Antireflective Surfaces Research Articles

Highly reproducible c-Si texturing by metal-free TMAH etchant and monoTEX agent

Surface texturing of a silicon solar cell is critical to provide surface antireflection and light trapping. The common texturing method based on KOH as an etchant with isopropyl alcohol (IPA) as a wetting agent suffers two disadvantages: introducing metal contamination and low repeatability. To circumvent the limitation of the KOH-IPA method, we develop a new texturing regime by substituting TMAH for KOH, and a commercial surfactant RENA monoTEX for IPA. This TMAH-monoTEX method shows advantages of non-metal contamination, high reproducibility, short process time and small random pyramids. IBC solar cells fabricated with the TMAH-monoTEX texture achieved an efficiency of 25% with Jsc of 42.9 mA/cm2, Voc of 719 mV and FF of 81.1%.

Fabrication of Anti-Reflective Surface with Superhydrophobicity/High Oleophobicity and Enhanced Mechanical Durability via Nanosecond Laser Surface Texturing.

In this work, anti-reflective surface with superhydrophobicity/oleophobicity and enhanced abrasion resistance was fabricated on steel alloy surface. Two different surface patterns (i.e., parallel microgrooves and spot arrays) were created by nanosecond laser ablation and chemical immersion. The surface micro/nanostructure, spectral reflectance, wettability, and abrasion resistance of all the samples were determined. The experimental results showed that the laser-chemical treated surfaces exhibited much lower spectral reflectance and significantly enhanced surface integrities compared with the untreated surface. Firstly, the contact angles of water, glycerol, and engine oil on the laser-chemical treated surfaces were increased up to 158.9°, 157.2°, and 130.0° respectively, meaning the laser-chemical treated surfaces achieved both superhydrophobicity and high oleophobicity. Secondly, the laser-chemical treated surface showed enhanced abrasion resistance. The experimental results indicated that the spectral reflectance of the laser-chemical treated surfaces remained almost unchanged, while the laser-chemical treated surface patterned with parallel microgrooves sustained superhydrophobicity with a water contact angle of 150.2° even after more than one hundred abrasion cycles, demonstrating the superior mechanical durability. Overall, this fabrication method has shown its effectiveness for fabrication of multifunctional metal surface integrating the surface functionalities of anti-reflectivity, superhydrophobicity/high oleophobicity, and enhanced abrasion resistance.

Anti-reflection silicon with self-cleaning processed by femtosecond laser

The creation of functional surfaces has been studied extensively in the past due to their potential applications in corrosion resistance, anti-fouling, drag-reduction, and self-cleaning. In this paper, we present a simple method to fabricate an anti-reflection silicon surface with good self-cleaning effect by combined femtosecond laser processing with chemical modification. The reflectance of the prepared silicon is lower than 5%, and the surface exhibits a contact angle of 166° and a sliding angle of 3° for water. The water droplets can easily carry the contamination particles away from the prepared surface. More importantly, by changing the defocusing amount, we find that there are two different anti-reflection mechanisms. In the first mechanism, the light enters the object mainly through small surface nanostructures with dimensions greater than the wavelength of the incident light. In the second mechanism, the incident light is mostly reflected back and forth in the micro-hole and then absorbed by the silicon. In both mechanisms, the micro-hole structures are more suitable as an anti-reflection structure. Finally, photo-thermal conversion experiments are conducted on the prepared anti-reflection silicon surface.

Highly transparent, hot water and scratch resistant, lubricant-infused slippery surfaces developed from a mechanically-weak superhydrophobic coating

Superhydrophobic surfaces are usually easy to damage due to their micro/nanoporous structures. As a solution, such a porous surface can be filled with lubricant forming an alternative water-repellent surface, namely, lubricant-infused slippery surface (LISS), which is supposed to be mechanically stronger owing to its dense texture. However, to what degree the mechanical reinforcement could achieve remains an issue without deep understanding. In this study, an extremely weak nanostructured superhydrophobic SiO2 coating is demonstrated capable of being converted into a robust, durable, and antireflective slippery surface with a simple lubrication process. Silicone oils of different viscosities are infused into the SiO2 coatings and the 20 and 50 cSt oils are found to generate superior droplet-shedding properties. These slippery coatings exhibit robust repellency against water jet impacts and hot-water splashes, withstand cotton and sandpaper abrasions, retain their slippery property when subjected to consecutive scratches, long-term immersion, high-speed spinning, water shear friction, and different pH liquids. These performances reflect the powerful role played by the infused oil in enhancing the cohesion of coating and the interactions between coating and substrate, and illustrate the available degree to which the mechanical reinforcement could achieve. This study provides a deep insight into the interactions between a porous coating and infused lubricant, and also a facile method for producing robust LISSs.

