A SURFACE OF A BODY

Field of the Invention

The invention relates to the field of nanosphere lithography . More specifically, the invention relates to a method for creating a pattern of nanoscale structures on a flat or curved body surface .

Background of the Invention

For several decades , nanosphere lithography (NSL ) has been considered a promising bottom-up approach to producing nanoscale patterns . The most significant advantage of NSL is it s simplicity and cost-ef fectivenes s . NSL requires minimal equipment and can be performed using nanospheres commercially available in various sizes that can be easily synthesized . Importantly, the literature often describes nanosphere lithography as a way to produce periodic patterns . Yet , nanosphere lithography based on a kinetically-controlled as sembly of nanoparticles into a 2D structure consisting of multiple crystalline domains lacks a long-range order . Fortunately, many nanotechnological applications , including, but not limited to, structures in optics , biology, and renewable energy, do not require patterns with long-range order, and nanosphere lithography is a promising, cost-ef fective patterning technique for such applications .

Despite numerous research works on nanosphere lithography and it s diverse applications , it s commercial potential has not been fully realized yet . The reasons for this may be debated, but two significant factors most likely prevent nanosphere lithography from being implemented in mas sproduction fabrications of nanoscale devices and systems . The first significant factor is the insufficient quality of the created nanoparticle (or nanosphere) monolayer. Scientific reports dealing with nanosphere lithography mostly show images of highly ordered and closely packed domains in the nanosphere layer, involving common defects - empty areas and areas of double or multilayers, whose abundance, in turn, greatly depends on the assembly technique applied. Spin coating, perhaps the easiest way to assemble nanoparticles into a monolayer, is known to produce the most significant rate of defects. Monolayers with relatively low defect rates can be formed by dip coating and solvent evaporation, as well as by the Langmuir-Blodgett technique, implemented in a roll-to-roll manner. Yet, defects cannot be avoided entirely, even when applying a high control regime to each one of these techniques.

The negative impact of these defects can be realized, for example, in one of the broadly-used fields and most appealing applications of nanosphere lithography - the fabrication of antiref lective "moth-eye" structures. A "moth-eye" sub-wavelength (dimensions of pm or nm) pattern of structures is widely used in transparent optical bodies, given that such a pattern substantially eliminates surface reflections and maximizes light transmission through the body. However, creating such nanoscale (or pm scale) structures (typically in cones, pyramids, spheres, etc. ) on glass, Sapphire, or a plastic surface is challenging. Various techniques are commonly used to create a moth-eye pattern; however, prior art techniques suffer drawbacks. Some of these techniques are complicated and incompatible with mass production. Other methods consume many hours, sometimes days, to complete. Some other techniques, while suitable for flat surfaces, are inadequate for moth-eye creation on curved surfaces. Some other techniques, particularly those targeted for moth-eye pattern creation on surfaces of Sapphire (or the like) , suffer from relatively fast product deterioration over time in harsh conditions, such as high temperatures, significant temperature variations, and/or strong vibrations. Some other techniques are complicated and not cost-effective.

When "nano-structures" or "nanoscale" bodies are used, it is also meant for structures with pm dimensions.

Theoretically, moth-eye structures can almost entirely eliminate surface reflections and maximize light transmission in specific light wavelengths or bandwidths. Moth-eye prototypes were fabricated under cautiously controlled electron beams and interference patterns. However, state-of-the-art moth-eye structures produced by nanosphere lithography are far from reaching the desired minimal reflection level, mainly due to the surface defects, as indicated, for example, by Ji et al. ACS Appl . Mater. Interfaces 2013, 5 (21) , 10731-10737) . The relatively low throughput achieved by prior art nanosphere lithography techniques is a second factor preventing the implementation of this technique in the mass fabrication of moth-eye surfaces in optical bodies. The coating of a several square centimeters' surface by a nanosphere monolayer, utilizing the Langmuir-Blodgett technique, elongates several hours, making this process impractical for mass production.

