Search

This work reports the fabrication of p‐type Si micropillar (MP) substrates decorated with AgxCu100−x bimetallic nanoparticles and their application as photocathodes for CO2 photoelectrochemical reduction. Metal deposition by metal‐assisted chemical etching is chosen as the nanoparticle synthesis method, to explore for the first time its capabilities for 3D structures. It is found to be applicable, allowing a good control of the composition, with nanoparticles distributed along the entire MP, but with a coverage gradient from top to bottom. The AgxCu100−x decorated Si MPs photocathodes show enhanced light trapping compared to flat Si, with 45 % lower reflectance values in the visible and significantly higher catalytic activity, in terms of photocurrent density, overpotential and power savings (4.7 % for Ag50Cu50/Si MPs vs. 3 % for Ag50Cu50/flat‐Si). Si MPs coated with Ag50Cu50 and Ag20Cu80 provide the highest gain in potential (440 and 600 mV vs. bare Si MPs) and an increased selectivity towards high energy density products (i. e., CH4) compared to monometallic photocathodes. These are promising features for efficient light‐driven CO2 conversion. However, a significant metal loss is observed during photoelectrolysis, especially for Cu‐rich compositions. Suggestions to improve the photocathode performance in terms of metal coating homogeneity and catalyst stability are presented. [ABSTRACT FROM AUTHOR]

Water contamination due to significant industrialization and urbanization has drawn the attention of numerous researchers to water remediation techniques like photocatalysis. The intriguing characteristics of silicon nanowires (SiNWs), like light trapping and catalytic activity for the removal of textile dyes, have drawn attention to this material. In this work, the synthesis of SiNWs and their modifications with metal particles like copper or silver with different concentrations has been reported. Metal‐assisted chemical etching, a cost‐effective and easy method, is used to synthesis SiNWs with an optimized aspect ratio. The as‐prepared materials and it photocatalysis performance are studied by X‐ray diffraction (XRD), field emission and transmission electron microscope (FESEM, TEM), and UV–visible spectroscopy. The XRD confirms the presence of the copper particles on SiNWs. The FESEM image reveals the formation of flower‐like structures with different morphologies for silver and copper‐modified SiNWs. The as‐prepared samples have shown efficacy in removing Rhodamine‐B by the process of photocatalysis under irradiation with UV light. It has been observed that when the concentration of the copper nanoparticles is increased, a significant increase in the photocatalytic activity is obtained. The removal efficiency came within the range of 50–65%. [ABSTRACT FROM AUTHOR]

Abstract This work reports the fabrication of p‐type Si micropillar (MP) substrates decorated with AgxCu100−x bimetallic nanoparticles and their application as photocathodes for CO2 photoelectrochemical reduction. Metal deposition by metal‐assisted chemical etching is chosen as the nanoparticle synthesis method, to explore for the first time its capabilities for 3D structures. It is found to be applicable, allowing a good control of the composition, with nanoparticles distributed along the entire MP, but with a coverage gradient from top to bottom. The AgxCu100−x decorated Si MPs photocathodes show enhanced light trapping compared to flat Si, with 45 % lower reflectance values in the visible and significantly higher catalytic activity, in terms of photocurrent density, overpotential and power savings (4.7 % for Ag50Cu50/Si MPs vs. 3 % for Ag50Cu50/flat‐Si). Si MPs coated with Ag50Cu50 and Ag20Cu80 provide the highest gain in potential (440 and 600 mV vs. bare Si MPs) and an increased selectivity towards high energy density products (i. e., CH4) compared to monometallic photocathodes. These are promising features for efficient light‐driven CO2 conversion. However, a significant metal loss is observed during photoelectrolysis, especially for Cu‐rich compositions. Suggestions to improve the photocathode performance in terms of metal coating homogeneity and catalyst stability are presented.

Hydrovoltaic devices (HDs) based on silicon nanowire (SiNW) arrays have received intensive attention due to their simple preparation, mature processing technology, and high output power. Investigating the impact of structure parameters of SiNWs on the performance of HDs can guide the optimization of the devices, but related research is still not sufficient. This work studies the effect of the SiNW density on the performance of HDs. SiNW arrays with different densities were prepared by controlling the react time of Si wafers in the seed solution (t seed) in metal-assisted chemical etching. Density of SiNW array gradually decreases with the increase of t seed. HDs were fabricated based on SiNW arrays with different densities. The research results indicate that the open-circuit voltage gradually decreases with increasing t seed, while the short-circuit current first increases and then decreases with increasing t seed. Overall, SiNW devices with t seed of 20 s and 60 s have the best output performance. The difference in output performance of HDs based on SiNWs with different densities is attributed to the difference in the gap sizes between SiNWs, specific surface area of SiNWs, and the number of SiNWs in parallel. This work gives the corresponding relationship between the preparation conditions of SiNWs, array density, and output performance of hydrovoltaic devices. Density parameters of SiNW arrays with optimized output performance and corresponding preparation conditions are revealed. The relevant results have important reference value for understanding the mechanism of HDs and designing structural parameters of SiNWs for high-performance hydrovoltaic devices. [ABSTRACT FROM AUTHOR]