Preparation of Moth-Eye Structures By Nanoimprinting Using Anodic Porous Alumina Molds

Moth-eye structures composed of an ordered array of tapered pillars have attracted increasing interest owing to their application such as displays, lenses and solar cells. A large number of methods have been reported for the preparation of moth-eye structures. Among them, nanoimprinting is a promising method for the high-throughput preparation of moth-eye structures with large sample areas. In our previous works, we have reported that an ordered anodic porous alumina can be used for a nanoimprinting mold to prepare seamless moth-eye surfaces with large sample areas [1,2]. In this process, the moth-eye structures with optimized antireflection properties was obtained by adjusting the preparation conditions of porous alumina molds. One problem currently limiting the practical use of moth-eye structures is their low durability. This problem originates from the fine, high-aspect geometrical features of moth-eye structures. Improved durability is essential for practical application of moth-eye structures as antireflection surfaces. In the present report, we describe the preparation of renewable antireflection surfaces by nanoimprinting using an anodic porous alumina mold. Renewable antireflection surfaces were formed by the lamination of polymer thin films with moth-eye structured surfaces [3]. Thin-film lamination was performed using a photocurable monomer as an adhesive. A renewed low-reflectance moth-eye structured surface could be exposed by peeling the uppermost film from the sample. Each exposed surface with moth-eye structure successfully lowered the reflection of incident light. The obtained renewable antireflection surfaces are expected to be applicable to several types of optical devices requiring high durability, such as the surface panels of displays. T. Yanagishita, K. Nishio, and H. Masuda, Appl. Phys. Express, 2, 022001 (2009).T. Yanagishita, T. Hidaka, M. Suzuki, and Hideki Masuda, J. Vac. Sci. Technol. B, 34, 021804 (2016).T. Yanagishita, T. Kondo, and H. Masuda, J. Vac. Sci. Technol. B, 36, 031802 (2018).

Effective Surface Texturing of Diamond-Wire-Sawn Multicrystalline Silicon Wafers Via Crystallization of the Native Surface Amorphous Layer

To increase the market shares of multicrystalline silicon (mc-Si) wafers obtained using diamond-wire sawing (DWS), it is necessary to develop efficient and cost-effective texturing methods. Surface texturing processes that increase light absorption are essential for manufacturing high-efficiency solar cells. The smooth surface, phase transformations, and amorphous silicon (a-Si) layer on mc-Si wafers manufactured via DWS hinder the effective texturing under conventional acidic conditions, which are typically used for multiwire slurry sawing (MWSS). To address this issue, this article focused on an efficient texturing process of DWS wafers by adapting a pre-thermal treatment (TT) process. We found that DWS mc-Si wafers could be effectively textured after the TT process by altering the surface roughness through the crystallization of surface amorphous silicon (a-Si) and phase transformation layers. For the DWS mc-Si wafers textured under conventional acidic etching conditions without TT, Rw was found to be 31.7%. The altered surface conditions achieved via the proposed TT method facilitate effective texturing on the DWS mc-Si wafer surface. Consequently, a weighted average reflectance (Rw) of 24.5% was obtained, which was comparable to that for MWSS mc-Si wafers subjected to conventional acidic etching (Rw = 24.4%). As a result of depositing a SiN x for surface passivation and antireflection coating in solar cell applications, Rw values of 8.1% and 8.3% were obtained for the thermal treated DWS mc-Si wafer and MWSS mc-Si wafer, respectively. The proposed texturing process for DWS mc-Si wafers can easily be applied to industrial inline processes using cost-effective existing acidic etching solutions.

