodiments, the present invention relates to an aforementioned method, wherein B is furyl.

In certain embodiments, the present invention relates to an aforementioned method, wherein X and B, taken together, are aryl or heteroaryl.

In certain embodiments, the present invention relates to an aforementioned method, wherein X and B, taken together, are aryl.

In certain embodiments, the present invention relates to an aforementioned method, wherein X and B, taken together, are pentafluorophenyl.

In certain embodiments, the present invention relates to an aforementioned method, wherein R ¹ is hydrogen or alkyl. In certain embodiments, the present invention relates to an aforementioned method, wherein R ¹ is hydrogen.

In certain embodiments, the present invention relates to an aforementioned method, wherein R ¹ is methyl.

In certain embodiments, the present invention relates to an aforementioned method, wherein X is -CH ₂ -, -CH ₂ CH ₂ -, or -CH ₂ CH ₂ CH ₂ -; B is -OH; and R ¹ is hydrogen or alkyl.

In certain embodiments, the present invention relates to an aforementioned method, wherein X is -CH ₂ CH ₂ -; B is -OH; and R ¹ is methyl. In other words, in certain embodiments, at least one of the organic layers comprises pHEMA, an optically clear flexible polymer. For certain applications, at least one of the organic layers will have a high transparency and a low refractive index.

In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers has a transparency of greater than about 80%. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers has a transparency of greater than about 85%. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers has a transparency of greater than about 90%. In certain embodiments, the present invention relates to an aforementioned method, wherein at least

one of the organic layers has a transparency of greater than about 95%. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers has a transparency of greater than about 98%.

In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers has a refractive index of between about 1 and about 8. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers has a refractive index of between about 1 and about 4. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one of the organic layers has a refractive index of between about 1 and about 2.

In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector comprises less than about twenty inorganic layers; and the distributed Bragg reflector comprises less than about twenty organic layers. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector comprises less than about fifteen inorganic layers; and the distributed Bragg reflector comprises less than about fifteen organic layers. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector comprises less than about five inorganic layers; and the distributed Bragg reflector comprises less than about five organic layers. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector comprises between five and fifteen inorganic layers; and the distributed Bragg reflector comprises between five and fifteen organic layers.

In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector is usable in the visible range or IR range. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector is usable between about 100 nm to about 900 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector is usable between about 100 nm to about 200 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector is usable between about 200 nm to about 300 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector is usable between about 300 nm to about 400 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein the

distributed Bragg reflector is usable between about 400 nm to about 500 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector is usable between about 500 nm to about 600 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector is usable between about 600 nm to about 700 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector is usable between about 700 nm to about 800 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector is usable between about 800 nm to about 900 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector exhibits rapid color switching. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector has a time required for a complete band shift; and the time required for a complete band shift is less than about 30 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein the time required for a complete band shift is less than about 25 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein the time required for a complete band shift is less than about 20 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein the time required for a complete band shift is less than about 15 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein the time required for a complete band shift is less than about 10 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein the time required for a complete band shift is less than about 5 minutes. In certain embodiments, the present invention relates to an aforementioned method, wherein the time required for a complete band shift is less than about 1 minute.

In certain embodiments, the present invention relates to an aforementioned method, wherein the inorganic and the organic layers are not cross-linked.

In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector has a stop band width of between about 10 db and 30 db. In certain embodiments, the present invention relates to an aforementioned method, wherein the distributed Bragg reflector has a stop band width of about 20 db.

In certain embodiments, the present invention relates to an aforementioned method, wherein at least one inorganic layer has a first thickness; wherein the first thickness between about 1 nm and 1 ,000 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one inorganic layer has a first thickness; wherein the first thickness between about 50 nm and 500 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one inorganic layer has a first thickness; wherein the first thickness between about 100 nm and 500 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one inorganic layer has a first thickness; wherein the first thickness between about 200 nm and 400 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one inorganic layer has a first thickness; wherein the first thickness about 300 nm.

In certain embodiments, the present invention relates to an aforementioned method, wherein at least one organic layer has a second thickness; wherein the second thickness between about 1 nm and 1,000 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one organic layer has a second thickness; wherein the second thickness between about 50 nm and 500 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one organic layer has a second thickness; wherein the second thickness between about 100 nm and 500 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one organic layer has a second thickness; wherein the second thickness between about 200 nm and 400 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein at least one organic layer has a second thickness; wherein the second thickness about 300 nm. In certain embodiments, the present invention relates to an aforementioned method, wherein said plurality of layers comprises at least 4 layers. In certain embodiments, the present invention relates to an aforementioned method, wherein said plurality of layers comprises at least 6 layers. In certain embodiments, the present invention relates to an aforementioned method, wherein said plurality of layers comprises at least 8 layers. In certain embodiments, the present invention relates to an aforementioned method, wherein said plurality of layers comprises at least 10 layers. In certain embodiments, the present invention relates to an aforementioned method, wherein said plurality of layers comprises at

least 20 layers. In certain embodiments, the present invention relates to an aforementioned method, wherein said plurality of layers comprises at least 50 layers.

In certain embodiments, the present invention relates to an aforementioned method, wherein the substrate comprises glass, paper, plastic or metal. In certain embodiments, the present invention relates to an aforementioned method, wherein the substrate comprises microscope glass, quartz, poly(carbonate), poly(vinyl chloride), poly(dimethylsiloxane), or paper. USE OF DISTRIBUTED BRAGG REFLECTORS

Distributed Bragg reflectors (DBRs) are frequently used simply as reflectors. Other applications include vertical-cavity surface-emitting lasers (VCSELs), as well as applications requiring filtering and wavelength division multiplexing (WDM). In addition, the distributed Bragg reflector (DBR) systems and methods discussed herein may be used, for example, with micro-electromechanical (MEMS) devices. The DBR systems and methods may also be used, for example, in spectrophotometers, photodetectors, tunable lasers, tunable semiconductor light-emitting-diodes, tunable organic light-emitting-diodes or any other device that uses DBRs without departing from the spirit and scope of the disclosure.

One aspect of the invention relates to an article comprising a distributed Bragg reflector comprising a plurality of layers on a substrate, wherein each layer is independently selected from the group consisting of inorganic layers and organic layers.