This work investigates how the saw damage from different processes affected the Silver-catalyzed Metal Assisted Chemical Etching. Multicrystalline silicon ingot was grown from a 15 kg Directional Solidification (DS) furnace. The wafers were extricated from silicon brick by using the blade or diamond wire cutting machine which leaves the saw damage in the substrate of the wafer. Surface texturization process is required to reduce the reflectance of the wafer and to trap more photons on the surface. Silver-catalyzed Metal Assisted Chemical Etching was deployed to texture the surface of the silicon wafer. Five Mc-Si wafers were prepared through blade cut, diamond wire cut, lapping, mechanical polishing and chemical polishing. The surface of those wafers was textured using Silver-catalyzed Metal Assisted Chemical Etching. The preliminary studies like weight measurement, thickness calculations, lifetime measurement and resistivity are made. From the preliminary studies, it is confirmed that the etching rate is directly proportional to the roughness of the surface. All the wafers are subjected to SEM, Optical Microscopy and UV-Vis-NIR analysis. It is concluded that the saw damage affected the proper metal coating at the surface. The nanostructures are found in mirror-like polished wafers which produce the lowest weighted average reflection of 2.573%. From the results obtained from the characterizations, the simulations were done to examine the efficiency of the solar cell made from differently processed silicon wafers. [ABSTRACT FROM AUTHOR]

Nanostructures and microstructures are fabricated on silicon surfaces to reduce the reflection and enhance the absorption of light. It can be used to improve infrared (IR) absorption-based MEMS bolometer applications. The cost-effective metal-assisted chemical etching (MACE) method is used to synthesize the silicon nanowires arrays for surface roughness. The fabricated Si nanowires reveal roughly 5 times increment in the full-wave half-maxima (FWHM) of the X-ray rocking curve in comparison to crystalline silicon (c-Si) due to the presence of structural defects on the surface which arises because of the anisotropic chemical etching. Electron microscopy results confirm the formation of nanowires in Omni-directions with tens of nanometre diameter and a few μm lengths. The infrared response of silicon nanowires shows that the broadband infrared absorption is enhanced about 2.5 – 3 times compared to that of polished silicon for the IR range (2.5 – 20 μm). The IR response of the Si nanowires provides promising potential applications as broadband IR absorbing/ sensing material. [ABSTRACT FROM AUTHOR]

Diffractive optical elements such as periodic gratings are fundamental devices in X‐ray imaging – a technique that medical, material science, and security scans rely upon. Fabrication of such structures with high aspect ratios at the nanoscale creates opportunities to further advance such applications, especially in terms of relaxing X‐ray source coherence requirements. This is because typical grating‐based X‐ray phase imaging techniques (e.g., Talbot self‐imaging) require a coherence length of at least one grating period and ideally longer. In this paper, the fabrication challenges in achieving high‐aspect ratio nanogratings filled with gold are addressed by a combination of laser interference and nanoimprint lithography, physical vapor deposition, metal assisted chemical etching (MACE), and electroplating. This relatively simple and cost‐efficient approach is unlocked by an innovative post‐MACE drying step with hexamethyldisilazane, which effectively minimizes the stiction of the nanostructures. The theoretical limits of the approach are discussed and, experimentally, X‐ray nanogratings with aspect ratios >40 are demonstrated. Finally, their excellent diffractive abilities are shown when exposed to a hard (12.2 keV) monochromatic X‐ray beam at a synchrotron facility, and thus potential applicability in phase‐based X‐ray imaging. [ABSTRACT FROM AUTHOR]

Metal assisted chemical etching is a promising method for fabricating high aspect ratio micro- and nanostructures in silicon. Previous results have suggested that P-type and N-type silicon etches with different degrees of anisotropy, questioning the use of P-type silicon for nanostructures. In this study, we compare processing X-ray zone plate nanostructures in N and P-type silicon through metal assisted chemical etching with a gold catalyst. Fabricated zone plates were cleaved and studied with a focus on resulting verticality, depth and porosity. Results show that for high aspect ratio nanostructures, both N and P-type silicon prove to be viable alternatives exhibiting different etch rates, but similarities regarding porosity and etch direction.

Silicon nanowires (SiNWs) have demonstrated great potential for energy storage due to their exceptional electrical conductivity, large surface area, and wide compositional range. Metal-assisted chemical etching (MACE) is a widely used top-down technique for fabricating silicon micro/nanostructures. SiNWs fabricated by MACE exhibit significant surface areas and diverse surface chemistry. Since the material composition and surface chemistry have a significant impact on the electrochemical energy storage performance, integrating SiNWs with diverse materials like porous carbon, metal oxides/sulfides, and polymers, can establish composites with excellent properties. Hence, it is imperative to meticulously fabricate SiNW-based materials with customizable morphologies and enhanced electrochemical energy-storage performance. This review provides an in-depth study of recent advancements in SiNW-based materials with enhanced performance for energy storage systems, such as supercapacitors (SCs) and lithium-ion batteries (LIBs). It includes a concise overview of the history, MACE synthesis, and characteristics of SiNWs. Further, it also explores the key elements that influence the MACE process of SiNWs and delves into structural engineering. Additionally, we introduce recent advances in SiNW-based materials for the design of high-performance energy-storage devices, namely SCs and LIBs. Finally, we present the crucial future prospects of SiNW-based materials for energy-storage applications., (© 2024 Wiley-VCH GmbH.)

Despite its high theoretical capacity, silicon anode has limited intrinsic conductivity and experiences significant volume changes during charge‐discharge. To overcome these issues, facile metal‐assisted chemical etching and in‐situ polymerization of aniline are employed to produce a dense 1D polyaniline/silicon nanowire forest without noticeable agglomeration as a free‐standing anode for lithium‐ion batteries. This hybrid electrode possesses high cycling performance, delivering a stable capacity capped at 2 mAh cm−2 for 346 cycles of charge‐discharge. Maximum capacity of 2 mAh cm−2 is also achievable at high‐rate cell testing of 2 mA cm−2, which cannot be obtained by the anode with plain silicon wafer and silicon nanowire only. The introduction of polyaniline on the silicon nanowire is shown to reduce the solid electrolyte interface (SEI) resistance, stabilize the SEI layer, further alleviate the effect of volume changes, and boost the conductivity of the hybrid anode, resulting in the high electrochemical performance of the anode. [ABSTRACT FROM AUTHOR]