Narrow-angle scatter of reflectivity-suppressing nanostructured surfaces

Antireflective nanostructured surfaces (ARSS) enhance optical transmission through suppression of Fresnel reflection at boundaries between layered media. Previous studies show that random ARSS (rARSS) exhibit broadband enhancement and polarization insensitivity in transmission when applied to flat optical windows. Zinc selenide windows with rARSS treatment were fully characterized (transmittance, reflectance, and angular scatter) in the midwave and long-wave infrared range (2 to 12 μm). Four morphologically different, random nanoroughness, antireflective surfaces were tested at: normal incidence transmission, at 15 deg angle of incidence, and 15 deg to 45 deg angle of reflection. The angular reflectance distribution resembles a diffuse dipole radiator due to the finite elongated beam cross section at the incidence surface. Scattering diagrams with main and side lobes are presented. Partially integrated scatter values were obtained, allowing the comparison of random antireflective boundary performance to optically flat surfaces. Comparing axial transmission and specular reflection with the scattered performance, an accurate determination of the redistribution of the incident energy is obtained. Measurements of the rARSS feature topology were determined from autocorrelation of the scanning electron microscope images of the nanoroughened substrates, to assess the structured surfaces’ feature scales. The results show differences in scattered intensity over the wavelength bands of interest, correlating with surface random feature populations.

Wafer-scale high anti-reflective nano/micro hybrid interface structures via aluminum grain dependent self-organization

Surface anti-reflection (AR) with micrometer or nanometer scaled surface texture has been studied extensively and showed excellent light extraction (or harvest) performance in corresponding opto-electronic devices. In this paper, a 2-inch anodized aluminum oxide (AAO) template with nano/micro hybrid structure was obtained directly through a simple lithography-free aluminum anodization process for the first time. This new nano/micro hybrid structure combines the advantages of sub-100 nm sub-wavelength structure (SWS) and micrometer scaled surface roughening. Aluminum grains were found to rearrange the distribution of the penetrated surface current during the anodization and eventually induced the micrometer scaled fluctuation underneath. The ultra-thin AAO replication scheme was introduced to fabricate and study the spectrum (300 nm to 800 nm) dependent AR performance of the nano/micro hybrid PDMS structure, which obtained an AR enhancement fraction of more than 42% higher than that of the nano-patterned one. Thin film and GaN based light-emitting diode (LED, 450 nm) models were built and studied. Compared to the flat LED, the AR enhancement of the nano/micro structured one can reach as high as more than 3 folds. These results suggest the nano/micro hybrid structure could be a good alternative for the applications of surface AR structure.

Discovering high-performance broadband and broad angle antireflection surfaces by machine learning

Eliminating light reflection from the top glass sheet in optoelectronic applications is often desirable across a broad range of wavelengths and large variety of angles. In this paper, we report on a combined simulation and experimental study of single-layer films, nanowire arrays, and nanocone arrays to meet these antireflection (AR) needs. We demonstrate the application of Bayesian learning to the multiobjective optimization of these structures for broadband and broad angle AR and show the superior performance of Bayesian learning to genetic algorithms for optimization. Our simulations indicate that nanocone structures have the best AR performance of these three structures, and we additionally provide physical insight into the AR performance of different structures. Simulations suggest nanocone arrays are able to achieve a solar integrated normal and 65° incidence angle reflection of 0.15% and 1.25%, respectively. A simple and scalable maskless reactive ion etching process is used to create nanocone structures, and etched samples demonstrate a solar integrated normal and 65° reflection of 0.4% and 4.9%, respectively, at the front interface.

Magnetic force assisted thermal nanoimprint lithography (MF-TNIL) for cost-effective fabrication of 2D nanosquare array

The work presented here describes a simple, low-cost, and unconventional technique to fabricate a 2D nanosquare array using magnetic force assisted thermal nanoimprint lithography (MF-TNIL). The nanofabrication process involves two steps: (i) fabrication of a 2D nanosquare array template on a laminated plastic sheet via sequential thermal nanoimprinting of linear nanograting polydimethylsiloxane (PDMS) stamp, and (ii) reversal imprinting of template on UV curable polymer using soft UV-nanoimprint lithography. Without using an expensive nanofabrication tool, our proposed technique can fabricate nanosquare array over an area of 1 × 1 cm2 with individual nanosquare having a feature size of about 383 nm × 354 nm × 70 nm. We believe that our proposed MF-TNIL represents a promising nanofabrication technique that will allow fabricating various types of nanostructures for their applications in developing sensors, anti-reflective surfaces, self-cleaning surfaces, etc.

Creating a three-dimensional surface with antireflective properties by using femtosecond-laser Bessel-beam-assisted thermal oxidation.