While not attempting to limit the pattern of the plurality of layers on the substrate, it is noted that various combinations of inorganic and organic layers may be employed, where the inorganic layer is "I" and the organic layer is "O", as exemplified by the following embodiments: I/O, I/O/I, O/I/O, O/O/I, I/I/O, O/I/I, I/O/O, O/O/O/I, O/O/I/O, I/I/O/O, I/O/I/O, I/O/O/I, O/O/I/I, O/I/O/I, O/I/I/O, O/O/O/I, I/I/I/O, O/I/I/I, VO/1/1, 1/I/O/I, I/O/O/O, O/I/O/O, O/O/I/O; wherein each "I" or "O" can be the same as, of different from, another "I" or "O" in the article. In addition, each DBR can comprise one repeating pattern, or a combination of patterns (such as one or more of those presented above), or no repeating pattern at all. Another aspect of the invention relates to an article comprising distributed Bragg reflector comprising a plurality of layers on a substrate, wherein each layer is independently selected from the group consisting of inorganic layers and organic layers; provided that the plurality of layers comprises alternating inorganic layers and organic layers. For example:

I/O/I/O; wherein each "I" or "O" can be the same as, of different from, another "I" or "O" in the article.

Another aspect of the invention relates to an article comprising a distributed Bragg reflector, wherein the plurality of layers wherein each layer is independently selected from the group consisting of inorganic layers and organic layers; provided that the plurality of layers comprises alternating inorganic layers and organic layers.

In certain embodiments, the present invention relates to an aforementioned article, wherein said article is a vertical-cavity surface-emitting laser or a micro-electromechanical (MEMS) device. In certain embodiments, the present invention relates to an aforementioned article, wherein said article is selected from the group consisting of spectrophotometers, photodetectors, tunable lasers, tunable semiconductor light-emitting-diodes, tunable organic light-emitting-diodes, eye protection (such as sun glasses), flexible displays, camouflaging materials, and window coverings (such as car windows and house windows). In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers comprises a metal oxide, a metal carbide or a metal nitride. In certain embodiments, the present invention relates to an aforementioned article, wherein said metal is selected from the group consisting of Si, Nb, Ge, Sn, Pb, V, W, Y, Al, Cr, Mo, Ta, Ti, Zr, Hf, Mn, Pt, Pd, Ir, Rh, Ru and Co. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers comprises a transition metal oxide, a transition metal carbide or a transition metal nitride. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers comprises a transition metal oxide. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers comprises TiO ₂ , Ta ₂ Os, Nb ₂ Os, ZrO ₂ , Y ₂ O ₃ , AlO ₃ , SiO ₂ , or a mixture thereof. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers comprises TiO ₂ .

In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers has a transparency of greater than about 80%. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers has a transparency of greater than about 85%. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers has a transparency of greater than about 90%. In certain

embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers has a transparency of greater than about 95%. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers has a transparency of greater than about 98%. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers has a refractive index of between about 1 and about 8. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers has a refractive index of between about 2 and about 8. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers has a refractive index of between about 3 and about 8.

In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers further comprises about 10 mol% carbon. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers further comprises about 20 mol% carbon. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers further comprises about 30 mol% carbon. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers further comprises between about 10 mol% carbon to about 30 mol% carbon. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the inorganic layers further comprises between about 1 mol% carbon to about 50 mol% carbon.

In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers comprises a polymer. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers comprises a homopolymer. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers comprises a copolymer.

In certain embodiments, the present invention relates to an aforementioned article, wherein the polymers, homopolymers or copolymers which make up at least one of the organic layers have pendant functionality which can non-covalently bind to a metal atom. In certain embodiments, the present invention relates to an aforementioned article, wherein the pendant functionality is a hydroxyl group. In certain embodiments, the present

invention relates to an aforementioned article, wherein the hydroxyl group is connected to the backbone of the polymer, homopolymer or copolymer by an alkylene moiety.

In certain embodiments, the present invention relates to an aforementioned article, wherein the polymers, homopolymers or copolymers which make up at least one of the organic layers are esters. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers comprises poly(acrylates), poly(methacrylates), or combinations thereof.

In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers comprises polymerized monomers selected from

wherein X is alkylene; B is alkyl, cycloalkyl, heterocycloalkyl, alkenyl, alkynyl, aryl, heteroaryl, polycyclyl, halogen, hydroxyl, nitro, cyano, amine, alkylamine, acylamino, amido, carboxyl, carbamoyl, oxime, sulfhydryl, alkylthiol, sulfonate, sulfate, sulfanamido, sulfamoyl, sulfonyl, or sulfoxido; or X and B, taken together, are aryl or heteroaryl; and R ¹ is hydrogen or alkyl.

In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers comprises polymerized monomers selected from

X.

^' B

\ R ¹ In certain embodiments, the present invention relates to an aforementioned article,

wherein at least one of the organic layers comprises polymerized monomers.

In certain embodiments, the present invention relates to an aforementioned article, wherein X is -(CH ₂ )D-; and n is an integer from 1 to 10 inclusive.

In certain embodiments, the present invention relates to an aforementioned article, wherein X is -CH ₂ -, -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ - or -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ -.

In certain embodiments, the present invention relates to an aforementioned article, wherein X is -CH ₂ -, -CH ₂ CH ₂ -, or -CH ₂ CH ₂ CH ₂ -.

In certain embodiments, the present invention relates to an aforementioned article, wherein X is -CH ₂ CH ₂ -. In certain embodiments, the present invention relates to an aforementioned article, wherein B is hydroxy.

In certain embodiments, the present invention relates to an aforementioned article, wherein B is an epoxide.

In certain embodiments, the present invention relates to an aforementioned article, wherein B is alkyl or cycloalkyl.

In certain embodiments, the present invention relates to an aforementioned article, wherein B is heteroaryl.

In certain embodiments, the present invention relates to an aforementioned article, wherein B is furyl. In certain embodiments, the present invention relates to an aforementioned article, wherein X and B, taken together, are aryl or heteroaryl.

In certain embodiments, the present invention relates to an aforementioned article, wherein X and B, taken together, are aryl.

In certain embodiments, the present invention relates to an aforementioned article, wherein X and B, taken together, are pentafluorophenyl.

