CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to U.S. Provisional Application No.

62/164,449, titled "TRANSPARENT METALLO-DIELECTRIC COATINGS, STRUCTURES, AND DEVICES, AND METHODS OF FABRICATION

THEREOF" and filed on May 20, 2015, the entire contents of which is incorporated herein by reference.

BACKGROUND

The present disclosure relates to materials and coatings incorporating thin metallic layers and dielectric layers for the control of optical and thermal radiation. In some aspects, the present disclosure relates to materials and coatings for forming transparent low-em issivity coatings.

Metals exhibit many unique and useful properties, however two of the most important and relevant in the modern era are their electrical and optical properties. Because of the high number of electrons in metals, they can conduct electricity very efficiently and are used in a variety of electrical devices as resistive heaters, electrical interconnects and electrodes. In addition to these applications of their conductive properties, the high concentration of electrons in metals also allows the electrons to move under the influence of an incident electric field, which in turn creates an opposing field that prevents the penetration of the field through the metal. In the case of an electromagnetic wave (light), this results in the incident electromagnetic energy being entirely reflected. Above a frequency known as the plasmon frequency, the electrons cannot move fast enough to adjust to the changing reflective electric field, thus allowing light to penetrate the metal, however this frequency is in the ultraviolet for all metals, and thus they reflect all optical, infrared, radio-wave and other long wavelength radiation incident on them. These optical properties have made metals suitable as optical mirrors, electromagnetic shielding materials, as well as heat retaining materials and low-emissivity materials, such as thermal blankets that act as heat mirrors, reflecting infrared radiation and allowing heat to be retained. Though the optical properties of metals make many of these extremely useful applications possible, in order to further develop new and unique devices, their intrinsic reflectivity of optical light can be a troublesome feature that must be overcome.

In order to further extend the usefulness of metal films, it is necessary to have control over the optical properties of the metallic films. The transmissivity of a metal film can be directly controlled by altering the thickness of the film itself. At nanoscale dimensions (1 -100 nm),

electromagnetic radiation incident on a metal, even below the plasmon frequency can partially penetrate through the film. In addition, the closer the frequency of the light is to the plasmon frequency, the more it will penetrate through the metal film. This results in more visible light than infrared light transmitting through a nanoscale metal film, opening up a variety of new applications where the other properties of metallic films, as well as high transmissivity are required.

For many years, transparent conducting materials have been utilized for electrical contacts in opto-electronic devices such as solar cells and LEDs. The most common materials used are transparent conducting oxides, however they have limited conductivity as well as high material costs, and therefore a low cost and highly conductive metal film with sufficient transparency is desired to advance this field.

Another common application is in heat mirrors and low-em issivity windows, such as those described above, which are also transparent. A low- emissivity coating can be applied on a window in order to reject or retain infrared radiation emitted from the sun or heated objects in a building, respectively, in order to reduce cooling load in the summer and heating load in the winter. In all of these applications, a key factor in determining the effectiveness and usefulness of the device is the ultimate transmissivity of the film. When using metal films, though the transmissivity can be improved by reducing the thickness of the film, there are physical limitations as to how thin a film can be developed and hence in order to further improve the

transmissivity, unique optical film structures are used.

Metallo-dielectric multilayer structures have been employed to form low-emissivity coatings. Such multilayer structures employ thin-film

technology utilizing alternating layers of a metal and dielectric material to generate optical interference and spectral selectivity, and were proposed in the early 1990s. When light travels through such a material, it is reflected off of each metal-dielectric interface, and these reflected rays of light interfere either constructively to enhance the reflection or destructively in order to enhance the transmission, depending on the thickness of the dielectric layers and the wavelength of light being transmitted. By tailoring the thickness of the dielectric layers and using a minimal thickness of metal, the transmissivity of the composite structure can be significantly enhanced.

Solar control coatings (SCC), a form of transparent heat mirror, are one such application in which metallo-dielectric films have been applied. Solar control coatings can be utilized by the building industry to mediate indoor temperature, reduce energy consumption, and provide comfort. Its name originates from its spectrally selective property of transmitting visible radiation while reflecting infrared radiation, effectively allowing control over the transmission of solar energy through a transparent material. Its infrared reflectivity further extends to the range at which room-temperature objects intrinsically emit heat, allowing for a secondary benefit of retaining energy of the interior environment.

The recent cultural shift in affinity toward green energy has effected changes in governmental policies on energy consumption. Architects designing new buildings have to comply with ever higher standards on the energy efficiency of a building, characterized by the intake of excess heat energy under direct solar radiation (SHGC - solar heat gain coefficient) and the level of insulation when subjected to a temperature difference between the interior and exterior (U-Factor). SCCs are a straightforward solution to the first requirement by reducing the intake of solar infrared energy, and have the added benefit of effectively increasing insulation in a cold environment through its heat infrared reflectivity.

One of the earliest SCC designs employed a thin layer of copper on top of copper oxide deposited on glass. The overall structure of a multi-layered SCC composed of alternating dielectric and metallic layers has persisted to the present through the effectiveness of its design. SCC are often now formed using the high infrared reflectance of nano-thin metal films, typically of silver, and enhance its visible transmission via interference effects by layering it between thin transparent dielectric films.