Metal surfaces with low reflectance have received considerable attention for their great optical, electrical, and thermal properties. However, the difficulty in achieving low reflectance on curved metal surfaces has hindered their practical applications. We propose a rapid and flexible method for processing a three-dimensional surface with antireflective properties. A Bessel beam created using an axicon is employed to generate ripple structures on the curved surface, thereby assisting subsequent thermal oxidation. Ripple structures coated with oxide semiconductor nanowires are then processed on a Cu substrate, thus further reducing reflectance. Antireflective properties with a minimum reflectance of less than 0.015 at a wavelength of 500-1200 nm could be achieved by using this method. This presented approach reduces dimensionality in laser processing, subsequently improving processing efficiency, and provides a foundation for the practical application of metal antireflective surfaces.

Substrate-engraved antireflective nanostructured surfaces for high-power laser applications

A critical component for all high-power laser systems that is particularly susceptible to laser damage is the antireflective coating, which maximizes energy transmission and minimizes scattered and stray light. We demonstrate the ability to generate substrate-engraved nanostructured surfaces (NS) for scalable and designable antireflective (AR) coatings that are monolithic to the substrate and can handle peak power levels comparable to the bulk material. Experimentally measured reflectance from these fabricated structures has validated our effective index theory-based transmission matrix model, demonstrating the designability of the AR properties. Upon exposure to sufficiently high fluences, a new mode of damage, nanostructured surface damage, has been observed and is likely the result of thermally driven material reflow accompanied by plasma initiation on the nanostructured surface. At 1053 nm, nanostructured surface damage onsets at 39 J / c m 2 with sample cleaning and 74 J / c m 2 after laser conditioning—very close to the reference substrate at 81 J / c m 2 . At 351 nm we show damage onset of 30 J / c m 2 , with reference substrate material damage onset of 47 J / c m 2 . Therefore, damage is close to the bulk material and represents an improvement with respect to other methods. The nanostructured surfaces were found to be mechanically durable and able to withstand cleaning procedures with sonication. Under normal incidence mechanical testing with a 200 µm radius indenter tip, the AR performance of these nanostructured surfaces was minimally impacted at pressures orders of magnitude higher than an average fingerprint pressure—indicating that incidental handling contact will not affect NS structures. Mechanical damage is attributed to plastic compression, not fracturing of the NS features. We demonstrate for the first time, to the best of our knowledge, that NS AR coatings, despite being rich in etched surface features, can tolerate laser fluences comparable to unprocessed optical surfaces. Furthermore, laser-damage features of NS indicate a unique non-growing failure mode whereby following absorption the featureless damage site does not precipitate future damage growth, reducing considerably the burdens for managing optics processing in high-power laser systems.

Effect of Etching Temperature on the Surface Texturing of Si{100} in an Extremely Low Concentration Tmah for Minimized Reflectivity

Among various renewable energy resources, solar energy is one of the most abundant energy available in nature. The solar energy can be utilized by converting photon energy into electrical energy by using solar cells as energy harvesters. Silicon-based solar cells dominate the current photovoltaic market because of its higher efficiency, excellent stability, non-toxicity, lower processing cost and excellent reliability in the outdoor conditions.1 However, the silicon solar cell efficiency can be further increased by reducing the front surface reflection from silicon, which is greater than 35%. In order to reduce the reflection from silicon surface, surface texturing is done where silicon surface is intentionally made rough. Wet anisotropic etching is most widely used in surface texturing of silicon because of its high throughput and lower cost. Potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) are two most extensively used alkaline solution for surface texturing of silicon. 2-4 In these two etchants, TMAH is preferred because it is fully compatible with CMOS process and also provide high etch selectivity between silicon and silicon dioxide. Surface texturing using low concentration TMAH (<5%) results in high surface roughness. This is a remarkable observation that can be applied in solar cell industries to minimize the reflection from silicon front surface.In this work, we have studied the effect of very low concentration TMAH (1.0-0.1 wt%) without adding any additive and agitation during etching for surface texturing of Si{100} surface. The main objective of this study is to achieve an optimized etched surface topography at lowest possible etching concentration and etching time to minimize the reflectance for application in solar cells. The average solar weighted reflectance (Rsw) of around 10% is obtained in a very mild etching conditions. Compared to the previous results reported in literatures and also the mild etching conditions, reflectance values obtained in this work are quite promising for large area surface texturing of silicon solar cell panels for enhancement in their efficiency. In addition, the use of very low concentration TMAH minimizes the chemical waste. This also helps in adopting the technique for fabricating anti-reflective silicon surfaces at large scale.

