Metal-assisted Chemical Etching Method Research Articles

Anisotropy of the conductivity of silicon nanowires

ABSTRACT This study reports the findings from an investigation into charge carrier transport within a silicon nanowire layer. The samples were prepared using the metal-assisted chemical etching method applied to crystalline silicon wafers with a resistance of 10–20 Ω·cm. The resulting silicon nanowires had a diameter of about 100 nm with a resistance of approximately 15 kΩ·cm. Electrical conductivity measurements were performed in both planar and sandwich configurations, revealing analogous conductivity mechanisms across different geometries. Frequency-dependent conductivity studies unveiled the presence of hopping conductivity. A hypothesis is proposed regarding the existence of a potential barrier at the interface between the nanowire layer and the substrate.

Nanoengineered micro-supercapacitors based on graphene nanowalls for self-powered wireless sensing system

This work presents a comprehensive investigation of micro-supercapacitors (MSCs) based on graphene nanowalls (GNWs), covering core material synthesis, device fabrication, evaluation, and application demonstrations. Three-dimensional hierarchical GNWs structures are grown successfully by a microwave plasma-enhanced chemical vapor deposition (MPECVD), with detailed descriptions of the synthesis process and underlying mechanisms. The structural and morphological properties of the GNWs are thoroughly analyzed. Several types of MSCs are reported, ranging from thin-film to three-dimensional (3D) MSCs, as well as symmetric to asymmetric MSCs. Thin-film MSC is developed by a novel micromachining process for one-step fabricating GNWs-Ni core-shell composite microstructures. A solid-state MSC utilizing 3D hierarchical electrode is created by a fully micro electro mechanical system (MEMS)-compatible process. This involves depositing GNWs-RuOx hybrid nanostructures onto microstructure scaffolds formed using deep reactive ion etching (deep RIE). Additionally, another 3D MSC utilizes GNWs-PANI electrode material deposited on silicon nanowires generated through metal-assisted chemical etching (MACE) method. To enhance MSCs performance, asymmetric MSC is proposed and realized, incorporating GNWs-MnO2 acting as the positive electrode and carbon black serving as the negative electrode. Furthermore, the successfully combination of the fabricated MSCs with an energy harvesting system is demonstrated. The self-powered sensing system driven by solar energy, with the harvested energy stored in MSCs, is effectively showcased, opening up new possibilities for futuristic MSCs to accumulate and store harvested energy as usable electricity. This demonstration has significant potential in fields such as self-powered wireless IoT sensing systems, offering valuable contributions towards sustainable and autonomous energy solutions.

Unlocking the plasma advantage in elevating the performance of silicon nanowires/ poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate) hybrid solar cell

Silicon Nanowires (SiNWs) can be easily synthesized by following the two-step electroless metal-assisted chemical etching method. These SiNWs are well known for their low reflectivity due to their excellent light-harvesting characteristics. In this paper, we demonstrated the effect of plasma treatment time on the performance of SiNWs solar cells. The 1 min plasma-treated SiNWs/Poly 3,4-[ethylene dioxy thiophene:Polystyrene sulfonate] (PEDOT׃PSS) solar cell showed increased power conversion efficiency than the untreated SiNWs/PEDOT׃PSS solar cell. The photo Current density-Voltage (J-V) analysis showed that the open circuit voltage (VOC) of the plasma treated solar cell for 1 min is higher (270 mV) than that of the untreated solar cell (120 mV). The increase in the value of VOC comes from different factors׃ one is due to the formation of a good interface between the SiNWs and PEDOT׃PSS layer; other is the reduction of defect densities in SiNWs/PEDOT׃PSS heterojunction, consequently the reduction in the recombination processes. Hence from this research, we found that by controlling the plasma treatment on SiNWs, it can improve the SiNWs properties which can further improve the efficiency of the solar cell.