In certain embodiments, the present invention relates to an aforementioned article, wherein R ¹ is hydrogen or alkyl.

In certain embodiments, the present invention relates to an aforementioned article, wherein R ¹ is hydrogen. In certain embodiments, the present invention relates to an aforementioned article, wherein R ¹ is methyl.

In certain embodiments, the present invention relates to an aforementioned article, wherein X is -CH ₂ -, -CH ₂ CH ₂ -, or -CH ₂ CH ₂ CH ₂ -; B is -OH; and R ¹ is hydrogen or alkyl.

In certain embodiments, the present invention relates to an aforementioned article, wherein X is -CH ₂ CH ₂ -; B is -OH; and R ¹ is methyl. In other words, in certain embodiments, at least one of the organic layers comprises pHEMA, an optically clear flexible polymer.

For certain applications, at least one of the organic layers will have a high transparency and a low refractive index.

In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers has a transparency of greater than about 80%. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers has a transparency of greater than about 85%. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers has a transparency of greater than about 90%. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers has a transparency of greater than about 95%. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers has a transparency of greater than about 98%.

In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers has a refractive index of between about 1 and about 8. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers has a refractive index of between about 1 and about 4. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one of the organic layers has a refractive index of between about 1 and about 2. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector comprises less than about twenty inorganic layers; and the distributed Bragg reflector comprises less than about twenty organic layers. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector comprises less than about fifteen inorganic layers; and the distributed Bragg reflector comprises less than about fifteen organic layers. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector comprises less than about five inorganic layers; and the distributed Bragg reflector comprises less than about five organic layers. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector comprises between five and fifteen inorganic layers; and the distributed Bragg reflector comprises between five and fifteen organic layers.

In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector is usable in the visible range or IR range. In certain

embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector is usable between about 100 nm to about 900 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector is usable between about 100 nm to about 200 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector is usable between about 200 nm to about 300 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector is usable between about 300 nm to about 400 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector is usable between about 400 nm to about 500 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector is usable between about 500 nm to about 600 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector is usable between about 600 nm to about 700 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector is usable between about 700 nm to about 800 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector is usable between about 800 nm to about 900 nm.

In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector exhibits rapid color switching. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector has a time required for a complete band shift; and the time required for a complete band shift is less than about 30 minutes. In certain embodiments, the present invention relates to an aforementioned article, wherein the time required for a complete band shift is less than about 25 minutes. In certain embodiments, the present invention relates to an aforementioned article, wherein the time required for a complete band shift is less than about 20 minutes. In certain embodiments, the present invention relates to an aforementioned article, wherein the time required for a complete band shift is less than about 15 minutes. In certain embodiments, the present invention relates to an aforementioned article, wherein the time required for a complete band shift is less than about 10 minutes. In certain embodiments, the present invention relates to an aforementioned article, wherein the time required for a complete band shift is less than about 5 minutes. In certain embodiments, the present invention relates to an

aforementioned article, wherein the time required for a complete band shift is less than about 1 minute.

In certain embodiments, the present invention relates to an aforementioned article, wherein the inorganic and the organic layers are not cross-linked. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector has a stop band width of between about 10 db and 30 db. In certain embodiments, the present invention relates to an aforementioned article, wherein the distributed Bragg reflector has a stop band width of about 20 db.

In certain embodiments, the present invention relates to an aforementioned article, wherein at least one inorganic layer has a first thickness; wherein the first thickness between about 1 nm and 1 ,000 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one inorganic layer has a first thickness; wherein the first thickness between about 50 nm and 500 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one inorganic layer has a first thickness; wherein the first thickness between about 100 nm and 500 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one inorganic layer has a first thickness; wherein the first thickness between about 200 nm and 400 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one inorganic layer has a first thickness; wherein the first thickness about 300 nm.

In certain embodiments, the present invention relates to an aforementioned article, wherein at least one organic layer has a second thickness; wherein the second thickness between about 1 nm and 1,000 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one organic layer has a second thickness; wherein the second thickness between about 50 nm and 500 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one organic layer has a second thickness; wherein the second thickness between about 100 nm and 500 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one organic layer has a second thickness; wherein the second thickness between about 200 nm and 400 nm. In certain embodiments, the present invention relates to an aforementioned article, wherein at least one organic layer has a second thickness; wherein the second thickness about 300 nm.

In certain embodiments, the present invention relates to an aforementioned article, wherein said plurality of layers comprises at least 4 layers. In certain embodiments, the present invention relates to an aforementioned article, wherein said plurality of layers comprises at least 6 layers. In certain embodiments, the present invention relates to an aforementioned article, wherein said plurality of layers comprises at least 8 layers. In certain embodiments, the present invention relates to an aforementioned article, wherein said plurality of layers comprises at least 10 layers. In certain embodiments, the present invention relates to an aforementioned article, wherein said plurality of layers comprises at least 20 layers. In certain embodiments, the present invention relates to an aforementioned article, wherein said plurality of layers comprises at least 50 layers.

In certain embodiments, the present invention relates to an aforementioned article, wherein the substrate comprises glass, paper, plastic or metal. In certain embodiments, the substrate comprises microscope glass, quartz, poly(carbonate), poly( vinyl chloride), poly(dimethylsiloxane), or paper. OTHER USE OF THE MULTILAYER STACK COMPOSITIONS OF THE INVENTION

While the compositions of the invention have been referred to a distributed Bragg reflectors, such reference was not intended to limit the inventive multilayer stacks to quarter-wave mirrors; the invention is intended to encompass all kinds of antireflective coatings/materials. For example, plasma CVD and liquid coating technologies have been used to build up multilayer stacks for "flexible electronics" (e.g., for barrier coatings for optoelectronic devices). See, for example, Creatore, M. et al. "Permeation barrier coatings for flexible electronics and polymer/inorganic layer interphase development in an expanding thermal plasma," XXVIIth ICPIG, Eindhoven, the Netherlands, 18-22 July, 2005, Topic number: 10; Schapkens, M. et al. "Ultrahigh barrier coating deposition on polycarbonate substrates," J. Vac. Sci. Technol. A. 2004, 22(4), 1716-1722; and Olsen, L. et al. "Barrier coatings for thin film solar cells," NCPV and Solar Program Meeting Review Meeting 2003, 911-913 (NREL/CD-520-33586). The inventive stacks described herein may also be used to make such barrier coatings (e.g., multilayer thin films for solar cells). An advantage to using the methods described herein to make such coatings is that the temperature is kept low (less than about 250 ⁰ C) and because of the flexibility of the materials produced roll to roll processing can be used.