Hyperspectral imaging for high-throughput, spatially resolved spectroscopic scatterometry of silicon nanopillar arrays.

Modern high-throughput nanopatterning techniques, such as nanoimprint lithography, make it possible to fabricate arrays of nanostructures (features with dimensions of 10's to 100's of nm) over large area substrates (cm2 to m2 scale) such as Si wafers, glass sheets, and flexible roll-to-roll webs. The ability to make such large-area nanostructure arrays (LNAs) has created an extensive design space, enabling a wide array of applications including optical devices, such as wire-grid polarizers, transparent conductors, color filters, and anti-reflection surfaces, and building blocks for electronic components, such as ultracapacitors, sensors, and memory storage architectures. However, existing metrology methods will have trouble scaling alongside fabrication methods. Scanning electron microscopy (SEM) and atomic force microscopy (AFM), for instance, have micron scale fields of view (FOV) that preclude comprehensive characterization of LNAs, which may be manufactured at m2 per minute rates. Scatterometry approaches have larger FOVs (typically 100's of µm to a few mm), but traditional scatterometry systems measure samples one point at a time, which also makes them too slow for large-scale LNA manufacturing. In this work, we demonstrate parallelization of the traditional spectroscopic scatterometry approach using hyperspectral imaging, increasing the throughput of the technique by a factor of 106-107. We demonstrate this approach by using hyperspectral imaging and inverse modeling of reflectance spectra to derive 3-dimensional geometric data for Si nanopillar array structures over both mm and cm-scale with µm-scale spatial resolution. This work suggests that geometric measurements for a variety of LNAs can be performed with the potential for high speed over large areas which may be critical for future LNA manufacturing.

Broadband, wide-angle antireflection in GaAs through surface nano-structuring for solar cell applications

We demonstrate broadband and wide-angle antireflective surface nanostructuring in GaAs semiconductors using variable dose electron-beam lithography (EBL). Various designed structures are written with EBL on a positive EB-resist coated GaAs and developed followed by shallow inductively coupled plasma etching. An optimized nanostructured surface shows a reduced surface reflectivity down to less than 2.5% in the visible range of 450–700 nm and an average reflectance of less than 4% over a broad near-infrared wavelength range from 900–1400 nm. The results are obtained over a wide incidence angle of 33.3°. This study shows the potential for anti-reflective structures using a simpler reverse EBL process which can provide optical absorption or extraction efficiency enhancement in semiconductors relevant to improved performance in solar photovoltaics or light-emitting diodes.

Mimicking flower petals to fabricate self-cleaning and antireflective polymer surfaces

This work explored a facile way to fabricate superhydrophobic and antireflective polymer surfaces using Canna indica flower petals. A simple, inexpensive two-step soft-lithography technique was employed to replicate the surface structures of C. indica flower petals onto two different polymer surfaces namely, polydimethylsiloxane (PDMS) — a hydrophobic polymer and resorcinol–formaldehyde (RF) xerogel — a hydrophilic polymer. First, a negative replica was prepared in PDMS using the flower petal as a template. Second, the negative PDMS replica was later used as a stamp to prepare a positive replica in both PDMS and RF xerogel. These replicated structured surfaces greatly influenced the wettability properties. The contact angle of the replicated PDMS surfaces increased to the nearly superhydrophobic values of 145° (negative PDMS replica) and 144° (positive PDMS replica) compared with that of the plain surface, which is 101°. Interestingly, the contact angle of the replicated RF surface significantly increased to 151° (superhydrophobic) compared with that of the planar RF surface, which is hydrophilic (68°). Furthermore, the replicated polymer surfaces exhibited not only excellent superhydrophobic properties but also antireflective properties. These multifunctional surfaces with superhydrophobicity as well as an omnidirectional antireflective property may find a wide range of applications, such as solar energy harvesting, optical displays and marine applications.

Black Metals: Optical Absorbers.