INVESTIGATION OF THE INFLUENCE OF SILICON NANOWIRE SYNTHESIS PARAMETERS ON THE CHARACTERISTICS OF PHOTOSENSITIVE SENSORS

Problem. Photosensitive sensors are widely used both in everyday life in climate systems and in communication devices and street lighting. In order to improve the performance parameters of photosensitive sensors, the use of silicon nanowires (SiNWs) has been proposed. A large number of articles are dedicated to the influence of synthesis parameters on the dimensions of SiNWs. However, there is a lack of research on the impact of the surface morphology of SiNW arrays on the electrical and photosensitive parameters of sensors based on them.The purpose of the work The aim of this work is to synthesize silicon nanowires using the metal-assisted chemical etching method, investigate their surface morphology, and fabricate photodiodes based on them to examine the influence of SiNW synthesis parameters on the characteristics of photosensitive sensors, considering the peculiarities of their structure.Research results. Photosensitive sensors of diode type based on SiNWs were synthesized and investigated. The influence of the following synthesis parameters of SiNWs on their lateral and vertical morphology as well as on characteristics of diode sensors based on them was demonstrated: the duration of the first and second stages of metal-assisted chemical etching (MACE), the content of silver nitride and hydrogen peroxide in the solutions of the first and second stages of MACE, as well as surface texturing and processing in isotropic and anisotropic etchants. The maximum operational parameters of the obtained photosensitivity sensors based on the SiNW array were as follows: rectification coefficient of 1320 and photosensitivity coefficient of 3.1 mA/lmV.Conclusions. The obtained results indicate that the technological parameters of the first and second stages of MACE, as well as pre- and post- chemical treatments, have a significant influence on increasing of the surface roughness, height, and porosity of SiNWs, which in turn affect the electric and photosensitive parameters of the sensors. Optimal SiNWs synthesis parameters for achieving of maximum photosensitivity have been established.

(Digital Presentation) Porous Silicon Formed by Electrochemical, Chemical and Combined Etching