As the technology of SCC has matured, their performance has been approaching the theoretical limit. Coatings with 70% VLT and 45% SHGC have been reported and the theoretical limit of SHGC at 70% VLT is 29%. However, the complexity of the coatings has also increased, with some having as many as 13 layers. Furthermore, many of the materials used in the coating are still made from expensive raw materials (in the case of ITO), employ metal-oxides (ΤΊΌ2 being very common) that can lead to degradation of silver via oxidation, employ expensive sputtering processes, and often employ toxic processing methods (such as the use of SiH ₄ gas in making S13N4). The commercial success and penetration of such devices has thus been limited by problems involving cost, complexity, stability, and toxicity.

SUMMARY

Various embodiments of the present disclosure provide metallo- dielectric low-emissivity coatings, structures coated with such low-emissivity coatings, and methods of fabrication thereof. The metallo-dielectric coatings are formed from a visibly-transparent, and heat-reflective, multi-layer structure including an transparent amorphous substrate having a nano-thin metal layer adhered thereto, wherein the nano-thin metal layer is adhered to a

transparent amorphous substrate via a transparent dielectric seeding layer. The transparent amorphous dielectric layer may include amorphous carbon. Various example embodiments are disclosed in which such coatings are employed as passive or active devices, such as transparent heat mirrors, transparent resistive heaters for windows, transparent electromagnetically isolating security films, near invisible radio transceivers and transmitters.

Accordingly, in a first aspect, there is provided a metallo-dielectric coating comprising:

a transparent amorphous dielectric layer;

a transparent dielectric seeding layer formed on the transparent amorphous dielectric layer; and

a nano-thin metal layer formed on the transparent dielectric seeding layer; and

wherein the transparent dielectric seeding layer is selected such that the nano-thin metal layer is formed with a continuous surface in the absence of isolated islands.

In another aspect, there is provided a metallo-dielectric structure comprising:

a transparent substrate;

a first transparent dielectric seeding layer formed on the transparent substrate;

a first nano-thin metal layer formed on the first transparent dielectric seeding layer;

a first transparent amorphous dielectric layer formed on the first nano- thin metal layer;

a second transparent dielectric seeding layer formed on the first transparent amorphous dielectric layer; a second nano-thin metal layer formed on the second transparent dielectric seeding layer;

a second transparent amorphous dielectric layer formed on the second nano-thin metal layer; and

a capping dielectric layer formed on the second transparent amorphous dielectric layer;

wherein the first nano-thin metal layer and the second nano-thin metal layer are intrinsically transparent within at least a portion of the visible spectrum, and wherein the first nano-thin metal layer and the second nano- thin metal layer are formed with a continuous surface in the absence of isolated islands.

In another aspect, there is provided a metallo-dielectric coating comprising:

a transparent amorphous dielectric layer; and

a nano-thin metal layer formed on the transparent amorphous dielectric layer; and

wherein the nano-thin metal layer is intrinsically transparent within at least a portion of the visible spectrum; and

wherein the transparent amorphous dielectric layer is doped with a dopant selected to produce a surface such that the nano-thin metal layer is formed with a continuous surface in the absence of isolated islands.

In another aspect, there is provided a method of fabricating a metallo- dielectric coating, the method comprising:

depositing, onto a transparent substrate, a transparent amorphous dielectric layer; depositing a transparent dielectric seeding layer onto the transparent amorphous dielectric layer; and

depositing a nano-thin metal layer on the transparent dielectric seeding layer, the nano-thin metal layer forming a continuous surface in the absence of isolated islands;

wherein the nano-thin metal layer is formed with a thickness such that the nano-thin metal layer is intrinsically transparent within at least a portion of the visible spectrum.

In another aspect, there is provided a method of fabricating a metallo- dielectric coating, the method comprising:

depositing, onto a transparent substrate, a transparent amorphous dielectric layer;

doping the transparent amorphous dielectric layer with a dopant; depositing a nano-thin metal layer on the transparent amorphous dielectric layer; and

depositing a transparent dielectric film on the nano-thin metal layer; wherein the dopant is selected such that the nano-thin metal layer is formed on the transparent amorphous dielectric layer with a continuous surface in the absence of isolated islands; and

wherein the nano-thin metal layer is formed with a thickness such that the nano-thin metal layer is intrinsically transparent within at least a portion of the visible spectrum.

A further understanding of the functional and advantageous aspects of the disclosure can be realized by reference to the following detailed description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the drawings, in which:

FIG. 1 illustrates an example embodiment of a metallo-dielectric multilayer formed on a given substrate.

FIG. 2 illustrates an example embodiment of a metallo-dielectric multilayer with each dielectric layer comprising two discrete dielectric films having distinct optical properties.

FIG. 3 illustrates an example implementation of a metallo-dielectric multilayer coating with each dielectric layer comprising continuously or quasi- continuously varying optical properties.

FIG. 4 plots the spectral variation of optical index of amorphous carbon at different RF plasma enhanced chemical vapour deposition power levels.

FIG. 5 plots the optical gap of amorphous carbon as a function of the RF PECVD power.

FIG. 6 illustrates and example implementation of a metallo-dielectric multilayer coating comprising two thin metallic films.

FIG. 7 illustrates an example implementation of a metallo-dielectric multilayer coating comprising two thin metallic films without a dielectric between the substrate and the seeding layer for the bottom metallic film.

FIG. 8 shows the experimental and modeled transmittance and reflectance of an example metallo-dielectric multilayer.