Nanosphere lithography has traditionally been viewed as a technique based on nanoparticle assembling from liquid suspension onto solid surfaces, driven by the meniscus drying at the liquid-solid-air interface. Nanoparticles can also be assembled by the so-called "dry assembling," by which nanoparticle powder is rubbed between two surfaces . Such an approach was demonstrated decades ago, e.g., by Iler, R. K. The Adhesion of Submicron Silica Particles on Glass. J. Colloid. Interface. Sci, 38(2), 496-500, (1972) ; however, this technique has not been popularized, probably due to the relatively low packing density and order of the obtained monolayer, as compared to those obtained by the Langmuir Blodgett and Dip-Coating techniques. The formation of a monolayer with a high density and uniform orientation of crystalline domains was demonstrated later utilizing rubbing between two elastomer surfaces - Park et al. Quick, Large-Area Assembly of a Single-Crystal Monolayer of Spherical Particles by Unidirectional Rubbing, Advanced Materials, 26 (27) , 4633-4638 (2014) . While this approach has opened a pathway to mass production and high-quality nanosphere lithography, it has been limited so far to the formation of monolayers on elastomer surfaces made of PolydimethylSiloxane (PDMS) , where the applicability of this fabrication approach excluded other materials, including solid ones.

It is an object of the present invention to provide a nanosphere lithography method capable of producing a motheye pattern on a curved or flat rigid body of any material.

Another object of the present invention is to provide a nanosphere lithography-based method that is simple, fast, reliable, and cost-effective.

Still, another object of the invention is to demonstrate how the method of the invention is applicable in different areas comprising optics and biomedicine.

Other objects and advantages of the invention become apparent as the description proceeds. Summary of the Invention

The invention relates to a method for creating a nanoscale or microscale pattern on a surface of a target body, which comprises: (a) providing a first elastomer substrate, and attaching it on top of a bottom platform; (b) adding a nanoscale or microscale random layer of spheres on a top surface of the first elastomer substrate, forming a first structue; (c) providing a second elastomer substrate, and attaching it to a bottom of a top platform; (d) bringing the top platform adjacent the first structure, such that the bottom surface of the second elastomer substrate faces and comes into contact with said random layer of spheres;

(e) simultaneously subjecting said two platforms to two different motions, respectively, thereby causing a rubbing operation and creating a spheres' monolayer on a surface of at least one of said two elastomers, one of said elastomers having a monolayer being defined as an active elastomer;

(f) providing a target body having a target surface; (g) coating the target surface with a layer of glue; (h) attaching said active elastomer to said target body such that said monolayer faces said layer of glue, thereby forming a combined structure comprising the target body and the elastomer attached to it; (i) removing the elastomer from the combined structure, thereby forming a target structure comprising said target surface coated by said monolayer; and (j) performing a pattern transfer process to the surface of the target body.

In an embodiment of the invention, the elastomers are selected from a group of materials comprising Polydimet hylSiloxane, Styrene-ethylene-butylene-styrene, Styrene Butadiene Styrene (SBS) , Polyisoprene, and

Polyurethane . In an embodiment of the invention, the nanoscale or microscale spheres are made of materials selected from the group comprising polystyrene , polymehylmethacrylate , and silicon dioxide .

In an embodiment of the invention, the target body is a rigid-material body .

In an embodiment of the invention, the target surface is flat or curved .

In an embodiment of the invention, a first of said dif ferent motions is a rotary motion and a second of said two dif ferent motions is a back-and-forth linear motion .

In an embodiment of the invention, the two simultaneous dif ferent motions are two oppositely rotational motions .

In an embodiment of the invention, the rigid target body is made of materials selected from the group comprising Sapphire , glas s , Silicon, and quart z .

In an embodiment of the invention, the pattern trans fer is etching protruding into the target material ' s body .

In an embodiment of the invention, the elastomer removal is made by peeling .

In an embodiment of the invention, the glue is selected from a group comprising Polyethylendiamine (PEI ) , polymer electrolytes and UV-curable polymers .