This work is devoted the thermophysical characteristics (TPC) of PS formed by Electrochemical, Metal-assisted chemical and combined etching methods. The TPC of PS/MACE+EC formed by the MACE+EC– method is higher than those of the PS/EC and PS/MACE samples formed by the EC and MACE methods. The energy activity of water splitting on the surface of PS/MACE+EC is higher than the energy activity of the PS/EC and PS/MACE samples. The combined (MACE+EC) method is the best method for obtaining PS, which has the highest energy activity in water splitting processes. The activation energy of water splitting processes Ea(PS/MACE+EC) is higher than the energy activity of the Ea(PS/EC) and Ea(PS/MACE) samples. The presence of Ni particles in the pores of PS<Ni> stabilizes the them TPC. The TPC of PS were studied in comparison with the TPC of crystalline (c-Si) and powdered silicon (powder-Si). It is known that PS has a high catalytic activity of hydrogen evolution during photoelectrochemical splitting of water. For example, the use of a surface enriched Ni layer on the surface of a PS photocathode PS<Ni> made it possible to increase its catalytic activity two times higher than the catalytic activity of the Pt- electrode in the reaction of hydrogen evolution [1]. The TPC of PS samples formed by EC, MACE and combined (MACE+EC)- etching methods are studied in comparison with the TPC of c-Si and powder-Si samples, Table. Method Electrolyte Composition Marked I Et1 HF:H2O2=1:1 EC II Et2 HF:H2O2: Ni(NO3)2 =1:1:1 МАСЕ III Et3 HF:H2O2: Ni(NO3)2 =1:1:1 EC+МАСЕ According of electron microscopy research the highest porosity is observed on the PS/MACE+EC samples, the smallest - on the PS/MACE sample formed by the MACE- method. The Raman spectra testify this, PS/MACE+EC(Et3) samples have a higher intensity of the Raman peak at a high-frequency shift due to electron-phonon scattering, the intensity and frequency of which depend on the concentration of scattering centers and, consequently, on the conditions for the formation of pores [2]. The TPC of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) spectra record changes in the mass Δm of the sample and heat flux ΔQ with an isobaric temperature change ΔT at the points of T-characteristic. An analysis of the calorimetric TPC and the TGA and DSC spectra shows that c-Si and powder have almost the same patterns of change in thermal conductivity, in contrast to the PS-spectra. The PS/EC, PS/MACE samples have the maximum change in heat flux Q(PS/EC)=187.6 mW, Q(PS/MACE)=231.6 mW, in contrast to powder-Si Q(powder-Si)=107.1 mW and c-Si ΔQ(c-Si)=65.02 mW. This dependence, which is responsible for the heat flux ΔQ change in the high T-range is associated with the maximum developed surface PS. Due to the fact that the presence of the Ni in the pores of PS<Ni>/MACE and PS<Ni>/MACE+EC stabilizes the TPC of PS, and thereby prevents significant changes in the TPC of Ni-containing PS<Ni>, in contrast to PS that does not Ni-contain in pores. Also have carried out experiments on the evaporation of water droplets at room temperature from the surface of c-Si and PS/EC, PS/MACE PS/MACE+EC samples. Experiments on the evaporation of water droplets at Troom from the surface of crystalline and PS samples obtained by various etching methods showed that the highest energy activity is observed in PS/MACE+EC samples, Ea(PS/MACE+EC) = 0.2087 eV, which is much higher than Ea(PS/EC) = 0.070 eV, Ea(PS/MACE) = 0.050 eV and Еа(c-Si) = 0.025 eV,The porous surface of the PS/MACE+EC sample has the highest energy activity compared to the PS/EC and PS/MACE samples, which is due to the high porosity of PS/MACE+EC. The PS/MACE and PS/MACE+EC samples showed high energy stability over 1 year in water evaporation experiments. The values of the heat capacities of various EC-, MACE-, EC+MACE - etching methods are established: - Cp(c -Si) = 20.7 KJ/gK, Cp(powder-Si) = 13.11 KJ/gK, Cp(PS/MACE) = 12.79 KJ/gK, Cp(PS/AE) = 5.62 KJ/gK.Combination of electrochemical etching with Ni-stimulated and chemical etching (EC+MACE) makes the possibility Ni-containing nanoporous silicon with high energy activity in water splitting processes: - Еа(PS/MACE+EC) = 0.2087 eV, Еа(PS/MACE) = 0.070 eV , Еа(PS/АЕ) =0.050 eV.The Ni- presence in the pores stabilizes the TPC of PS/MACE and PS/MACE+EC. The stability of Ni-containing samples PS/MACE+EC) and Ea(PS/MACE) is maintained for one year. [1] K.B. Tynyshtykbayev et al. Russian Microelectronics, 2016, Vol. 45, Nos. 8–9, pp. 603–612. https://doi.org/10.1134/S106373971608014X[2] K. Tynyshtykbayev et al. ECS Journal of Solid State Science and Technology, 2021 10 013009 DOI: 10.1149/2162-8777/abdd86

Role of Metal Nanoparticles in the Fabrication of Porous Silicon: A Material for Solar Cell Applications

Metal-Assisted Chemical Etching method (MACE) has emerged as an effective tool to fabricate silicon nanostructures. This technique requires a catalytic mask that is commonly composed of a metal. In the present work, the role of Silver nanoparticles (AgNPs) in the etching mechanism of Porous Silicon (PS) is investigated by studying the effect of AgNP coverage on the surface porosity and the different properties of PS. XRD spectra consist of the two peaks corresponding to silicon and AgNPs respectively and the peak intensity of Ag decreased with an increase in etching time which indicates that as the etching time increases the dissolution of silver metal also increases. Thus, the pore depth depends on the dissolution of AgNP. The pore depth and porosity are calculated at different etching times by SEM analysis. It is observed that porosity is modifiable with the variation of AgNP coverage which in turn modifies the optical properties of PS. The porosity increased with the increase of etching time and the highest porosity obtained was 78% after 240 minutes. The refractive index of PS decreased with increasing porosity in the visible region. The variation of the refractive index results in the tuning of optical energy gap which is more essential in increasing the efficiency of solar cells.