FIG. 9 plots the modeled transmittance and reflectance of an optimized metallo-dielectric multilayer.

FIG. 10 plots the visible light transmittance (VLT) and total solar energy rejection (TSER) of metallo-dielectric multilayer coatings.

FIG. 11 illustrates and example implementation of a metallo-dielectric multilayer coating with a capping encapsulating overlying layer.

FIG. 12 illustrates and example implementation of a metallo-dielectric multilayer coating with capping encapsulating overlying and underlying layers.

FIG. 13 M illustrates and example implementation of a metallo- dielectric multilayer coating with point electrical contacts on a metallic layer.

FIG. 14 illustrates and example implementation of a metallo-dielectric multilayer coating with electrical busbar contacts on a metallic layer.

FIG. 15 presents experimental and modeled temperature change as a function of time of a metallo-dielectric coating.

FIGS. 16A-C provides thermal maps of a metallo-dielectric coating with point electrical contacts.

FIGS. 17A-C provides thermal maps of the metallo-dielectric coating with busbar electrical contacts.

FIG. 18 Metallo-dielectric multilayer coating with zonal metallic films and corresponding electrical contacts.

FIG. 19 is a table illustrating various example materials for forming transparent dielectric seeding layers suitable for silver.

FIG. 20 is a table providing example parameter ranges for an example metallo-dielectric structure formed from a-C:H, AIN and Ag.

FIG. 21 is a table itemizing various example categories of amorphous carbon (a-C) films.

FIG. 22 shows a ternary phase diagram of the various forms of amorphous carbon films. DETAILED DESCRIPTION

Various embodiments and aspects of the disclosure will be described with reference to details discussed below. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosure.

As used herein, the terms "comprises" and "comprising" are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in the specification and claims, the terms "comprises" and

"comprising" and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components.

As used herein, the term "exemplary" means "serving as an example, instance, or illustration," and should not be construed as preferred or advantageous over other configurations disclosed herein.

As used herein, the terms "about" and "approximately" are meant to cover variations that may exist in the upper and lower limits of the ranges of values, such as variations in properties, parameters, and dimensions. Unless otherwise specified, the terms "about" and "approximately" mean plus or minus 25 percent or less.

It is to be understood that unless otherwise specified, any specified range or group is as a shorthand way of referring to each and every member of a range or group individually, as well as each and every possible sub-range or sub -group encompassed therein and similarly with respect to any subranges or sub-groups therein. Unless otherwise specified, the present disclosure relates to and explicitly incorporates each and every specific member and combination of sub-ranges or sub-groups.

As used herein, the term "on the order of", when used in conjunction with a quantity or parameter, refers to a range spanning approximately one tenth to ten times the stated quantity or parameter.

Unless defined otherwise, all technical and scientific terms used herein are intended to have the same meaning as commonly understood to one of ordinary skill in the art. Unless otherwise indicated, such as through context, as used herein, the following terms are intended to have the following meanings:

As used herein, the phrase "intrinsically transparent", when referring to a layer of a multilayer structure (e.g. a layer of a multilayer coating or structure) refers a layer having an intrinsic transmittance (within the layer, based on absorption) of at least 25%, 50%, 75%, 80%, 85%, 90%, or 95%, within at least a portion of the visible spectrum. For example, silver, if provided with a sufficiently thin thickness, exhibits transparency across the visible spectrum.

As used herein, the phrase "transparent", when referring a multilayer coating or structure, refers to a coating or structure having an external transmittance of at least 25%, 50%, 75%, 80%, 85%, 90%, or 95%, within at least a portion of the visible spectrum, based on both optical interference and optical absorption effects. As used herein, the phrase "nano-thin", when referring to a metal layer, refers a layer having a thickness that is sufficiently thin to render the metal layer to be transparent. For example, a nano-thin layer of silver that is configured to exhibit intrinsic transparency across the full visible spectrum has a thickness less than approximately 10-20, 7-10, or 3-7 nm.

A given set of metallo-dielectric multilayers is collectively also referred to as a "coating". Such a coating may be provided as a free-standing structure (e.g. a film), or may be coated, bonded, or otherwise attached to a substrate.

Various embodiments of the present disclosure provide metallo- dielectric low-emissivity coatings formed from a transparent and heat- reflective, multi-layer structure including a transparent amorphous carbon layer having a nano-thin metal layer adhered thereto. The nano-thin metal layer has a thickness suitable for rendering the overall multilayer coating structure transparent within a least a portion of the visible spectrum.

According to various example embodiments, the nano-thin metal layer is formed adjacent a base substrate.

Generally in large scale, low cost applications, this substrate is an amorphous material such as glass or another amorphous dielectric material. Unfortunately, the present inventors found that due to the crystalline structure of metals, they often do not form tight bonds with the substrate, and thus tend to group together to form clumps or islands during deposition. For example, silver tends to grow in the Volmer-Weber mode, initially forming disjoint islands on the substrate. This growth mode is unfavourable because the properties of a system of disjoint silver islands are vastly different from that of a smooth continuous silver film. This results in a large amount of roughness, which causes two main issues. The first issue is that the contact between the metal and dielectric becomes very rough and high in defects, thus creating optical scattering and increased reflections from the surface.