The method of the invention may be applied to an optical body, to create an antiref lective surface . In an embodiment of the invention, the pattern transfer creates a body surface structured with a periodic array of elastic micropillars, for use in anactivation of T-cells.

Brief Description of the Drawings

In the drawings :

- Fig. 1 generally illustrates the method for creating a moth-eye (or another) pattern on a surface of a rigid optical body, according to an embodiment of the invention;

- Fig. 2 shows the machinery used in the experiments carried out by the inventors;

- Fig. 3 shows a rigid flat target body, made of Silicon, covered by a polycrystalline monolayer of 200nm polystyrene nanospheres;

- Fig. 4 shows a rigid convex target body 102, made of glass, covered by a polycrystalline monolayer of lOOOnm polystyrene nanospheres;

- Figs. 5a-5c show moth-eye antiref lective structures on a flat substrate of Silicon, which was designed for the mid-IR (3.7-4.3 microns) ;

- Fig. 5d shows the measured and simulated spectra compared to bare Silicon, as measured in an experiment with the body of Figs. 5a-5c;

- Figs. 6a-6c show moth-eye antiref lective structures on a flat substrate of Silicon designed for the visible spectra;

- Fig. 6d shows the measured and simulated spectra compared to bare Silicon;

- Figs. 7a - 7f schematically illustrate the steps as performed in an experiment, beginning from a sphere monolayer on Sapphire (Fig. 7a) and ending with a hole-based array of moth-eye structures in the Sapphire - Fig. 7f;

- Fig. 8a shows a window of Sapphire covered with motheye structures fabricated by the method of Fig. 7a- 7f ;

- Fig. 8b shows a Scanning Electron Micrograph of the structures of Fig. 8a;

- Fig. 8c shows the measured reflection spectrum of the Sapphire (of Figs. 8a-8b) with the structures vs. that of bare Sapphire;

- Figs. 9a - 9f illustrate a rigidity test performed on a patterned surface created by the method of the invention;

- Fig. 10a generally illustrates a fast process suitable for the mass production of elastomer-based brush arrays to activate T cells;

- Fig 10b shows a Scanning electron micrograph of the surface of the Silicon mold, which was produced by the invention method and later used to replicate the elastomer brush.

- Fig 10c shows a false-colored SEM image of a T cell stimulated on the PDMS brush replicated from the mold shown in FIG. 10b; and

- Fig lOd shows the proliferation of T cells activated on elastomer brushes with different geometries compared to T cells activated by state-of-the-art methods .

Detailed Description of Preferred Embodiments

Fig. 1 generally illustrates the method for creating a moth-eye (or another) pattern on a surface of a rigid optical body, according to an embodiment of the invention. In step (A) , a top surface of a first elastomer substrate 106 is covered by a random (mono or multi) layer of spheres 104 to form a first temporary structure 120. Then, in step (B) , a second elastomer substrate 108 is brought into contact with the first temporary structure 120 such that the layer of spheres 104 is sandwiched between substrates 106 and 108. Still in step (B) , two different, substantially horizontal motions are applied to the bottom elastomer substrate 106 and top elastomer substrate 108. For example, bottom layer 106 is subjected to a rotational motion 112, while top layer 108 is subjected to a back- and-forth linear motion 122. In another option, although not optimal, two opposite rotational motions may be applied to the two substrates 106 and 108. Other types of motions may be provided to the two substrates 106 and 108, respectively, as long as the motions are not identical. A force 128 is also applied during the motions to maintain contact between the components of the "sandwich" structure 120 + 108. These motions 112 and 122, and force 128 cause a rubbing operation. Following the rubbing operation, a second temporary structure 130 is formed, which includes a monolayer 104a at each of substrates 106 and 108 (or at least at the surface of one of these substrates) , as shown in (C) . step (C) shows the top substrate 108 coated by monolayer (single molecule layer) 104a.