Trace level sensitivity and selectivity of room temperature NH3 gas sensors based on RGO/ZnO@SiNWs heterostructure

Ammonia (NH3) is one of the most common gaseous pollutants in various environmental and industrial processes which is accountable for various health issues, even for life-threatening situations. Due to this, high-precision detection of NH3 has become a top priority for various sectors so that healthy and safe environment could be ensured. Therefore, this work aims to develop a simple, reliable, and effective sensor with spatially distributed monitoring of NH3 gas wherein reduced graphene oxide (RGO) and Zinc oxide (ZnO) nanocomposite structure prepared using refluxing method were chosen to interact with NH3 gas. The vertically aligned silicon nanowires (SiNWs) were developed by using metal-assisted chemical etching (MACE) method. The RGO/ZnO nanostructure was then deposited on SiNWs to develop a selective and stable sensor for the trace level detection of NH3 gas with varying concentration from 0.01 ppm to 5 ppm at Room temperature (∼30 °C). The prepared materials were characterized using scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), X-ray diffractometer (XRD), Raman spectrometer, X-Ray Photoelectron Spectrometer (XPS) and Ultraviolet–visible spectrophotometer which provide a thorough explanation about the developed nanostructures. The sensitivity of the sensor was observed to lie between 21 % at 0.01 ppm and 176 % at 5 ppm concentration of NH3 wherein the response/recovery time was measured to be 3 s/6 s and 5 s/12 s respectively. The fast response of the sensor for NH3 gas at low limit of detection (LOD) could be attributed due to the precise interaction of the analyte at the interface of RGO/ZnO@SiNWs Schottky heterostructure. Hence, the reported sensor can continuously be utilized to monitor the target analyte that is NH3 gas at low concentrations and reduces the chance of an unfortunate incident.

Diameter and gap controlled fabrication of periodic SiMW/SiNW arrays: A broadband absorber for high efficiency silicon solar cell

Vertically aligned and periodic silicon micro/nano-wire (SiMW/SiNW) arrays of different diameters were synthesized by combining lithography-free silica particle patterning, reactive ion etching (RIE), and modified metal-assisted chemical etching (MACE) methods. All required silica particles were synthesized, and process parameters were optimized to fabricate sub 50 nm SiNW to large size SiMW with the controlled inter-wire gap. Fabricated SiMW/SiNW array samples show a significant reduction of reflectance (7–9 %) in the silicon absorption band (300 nm–1000 nm). Additional absorption of 25–33 % compared to the planar silicon is observed in the sub-bandgap region of silicon (1100–2000 nm) for these samples, which signifies the effect of field confinement within these structures. The estimated short circuit current density (JSC) using the experimental absorption spectrum of SiMW is 49.96 mA/cm2, which is 16 % higher than the Lambertian limit of ∼43 mA/cm2. This result can lead to the theoretical efficiency of the solar cell up to 28.73 % without the inclusion of the surface passivation effect.

Fabrication and Characterization of Silicon Nanowires Heterojunction Solar Cell

Silicon nanowire arrays (SiNWs) are created utilizing the metal-assisted chemical etching method with an Ag metal as a catalyst and different etching time of 15, 30, and 60 minutes using n-Si (100). Physical properties such as structural, surface morphology, and optical properties of the prepared SiNWs are studied. The diameter of prepared SiNWs ranged from 20 to 280 nm, and the reflectance in the visible part of the wavelength spectrum was less than 1% for all prepared samples. The obtained energy gap of prepared SiNWs was around 2 eV, which is higher than the energy gap of bulk silicon. X-ray diffraction (XRD) has diffraction peaks at 68.70o for all prepared samples. The heterojunction solar cell was fabricated based on the n-SiNWs/ P3HT/PEDOT: PSS structure. The heterojunction solar cell produced for 60 minutes has the highest Jsc of 11.55 mA.cm-2 and a conversion efficiency of 0.93%. Based on SiNWs prepared for etching time of 15 min, the solar cell demonstrated Jsc and Voc of 2.73 mA/cm2 and 0.46 V, respectively, and a conversion efficiency of 0.34%.