In certain embodiments, the multilayer stacks of the invention are bandpass filters, Fabry-Perot filters, solid Fabry-Perot filters, narrow band dielectric filters, circular variable

filters, linear variable filters, reflex or phase conjugate filters, beam splitters (e.g., wideband or neutral density beam splitters, slab beam splitters, cube beam splitters), dichroic filters, trichoric filters, dark mirrors, selective absorbers, induced absorbers, solar absorbers, notch filters, transparent conductive coatings, patterned dielectric coatings, coatings from high-power laser beam reflectors, color correcting coatings, switching filters, emissivity reducing coatings or emissivity enhancing coatings. See, for example, Rancourt, J. D. "Optical Thin Films User Handbook," SPIE Optical Engineering Press, 1996, Chapter 4. DEFINITIONS

For convenience, definitions of certain terms employed in the specification, examples, and appended claims are collected here.

As used herein, the term "Bragg reflector" is a structure which consists of an alternating sequence of layers of two different optical materials. In certain embodiments, each optical layers thickness corresponds to one quarter of the wavelength for which the reflector is designed. Bragg reflectors are also known as dielectric mirrors or quarter-wave mirrors.

As used herein, the term "polymer" means a molecule, formed by the chemical union of two or more oligomer units. The chemical units are normally linked together by covalent linkages. The two or more combining units in a polymer can be all the same, in which case the polymer is referred to as a homopolymer. They can be also be different and, thus, the polymer will be a combination of the different units. These polymers are referred to as copolymers. In certain embodiments, the polymer coating is a block copolymer, random copolymer, graft polymer, or branched copolymer.

The phrase "weight average molecular weight" refers to a particular measure of the molecular weight of a polymer. The weight average molecular weight is calculated as follows: determine the molecular weight of a number of polymer molecules; add the squares of these weights; and then divide by the total weight of the molecules.

The phrase "number average molecular weight" refers to a particular measure of the molecular weight of a polymer. The number average molecular weight is the common average of the molecular weights of the individual polymer molecules. It is determined by measuring the molecular weight of n polymer molecules, summing the weights, and dividing by n.

The phrase "polydispersity index" refers to the ratio of the "weight average molecular weight" to the "number average molecular weight" for a particular polymer; it reflects the distribution of individual molecular weights in a polymer sample.

The term "heteroatom" is art-recognized and refers to an atom of any element other than carbon or hydrogen. Illustrative heteroatoms include boron, nitrogen, oxygen, phosphorus, sulfur and selenium.

The term "alkyl" is art-recognized, and includes saturated aliphatic groups, including straight-chain alkyl groups, branched-chain alkyl groups, cycloalkyl (alicyclic) groups, alkyl substituted cycloalkyl groups, and cycloalkyl substituted alkyl groups. In certain embodiments, a straight chain or branched chain alkyl has about 30 or fewer carbon atoms in its backbone (e.g., C ₁ -C ₃₀ for straight chain, C ₃ -C ₃₀ for branched chain), and alternatively, about 20 or fewer. Likewise, cycloalkyls have from about 3 to about 10 carbon atoms in their ring structure, and alternatively about 5, 6 or 7 carbons in the ring structure. Unless the number of carbons is otherwise specified, "lower alkyl" refers to an alkyl group, as defined above, but having from one to about ten carbons, alternatively from one to about six carbon atoms in its backbone structure. Likewise, "lower alkenyl" and "lower alkynyl" have similar chain lengths.

The term "alkylene," is art-recognized, and as used herein, pertains to a bidentate moiety obtained by removing two hydrogen atoms, either both from the same carbon atom, or one from each of two different carbon atoms, of a hydrocarbon compound, which may be aliphatic or alicyclic, or a combination thereof, and which may be saturated, partially unsaturated, or fully unsaturated. Examples of linear saturated Ci_ioalkylene groups include, but are not limited to, -(CH ₂ ) _n - where n is an integer from 1 to 10, for example, - CH ₂ - (methylene), -CH ₂ CH ₂ - (ethylene), -CH ₂ CH ₂ CH ₂ - (propylene), -CH ₂ CH ₂ CH ₂ CH ₂ - (butylene), -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ - (pentylene) and -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ - (hexylene). Examples of branched saturated Ci_i _O alkylene groups include, but are not limited to, -CH(CH ₃ )-, -CH(CH ₃ )CH ₂ -, -CH(CH ₃ )CH ₂ CH ₂ -, -CH(CH ₃ )CH ₂ CH ₂ CH ₂ -, - CH ₂ CH(CH ₃ )CH ₂ -, -CH ₂ CH(CH ₃ )CH ₂ CH ₂ -, -CH(CH ₂ CH ₃ )-, -CH(CH ₂ CH ₃ )CH ₂ -, and - CH ₂ CH(CH ₂ CH ₃ )CH ₂ -. Examples of linear partially unsaturated Ci_ioalkylene groups include, but are not limited to,-CH=CH- (vinylene), -CH=CH-CH ₂ -, -CH=CH-CH ₂ -CH ₂ -, - CH=CH-CH ₂ -CH ₂ -CH ₂ -, -CH=CH-CH=CH-, -CH=CH-CH=CH-CH ₂ -, -CH=CH-CH=CH- CH ₂ -CH ₂ -, -CH=CH-CH ₂ -CH=CH-, and -CH=CH-CH ₂ -CH ₂ -CH=CH-. Examples of

branched partially unsaturated Ci_ioalkylene groups include, but are not limited to, -C(CHs)=CH-, -C(CHs)=CH-CH ₂ -, and -CH=CH-CH(CH ₃ )-. Examples of alicyclic saturated Ci_ioalkylene groups include, but are not limited to, cyclopentylene (e.g., cyclopent-l,3-ylene), and cyclohexylene (e.g., cyclohex-l,4-ylene). Examples of alicyclic partially unsaturated Ci_ioalkylene groups include, but are not limited to, cyclopentenylene (e.g., 4-cyclopenten-l,3-ylene), and cyclohexenylene (e.g., 2-cyclohexen-l,4-ylene, 3- cyclohexen-l,2-ylene, and 2,5-cyclohexadien-l,4-ylene).