In step (D) , a target (flat or curved) surface of a rigid body 102 is coated by layer 116 of a suitable glue. Next, the second temporary structure 130 is brought into contact with target body 102, so monolayer 104a faces the adhesive layer 116. A proper force 138 is also applied. After some period t, for example, 0.5 minutes , in step (E) the second elastomer substrate 108 is removed (e.g., peeled from the structure or dissolved using some suitable solvent) , leaving a target structure 140 that includes the rigid target substrate 102, coated by the monolayer sphere- coating 104b. Given the target structure 140, various nm or pm patterns 118 of cylinders, cones, pyramids, spheres, or similar may be created using any known etching techniques 137 (not shown in Fig. 1) to form a target rigid body 150 (for example, Sapphire) with a moth-eye pattern of structures 118 as shown in (F) .

It should be noted that while other types of motions (than those mentioned above) may be used, the combination of linear and rotational motions, 112 and 122, respectively, shown in Fig.l, was found optimal to form a homogenous and high-quality monolayer 104a.

Elastomers 108 may be selected from the materials of PDMS, Styrene-ethylene-butylene-styrene (SEBS) , Styrene Butadiene Styrene (SBS) , Polyisoprene, and Polyurethane. Spheres 104 may be made of a polymer, i.e., polystyrene or polymethylmethacrylate (PMMA) , or an inorganic material such as Silicon dioxide, in a diameter of 200nm to lOOOOOnm, depending on the light wavelength at which the optical body is designed to operate in. Rotation 112 may be in the range of 5 rpm to 60rpm. Linear motion 122 may be in a rate of between 1 mm and 40 mm., and with a frequency between 0.1 Hz to 1 Hz. Structures 118, each having nanoscale or microscale dimensions, have a periodicity determined by the sphere diameter. Surface 116 may be made of any solid material (e.g., glass, Silicon, quartz) and may be flat or curved.

Further Discussion and Experiments

The invention relates to a nanosphere lithography technique for the creation of a pattern (for example, polycrystalline structure) 118 on a surface of a rigid target optical body 102, which in general, comprises the steps of (a) dry rubbing nanosphere particles 104 between respective surfaces of elastomers 10 6 and 108 to form a dense particle monolayer 104a on at least one of the elastomer surfaces ;

(b ) Coating the ( flat or curved) surface of the target rigid optical body by glue to form an adhesive layer ; ( c ) Bringing the monolayer 104a of one of the elastomers into contact with the adhesive layer on the target body; and ( d) removing the elastomer, resulting in a monolayer 104b on the surface of the rigid body; and ( e ) etching the monolayer 104b to form moth-eye pattern on the surface of the rigid target body .

Utilizing the technique described in Fig . 1 , The inventors succes s fully fabricated structures with 200nm - 2pm periodicities . The inventors also demonstrated two dif ferent applications of this fabrication approach : ( a ) fabrication of optical structures with antiref lective functionality; and (b ) fabrication of bioactive nontopographical structures for the activation and proliferation of human T cells - white blood lymphocytes that provide a base for novel immunotherapy against cancer . The invention provides a new scalable and highly ef fective nanofabrication technique with numerous nanotechnological applications .

An initial step in the method of the invention is the mechanical rubbing of nanoparticles between two elastomer substrates . Notably, previously reported unidirectional rubbing has been shown to control the orientation of crystalline domains in the nanoparticle layer . In contrast , the method of the invention is insensitive to the orientation of the crystalline domains . Given this orientation insensibility, the inventors employed another rubbing approach . The inventors found that the easiest and most robust formation of the monolayer can be achieved by rubbing the particles (spheres) 104 between two elastic surfaces (specifically, elastomers) 106, 108, one with a rotational motion 112 and another with an oscillating linear motion 122 (Fig. 1) . The inventors have found that this combination of movements produces the most effective and uniform evacuation of the excess of the nanoparticles from the interface between the surfaces of the two elastomers 106, 108, resulting in defect-free particle monolayers on both the surfaces. Such a rubbing process can be performed either manually or automatically.