Photocatalytic fuel cell based on integrated silicon nanowire arrays/zinc oxide heterojunction anode for simultaneous wastewater treatment and electricity production

Photocatalytic fuel cells (PFCs) convert organic waste into electricity, thereby providing a potential solution for remediating environmental pollution and solving energy crises. Most PFCs for energy generation applications use powder photocatalysts, which have poor mechanical stability, high internal resistance, and may detach from the substrate during reactions, leading to unstable performance. Integrated photoelectrodes can overcome the drawbacks of powder catalysts. In this study, an integrated photoanode was prepared based on a silicon nanowire arrays/zinc oxide (Si NWs/ZnO) heterojunction by combining metal-assisted chemical etching (MACE) and hydrothermal methods. The resulting photoanode was used to assemble a PFC for simultaneous electricity generation and Rhodamine (RhB) dye wastewater degradation. This PFC showed excellent cell performance under irradiation, with a short-circuit current density of 0.183 Am−2, an open-circuit voltage (OCV) of 0.72 V, and a maximum power density of 0.87 W m−2. It could also be used continuously 20 times while degrading > 90% of RhB. This performance was ascribed to the three-dimensional (3D) structure and large surface area of Si NWs, as well as the matched band structure of ZnO, which facilitated the efficient separation and transport of photogenerated carriers in Si NWs/ZnO. The integrated structure also shortened the carrier transport pathways and suppressed carrier recombination. This research provides a foundation for the development of efficient, stable, low-cost, small-scale PFCs.

Strong enhancement of the optical properties of SiNWs by the deposition of snowball-like V2O5 nanoparticles

In this work, the morphological and optical properties of vanadium pentoxide (V2O5) nanoparticles deposited on silicon nanowires (SiNWs) have been investigated. SiNWs are obtained by metal-assisted chemical etching (MACE) method. The deposition of vanadium pentoxide on SiNWs layer was performed by vacuum thermal evaporation system for different durations. Scanning electronic microscope (SEM) images show the formation of snowball-like V2O5 nanoparticles on the SiNWs surface. A large condensation of V2O5 elements was observed by increasing the evaporation time. The changes in bonds and chemical composition at the surface of the SiNWs-V2O5 nanocomposites were examined by Raman and Fourier transform infrared (FTIR) spectroscopies. The X-ray Diffraction (XRD) technique revealed the presence of orthorhombic structure of V2O5 layer with good crystallinity. The SiNWs-V2O5 composites show strong visible PL due to the contribution of the radiative band edge transitions of vanadium pentoxide. The emission of V2O5 layer is in the same energy range as that of SiNWs thus leading to a large increase in PL intensity. Optical band gap (Eog) was determined from UV–Vis-IR spectroscopy. The presence of vanadium pentoxide on the SiNWs surface causes an increase in the value of Eog from 1.851 to 2.075 eV. This increase was explained by Burstein-Moss effect.

Construction of Si nanowires/ZnFe2O4/Ag photocatalysts with enhanced photocatalytic activity under visible light and magnetic field

The Si nanowires/ZnFe2O4/Ag composite photocatalyst is prepared by metal-assisted chemical etching and hydrothermal methods. Photoelectric conversion and photodegradation experiments show that the composite structure offers high photocatalytic performance under visible light. The photocurrent density of Si nanowires/ZnFe2O4/Ag is 1.76 mA/cm2, and the Methyl orange photodegradation rate is 19 % within 90 min. Furthermore, the photocatalytic activity of composite photocatalysts was studied under the magnetic field, which further improves the photocatalytic efficiency significantly. Energy band structure studies revealed that the interfacial contact in the Si nanowires/ZnFe2O4/Ag increases carrier transfer and charge separation, thereby improving photocatalytic performance. It can be seen from the I-V results that the Si nanowires/ZnFe2O4/Ag has a negative magnetoresistance. Therefore, in the presence of a magnetic field, photogenerated carriers can be more effectively transferred to the electrode surface to participate in the photocatalytic reaction with improved photocatalytic performance.