We demonstrate a concept and fabrication of lithography-free layered metal-SiO2 thin-film structures which have reduced reflectivity (black appearance), to as low as 0.9%, with 4.9% broadband reflectance (8.9% for soda lime) in the 500–1400 nm range. The multi-layered (four layers) thin-film metamaterial is designed so that optical impedance matching produces minimal reflectance and transmittance within the visible and infra-red (IR) spectral region for a range of incident angles. The structure has enhanced absorbance and is easily tuned for reduced minimal transmission and reflection. This approach should allow for novel anti-reflection surfaces by impedance matching to be realized.

Shape anisotropic Fe3O4 nanotubes for efficient microwave absorption

Although Fe3O4 particles have exhibited excellent microwave absorbing capacity and widely used in practical application due to the synergistic effect of magnetic loss and dielectric loss, their applications are still limited for the required high mass fraction in absorbers. To overcome this problem, the development of Fe3O4 materials with low dimensional structures is necessary. In this study, the shape anisotropic Fe3O4 nanotubes (NTs) with low mass ratios were applied to realize efficient microwave absorption. The NTs with different aspect ratios were prepared through facile electrospinning followed by two-step thermal treatments and mechanical shearing. The cross-linked nanotubular structure enabled the absorbers to have much higher electrical conductivity, multiple scattering, polarization relaxation and better anti-reflection surface, while the shape anisotropic NTs maintained significant multiple resonances with stronger coercivity. These all were beneficial to microwave absorption with enhanced dielectric loss, magnetic loss and sterling impedance matching. Results showed that the absorber with 33.3 wt.% of short Fe3O4 NTs had minimum reflection loss of -58.36 dB at 17.32 GHz with a thickness of 1.27 mm, and had the maximum effective absorbing bandwidth (EAB) of 5.27 GHz when the thickness was 1.53 mm. The absorber with 14.3 wt.% of long Fe3O4 NTs presented the widest EAB in certain radar band with attenuated 80.75% X band and 85% Ku band energy bellow -10 dB at the thickness of 2.65 and 1.53 mm, respectively. This study provided an approach for the development of shape anisotropic magnetic absorbing materials, and broadened their practical applications as magnetic absorbers.

Growth of porous chitin-nanofibrous structure via layer-by-layer self-assembly under existing ionic effects for antireflective and antifogging coatings

Antireflection surfaces reduce reflectance and maximize light transmission. Therefore, these types of surfaces play an important role in optical technologies. The precise control of coating thickness and refractive index via self-assembly from nano- to microscales has accelerated the development of antireflection surfaces. One promising technique for the production of antireflection coatings is the layer-by-layer (LbL) method, which has recently received significant improvements, particularly in the utilization of fiber materials. However, given that the ionic effect hinders self-assembly and degrades the porous nanofiber structure, nanofiber LbL films remain difficult to fabricate. To address this issue, this study fabricates antireflective nanofibril coatings by controlling the porosity under various ionic conditions in an LbL approach. The addition of NaCl modifies the ionic condition and transforms the polymer conformations, thus increasing the porosity inside the membrane, which consists of cationic chitin nanofibers and anionic poly(acrylic acid). The resulting structure has a transmittance of 93.7 % at 550 nm and a refractive index of 1.30. The coating reduces fogging because of the hydrophilic surface and the strong hydrogen bonding of the chitin nanofibers. This versatile procedure for producing porous materials should prove valuable for a wide variety of industrial applications.

On the importance of light scattering for high performances nanostructured antireflective surfaces

An antireflective coating presenting a continuous refractive index gradient is theoretically better than its discrete counterpart because it can give rise to a perfect broadband transparency. This kind of surface treatment can be obtained with nanostructures like moth-eye. Despite the light scattering behavior must be accounted as it can lead to a significant transmittance drop, no methods are actually available to anticipate scattering losses in such nanostructured antireflective coatings. To overcome this current limitation, we present here an original way to simulate the scattering losses in these systems and routes to optimize the transparency. This method, which was validated by a comparative study of coatings presenting refractive indices with either discrete or continuous gradient, shows that a discrete antireflective coating bilayer made by oblique angle deposition allows reaching ultra-high mean transmittance of 98.97% over the broadband [400–1800] nm. Such simple surface treatment outperforms moth-eye architectures thanks to both interference effect and small dimensions nanostructures that minimize the scattering losses as confirmed by finite-difference time domain simulations performed on reconstructed volumes obtained from electron tomography experiments.