The roughness strongly effects both the optical and electronic properties of the metal layer. While each metal island contains a large number of free electrons, these electrons cannot easily travel between islands and are bound to each island due to the high electrical resistivity of substrate. The electrical conductivity is greatly reduced, the near-infrared reflectance weakened, and the phenomenon of localized surface plasmon resonance (LSPR) emerges to give the film undesirable absorption in the visible region.

Furthermore, by Fusch's theory, higher surface roughness lowers the mean free path of free electrons, and thus, the electrical conductivity of the film. Even at the percolation threshold, when the islands have grown large enough in size to coalesce into a continuous film, its electrical conductivity will still be lower than that of a smooth continuous film.

In addition, the high roughness means that the film must reach a relatively large thickness before it can form a continuous highly conductive film. This need for a large thickness limits the optical transmissivity of the film, as thicker metal films have a longer optical path length over which they can reflect and absorb incident light.

These problems were previously encountered by some of the inventors when developing low-emissivity structures based on diamond-like carbon (DLC) and thin silver layers. As described in Mahtani et al., Solar Energy Materials & Solar Cells 95 (2011 ), 1630-1637, it was found that the deposition of thin silver films led to the formation of silver islands, and that the thickness of the silver layer had to be increased in order to avoid the aforementioned problems associated with surface roughness.

The present inventors considered the use of an adhering layer formed from a metal, such as chrome or copper, as practiced in the electronic arts. The high surface tension of such a metal adhering layer allows for a silver layer deposited therein to spread smoothly across the thin layer of the metal film created. However, the present inventors realized that such a metallic adhering layer would not provide a technical solution to the present problem, due to the inherent optical absorption of the metal of the metallic adhering layer. This optical absorption would prevent the overall coating or structure from exhibiting visible transparency, thus failing to meet the requirements of applications such as low-emissivity coatings.

Indeed, the metallic adhering layers presently employed by those skilled in the art employ metals that have much higher optical absorption than the metal contact films, such as silver, themselves. This means that though such a metallic adhering layer allows the formation of a continuous nano-thin metal layer thereon, the absorption of such a metallic adhering layer counteracts any benefit given by reducing the thickness and improving the continuity of the nano-thin metal layer.

Transparent Dielectric Seeding Layers for Growth of Nano-Thin Metal Layers

As described in detail below, the present inventors have found that the aforementioned problems associated with metallic adhering layers can be overcome by employing a transparent dielectric seeding layer, where the transparent dielectric seeding layer is configured to support the growth of a continuous and nano-thin metal layer thereon.

The transparent dielectric seeding layer may be configured for the growth, via deposition thereon, of a continuous and nano-thin metal layer by selecting a dielectric material for which the metal (e.g. silver) has a low contact angle therewith. The low contact angle may be, for example, due to a high surface tension or a low surface tension between the metal and the dielectric.

The dielectric layer may also be selected to exhibit a similar crystal structure to that of the metal. Accordingly, the similar crystal structure and high surface tension allows a metal film to form overtop of, and to spread evenly across, the surface of the transparent dielectric seeding layer and form a smooth continuous layer at relatively low thicknesses, in the nano-thin range.

Due to the uniformity and continuity of the nano-thin metal layer formed on the dielectric seedling layer, the metal layer will be highly conducting.

Furthermore, the nano-thin layer will exhibit visible transparency due to its low thickness. With the use of a dielectric seeding layer as opposed to a metallic seeding layer, the seeding layer's optical properties do not ultimately affect the transmissivity of the final film structure.

As noted above, in order to achieve a suitable interface between the nano-thin metal film and the transparent dielectric seeded layer, the transparent dielectric seeding layer is selected exhibit a similar crystal geometry and size as the metal. For this reason, dielectric seeding layers for metal films have generally been ignored in the past by those skilled in the art.

Without intending to be limited by theory, it is believed that during the deposition of a transparent dielectric seeding layer on an amorphous dielectric layer, the dielectric seeding layer material strikes the surface of the amorphous dielectric layer in clusters of one to several molecules. After striking the surface, the clusters can diffuse slightly and move along the surface of the amorphous dielectric layer. In an ideal seeding layer, this diffusion is minimized to prevent the agglomeration of clusters into larger nanoparticles. Because of the limited diffusion, as the number of clusters that have hit the surface increases, the spacing between the clusters will shrink, and eventually a solid film will form. Should diffusion occur, then the particles will grow vertically before forming a solid film and the roughness will be increased.

Once a solid film is formed, the seeding layer is prepared for the deposition of the metal film. The seeding layer is selected to present a crystal plane that has a similar structure to that of the deposited metal film, and therefore the silver film can grow smoothly across the surface. According to this method, a continuous metal film can be formed on the surface of the transparent dielectric seeding layer, allowing a nano-thin metal layer utilized while still obtaining a highly conductive and IR reflective film.

As noted above, a suitable transparent dielectric material may be selected according to several criteria. For example, in order to minimize the amount of diffusion of the seeding layer molecules, the transparent dielectric seeding layer material may be selected such that its molecules are highly reactive with the molecules at the surface of the amorphous dielectric. This ensures that after striking the surface, they will bond tightly and cease to move. One suitable measure of the reactivity of the transparent dielectric seedling layer molecules is the heat of formation of the chemical reactions between the atomic constituents of the transparent dielectric seeding layer and the amorphous dielectric layer. If the heat of formation is sufficiently negative, then the seeding layer molecules will react readily forming intermediate compounds that prevent the diffusion of the initial clusters. For example, the heat of formation may be selected to be less than -100 kJ/mol, or less than -200 kJ/mol, or less than -300 kJ/mol, or less than -500 kJ/mol or in the range of -100 to -500 kJ/mol, or in the range of -100 to -1000 kJ/mol, or in the range of -100 to -2000 kJ/mol, or in the range of -500 to -2000 kJ/mol. As an example of a suitable transparent dielectric seeding material, AIN acts as a good seeding layer on glass due to the extremely low heat of formation for AIO, a reaction which occurs between the Al in AIN and the O in Si0 ₂ .