Most of the recent articles addressing the texturing issues of diamond wire sawn multi-crystalline silicon (mc-Si) wafers propose metal-assisted chemical etching (MACE) inverted pyramid texturing scheme as the best suited industrial process for the fabrication of low-cost, high efficiency solar cells. However, a detailed generation loss analysis of such textured solar cells are not widely investigated yet, especially after module conversion. We present a comprehensive analysis of various optical losses in MACE inverted pyramid textured mc-Si solar cells and modules using the SunSolve module ray-tracer simulator from PV Lighthouse. The simulation model accurately predicted the optical properties of MACE inverted pyramid textured samples and the simulated reflectance values were nearly identical to experimentally measured values at different stages of solar cell processing (before and after ARC). This study quantifies and benchmarks the optical generation losses of not-encapsulated and encapsulated inverted pyramid textured cells with well established models of random pyramid textured and iso-textured solar cells for aluminum back surface field (Al-BSF) architecture. Moderate cell to module (CTM) generation current loss was noticed for inverted pyramid textured solar cells, which was nearly 0.71 mA-cm−2 lower than random pyramid textured and 1.05 mA-cm−2 higher than iso-textured solar cells. We find that adoption of MACE inverted pyramid texturing over acid texturing enhances the photo-generation in mc-Si modules by ∼ 0.5% and that the total photo-generation current density in mc-Si solar modules approach 99.6% of that in random pyramid textured c-Si modules. • Optical generation losses in inverted nano-pyramid textured wafers are presented. • CTM generation losses are estimated using ray-tracing simulations. • CTM generation losses are compared with iso- and random pyramid textured samples. • Generation losses in different textures changes significantly after encapsulation. • Nano-texturing offers 0.5% enhancement in photo-generation after module conversion. [ABSTRACT FROM AUTHOR]

An inclusive approach for analysing size dependent field emission properties of silicon nanowires has been presented in the current study. The proposed framework complements the traditionally used method of analysis (using Fowler-Nordheim framework) which takes care of the tunnelling current corresponding to low as well as high electric fields. The present model uses boost factor (which is deduced based on effective work function) and field emission power density as parameters to quantify the field emission in addition to the "field enhancement factor" used previously. Silicon nanowires, obtained using metal induced etching technique, show low turn on voltage, high boost factor and high field emission power for smaller nanostructures due to quantum effects leading to quantization of energy levels thus pushing the effective work function closer to the vacuum level. A new empirical formula, showing a hyperbolic behaviour, has also been proposed to represent and quantify the size dependent field emission power density. Overall, the proposed framework complements the classic Fowler-Nordheim methodology to be used more efficiently for nanomaterials. [ABSTRACT FROM AUTHOR]

In this study, nanostructured pyramidal black silicon is prepared by metal assisted chemical etching method, in which the silver nitrate (AgNO3) is used as the metal catalyst. Effects of the concentration of AgNO3 on passivation and optical properties of the black silicon are investigated. The experimental results show that at the AgNO3 concentration of 0.03 M, the nanostructure length is about 300 nm, and the reflectance of the black silicon with a stack of silicon nitride (SiNx) and aluminum oxide (Al2O3) is 0.8%, which is comparable to that of the conventional black silicon with micrometer-long nanowires. In addition, an acceptably low surface recombination rate of 42 cm/s can be obtained. Plasma chemical vapor deposited SiNx is deposited well on the top of nanostructures of black silicon, but shows poor coverage at the bottom region. Spatial atomic layer deposited Al2O3 can conformally cover the nanostructures with high passivation quality. Simulation result indicates an improvement of 5.5% of conversion efficiency for the nanostructured pyramidal black silicon solar cell compared to industrial silicon solar cell. The short nanostructured pyramidal surface with low reflectance and high passivation is expected to be helpful for black silicon technology applied to photovoltaic applications.

We present a comprehensive comparative analysis of acid textured and MACE (Metal Assisted Chemical Etching) nano-textured multi crystalline silicon (mc-Si) solar cells processed in an industrial cell line in terms of performance parameters. The batch average open circuit voltage of nano-textured solar cells was marginally lower and the measures for improving the same are discussed. Batch average short circuit current (J S C) and fill factor (FF) were respectively 0.65 mA-cm−2 and 0.7% (absolute) higher for MACE nano-textured solar cells. Significantly lower surface reflectance in MACE nano-textured cells in the blue and near infrared regions are found to be the reason for the enhancement in J S C. The main component of FF gain is identified as the lower series resistance in MACE cells. The contact formation mechanism in screen printed mc-Si solar cells, investigated using scanning electron microscopy, revealed that the elevated portions at the boundaries of the textures act as favorable sites for silver crystallite precipitation. A larger areal density of such sites is observed on the MACE nano-textured surface than in case of acid textured solar cells, leading to a much lower series resistance. The results suggest the potential for the application of MACE in the more popular mono-crystalline silicon cell technology for further reduction of contact resistance. Alternatively, MACE may be used to obtain similar contact resistance with lower amount of silver paste, compared to iso- and pyramid textured solar cells. • MACE nano-textures offer lower reflection and higher fill factor than iso-textures. • Gain in fill factor in nano-textured cells is due to lower series resistance. • Elevated portions of textures are the favorable Ag crystallite precipitation sites. • Large area density of MACE nano-textures lower the series resistance significantly. [ABSTRACT FROM AUTHOR]

Two different methods of dual metal ion implantation technique and metal-assisted chemical etching are used to fabricate silicon nanostructures. Raman scattering and photoluminescence techniques have been employed to study the optical properties of formed Si nanostructures. Scanning Electron Microscopy images indicate the change in the surface morphology of Si nanowires with respect to the etching time. Dual ion implantation sample and metal-assisted chemical etching, prepared for 45 min exhibit similar optical properties. With a possible mechanism of their formation at room temperature, synthesizability of Si NWs in large scale for commercial purposes is discussed. It is expected that these Si NWs have got potential applications in optoelectronics, photonics and sensors. [ABSTRACT FROM AUTHOR]