Fig. 2 shows the machinery used in the experiments. The inventors used a precision lens polisher (Strassbaugh 6Y) , in which the lower elastomer 106 substrate (not seen in the figure) was attached to a rotating plate 206, and the upper elastomer 108 substrate (not seen) was attached to plate 208 at the bottom of a spindle making oscillatory linear motion 122. The process parameters were carefully controlled, such as the pressure between the two surfaces and the movement direction, periodicity, speed, and amplitude. The control assured high repeatability of the process and adaptation to the particle size.

The prior art rubbing approach was limited to creating nanosized or microsized sphere monolayers on the surface of elastomers such as PDMS . However, the invention demonstrates how monolayers can be formed on the surface of non-elastomer bodies (for example, rigid) that can be used, for instance, as lithographic masks. To achieve this, the inventors developed a process for initially creating a nanoparticle monolayer on an elastomer' s surface and then transferring the monolayer from the elastomer to a target substrate made of any rigid material. As noted, the target substrate is initially coated by a thin film of a molecular glue that attracts the nanoparticles by electrostatic forces; then, the elastomer surface covered by the monolayer is controllably pressed against the adhesive surface of the target body; Then, the elastomer is detached from the target substrate, leaving the nanoparticles attached to the target substrate. The final rigid product can be used as a mask for producing nanoscale or microscale structures on top of the rigid body. The inventors found that Polyethylendiamine (PEI) , which is dissolved in ethanol and applied onto the target surface by spin-coating, can form the thin glue layer 116 (Fig. 1) . Layer 116, made in a controlled thickness, acts as a highly efficient molecular glue, enabling the full transfer of the nanoparticles onto the target surface. Other glue materials, such as solid polymer electrolytes and UV-curable polymers, may alternatively be used. In the experiments, excess of the PEI was later removed by soaking the target substrate with the nanoparticle in ethanol for a few hours at room temperature, making the particle monolayer on the target substrate ready for the further pattern transfer process (for example, by any etching process known in the art) . The inventors successfully transferred monolayers of nanoparticles of different sizes to either flat or curved surfaces of target bodies. Fig. 3 shows a rigid flat target body 102, made of Silicon, covered by a polycrystalline monolayer of 200nm polystyrene nanospheres. Fig. 4 shows a rigid convex target body 102, made of glass, covered by a polycrystalline monolayer of lOOOnm polystyrene nanospheres.

This new fabrication approach is useful in various applications: For example, the invention may be used for fast and highly efficient fabrication of moth-eye ant iref lect ive structures, in which the pattern formed by the particle monolayer is transferred into the substrate by plasma etching. The example of Figs. 5a-5c shows moth-eye ant iref lect ive structures on a flat substrate of Silicon, which was designed for the mid-IR (3.7-4.3 microns) . Fig. 5d shows the measured and simulated spectra compared to bare Silicon. The example of Figs. 6a-6c shows moth-eye ant iref lect ive structures on a flat substrate of Silicon, which was designed for the visible spectra. Fig. 6d shows the measured and simulated spectra compared to bare Silicon. The monolayers of the examples of Figs. 5a-5c and 6a-6c were fabricated from Polystyrene spheres with a diameter of 1 micron and 500nm, respectively. In both cases, the nanosphere monolayer was first applied on PDMS, followed by the rubbing operation of Fig. 1 (A) , and transferred from a PDMS substrate 108 to a rigid Silicon layer 102. The patterning process included trimming the nanospheres by Oxygen plasma etching and Silicon plasma etching through the nanosphere mask and removing the nanospheres by rinsing in acetone.

More specifically, Figs. 5a to 5d show experimental reflection results for a target flat rigid body (shown in Fig. 5a) , covered antiref lective moth-eye structures produced from 1 -micron spheres. The reflection in mid-IR spectra produced by the fabricated moth-eye structures was compared between measured bare Silicon, simulation spectra, and measurements for the dense structures' surface. All structures had 800nm height and 800nm base diameter conical shapes. The ability of the fabricated structures to reduce the reflection, compared to a bare-Silicon surface, was found to be comparable to state-of-the-art moth-eye structures fabricated by much more complicated and expansive methods , such as interference lithography or electron beam lithography .