The term "aralkyl" is art-recognized and refers to an alkyl group substituted with an aryl group (e.g., an aromatic or heteroaromatic group). The terms "alkenyl" and "alkynyl" are art-recognized and refer to unsaturated aliphatic groups analogous in length and possible substitution to the alkyls described above, but that contain at least one double or triple bond respectively.

The term "aryl" is art-recognized and refers to 5-, 6- and 7-membered single-ring aromatic groups that may include from zero to four heteroatoms, for example, benzene, naphthalene, anthracene, pyrene, pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine, pyridazine and pyrimidine, and the like. Those aryl groups having heteroatoms in the ring structure may also be referred to as "aryl heterocycles" or "heteroaromatics." The aromatic ring may be substituted at one or more ring positions with such substituents as described herein, for example, halogen, azide, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, alkoxyl, amino, nitro, sulfhydryl, imino, amido, phosphonate, phosphinate, carbonyl, carboxyl, silyl, ether, alkylthio, sulfonyl, sulfonamido, ketone, aldehyde, ester, heterocyclyl, aromatic or heteroaromatic moieties, fluoroalkyl, cyano, or the like. The term "aryl" also includes polycyclic ring systems having two or more cyclic rings in which two or more carbons are common to two adjoining rings (the rings are "fused rings") wherein at least one of the rings is aromatic, e.g., the other cyclic rings may be cycloalkyls, cycloalkenyls, cycloalkynyls, aryls and/or heterocyclyls.

The terms ortho, meta and para are art-recognized and refer to 1,2-, 1,3- and 1,4- disubstituted benzenes, respectively. For example, the names 1,2-dimethylbenzene and ortho-dimethylbenzene are synonymous.

The terms "heterocyclyl", "heteroaryl", or "heterocyclic group" are art-recognized and refer to 3- to about 10-membered ring structures, alternatively 3- to about 7-membered rings, whose ring structures include one to four heteroatoms. Heterocycles may also be

poly cycles. Heterocyclyl groups include, for example, thiophene, thianthrene, furan, pyran, isobenzofuran, chromene, xanthene, phenoxanthene, pyrrole, imidazole, pyrazole, isothiazole, isoxazole, pyridine, pyrazine, pyrimidine, pyridazine, indolizine, isoindole, indole, indazole, purine, quinolizine, isoquinoline, quinoline, phthalazine, naphthyridine, quinoxaline, quinazoline, cinnoline, pteridine, carbazole, carboline, phenanthridine, acridine, pyrimidine, phenanthroline, phenazine, phenarsazine, phenothiazine, furazan, phenoxazine, pyrrolidine, oxolane, thiolane, oxazole, piperidine, piperazine, morpholine, lactones, lactams such as azetidinones and pyrrolidinones, sultams, sultones, and the like. The heterocyclic ring may be substituted at one or more positions with such substituents as described above, as for example, halogen, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, amino, nitro, sulfhydryl, imino, amido, phosphonate, phosphinate, carbonyl, carboxyl, silyl, ether, alkylthio, sulfonyl, ketone, aldehyde, ester, a heterocyclyl, an aromatic or heteroaromatic moiety, fluoroalkyl, cyano, or the like.

The terms "polycyclyl" or "polycyclic group" are art-recognized and refer to two or more rings (e.g., cycloalkyls, cycloalkenyls, cycloalkynyls, aryls and/or heterocyclyls) in which two or more carbons are common to two adjoining rings, e.g., the rings are "fused rings". Rings that are joined through non-adjacent atoms are termed "bridged" rings. Each of the rings of the poly eye Ie may be substituted with such substituents as described above, as for example, halogen, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, amino, nitro, sulfhydryl, imino, amido, phosphonate, phosphinate, carbonyl, carboxyl, silyl, ether, alkylthio, sulfonyl, ketone, aldehyde, ester, a heterocyclyl, an aromatic or heteroaromatic moiety, fluoroalkyl, cyano, or the like.

The term "carbocycle" or "cycloalkyl" is art-recognized and refers to an aromatic or non-aromatic ring in which each atom of the ring is carbon. The term "nitro" is art-recognized and refers to -NO ₂ ; the term "halogen" is art- recognized and refers to -F, -Cl, -Br or -I; the term "sulfhydryl" is art-recognized and refers to -SH; the term "hydroxyl" means -OH; and the term "sulfonyl" is art-recognized and refers to -SO ₂ ^" . "Halide" designates the corresponding anion of the halogens, and "pseudohalide" has the definition set forth on page 560 of "Advanced Inorganic Chemistry" by Cotton and Wilkinson.

The terms "amine" and "amino" are art-recognized and refer to both unsubstituted and substituted amines, e.g., a moiety that may be represented by the general formulas:

R50

R50

I +

-N -N R53

\

R51 R52 wherein R50, R51, R52 and R53 each independently represent a hydrogen, an alkyl, an alkenyl, -(CH2) _m -R61, or R50 and R51 or R52, taken together with the N atom to which they are attached complete a heterocycle having from 4 to 8 atoms in the ring structure; R61 represents an aryl, a cycloalkyl, a cycloalkenyl, a heterocycle or a polycycle; and m is zero or an integer in the range of 1 to 8. In other embodiments, R50 and R51 (and optionally R52) each independently represent a hydrogen, an alkyl, an alkenyl, or -(CH2) _m -R61. Thus, the term "alkylamine" includes an amine group, as defined above, having a substituted or unsubstituted alkyl attached thereto, i.e., at least one of R50 and R51 is an alkyl group. The term "acylamino" is art-recognized and refers to a moiety that may be represented by the general formula:

wherein R50 is as defined above, and R54 represents a hydrogen, an alkyl, an alkenyl or -(CH ₂ )m-R61, where m and R61 are as defined above. The term "amido" is art recognized as an amino-substituted carbonyl and includes a moiety that may be represented by the general formula:

wherein R50 and R51 are as defined above. Certain embodiments of the amide in the present invention will not include imides which may be unstable. The term "alkylthio" refers to an alkyl group, as defined above, having a sulfur radical attached thereto. In certain embodiments, the "alkylthio" moiety is represented by one of -S-alkyl, -S-alkenyl, -S-alkynyl, and -S-(CH2) _m -R61, wherein m and R61 are defined above. Representative alkylthio groups include methylthio, ethyl thio, and the like.