In this paper, we exploit the perspective of luminescent Si nanowires (NWs) in the growing field of commercial biosensing nanodevices for the selective recognition of proteins and pathogen genomes. We fabricated quantum confined fractal arrays of Si NWs with room temperature emission at 700 nm obtained by thin-film, metal-assisted, chemical etching with high production output at low cost. The fascinating optical features arising from multiple scattering and weak localization of light promote the use of Si NWs as optical biosensing platforms with high sensitivity and selectivity. In this work, label-free Si NW optical sensors are surface modified for the selective detection of C-reactive protein through antigen–gene interaction. In this case, we report the lowest limit of detection (LOD) of 1.6 fM, fostering the flexibility of different dynamic ranges for detection either in saliva or for serum analyses. By varying the NW surface functionalization with the specific antigen, the luminescence quenching of NW biosensors is used to measure the hepatitis B-virus pathogen genome without PCR-amplification, with an LOD of about 20 copies in real samples or blood matrix. The promising results show that NW optical biosensors can detect and isolate extracellular vesicles (EV) marked with CD81 protein with unprecedented sensitivity (LOD 2 × 105 sEV/mL), thus enabling their measurement even in a small amount of blastocoel fluid.

Copyright of Journal of Beijing University of Technology is the property of Journal of Beijing University of Technology, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, nanostructured pyramidal black silicon is prepared by metal assisted chemical etching method, in which the silver nitrate (AgNO 3) is used as the metal catalyst. Effects of the concentration of AgNO 3 on passivation and optical properties of the black silicon are investigated. The experimental results show that at the AgNO 3 concentration of 0.03 M, the nanostructure length is about 300 nm, and the reflectance of the black silicon with a stack of silicon nitride (SiN x) and aluminum oxide (Al 2 O 3) is 0.8%, which is comparable to that of the conventional black silicon with micrometer-long nanowires. In addition, an acceptably low surface recombination rate of 42 cm/s can be obtained. Plasma chemical vapor deposited SiN x is deposited well on the top of nanostructures of black silicon, but shows poor coverage at the bottom region. Spatial atomic layer deposited Al 2 O 3 can conformally cover the nanostructures with high passivation quality. Simulation result indicates an improvement of 5.5% of conversion efficiency for the nanostructured pyramidal black silicon solar cell compared to industrial silicon solar cell. The short nanostructured pyramidal surface with low reflectance and high passivation is expected to be helpful for black silicon technology applied to photovoltaic applications. [ABSTRACT FROM AUTHOR]

Diffractive optics play a key role in hard X‐rays imaging for which many scientific, technological, and biomedical applications exist. Herein, high‐aspect‐ratio microfabrication of gratings for X‐ray interferometry is demonstrated using Pt as a catalyst for the metal assisted chemical etching of Si in a solution of HF and H2O2. The Pt layer is thermally treated to realize a porous catalyst layer that stabilizes the etching of a pattern with a pitch size from 4.8 to 20 μm in the direction perpendicular to the <100> Si substrate and an aspect ratio up to 60:1. The superior etching performance of Pt as a catalyst and its stability in a solution with high HF content are reported in direct comparison with the Au catalyst for the same grating parameters. The Si structure is then used as a template for filling with Au, as a high absorbing X‐ray material. The Pt catalyst layer is used as a conductive seed for Au electroplating. The quality of the overall process is assessed by obtaining a visibility map using 30 μm‐thick Au grating in an X‐ray interferometric setup at 20 keV. [ABSTRACT FROM AUTHOR]

Silicon nanowire (SiNW) metal-oxide-semiconductor (MOS) capacitors with Al2O3/TiO2/Al2O3 (ATA) stacked dielectric films were fabricated by metal-assisted chemical etching (MACE) and atomic layer deposition (ALD). High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images revealed that SiNWs were conformally coated with ATA although the cross-sectional shapes of MACE-SiNWs were non-uniform and sharp spikes can be seen locally. The dielectric capacitance density of 5.9 μF/cm2 at V = −4 V of the perfect accumulation region was achieved due to the combination of the large surface area of the SiNW array and the high dielectric constant of ATA. The capacitance changed exponentially with the voltage at V < −4.3 V and the capacitance of 84 μF/cm2 was successfully achieved at V = −10 V. It was revealed that not only 3D structure and high-k material but also local nanostructure of SiNWs and stacked dielectric layers could contribute to the considerable high capacitance.

Copper (Cu) and Indium (In) doped titanium dioxide (TiO2) obtained by a solvothermal method was confined in Porous Silicon (PS) prepared by Metal-Assisted Chemical Etching -MACE-, a low-cost and versatile method to investigate the morphological, structural, optical, and electrical properties of the TiO2:X/PS/Si structure (X = In, Cu, 0). According to Scanning Electron Microscopy, different morphologies were found, such as small particles (without dopant) or well-defined geometries such as cubes (indium-doped) and micro-flowers (copper-doped) that covered the PS surface depending on the kind of dopant elements. Cross-section images showed that the TiO2 nanoparticles decorated and filled the macroporous silicon and that they can even form conformal deposits. Raman spectroscopy and x-ray diffraction patterns revealed the crystalline phase structure of the In and Cu-doped TiO2 materials, which correspond to anatase and rutile, respectively. Furthermore, the lattice parameters corroborated the incorporation of the dopant elements. The photoluminescence (PL) spectra show broad-bands around 2.8 eV, which can be related to oxygen vacancies. Additionally, a blue shift was observed in the PL spectra when the dopant changed from Cu to In. Diffuse reflectance and the Kubelka-Munk plots were used to determine the optical bandgap of the TiO2 structures with and without dopant. Bandgap reduction was observed due to the dopant changes. Current-voltage curves showed a rectifying behavior for negative voltages; however, a negative differential resistance effect was observed for positive voltages in all the samples. Finally, current-voltage curves showed a rectifying behavior for negative voltages; however, it was observed a negative differential resistance effect for positive voltages in all the samples. Besides, these current voltages curves were carried out under dark and illumination conditions, which revealed a photocurrent effect. [ABSTRACT FROM AUTHOR]