SERS Nanowire Chip and Machine Learning-Enabled Classification of Wild-Type and Antibiotic-Resistant Bacteria at Species and Strain Levels.

Antimicrobial resistance (AMR) is a major health threat worldwide and the culture-based bacterial detection methods are slow. Surface-enhanced Raman spectroscopy (SERS) can be used to identify target analytes in real time with sensitivity down to the single-molecule level, providing a promising solution for the culture-free bacterial detection. We report the fabrication of SERS substrates having tightly packed silver (Ag) nanoparticles loaded onto long silicon nanowires (Si NWs) grown by the metal-assisted chemical etching (MACE) method for the detection of bacteria. The optimized SERS chips exhibited sensitivity down to 10-12 M concentration of R6G molecules and detected reproducible Raman spectra of bacteria down to a concentration of 100 colony forming units (CFU)/mL, which is a thousand times lower than the clinical threshold of bacterial infections like UTI (105 CFU/mL). A Siamese neural network model was used to classify SERS spectra from bacteria specimens. The trained model identified 12 different bacterial species, including those which are causative agents for tuberculosis and urinary tract infection (UTI). Next, the SERS chips and another Siamese neural network model were used to differentiate AMR strains from susceptible strains of Escherichia coli (E. coli). The enhancement offered by SERS chip-enabled acquisitions of Raman spectra of bacteria directly in the synthetic urine by spiking the sample with only 103 CFU/mL E. coli. Thus, the present study lays the ground for the identification and quantification of bacteria on SERS chips, thereby offering a potential future use for rapid, reproducible, label-free, and low limit detection of clinical pathogens.

Photoelectrocatalysis Synthesis of Ammonia Based on a Ni-Doped MoS2/Si Nanowires Photocathode and Porous Water with High N2 Solubility

The synthesis of ammonia through photocatalysis or photoelectrochemistry (PEC) and nitrogen reduction reaction (NRR) has become one of the recent research hotspots in the field, where the catalyzed materials and strategies are critical for the NRR. Herein, a Ni-doped MoS2/Si nanowires (Ni-MoS2/Si NWs) photocathode is prepared, where the Si NWs are formed on the surface of a Si slice by the metal-assisted chemical etching method, and the hydrothermally synthesized Ni-MoS2 nanosheets are then cast-coated on the Si NWs electrode. Porous water with high solubility of N2 is prepared by treating a hydrophobic porous coordination polymer with hydrophilic bovine serum albumin for subsequent aqueous dispersing. The relevant electrodes and materials are characterized by electrochemistry, UV-vis spectrophotometry, scanning electron microscopy/energy dispersive spectroscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller method, and zeta potential method. The uses of the Ni-MoS2/Si NWs photocathode and the porous water with high nitrogen solubility for PEC-NRR give a yield of NH3 of 12.0 mmol h-1 m-2 under optimal conditions (e.g., at 0.25 V vs RHE), and the obtained apparent Faradaic efficiency higher than 100% is discussed from the inherent photocurrent-free photocatalysis effect of the photoelectrodes and the suggested classification of three kinds of electrons in PEC, which may have some reference value in understanding and improving other PEC-based processes.

Effect of High-Temperature Annealing on Raman Characteristics of Silicon Nanowire Arrays

We demonstrate two distinct experimental processes involving the large-area growth of ordered and disordered silicon nanowire arrays (SiNWs) on a p-type silicon substrate using the metal-assisted chemical etching method. The two processes are based on the etching of monocrystalline silicon wafers by randomly distributed Ag films and ultra-thin Au films with ordered nano-mesh arrays, respectively, wherein the growth of SiNWs is implemented using a specific proportion of a HF-containing solution at room temperature. In this study, the microstructural change mechanisms for the two morphologically different arrays before and after annealing were investigated using Raman spectra. The effects of various mechanisms on the observed Raman scattering peak’s deviation from symmetry, redshift and broadening were analyzed. The evolution of the unstable amorphous structures of nanoscale materials during the high-temperature annealing process was observed via high-resolution scanning electron microscope (SEM) observations. The scattering peak parameters determined from the Raman spectra led to conclusions concerning the various mechanisms by which high-temperature annealing influences the microstructures of the two morphologically different SiNWs fabricated on the p-type silicon substrate. Therefore, the deviation of SiNWs from the monocrystalline silicon scattering peak at 520.05 cm−1 when changing the diameter of the nanowire columns was calculated to further analyze the effect of thermal annealing on Raman characteristics.