As noted above, another example criterion is the similarity between the exposed crystal face of the transparent dielectric seeding layer and the crystal planes of the metal film to be deposited thereon. In one example

implementation, the transparent dielectric seeding material and the metal are selected such that they share the same crystal structure, (e.g. both exhibit a cubic structure such as FCC or BCC), or their crystals have a plane or several planes that have the same geometry (e.g. the planes of FCC and HCP or the ( ) plane of BCC and the (1 10) plane of FCC).

Another relevant criterion, as noted above, is the similarity of the lattice parameters of the aforementioned crystal planes (not necessarily the same as the lattice parameter of the crystal itself). For example, the transparent dielectric seeding material and the metal may be selected such that the lattice parameters of the crystal plane of the transparent dielectric seeding material are close in magnitude (e.g. differ by less than 5%, less than 1 0%, or less than 12.5%) to a scalar multiple of the metal plane's lattice parameter. For example, AIN and Ag have a crystal structure of Wurtzite and FCC

respectively.

Another example criterion is that the transparent dielectric seeding layer exhibits a higher surface tension than the metal layer. This ensures that metal clusters initially formed on the material surface will have a low contact angle and will this spread across the surface, rather than forming beads with spherical geometries.

Referring now to FIG. 19, a list of example transparent dielectric seeding layer materials are provided that satisfy the criteria described above for the seeding of silver films. The table also provides selected relevant properties for the materials. It should be noted that the example material disclosed herein are not intended to provide an exhaustive list, and are instead provided to illustrate several example and suitable species.

As described below, the preceding example embodiments may be employed for the fabrication of visibly transparent, low-em issivity, metallo- dielectric structures that employ one or more transparent amorphous carbon layers and one or more nano-thin metallic layers, where the refractive index of the transparent amorphous carbon is employed to control (prescribe or select) suitable visible transmittance while the nano-thin metal layer is included to provide infra-red reflectivity, and where a transparent dielectric seeding layer is employed to support the growth of a nano-thin metal layer on the amorphous dielectric layer. In other alternative embodiments, as further described below, the amorphous dielectric layer may be suitably doped in order to provide a surface region that is suitable for forming the nano-thin metal layer thereon.

According to various example embodiments described below, metallo- dielectric multilayer coatings and structures may be formed comprising of a combination of one or more amorphous dielectric layers (films; which may have a nanoscale thickness) and one or more nano-thin metallic layers (films). The amorphous dielectric layers may include amorphous carbon films, which include a range of hydrogenated and non-hydrogenated amorphous carbon films and its alloys (for example, diamond-like hydrogenated amorphous carbon (DLC:H), hydrogenated tetrahedral amorphous carbon (TAC:H), polymeric-like hydrogenated amorphous carbon (PLC:H), doped TAC:H, doped DLC:H, doped PLC:H wherein the dopants include non-metals (for example, C, N), semi-metals/metalloids (for example, B, Si, Ge) and metals (for example, Ag, Cu, Al ); and wherein metallic films include a range of metals and metal alloys (for example, Ag and its alloys, Cu and its alloys, Al and its alloys).

An example of a metallo-dielectric multilayer coating is shown in FIG. 1 wherein 100 represents the substrate which includes rigid, flexible and curved substrates (example include glass, a polymeric film (such as polyethylene terephthalate)), 105 represents the underlying dielectric layer (e.g. an amorphous dielectric layer), which may be a nano-thin film (for example, polymeric-like hydrogenated amorphous carbon), 1 15 represents the nano- thin metallic film (for example, Ag), and 20 represents an overlying dielectric film that may be formed on the nano-thin metallic firm, where the overlying dielectric film may be a nano-thin film (for example, hydrogenated amorphous carbon). The films 105 and 120 in general have different optical properties (such as index, optical gap) and different thicknesses. The thicknesses of any one or more of layers 120, 1 05, and 1 15 (described below) may be selected to control the optical interference within the coating, and thus control the optical transmittance of the structure.

Another example embodiment of a metallo-dielectric multilayer coating is shown in FIG. 2 wherein the underlying nano-thin dielectric films 106 and 107 are both polymeric-like hydrogenated amorphous carbon however layers 106 and 107 have different optical properties and thicknesses. Similarly, the overlying nano-thin dielectric films 121 and 122 are both polymeric-like hydrogenated amorphous carbon where layers 121 and 122 have different optical properties and thicknesses. The selection of the optical properties and thicknesses of layers 106, 1 07, 121 and 122 is based on optical impedance matching that promotes an optimized transmissivity and modulation over the optical, near infrared and mid infrared regions of the electromagnetic spectrum.