This work presents a thorough study of Si microwires obtained by a novel combination of chemical etching steps, for their application as anode material in Li-ion batteries. The fabrication process starts with standard photolithography followed by a metal-assisted chemical etching step and anisotropic etching. This process can be performed in any chemical laboratory. The final structures possess a diameter and a length of 1.5 and 24 µm, respectively. Paste electrodes were prepared using the Si microwires and were tested in half-battery cells. Cyclic voltammetry and impedance spectroscopy evidenced the formation of Li–Si alloys and a solid electrolyte interface. The lithiated wires are mechanically stable upon lithiation, even when they expand to the 256% of their original volume. [ABSTRACT FROM AUTHOR]

Deep etching of silicon (Si) is very much desirable for wide variety of applications. Under the context, a cost effective and reproducible through etching of ∼375 μm thick Si wafer is demonstrated through long hour metal assisted chemical etching (MACE) followed by short duration KOH etching. During MACE, apart from pH and temperature, metal catalyst size and coverage density during electroless plating plays an important role. Optimization of gold deposition in terms of plating solution concentration and deposition time during MACE is studied for effective through etching. HAuCl 4 concentration of ∼5 mM for 30 s is found to be best suited for MACE and produces deep and highly dense pores in Si with threshold pore radius ∼250 nm and above. Following the MACE, KOH etching effectively scoops out porous Si to realize through etching. [ABSTRACT FROM AUTHOR]

• Silicon nanowires on p-type Si substrate were formed by the MacEtch method with silver as the catalyst in optimized conditions. • Both the theoretical modeling of optical parameters by FDTD method and experimental results demonstrated high light trapping. • Solar cells with radial (coaxial) p-n junction were formed and high energy conversation was demonstrated with efficiency of 7%. In our studies the absorption, transmittance and reflectance spectra for periodic nanostructures with different parameters were calculated by the FDTD (Finite-Difference Time-Domain) method. It is shown that the proportion of reflected light in periodic structures is smaller than in case of thin films. The experimental results showed the light reflectance in the spectral range of 400–900 nm lower than 1% and it was significantly lower in comparison with surface texturing by pyramids or porous silicon. Silicon nanowires on p-type Si substrate were formed by the Metal-Assisted Chemical Etching method (MacEtch). At solar cells with radial p-n junction formation the thermal diffusion of phosphorus has been used at 790 °C. Such low temperature ensures the formation of an ultra-shallow p-n junction. Investigation of the photoelectrical properties of solar cells was carried out under light illumination with an intensity of 100 mW/cm2. The obtained parameters of NWs' solar cell were I sc = 22 mA/cm2, U oc = 0.62 V, FF = 0.51 for an overall efficiency η = 7%. The relatively low efficiency of obtained SiNWs solar cells is attributed to the excessive surface recombination at high surface areas of SiNWs and high series resistance. [ABSTRACT FROM AUTHOR]

Abstract In this work, random inverted nanopyramids (INPs) are fabricated as light trapping structures on ultrathin c -Si through a simple and cost-effective wet chemical method, followed by a systematic investigation of the photo-capturing properties of INPs combining experiments and simulations. In comprehensive consideration of thickness loss and light trapping performance, random INPs are applied onto 45 μm ultrathin c -Si solar cell and a high short-current density (Jsc) (36.6 mA/cm2) and energy-conversion efficiency (17.0%) are achieved, which are 0.3 mA/cm2 and 0.13% respectively higher than that in micro pyramid textured one, and our electrical simulation also demonstrates that the advantages of INPs are more obvious on thinner c -Si compared with conventional micro pyramids. Finally, through electrical simulation, INPs textured 45 μm c -Si solar cell is expected to have a large improvement room for efficiency by controlling the front and rear surface recombination velocity. All the findings not only offer additional insight into the light-trapping mechanism in the random INPs but also provide controllable and efficient broadband light harvesters for next-generation cost effective flexible photovoltaics. Graphical abstract Image 1 Highlights • Size control of IPs from nano to microscale was achieved by varying MACE temperature. • Near-Yablonovitch limit absorptance was achieved on 45 μm c-Si by using random IPs. • 45 μm random IPs cell achieve 36.6 mA/cm2 current density and 17.0% efficiency. • A theoretical efficiency of 26.3% can be on 45 μm c-Si by optimization. [ABSTRACT FROM AUTHOR]

The Silicon Electron Multiplier (SiEM) sensor is a novel sensor concept that enables charge multiplication by high electric fields generated by embedded metal electrodes within the sensor bulk. Metal assisted chemical etching (MacEtch) in gas phase with platinum as a catalyst has been used to fabricate test structures consisting of vertically aligned silicon pillars and strips on top of a silicon bulk. The pillars are around 10 µm in height with a diameter of 1.0 µm and are arranged as a hexagonal lattice with a pitch of 1.5 µm. Electrical characterisations through current–voltage measurements inside a scanning electron microscope and a climate chamber have demonstrated that the MacEtch process is compatible with p–n junctions. [ABSTRACT FROM AUTHOR]

The absence of an effective texturing technique for diamond-wire sawn multi-crystalline silicon (DWS mc-Si) solar cells has hindered commercial upgrading from traditional multi-wire slurry sawn silicon (MWSS mc-Si) solar cells. In this work, we present a novel method for the removal of diamond-wire-sawn marks in a multi-crystalline silicon wafer based on metal assisted chemical etching process with Cu/Ag dual elements and nano-structure rebuilding (NSR) treatment to make a uniform inverted pyramid textured structure. The temperature effect of NSR solution was systematically analyzed. It was found that the size of the inverted pyramid structure and the reflectance became larger with the increase of the NSR treatment temperature. Furthermore, the prepared unique inverted pyramid structure not only benefited light trapping, but also effectively removed the saw-marks of the wafer at the same time. The highest efficiency of 19.77% was obtained in solar cells with an inverted pyramid structure (edge length of 600 nm) fabricated by NSR treatment at 50 °C for 360 s, while its average reflectance was 16.50% at a 400–900 nm wavelength range.