The term "carboxyl" is art recognized and includes such moieties as may be represented by the general formulas:

wherein X50 is a bond or represents an oxygen or a sulfur, and R55 and R56 represents a hydrogen, an alkyl, an alkenyl, -(CH ₂ ) _m -R61or a pharmaceutically acceptable salt, R56 represents a hydrogen, an alkyl, an alkenyl or -(CH2) _m -R61, where m and R61 are defined above. Where X50 is an oxygen and R55 or R56 is not hydrogen, the formula represents an "ester". Where X50 is an oxygen, and R55 is as defined above, the moiety is referred to herein as a carboxyl group, and particularly when R55 is a hydrogen, the formula represents a "carboxylic acid". Where X50 is an oxygen, and R56 is hydrogen, the formula represents a "formate". In general, where the oxygen atom of the above formula is replaced by sulfur, the formula represents a "thiolcarbonyl" group. Where X50 is a sulfur and R55 or R56 is not hydrogen, the formula represents a "thiolester." Where X50 is a sulfur and R55 is hydrogen, the formula represents a "thiolcarboxylic acid." Where X50 is a sulfur and R56 is hydrogen, the formula represents a "thiolformate." On the other hand, where X50 is a bond, and R55 is not hydrogen, the above formula represents a "ketone" group. Where X50 is a bond, and R55 is hydrogen, the above formula represents an "aldehyde" group.

The term "carbamoyl" refers to -0(C=O)NRR', where R and R are independently H, aliphatic groups, aryl groups or heteroaryl groups. The term "oxo" refers to a carbonyl oxygen (=0).

The terms "oxime" and "oxime ether" are art-recognized and refer to moieties that may be represented by the general formula:

wherein R75 is hydrogen, alkyl, cycloalkyl, alkenyl, alkynyl, aryl, aralkyl, or -(CH2) _m -R61. The moiety is an "oxime" when R is H; and it is an "oxime ether" when R is alkyl, cycloalkyl, alkenyl, alkynyl, aryl, aralkyl, or -(CH ₂ ) _m -R61.

The terms "alkoxyl" or "alkoxy" are art-recognized and refer to an alkyl group, as defined above, having an oxygen radical attached thereto. Representative alkoxyl groups

include methoxy, ethoxy, propyloxy, tert-butoxy and the like. An "ether" is two hydrocarbons covalently linked by an oxygen. Accordingly, the substituent of an alkyl that renders that alkyl an ether is or resembles an alkoxyl, such as may be represented by one of -O-alkyl, -O-alkenyl, -O-alkynyl, -O-(CH2) _m -R61, where m and R61 are described above.

The term "sulfonate" is art recognized and refers to a moiety that may be represented by the general formula:

O

-OR57

O in which R57 is an electron pair, hydrogen, alkyl, cycloalkyl, or aryl.

The term "sulfate" is art recognized and includes a moiety that may be represented by the general formula:

O

O S OR57

O in which R57 is as defined above.

The term "sulfonamido" is art recognized and includes a moiety that may be represented by the general formula:

O

-N S OR56

R50 O in which R50 and R56 are as defined above.

The term "sulfamoyl" is art-recognized and refers to a moiety that may be represented by the general formula:

in which R50 and R51 are as defined above.

The term "sulfonyl" is art-recognized and refers to a moiety that may be represented by the general formula:

O

-R58

O in which R58 is one of the following: hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclyl, aryl or heteroaryl.

The term "sulfoxido" is art-recognized and refers to a moiety that may be represented by the general formula:

in which R58 is defined above. Analogous substitutions may be made to alkenyl and alkynyl groups to produce, for example, aminoalkenyls, aminoalkynyls, amidoalkenyls, amidoalkynyls, iminoalkenyls, iminoalkynyls, thioalkenyls, thioalkynyls, carbonyl-substituted alkenyls or alkynyls.

The definition of each expression, e.g., alkyl, m, n, and the like, when it occurs more than once in any structure, is intended to be independent of its definition elsewhere in the same structure.

The abbreviations Me, Et, Ph, Tf, Nf, Ts, and Ms represent methyl, ethyl, phenyl, trifluoromethanesulfonyl, nonafluorobutanesulfonyl, /?-toluenesulfonyl and methanesulfonyl, respectively. A more comprehensive list of the abbreviations utilized by organic chemists of ordinary skill in the art appears in the first issue of each volume of the Journal of Organic Chemistry; this list is typically presented in a table entitled Standard List of Abbreviations .

It will be understood that "substitution" or "substituted with" includes the implicit proviso that such substitution is in accordance with permitted valence of the substituted atom and the substituent, and that the substitution results in a stable compound, e.g., which does not spontaneously undergo transformation such as by rearrangement, cyclization, elimination, or other reaction.

The term "substituted" is also contemplated to include all permissible substituents of organic compounds. In a broad aspect, the permissible substituents include acyclic and

cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and nonaromatic substituents of organic compounds. Illustrative substituents include, for example, those described herein above. The permissible substituents may be one or more and the same or different for appropriate organic compounds. For purposes of this invention, the heteroatoms such as nitrogen may have hydrogen substituents and/or any permissible substituents of organic compounds described herein which satisfy the valences of the heteroatoms. This invention is not intended to be limited in any manner by the permissible substituents of organic compounds.

For purposes of this invention, the chemical elements are identified in accordance with the Periodic Table of the Elements, CAS version, "Handbook of Chemistry and Physics", 67th Ed., 1986-87, inside cover.

EXEMPLIFICATION

The invention now being generally described, it will be more readily understood by reference to the following examples, which are included merely for purposes of illustration of certain aspects and embodiments of the present invention, and are not intended to limit the invention.