In similarity to the experiment s of Figs . 5a to 5d, Figs . 6a to 6d show experimental reflection result s for a flat target rigid body ( shown in Fig . 6a ) , covered by moth-eye structures produced from 500nm spheres - Figs . 6b and 6c . The reflection in the visible spectra from the fabricated moth-eye structures was compared between measured bare Silicon and the dense structures ' surface measurement s . All structures had cylindrical shapes of 3000nm height and 230nm base diameter , ( again, compared to bare Silicon surface , the fabricated structures ' ability to reduce the reflection was comparable to state-of-the-art moth-eye structures fabricated by much more complicated and expansive methods , such as interference or electron beam lithography .

Moth-eye antiref lective structures are commonly produced as cylindrical or conically shaped bumps with a base diameter in the light of interest subwavelength range . This form is bioinspired from nanometric bumps on the cornea of nocturnal moths . Alternatively, antiref lective structures with similar optical functionality can also be realized as an array of holes with a subwavelength diameter as soon as the air-material volume ratio that determines the ef fective refractive index in the formed ant iref lective layer is kept the same as in an array of bumps . The arrays of holes are more attractive for optics since they are more mechanically durable than an array of bumps . However, fabricating an array of holes is more complicated than bumps . The inventors demonstrated that the nanosphere lithography approach of the invention succes s fully produces hole-shaped ant iref lective structures in Sapphire . Sapphire is a broadly used optical material , especially in high-end optics , but also in consumable devices , such as windows for iPhone cameras and windows for luxury watches , as it combines excellent optical transmittance with mechanical and environmental stabilities . At the same time , reflection from Sapphire must be eliminated or minimized for most of it s optical applications . Standard vacuum-deposited ant iref lect ive thin films on Sapphire suf fer from low mechanical stability and have a thermal expansion coef ficient substantially dif ferent from that of Sapphire , resulting in thermal stres ses that , in turn, lead to cracks and delamination . While providing a moth-eye layer as an ant iref lect ive solution in Sapphire is attractive , the fabrication of such a layer is extremely challenging due to the dif ficulty of Sapphire etching by plasma . So far, mas s production of moth-eye structure s on Sapphire has been demonstrated only for the visible spectrum, where the etching depth does not exceed 200nm . On the other hand, Sapphire is also broadly used in mid-infrared applications . Yet , moth-eye structures for mid-infrared wavelength, whose vertical dimension should be about 1 micron, depending on the desired wavelength, have been demonstrated only by direct laser writing, which is highly complicated for mas s production and impractical .

The nanosphere lithography approach of the invention is simple and suitable for mass fabricating moth-eye structures on Sapphire , including for the mid-infrared spectrum ( 4 microns to 5 microns ) .

In another experiment , a rubbered monolayer of 1pm Polystyrene spheres was transferred to a sapphire previously coated with 200nm film of Polybenzylmethacrylate (PBMA) and 300nm of PEI . The sphere trans fer was followed by removing the exces s PEI by soaking in ethanol for a few hours and etching with Oxygen plasma, which had three simultaneous purposes: (i) reducing the size of polystyrene spheres; (ii) removal of the excess of PEI; and (iii) etching of PBMA in the open air. This etching also produced an undercut in the PBMA. Then, 330nm of Nickel, a commonly used masking material for Sapphire plasma etching, was deposited by e-gun evaporation, and a meshlike Nickel mask was obtained after liftoff. The thickness of the Nickel mask was chosen based on the known Ni-Saphire selectivity of 1:3 in BCI3 plasma used here to etch Sapphire, and the relatively thick Nickel film ensured that the mask would not disappear during the etching process. The PBMA sacrificial layer was used here to elevate the nanospheres above the Saphire surface. This elevation and the undercut in PBMA were essential for the successful liftoff after the deposition of such a thick Nickel film. Finally, the sapphire body was plasma-etched, and the rest of the Nickel mask was removed with hot Piranha solution. Figs. 7a - 7f schematically illustrate the steps as performed in an experiment, beginning from a sphere monolayer on Sapphire (Fig. 7a) and ending with a holebased array of moth-eye structures in the Sapphire - Fig. 7f. In the first step, the spheres are transferred to the body surface, which has been previously coated with a thin film of polymer (200nm of Polybenzylmathacrlate, PBMA) , in this case, and a glue (300nm of PEI in this case) , (Fig. 7a) . Then, the spheres are partially etched to reduce their diameter, using Oxygen plasma (Fig. 7b) . The same etching also removes the polymer and glue in the areas between the spheres, and produces undercut in the spheres. Then, a film of metal mask is evaporated through the etched spheres (300nm of Nickelin in this case) (Fig 7c) , and the spheres with the polymer films are removed by liftoff in an organic solvent such as boiling acetone, leaving metallic mesh-like mask on the surface of the body (Fig . 7d) . Finally, Sapphire is etched through the mask by reactive plasma based on Boron tri-chloride (Fig . 7e ) , and the remnant s of Nickel mask are removed from the surface by wet etching using a reactive medium such as piranha solution (hot mixture of sulfuric acid and hydrogen peroxide ) .