A simple and inexpensive method to obtain Si conical structures is proposed. The method consists of a sequence of steps that include photolithography and metal assisted chemical etching (MACE) to create porous regions that are dissolved in a post-etching process. The proposed process takes advantage of the lateral etching obtained when using catalyst particles smaller than 40 nm for MACE. The final shape of the base of the structures is mainly given by the shape of the lithography mask used for the process. Conical structures ranging from units to hundreds of microns can be produced by this method. The advantage of the method is its simplicity, allowing the production of the structures in a basic chemical lab.

It is important to improve the efficiency of solar cells textured by the MACE method, and the surface morphology has a significant effect on the efficiency. In this paper, we textured multicrystalline wafer using MACE method, and the surface morphology was further modified by post-etching process to achieve high efficiency. The influence of structure on diffusion and surface passivation was studied. It reveals that surface structure has a big effect on diffusion and passivation, thus affecting the efficiency. Structure with large aspect ratio results in heavily doped regions and poor passivation performance. Finally, large area solar cells with the efficiency of 19.08% and 19.11% were obtained on slurry wire and diamond wire saw multicrystalline wafer respectively, which is 0.5% and 0.8% absolutely higher than the cells with traditional acid texturing. [ABSTRACT FROM AUTHOR]

Micro and nanostructured surfaces can significantly improve the heat transfer capability and shift the Leidenfrost temperature of impacting droplets. In this study, the effect of overheated random Si Nanowires on impacting water droplets is presented. The cooling performance was studied in term of droplet evaporation time and surface temperature while the boiling dynamics was observed through high-speed visualization. The Si Nanowires can increase almost twice the Leidenfrost temperature compare to the similar case of plain Si surface. At the same time, the heat transfer is enhanced by widening the transition boiling region about 150 K. In this regime, the film liquid lift-off behavior is observed in the range of the We numbers studied. [ABSTRACT FROM AUTHOR]

Ultrathin c -Si solar cells (≤50 μm) are believed to be applied in military, aerospace and other special circumstances in the future due to their flexibility and high specific power density, and thus has attracted a great deal of research interest. However, until now, lacking fabrication means of high-quality ultrathin c -Si materials accompanied with their inefficient absorption of near-infrared light greatly limits their further application. In this work, we present a simple and novel method to realize rapid thinning and texturing of bulk c -Si at room temperature by varying the ρ ([HF]/([HF] + [H 2 O 2 ])) values during the one-step Cu-assisted chemical etching process, followed by a systematic investigation of the formation mechanism of the surface structures. It is found that the sizes of surface structures accompanied with the etching rate increase with increasing the ρ values from 40% to 95% during the double sided etching process, and a high etching rate of 29.6 µm/min is obtained under the ρ value of 95%. For rapid thinning and efficient absorption of near-infrared light, 45 µm c -Si solar cell with asymmetric front and back light trapping structures is rapidly fabricated by directly immersing as-sawn bulk c -Si substrate into the thinning (ρ = 95%) and texturing (ρ = 60%) solution successively for only a few minutes. A high short-current density (Jsc) (36.12 mA/cm 2 ) and energy-conversion efficiency (17.3%) are achieved, which are 1.09 mA/cm 2 and 0.4% higher respectively than that in 45 µm c -Si with flat back surface. Based on the absorption spectra, it is demonstrated that the 45 µm c -Si cell with our asymmetric structures yields a high theoretical Jsc of 42.47 mA/cm 2 , which nearly approaches the Yablonovitch limit of 42.56 mA/cm 2 . All the findings offer additional insight into the structure formation mechanism and pave a rapid and novel way for exploration of next-generation flexible photovoltaics. [ABSTRACT FROM AUTHOR]

Fractal nature of porous silicon (Si), where porous nanowires (NWs) of Si has been observed inside the porous membrane matrix, has been revisited this time by metal assisted chemical etching (MACE) also known as metal induced etching or MIE. While carrying out MACE of Si wafer with silver nanoparticles (AgNPs) as the etching metal, it is observed that non vertical chemical etching take place. An SEM study reveals that the usual well aligned SiNWs, approximately 50 nm thick, consists of nanometer wide pores in themselves. The nanometer sized pores in turn results in Si NSs of a few nanometers in these thick looking SiNWs and are capable of showing quantum confinement effects. The SEM and TEM studies have been consolidated to model the growth mechanism for the observed fractal porous Si. [ABSTRACT FROM AUTHOR]