As described below, rapid (0.3 s) and reversible biomimetic response of flexible dielectric mirrors was achieved by alternating inorganic (titania) and organic (poly(2- hydroxyethyl methacrylate, pHEMA) layers. Tunable reflectance bands in the visible range resulted from water swelling of the un-cross-linked pHEMA layers, without affecting the optical thickness of the high refractive index inorganic layer, which is in precise analogy to the structural color changing mechanism employed by many natural species. Larger refractive index contrast than accessible for all organic mirrors allow the desired reflectivity to be achieved with fewer layers and hence less overall thickness. The observed optical responses quantitatively match model predictions and are completely reversible. There is no loss in reflectivity intensity upon swelling. Hybrid heterostructures were grown within a single hot-wire chemical vapor deposition (CVD) chamber, resulting in smooth and uniform nanoscale layers of high interfacial quality. Remarkably, this approach results in a combination of an inorganic thin film with a fully functional polymer thin film having interfacial smoothness at the nanoscale. The room-temperature solventless HWCVD process is scalable to large area roll-to-roll deposition and is compatible with deformable substrates such as paper and plastic. Preparation of Multilayer Films

Multilayer films were deposited on silicon, glass, quartz, polycarbonate and paper substrates in a custom build vacuum chamber. Gupta, M., Gleason, K. K. Large scale initiated chemical vapor deposition of poly(glycidyl methacrylate) thin films. Thin Solid Films 515, 1579-1584 (2006). In the HWCVD process, the thermal excitation of the reactant gases were achieved by resistively heating a tungsten wire array mounted next to the water circulated cooling plate on which the substrates were placed. The clearance between the filament array and the cooling plate was 35 mm. All depositions were carried out at a substrate temperature of 30 ⁰ C. For the high index layers, titanium (IV) tetra isopropoxide (TTIP) (99.999%, Aldrich) was fed to the reactor as 0.5 seem through a temperature controlled bubbler at 50 ⁰ C, using 50 seem O ₂ (99.999%) as the carrier gas into a 20 Pa reactor pressure and a filament temperature of 600 ⁰ C. For the low index layers, the monomer 2-hydroxyethyl methacrylate (HEMA) (99.999%, Fluka) and the initiator tert- butyl peroxide (TBPO) (98%, Aldrich) were used as received. HEMA monomer was vaporized in a metal jar kept at 75 ⁰ C, and fed to the reactor through a needle valve at a flow rate of 4 seem. TBPO was kept in a glass jar and fed to the reactor through a mass flow controller at a flow rate of 4 seem. The Poly 2-hydroxyethyl methacrylate p(HEMA) depositions were carried out at a filament temperature of 280 ⁰ C and a chamber pressure of 35 Pa. Under these conditions, the observed deposition rates were of 6 nm/min for titania and 15 nm/min pHEMA. Hence, the deposition time for each pair in the stack was less than about 17 min.

Film Characteristics

Real time thickness controls of the depositions were made using an interferometer equipped with a 633 nm HeNe laser source (JDS Uniphase). The ex-situ determinations of layer thicknesses and optical constants of layers were carried out using an ellipsometer (Woollam M-2000) at an angle of 70° and within a spectral range of 315 to 720 nm.

In order to characterize the flexibility of materials, a flexibility tester was designed from off-the-shelf-materials and machined in the MIT Central Machine Shop. The device design shown in Figure 6a accommodates 6" samples; Figure 6b is a photo of the installed device. The reflectivity measurements were carried out using a UV-VIS-NIR spectrophotometer (Cary 600Oi) at near normal angle. For UV-Vis-NIR analysis, multilayer hybrid structures were deposited on quartz substrates, which were later mounted on a gas cell to allow for swelling experiments. A temperature controlled bubbler was utilized to

carry saturated water vapor into the gas cell, using nitrogen as carrier gas. The reflectivity responses of the substrates were obtained at different water vapor molar fractions in the gas cell. Theoretical calculations were based on transfer matrix method, in which optical contribution of each layer is defined by a 2x2 matrix using layer thicknesses and optical constants. Theoretical responses were obtained by multiplying all of the matrices contributing to the structure in a sequential order.

Fourier transform infrared (FTIR) measurements were done on a Nicolet Nexus 870 spectrometer in normal transmission mode over the range of 400 to 4000 cm ^"1 at a 4 cm ^"1 resolution. X-Ray photoelectron spectroscopy (XPS) was carried out on a Cratos Axis Ultra spectrometer using a monochromatized Al Kr source. The cross-sectional image of the hybrid Bragg structure was obtained with Transmission Electron Microscopy (TEM) (JEOL 200CX). Surface roughnesses of the deposited films were obtained from atomic force microscopy (AFM) (Digital Instruments Dimension 3000) under tapping mode using an etched standard silicon tip. Thicknesses and optical constants of individual titania and pHEMA layers deposited on silicon substrates were determined by using spectroscopic ellipsometry at an incident angle of 70°. Refractive indices of the titania and pHEMA layers at λ=500 nm were determined to be 1.81 and 1.51, respectively, with negligible extinction coefficients. The refractive index of the titania layer is lower than that of amorphous TiO ₂ (about 2) and can be attributed to carbon incorporation from titanium tetra isopropoxide (TTIP) precursor, as is commonly observed in metal oxide deposition at low substrate temperature. Babelon, P., Dequiedt, A. S., Mostefa-Sba, H., Bourgeois, S., Sibillot, P., Sacilotti, M. SEM and XPS studies of titanium dioxide thin films grown by MOCVD. Thin Solid Films 322, 63-67 (1998). XPS analysis indicates an O/Ti atomic ratio between 2 and 3, with a carbon content of about 20%.

In Figure 7a, the high-resolution XPS spectrum shows intense peaks for Ti _2p 3/ ₂ and Ti _2p i/2 centered at the binding energy values of 459.2 and 464.9 eV correspond, respectively, to the identical binding energies observed for stoichiometric TiO ₂ . Babelon, P.; Dequiedt, A. S.; Mostefa-Sba, H.; Bourgeois, S.; Sibillot, P.; Sacilotti, M. Thin Solid Films 1998, 322, 63. The nonlinear least-squares fit of the Ols state (Figure 7b) indicates a major component centered at a binding energy value of 530.8 eV, which indicates Ti-O bond. The shoulder on the left-hand side of Figure Ib centered at 532.3 eV corresponds to

the hydroxyl species, which are most probably incorporated from the H ₂ O, which is formed in the CVD chamber as a reaction byproduct.