Another example embodiment of a metallo-dielectric multilayer coating is shown in FIG. 3 wherein the underlying nano-thin dielectric film 108 is polymeric-like hydrogenated amorphous carbon which has continuously or quasi-continuously varying optical properties. Similarly, the overlying nano- thin film 123 is polymeric-like hydrogenated amorphous carbon which has continuously or quasi-continuously varying optical properties. The thicknesses of layers 108 and 123 are in general different. The selection of variation in the optical properties of layers 108 and 123 and the selection of the thicknesses of these layers is based on optical impedance matching that promotes a further optimization on the transmissivity and modulation over the optical, near infrared and mid infrared regions of the electromagnetic spectrum.

As an example, amorphous carbon dielectric layers (for example, polymeric-like hydrogenated amorphous carbon) can be deposited using plasma enhanced chemical vapour deposition technique (PECVD) (for example, radio frequency PECVD, microwave PECVD) with precursor gases that comprise hydrocarbon species (for example, methane, ethane, ethylene, acetylene), or other techniques yielding films with equivalent properties. Further, the properties of the amorphous carbon dielectric films can be readily varied by appropriate variation of the deposition parameters (for example, these include the plasma power density, chamber/deposition pressure, precursor gas composition or/and flow rate). Moreover, the precursor gases can also include other species (for example, hydrogen or other dopant gases such as nitrogen, boron) to appropriately vary the film properties.

FIGS. 4 and 5 illustrate the spectral variation of the optical index of hydrogenated amorphous carbon films and the variation of the optical gap (also referred to as the E ₀₄ energy) as a function of the RF power. Thus, metallo-dielectric multilayers wherein the optical properties of a given amorphous carbon dielectric layer are varied discretely or continuously which is made possible by corresponding discrete or continuous change in the deposition parameter(s) (for example, RF power).

As described in detail above, a seeding layer may be provided within the metallo-dielectric multilayer structure in order to provide a site for the controlled growth of a continuous and nano-thin metal layer. Indeed, a seeding layer may be provided between the nano-thin amorphous carbon films and nano-thin metallic films to enable the formation of nano-thin or ultra- thin continuous metallic films. The seeding layer is denoted by 1 10 in FIG. 1 . The seeding layer 1 1 0 serves to effectively reduce the percolation threshold of the metallic film 1 15. The seeding layer 1 10 can also promote the formation of a smooth (less rough) or ultra-smooth metallic film 1 15 and accordingly provide an electrically less resistive or more conductive nano-thin metallic film.

Metallo-dielectric multilayers may be formed wherein the seeding layer 1 10 comprises the class of refractory/ceramic compounds (for example, aluminum nitride, titanium nitride, silicon nitride over a range of

stoichiometries and its alloys). The said class of compounds, in addition to reducing the percolation threshold and promoting smooth or ultra-smooth metallic films, are optically transparent and thereby obviate any optical absorption losses within the framework of the metallo-dielectric multilayer coatings and thus contribute towards the attainment of highly transmissive optical coatings in the visible while providing modulation over the near infrared and mid infrared regions of the electromagnetic spectrum.

The metallic layer within the metallo-dielectric multilayer coating may be deposited using RF or DC magnetron sputtering or other equivalent techniques. The metallic layer include Ag or Ag and its alloys, Al or Al and its alloys, Cu and Cu and its alloys, which are deposited using RF or DC magnetron sputtering or co-sputtering. Alloying elements can include Al, Cu, Si, and Nb. Further, a variety of sputter gases can be utilized for optimal sputter or co-sputter deposition of the metallic layers; sputter gases include Ar, He, N ₂ or mixtures thereof. Further, optical illumination (for example, UV illumination) can be used to illuminate the depositing surface in order to promote the build-up of static charge density on the surface and thus favourably affect the percolation threshold by virtue of restricting the diffusion of the species being deposited.

Deposition of the seeding layer, for example ceramic/refractory compound aluminum nitride, may be achieved using RF or DC magnetron sputtering using Ar and reactive N ₂ gases. Moreover, optical illumination (for example, UV illumination) during deposition can be utilized to further enhance the properties of the seeding layer.

In one example implementation, two or more of the layers may be formed within a single sputtering chamber and sputtering multiple targets (e.g. using a sputtering crucible containing multiple targets).

In one example embodiment, the seeding layer 1 10 may be formed from an amorphous carbon layer. For example, in one example

implementation, with an underlying dielectric layer comprising a polymeric-like hydrogenated amorphous carbon, a hard diamond-like hydrogenated amorphous carbon layer akin to a ceramic-like surface can also serve as a seeding layer.

In an alternative embodiment, the amorphous dielectric layer may be suitably doped in order to provide a surface region that is suitable for forming the nano-thin metal layer thereon. In such an embodiment, a separate transparent dielectric seedling layer need not be provided, and the seeding of the nano-thin dielectric layer may be achieved by the doped surface region of the amorphous layer. For example, a doped amorphous carbon layer may act as a seeding layer. An example of a doped amorphous carbon layer is a doped polymeric-like amorphous carbon layer, where examples of dopant atoms include Ag, Al, and N. Dopant atoms in amorphous carbon can be introduced through the use of precursor gases or/and through the use of metallo-organic evaporants/precursors.