A systematic investigation is performed to determine the effects of the concentration of silver on metal assisted chemical etching (MaCE) for nanostructure formation mechanisms on silicon as well as their resultant optical properties. Silver nitrate concentrations of 8 mM, 4 mM, 3 mM and 2 mM with hydrogen fluoride were used for the preparation of p-type silicon nanostructures. Experimentally, it is observed that when the catalysis molarity concentration is decreased in the etching processes, it resulted in nanostructures ranging from 140 to 60 nm, respectively over the concentrations investigated. A detailed analysis of the optical properties and structure provided insight into the physics of their formation. In addition, the results show the silicon nanostructures formed black silicon where in the visible region of the spectrum the reflectance dropped by an order of magnitude. The results indicate MaCE is a promising approach to the manufacturing of antireflection coatings on black silicon-based solar photovoltaic cells. MaCE is a simple and scalable approach to enhance the optical absorption of silicon and improve the overall efficiency of the solar cell without adding significantly to the complexity, capital expenditure or cost of production. [ABSTRACT FROM AUTHOR]

Hybrid planar solar cells based on bulk n-doped Si wafers and poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) with a back-junction geometry demonstrated an excellent power conversion efficiency of more than 11%. When a random pyramid or a Si nanowire antireflection structure was incorporated into the front of the cell surface, the power conversion efficiencies were further enhanced to 13.9% or 14.5%, respectively. Moreover, the cells with the Si nanowire antireflection structure displayed omnidirectional light-trapping characteristics over the random pyramid structures. These cells also maintained a constant power conversion efficiency even at an incident angle of 60°. [ABSTRACT FROM AUTHOR]

In this work, vertically aligned silicon nanowires (SiNWs) with relatively high crystallinity have been fabricated through a facile, reliable, and cost-effective metal assisted chemical etching method. After introducing an itemized elucidation of the fabrication process, the effect of varying etching time on morphological, structural, optical, and electrical properties of SiNWs was analysed. The NWs length increased with increasing etching time, whereas the wires filling ratio decreased. The broadband photoluminescence (PL) emission was originated from self-generated silicon nanocrystallites (SiNCs) and their size were derived through an analytical model. FTIR spectroscopy confirms that the PL deterioration for extended time is owing to the restriction of excitation volume and therefore reduction of effective light-emitting crystallites. These SiNWs are very effective in reducing the reflectance to 9−15% in comparison with Si wafer. I−V characteristics revealed that the rectifying behaviour and the diode parameters calculated from conventional thermionic emission and Cheung’s model depend on the geometry of SiNWs. We deduce that judicious control of etching time or otherwise SiNWs’ length is the key to ensure better optical and electrical properties of SiNWs. Our findings demonstrate that shorter SiNWs are much more optically and electrically active which is auspicious for the use in optoelectronic devices and solar cells applications.

Surface-enhanced Raman spectroscopy (SERS) has advanced over the last four decades and has become an attractive tool for highly sensitive analysis in fields such as medicine and environmental monitoring. Recently, there has been an urgent demand for reusable and long-lived SERS substrates as a means of reducing the costs associated with this technique To this end, we fabricated a SERS substrate comprising a silicon nanowire array coated with silver nanoparticles, using metal-assisted chemical etching followed by photonic reduction. The morphology and growth mechanism of the SERS substrate were carefully examined and the performance of the fabricated SERS substrate was tested using rhodamine 6G and dopamine hydrochloride. The data show that this new substrate provides an enhancement factor of nearly 1 × 108. This work demonstrates that a silicon nanowire array coated with silver nanoparticles is sensitive and sufficiently robust to allow repeated reuse. These results suggest that this newly developed technique could allow SERS to be used in many commercial applications.

This paper presents a metal-assisted chemical etching (MACE) method for high aspect silicon structures. Ultrahigh aspect trenches and pillars of 400 and 80, respectively, have been achieved using MACE. A survey of the MACE method investigated the etching time, pattern sizes, and concentration of etching solution. In addition, a comparison of the etching methods related to the etching depth, surface roughness, and aspect ratio structure, etc., between the deep reactive ion etching and MACE methods has been reported. A simple method for cantilever fabrication has been proposed and demonstrated. Cantilever-based pillars fabricated by MACE were successfully produced via an assembly technology. The pillars were assembled onto a glass substrate and fixed with a conductive glue. The fabricated cantilever showed a resonance frequency of 235 kHz and a quality factor of 800. [ABSTRACT FROM PUBLISHER]

Wet etching is an essential and complex step in semiconductor device processing. Metal-Assisted Chemical Etching (MacEtch) is fundamentally a wet but anisotropic etching method. In the MacEtch technique, there are still a number of unresolved challenges preventing the optimal fabrication of high-aspect-ratio semiconductor micro- and nanostructures, such as undesired etching, uncontrolled catalyst movement, non-uniformity and micro-porosity in the metal-free areas. Here, an optimized MacEtch process using a nanostructured Au catalyst is proposed for fabrication of Si high aspect ratio microstructures. The addition of isopropanol as surfactant in the HF-H 2 O 2 water solution improves the uniformity and the control of the H 2 gas release. An additional KOH etching removes eventually the unwanted nanowires left by the MacEtch through the nanoporous catalyst film. We demonstrate the benefits of the isopropanol addition for reducing the etching rate and the nanoporosity of etched structures with a monotonic decrease as a function of the isopropanol concentration. [ABSTRACT FROM AUTHOR]