Fig . 8a shows a window of Sapphire covered with moth-eye structures fabricated by the method of Fig . 7a-7 f . Fig . 8b shows a Scanning Electron Micrograph of these structures . Fig . 8 c shows the measured reflection spectrum of the Sapphire with the structures vs . that of bare Sapphire . The plot also shows the simulated spectrum of the structures . The simulations were done using homemade software based on the ef fective medium approach . It can be seen that the fabricated structures reduced the reflection in the desired spectral range from ~ 6 . 5% down to ~2 % . The inventors believe that this reflection can be further reduced by optimizing the geometry of the antiref lective structures .

State-of-the-art moth-eye structures fabricated by prior art methods , such as electron beam lithography, interference lithography, or Langmuir Blodgett as sembly, are unlikely suitable for practical optical applications due to the low throughput and high cost . A more cost- ef fective alternative to these structures , which also seems more suitable for mas s production, includes randomly shaped ant iref lective structures . These randomized structures may be produced either by maskles s plasma etching or by etching through a mask formed by dewetting metallic films . Today, randomized antiref lective structures are commercially available . However, their main drawback is that they are very fragile due to their uncontrolled shape and high-aspect ratio . This fragility makes the optical body surfaces covered by these random structures completely intolerable to any mechanical contact . For instance , such surfaces cannot be cleaned by methods commonly used in optics , such as wiping, substantially limiting the applications of these structures . In contrast , the moth-eye structures produced by the invention pos ses s extreme mechanical stability and can withstand even mechanically aggres sive clearing .

Figs . 9a - 9f illustrate a rigidity test performed on a patterned surface created by the method of the invention . The inventors performed a commonly used pencil test (Fig . 9a ) to test the mechanical stability . A line was drawn on the patterned surface with a pencil of HB hardnes s (Figs . 9b and 9c ) . Then, the same area was wiped with cleaning paper soaked in isopropanol , dried, and wiped again using a rubber eraser . Naturally, the wiping paper used and erasing operation did not remove the graphite line written by the pencil from the surface . Finally, the graphite was entirely removed by 10 minutes of immersing the surface in hot piranha solution, followed by water rinsing and drying . Microscopic observation of the drawing area showed ( see Figs . 9d-9f ) that the surface pattern structure shape was unaf fected by the pencil drawing and the subsequent attempt s to clean it .

Besides the fabrication of optical nano-structures , the high-throughput production of periodic nanopatterns with polycrystalline structures can be used in many additional applications , for example , in biology and biomedicine . These emerging applications are included but not limited to the fabrication of high-resolution biosensors for the detection of various biomarkers and analytes , the fabrication of precisely patterned surfaces that can influence cell behavior and guide tis sue growth, as well as promote cell adhesion, proliferation, and dif ferentiation, thereby facilitating the development of functional tis sues . Overall , the applications of nanosphere lithography in biomedicine hold immense potential for advancing diagnostics , tis sue engineering, and therapeutic interventions .