Another example embodiment of a metallo-dielectric multilayer coating is shown in FIG. 6. Layer 125 represents a second seeding layer atop the overlying nano-thin dielectric layer, layer 130 represents a second nano-thin metallic layer atop the second seeding layer 125, and layer 135 represents a second overlying nano-thin dielectric layer atop the second nano-thin metallic layer. This metallo-dielectric coating further enables modulation of the optical, near infrared and mid infrared regions of the electromagnetic spectrum. The foregoing variation can be further enhanced by similarly adding/depositing additional seeding, metallic and dielectric layers atop the second overlying nano-thin dielectric layer.

For certain choices of the dielectric layer and metallic layer, the modulation of the optical, near infrared, and mid infrared regions of the electromagnetic spectrum can be high even without the underlying dielectric between the substrate and the seeding layer for the metallic layer. FIG. 7 shows an example embodiment of such a metallo-dielectric multilayer coating where the first seeding layer 1 10 is deposited directly on the substrate and the subsequent layers on top built like the multilayer shown in FIG. 6 but without the underlying dielectric layer 105.

The foregoing embodiments enable the attainment of solar control coatings suitable for the modulation of visible, near infrared and mid infrared parts of the electromagnetic spectrum. An example of such an embodiment is illustrated in FIG. 8, where the thicknesses of one or more layers of the metallo-dielectric coating are selected to generate optical interference, such that the metallo-dielectric coating is transmissive in a visible spectral region and reflective in an infrared spectral region.; the dashed curves represents the properties (transmittance and reflectance spectra) of solar control coating sample while the solid curves represents the ideal modeled data. The visible light transmittance (which is the photonic weighted transmittance) of the experimental sample is 0.75 and the total solar energy rejection is 0.54.

FIG. 9 illustrates the modeled transmittance and reflectance curves for an optimally designed solar control coating which yields a visible light transmittance of 0.84 and total solar heat rejection of 0.56.

FIG. 10 further illustrates examples of possible solar control coatings tuned to yield a range of visible light transmittance values and total solar heat rejection values.

The foregoing embodiments may be employed to provide a metallo- dielectric multilayer stack which is non-oxygen/non-oxide based and accordingly yields a non-oxidizing construct which provides an inherently stable host for thin metallic films, such as Ag and Al, which tend to oxidize and tarnish upon contact to contiguous oxygen containing compounds within the construct.

FIG. 1 1 illustrates an example metallo-dielectric multilayer structure with a capping layer 140 (for example, amorphous carbon, refractory compound) that provides encapsulating properties (for example, stability against optical and thermal exposure, hard protective coating). The use of a refractory compound such as aluminum nitride provides excellent

capping/encapsulating properties considering its uniform microstructure and chemical stability against 0 ₂ , C0 ₂ and H ₂ to very high temperatures (~800°C or higher) and its hardness. Further, aluminum nitride is an excellent dielectric having very high electrical resistivity. FIG. 12 illustrates a similar metallo- dielectric multilayer structure but now with both underlying and overlying capping layers 140.

The aforementioned metallo-dielectric multilayer coatings can be applied directly to a glass surface or appropriate rigid planar or curved transparent medium. Additionally, the said coating can be applied onto a polymeric substrate which in turn with the use of an adhesive can be applied directly to a window/glass surface or appropriate rigid planar or curved transparent medium.

In one example embodiment, a metallo-dielectric coating as described above may be augmented with electrical contacts on the metallic layer(s) to enable active devices, such as for the resistive heating of a surface area through the application of this coating on the said surface; for example, windows and windshields (such as in automobiles including electric vehicles). The metallic layer is well insulated with dielectric layers abutting it on either side. Further, the non-oxide host material of the said metallo-dielectric multilayers provides an inherently stable environment against oxidation of the metallic films. Moreover, the capping layers further ensure stability of the films owing to their impermeable encapsulating properties. Example application examples include defogging of windows, windshields back-glass and side- windows in vehicles (for example, automobiles); defrosting or deicing of windows, windshields back-glass and side windows in vehicles; defogging of mirrors.

FIGS. 13 and 14 illustrate two example embodiments involving the use of a transparent metallo-dielectric material for resistive heating applications. In FIG. 13, layer 1 10 represents the silver metallic film or equivalent while leads 145 and 150 (one of which is held at a positive potential while the other is held at ground potential) are point electrical contacts to render Joule heating of the said silver metallic film. In FIG. 14, layer 1 10 represents the silver metallic film or equivalent while 155 and 160 are busbar electrical contacts (one of which is held at a positive potential while the other is held at ground potential) to render uniform Joule heating of the said silver metallic film. The arrow in both diagrams represents the direction of positive charge flow.

FIG. 15 shows the experimentally measured temperature change on a glass surface, on which exists a metallo-dielectric layer connected to point electrical contacts. The figure also includes the modeled temperature change.

FIGS. 16A-C and 17A-C illustrate the modeled temperature

distributions (thermal maps) for the two cases of point contacts and bus bar contacts; each figure shows the thermal map at 50 seconds, 100 seconds, and 300 seconds.