While TiO ₂ layers can often quite rough (see Bernardi, M. I. B., Lee, E. J. H., Lisboa-Filho, P. N., Leite, E. R., Longo, E., Varela, J. A. TiO ₂ thin film growth using the MOCVD method. Mat. Res. 4, 3, 223-226 (2001); and Huang, H., Yao, X. Preparation and characterization of rutile TiO ₂ thin films by mist plasma evaporation. Surface & Coatings Technology 191, 54-58 (2005)), Atomic Force Microscopy (AFM) reveals that the HWCVD titania layers are extremely smooth (rms roughness of about 0.8 nm), most likely indicating an amorphous nature as a result of the carbon moieties. The refractive index of pHEMA layers is the same as previously reported values. Chan, K., Gleason, K. K. Initiated chemical vapor deposition of linear and cross-linked poly(2-hydroxyethyl methacrylate) for use as thin film hydrogels. Langmuir 21, 19, 8930-8939 (2005). FTIR analysis of the pHEMA films deposited on silicon substrates indicated the full retention of the pendant hydroxyethyl (-CH ₂ CH ₂ OH) group, which is responsible for the hydrophilic nature of the films and allow for the polymer to swell in water extensively. The large refractive index difference between the organic and inorganic layers allows high reflectivity values with low number of pairs; hence the resultant highly reflective structures can be extremely thin. The cross-sectional image of a hybrid Bragg structure (Figure 1) was obtained with Transmission Electron Microscopy (TEM) (JEOL 200CX) and clearly resolves the precise layering of 9 successive organic-inorganic layers within just 300 nm thick film. The high density titania regions are much darker than the low density polymer layers. Such a high quality layering of organic and inorganic thin films in a multilayer stack of a few hundreds of nanometers thickness was not observed clearly in previous studies. The sharp interface between the organic and inorganic phases and highly reproducible layer thickness accounts for the high performance of these multilayer structures as optical dielectric coatings.

The ability to produce the hybrid multilayer structures at room temperature and in a solvent- free, dry atmosphere allowed many different types of substrates to be coated (Figure 2): microscope glass, quartz, polymer (polycarbonate, poly vinyl chloride and PDMS sheets) and paper substrates. The mechanical integrity of the multilayer stack on the flexible substrates is evidenced by the lack of change on the visual appearance or on the structural integrity of the structures even after hundreds of deformation events. A seven layer hybrid structure of (titania-pHEM A) ₃ -titania multilayer film was deposited on a

quartz disk (Figure 2b), which was subsequently mounted as the window of a gas cell of a UV-visible spectrophotometer (Figure 4). The experimental reflectance spectra of the Bragg structure (Figure 3 a) are plotted as a function of wavelength, together with the theoretical reflectance spectra (black lines). In order to find the overall theoretical reflectivity of the multilayer film, the transfer matrix method was utilized. Born, M.; Wolf, E. Principles of Optics, 6th ed.; Cambridge University Press: Oxford, U.K., 1980; Vol. 5, pp 1-70. For each layer in the structure, a 2 x 2 matrix was defined using the layer thickness and refractive index. Overall theoretical responses were obtained by multiplying all of the matrices contributing to the structure in the order they appear in the structure. Curve I in Figure 3 a shows the reflectivity of an as-deposited dry stack in which the layer thickness of 64 nm for the titania and 77 nm for pHEMA both correspond to λ/4 = 115 nm. As expected, the observed maximum intensity of reflection occurs at 460 nm. Upon exposure to the saturated water vapor, the reflectivity band shifted in less than 1 s to the longer wavelengths (490 nm). Curve II in Figure 6a shows a band shift of 30 nm caused by 6.7 mol % water vapor in nitrogen. The shift in the reflectivity band increased up to 70 nm at 10 mol % of water vapor (curve III). Decreasing the water percentage back to 6.7 mol %, the reflectivity band returned to curve II (see dashed line), and when the water vapor exposure ceased, all spectra returned to the original position (curve I, dashed line), indicating reversible performance. Almost the same optical responses were observed after many swelling-shrinkage cycles, which indicates that the structural integrity of the films was preserved even after the repeated exposure to the solvent vapors. Another important outcome of Figure 3a is that the shapes of the reflectance peaks in each case do not change with swelling-shrinkage cycles. This implies equivalent swelling of each individual polymer layer in the stack. If differences in behavior had existed between the polymer layers, asymmetric reflectance peaks would be observed upon swelling of the stack. Another advantage of the hybrid Bragg structure is that there is not any intensity loss upon swelling (Figure 3 a). One may expect that there should be some loss in intensity of the reflectance band upon swelling, because of the disruption of the quarter wave periodicity. However, that loss in intensity is balanced with a decrease in the refractive index of the low index polymer layer. The response of the Bragg reflector in the presence of water vapor is very quick. Figure 4 shows the photographs of the coated swelling cell window during a color tuning cycle in the presence of solvent vapor. The quartz cell window contains a 7 layer (titania-pHEMA)3-

titania hybrid structure, designed to reflect greenish light with λ/4 = 140 nm. The change from green to red phase is accomplished within approximately 0.3 s. The complete reversal back to the green state also occurs in approximately 0.3 s. Overall swelling cycle occurs in less than a second. The extremely short cycle times result from combining the very thin nature of the hybrid stack together with the linear structure of the acrylic polymer layer, which maintains full retention of the hydrophilic chemical functionality. Both the overall thinness and lack of crosslinking in the organic layer promote rapid solvent diffusion in comparison to previously reported thicker stacks comprised of cross-linked polymer layers. Monch, W.; Denhert, J.; Prucker, O.; Ruhe, J.; Zappe, H. Appl. Opt. 2006, 45, 18, 4284. Such short response times are typical for the Bragg structures observed in natural species, such as scales of paradise whiptail, for which the phase transition from blue resting phase to the red phase occurs within around 0.25 s ² .

In addition to the response speed, the response sensitivity is another important measure to evaluate sensing performance of the Bragg structures for any sensor application. The sensitivity of the hybrid Bragg structure is illustrated in Figure 10, where the shift in the position of the high reflectivity peak before and after exposure to the water vapor at different mole fractions are presented. A linear dependence of the absorptance peak shift on the water vapor concentration in nitrogen was observed, and a sensitivity value of 0.42 pm/ppm was estimated in the visible portion of the electromagnetic spectrum for the studied composition range.

INCORPORATION BY REFERENCE

All of the U.S. patents and U.S. published patent applications cited herein are hereby incorporated by reference.

EQUIVALENTS Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.