The inventors have demonstrated the versatility of the "dry" nanosphere lithography method of the invention in a biomedical application ( as one example ) . In recent years , immunotherapeutic applications of T cells have gained significant attention in cancer treatment . One notable approach is adoptive cell trans fer (ACT ) , where T cells are isolated from a patient , genetically engineered or modified to enhance their targeting capabilities , and then reinfused back into the patient ' s body . These modified T cells can ef fectively target and destroy cancer cells , leading to remarkable responses in patient s with certain hematological malignancies . The ability to genet ically modify T cells and enhance their therapeutic potential greatly relies on their ex-vivo activation and proliferation . This activation is commonly done with magnetic polymer microbeads covered with antibodies against the activating and costimulatory receptors . However, such beads were originally developed for selective cell separation, and neither their shape nor mechanical properties have been ever optimized for T cell activation . In the last decade , intensive research has aimed at developing new material-based approaches for the ef fective ex-vivo activation of T cells . One such approach was recently demonstrated by using a surface structured with a periodic array of elastic micropillars , which produced much more ef fective activation and proliferation of T cells compared to those produced by standardly used magnetic beads (Pandey, A . CS Appl . Mater . Interfaces 2023) . Remarkably, the fabrication of such arrays was based on the relatively easy and simple casting of elastomer precursors from a prefabricated mold, which was, however, produced by electron beam lithography. Thus, the key limitation of this approach has been so far that electron beam-lithography is a serial, low-throughput patterning method, which is unsuitable for mass fabricating large-area surfaces to activate therapeutic amounts of T cells.

The inventors demonstrated how the nanopatterning method of the invention could address and resolve the above limitation of e-beam lithography for the quick and mass production of elastomer-based brush arrays for the activation of T cells . To fabricate the brushes, the inventors assembled polystyrene microspheres (diameters of 1 micron and two microns were used) on PDMS, transferred the obtained microsphere monolayer to Silicon substrate, etched Silicon through the formed microsphere mask to get an array of Silicon pillars, and transferred this geometry to PDMS by double replication (Fig. 10a) . The inventors probed different arrays and different geometries, with the periodicities in the range of 1-2 microns, pillar diameter in the range of 260nm to 1.1 microns, and pillar height in the range of 1.3 micron to 2.3 microns. An example is shown in the SEM image in Fig 10b. The obtained PDMS substrate with the pillar arrays on its surface was precisely cut and placed in the bottom of a cell culture dish. Before the activation of T cells, the surface of the PDMS pillars was treated with UV ozone, coated with chemisorbed (3- Aminopropyl ) t riethoxysilane (APTES) , followed by the attachment of anti-CD3 and anti-CD-28, which are the activating and costimulatory antibodies for T cells, respectively . Tbhe inventors isolated human T cells from the peripheral blood of healthy donors and stimulated them on the fabricated surface for 24 hours . Fig 10 c shows a false- colored SEM image of a T cell stimulated on PDMS pillars . Then, the inventors separated the cells from the activating surfaces and cultured them in culturing media for seven days . IL-2 supplement was added during the culturing period . Commercial magnetic beads coated with anti-CD3 and anti- CD28 (DynabeadsTM, Thermofisher ) and the bottom of a plastic 24-well plate with no antibodies were used as activation controls . The proliferation of T cells was measured after seven days (Fig . l Od) . It can be observed that for all the probed pillar geometries , the proliferation of T cells was either comparable to or higher than that produced by the beads . Yet , it was also observed that the pillar geometry could tune the proliferation . To summarize , the inventors introduced a high-throughput method for producing T-cell activating surfaces using nanosphere lithography .

While some embodiment s of the invention have been described by way of illustration, it will be apparent that the invention can be carried into practice with many modifications , variations , and adaptations , and with the use of numerous equivalent or alternative solutions that are within the scope of persons skilled in the art , without departing from the spirit of the invention or exceeding the scope of the claims .