FIG. 18 illustrates an example variation of FIG. 14 wherein two zones are defined. Specifically, the first zone (that is, the upper zone) is defined by 1 1 1 which represents the Ag metallic film or equivalent and the second zone (that is, lower zone) is defined by 1 12 which represent the Ag metallic film or equivalent. The demarcation between the two zones is indicated by 165 wherein the region within the dashed lines the Ag metallic film or equivalent is absent and thus 165 provides a break in electrical continuity between the upper zone 111 and lower zone 112. The upper zone is electrically connected via contacts to the busbar regions 156 and 161 and thus achieving a potential difference \ - V ₂ ; the arrow pointing from Vi to V ₂ indicates the flow of electrical charge. Similarly, the lower zone is electrically connected via contacts to the busbar regions 157 and 162 and thus achieving a potential difference V ₃ - V ₄ ; the arrow pointing from V ₃ to V ₄ indicates the flow of electrical charge. The above embodiment enables selective zone heating. EXAMPLES

The following examples are presented to enable those skilled in the art to understand and to practice embodiments of the present disclosure. They should not be considered as a limitation on the scope of the disclosure, but merely as being illustrative and representative thereof.

Example 1 : Transparent Metallo-Dielectric Coating formed using

Hydrogenated Amorphous Carbon, AIN, and Silver

In one example embodiment of a metallo-dielectric structure, an hydrogenated amorphous carbon (a-C:H ) film is employed as the dielectric layer. a-C:H is a set of materials out of the larger class of amorphous carbon. The microstructure of amorphous carbon can vary significantly to give rise to different material properties. The hydrogenated nature of a-C:H decreases the number of other carbon atoms a carbon atom is bonded to and thus gives rise to a morphology that is more polymeric than crystalline. Within this polymeric form, the types of bond formed between the carbon atoms can further vary. Specifically, the ratio of the density of sigma bonds versus pi bonds can be anywhere from all sigma bonds to all pi bonds. The sigma bonds are the bonds formed by the diamond form of carbon, whereas the pi bonds are the bonds formed by the graphite form of carbon. In describing the characteristic of an a-C:H film, the terms diamond-like and graphite-like are often used.

The difference in bond types affects the optical bandgap energy of the a-C:H film by reducing it with more pi bonds. This shifts the absorption spectrum of the film such that a-C:H becomes less transparent the more graphitic it is. However, at greater than 60% sigma bonds, a-C:H is almost 100% transparent. The shift in optical bandgap energy affects the refractive index of a-C:H as well, and a range of refractive index from 1.6 to 2.2 can be obtained.

a-C:H may be formed using the plasma-enhanced chemical vapour deposition (PECVD) process. The process environment is composed of two electrodes separated by a distance in a chamber pumped down to high vacuum (~1e-8 Torr). The substrate on which a-C:H is deposited is secured to one electrode. During deposition, methane gas is introduced into the chamber and maintained at a set pressure in the range of 10 mTorr. An RF power source in the range of 3W to 80W is then supplied to the electrodes to ignite the methane gas into methane plasma. The charged ions and radicals formed in the methane plasma are driven by the electric potential across the electrodes and bombard the substrate to form amorphous carbon films.

The ratio of sigma bonds to pi bonds of a-C:H is controlled by the RF power during the PECVD process. The distribution of ion and radical species derivative of methane is shifted by changing the energy in the chamber plasma. This allows for control of the growth of graphite-like carbon versus diamond-like carbon. It was found that the film with primarily diamond bonds deposited at 5W had the highest clarity and a suitable refractive index in the range of 1.6 to 1.7 in the visible range.

FIG. 20 provides a non-limiting set of example layer properties for forming a visibly transparent, low-emissivity, metallo-dielectric structure using hydrogenated amorphous carbon as a dielectric substrate layer, silver as a nano-thin metal layer, and AIN as a transparent dielectric seeding layer.

Example 2: Amorphous Carbon

Amorphous carbon (a-C) is a non-crystalline form of carbon that only has short range structural order. The term a-C is also used to include hydrogen-containing (hydrogenated) forms of non-crystalline carbon. While the two primary crystalline forms of carbon exhibit either 100% sp ³ bonding (diamond) or 100% sp ² bonding (graphite), a-C films contain a mixture of sp ³ and sp ² bonding. It is the ability to control the ratio of sp ³ to sp ² bonds through growth conditions that allows the development of a-C films that exhibit astonishingly different mechanical, electrical, and optical properties. In addition to bonding hybridization, a second parameter, hydrogen content, plays an important role in determining the film properties.

Based on the percentage of sp ³ bonds and the percentage of hydrogen in the film, a-C films are separated into different categories as shown in Error! Reference source not found, and qualitatively illustrated in FIG. 22. The naming of these categories is based on historical publications. Tetrahedral carbon or hydrogenated tetrahedral amorphous carbon is generally the hardest of the amorphous carbon films followed by the so-called hydrogenated diamond-like amorphous carbon. While these forms of amorphous carbon exhibit hardness character likening diamond they generally do not exhibit optical properties of diamond. On the other polymeric- like hydrogenated carbon does not exhibit the hardness of diamond yet it can approach the optical properties of diamond vis-a-vis optical gap and index. It is the accessibility of this range of optical and mechanical properties of amorphous carbon along with its inherently dielectric nature that does not support electrical conduction in general that yields the potential of innovative constructs and applications of this material.

The superior mechanical properties of a-C, namely TAC, TAC:H and

DLC:H, have motivated most of the research in the field over the past thirty years. While a-C films have excellent mechanical properties, the infrared transparency, large optical gap, and the tunable refractive index (1 .4-2.8) of these films also present intriguing possibilities for optical applications. Also, while research into the mechanical properties of a-C has been in-depth and has reached a level of maturity, studies into the optical properties of a-C have been sparse and application specific.

The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.