• CMOS-compatible electrochemical nanoimprint lithography was developed by replacing the platinum (Pt) metallized imprint mold by a glassy carbon one. • The contaminants, i.e., the metal residuals and metal ions trapped in the fabricated microstructures, were avoided by designing a spatially separated corrosion cell. • The corrosion rate and machining efficiency was promoted and comparable to Pt electrocatalyst, dramatically higher than the carbon materials reported before. Metal assisted chemical etching (MACE), as an emerging wet chemical etching method for fabricating semiconductor micro/nano-structures (MNS), has attracted wide attentions because of the advantages of simple processes, high accuracy and no damages. However, the conventionally used noble metal catalysts (such as Au, Pt,) trapped in the micro/nano-structures are difficult to be removed or reused, not only harming the electronic performances of the CMOS devices but also increasing the fabrication cost. Here, we propose an electrochemical nanoimprint strategy by using a glassy carbon (GC) imprint mold. To overcome the poor electrocatalytic activity of GC, the GC imprint mold was connected to a Pt sheet in the cathodic chamber. To avoid the contaminations of metal and metallic cations in the fabricated MNS, the cathodic chamber was separated from the anodic one by a proton exchange membrane. By optimizing the technical parameters, including the contact pressure between GC imprint mold and GaAs wafer, the concentration of electron acceptor in the cathodic chamber, the imprinting time, etc., a remarkable corrosion rate of about 130 nm/min was achieved, comparable with that of platinum electrocatalyst. Furthermore, by using a GC imprint mold in the spatially separated corrosion cell, the contaminations caused by both the metal catalysts and metallic ions can be eliminated. Thus, this work provides a potential approach to the high throughput fabrication of CMOS-compatible semiconductor microdevices. [ABSTRACT FROM AUTHOR]

Structuring Si in arrays of vertical high aspect ratio pillars, ranging from nanoscale to macroscale feature dimensions, is essential for producing functional interfaces for many applications. Arrays of silicon 3D nanostructures are needed to realize photonic and phononic crystals, waveguides, metalenses, X-ray wavefront sensors, detectors. In particular, arrays of Si nanopillars are used as bio-interfaces in neural activity recording, cell culture, microfluidics, sensing and on-chip manipulation. Here, we demonstrate a strategy for realizing arrays of protruding sharp Si nanopillars, using displacement Talbot lithography combined with metal-assisted chemical etching (MacEtch) in gas phase. Such combination enables reliable and low cost pathway for fabrication of ordered nanopillars arrays on large scale. With the double exposure of a linear grating mask in orthogonal orientations and the lift-off technique, we realized a catalyst pattern of holes in a Pt thin film with a period of 1 μm and hole diameter in the range of 100–250 nm. MacEtch in gas phase by using vapor HF and oxygen from air allows to etch arrays of protruding Si nanopillars 200 nm-thick and aspect ratio in the range of 200 (pillar height/width) with an etching rate up to 1 μm/min. Gas-MacEtch has the advantage of no capillary stiction, no ion beam damage of the Si substrate, nanometric resolution and high fidelity of pattern transfer. In combination with controlled uniformity of feature size on large area, spatial frequency doubling and high resolution of Talbot lithography, the proposed method is an easy-to-scale-up processing that can support the fabrication of Si pillars arrays for many valuable applications both at micro and nano-scale. [ABSTRACT FROM AUTHOR]

Here we report spontaneous redox reactions at the Pt/Si/electrolyte three-phase interface and propose an electrochemical method for nanoimprint lithography on a crystalline Si wafer that does not require thermoplastic and photocuring resists. When the Pt metallized imprint mold is compacted on the n-type Si (111) wafer, electrons will transfer from the n-type Si to Pt due to their different electron work functions. At equilibrium, the Fermi levels of the electrons in each phase become equal, resulting in an electric field and a contact potential at the Pt/Si interface. When immersed in an electrolyte solution, the potentials of the Pt/electrolyte interface and the Si/electrolyte interface are observed to shift in opposite directions. Hydrogen peroxide is spontaneously reduced on the Pt surface. Meanwhile, the electrons in Si will tunnel to Pt and the residual holes will oxidize Si along the three-phase interface. In this way, the micro-/nanostructures on the Pt metallized imprint mold are transferred to the Si wafer. [ABSTRACT FROM AUTHOR]

In this paper, we report inverted pyramidal nanostructure based multi-crystalline silicon (mc-Si) solar cells with a high conversion efficiency of 18.62% in large size of 156 × 156 mm 2 wafers. The nanostructures were fabricated by metal assisted chemical etching process followed by a post nano structure rebuilding (NSR) solution treatment. With increasing NSR treatment time, the reflectance and the dimensions of micro oval pits were both influenced. Resulting from both the light trapping ability and passivation efficiency, 500 nm inverted pyramid structure exhibited an ideal solar cell performance. The best solar cell showed a low reflectivity of 3.29% and a 0.91 mA cm −2 increase of short-circuit current density, and its efficiency was 0.45% higher than the acid textured solar cell. This technique presented a great potential to be a standard process for producing highly efficient mc-Si solar cells in the future. [ABSTRACT FROM AUTHOR]

We report the critical factors that control the geometry of silicon nanostructures produced by metalassisted chemical etching (MacEtch) using self-assembled islands from an ultrathin film of gold. We have conducted a systematic study of the process parameters that control the geometry of the metal structures and the resulting etched nanostructures. Compared to prior reports, which have focused on the crystal orientation and solution stoichiometry, our study finds that the anisotropy of the etched nanostructures is primarily controlled by the deposited metal geometry, while solution stoichiometry and crystal orientation play relatively minor roles. Using an optimized self-assembled geometry and etch process, we demonstrate what we believe is the highest aspect ratio to date (greater than 5000:1) for high density top-down etched silicon nanostructures. These structures, which we refer to as silicon nanowalls, are in the size regime where quantum confinement effects could potentially be exploited for next-generation optoelectronic components and devices. [ABSTRACT FROM AUTHOR]

Hybrid solar cells have gained much attention because of their simple mechanism and low cost as compared to the conventional p-n Si solar cells. We fabricated hybrid solar cells using micro(nano) patterned n-Si substrates. The patterns were formed using nanoimprint lithography and a simple metal-assisted chemical etching method. Owing to the increased light absorption and superior carrier collection ability of the cells, more carriers were generated and effectively collected, which resulted in higher short circuit currents. The short circuit current density and conversion efficiency of PEDOT:PSS Si hybrid solar cell containing the nano-hole patterned Si structures were 24% and 40%, respectively. [ABSTRACT FROM AUTHOR]