Fabrication of superhydrophobic surfaces for applications in total internal reflection effects

Superhydrophobic surfaces have attracted significant attention in the applied science community. This paper presents three different methods for fabricating superhydrophobic surfaces, which can be applied in liquid light guides with the total internal reflection effect playing a central role. The selective bi-polymer etching only produces a hydrophobic porous poly(methyl methacrylate) surface but is simple and versatile for use on an arbitrary surface. In metal-assisted chemical etching, wet etching of a silver layer on a silicon sample creates porous silicon with superhydrophobicity, characterized by a water contact angle of 160°. The metal-assisted chemical etching method modified with the presence of polystyrene nanoparticles further improved the water contact angle to 164° by creating a nanopillar silicon structure. The metal-assisted chemical etching methods are more complicated but can produce superhydrophobic surfaces with very high water contact angles. These results show that superhydrophobic surfaces fabricated by methods in this study can be used for total internal reflection effect at the interface between water with huge potential applications in liquid light guides.

Development of a metal-assisted chemical etching method to improve light-capture in monocrystalline silicon solar cells

Development of a metal-assisted chemical etching method to improve light-capture in monocrystalline silicon solar cells

Modeling and Simulation of Si Grating Photodetector Fabricated Using MACE Method for NIR Spectrum

In this research, we modeled a silicon-based photodetector for the NIR-IR spectrum using a grating structure fabricated using the metal-assisted chemical etching method. A nanostructure fabricated by using this method is free of defects such as unwanted sidewall metal depositions. The device is simulated using Lumerical finite difference time domain (FDTD) for optical characteristics and Lumerical CHARGE for electrical characteristics. First, we optimized the grating structure duty cycle parameter for maximum optical power absorption using the particle swarm optimization algorithm provided in Lumerical FDTD, and then used the optimized parameter for our simulations. From Lumerical FDTD simulations, we found that the Cr masker metal used in the fabrication process acts as a resonant cavity and a potential candidate for internal photo emission (IPE) effects. By using Lumerical CHARGE, we performed electrical simulation and by adding the IPE calculation we found that at 850 nm wavelength the Si grating photodetector device exhibited 19 mA/W responsivity and detectivity of 2.62 × 106 Jones for −1 volt operating voltage.

Freestanding Metal Nanomembranes and Nanowires by Template Transfer with a Soluble Adhesive.

The fabrication of nanostructures usually involves chemical processes that have in certain steps. Especially, it is necessary to use the chemical etching method to release the as-patterned structures from the substrate in most of the transfer techniques. Here, a novel scheme of template transfer as developed for the fabrication of freestanding Au nanomembranes and nanowires by using a soluble PVP adhesive. The nanomembranes feature the periodic nanohole arrays with high uniformity. Without the substrates, these plasmonic nanohole arrays show symmetric and antisymmetric resonance modes with bright and dark spectral features, respectively, in transmission. Through the spectral analysis for reflection, we have disclosed that the usual dark mode in transmission is not really dark, but it reveals a distinct feature in reflection. Two coupling modes present distinct spectral features in transmission and reflection due to their different loss channels. To show their versatility, the freestanding nanomembranes were also employed as secondary templates to form Si nanowire arrays by the metal-assisted chemical etching method.

β-Ga2O3 FinFETs with ultra-low hysteresis by plasma-free metal-assisted chemical etching

In this work, β-Ga2O3 fin field-effect transistors (FinFETs) with metalorganic chemical vapor deposition grown epitaxial Si-doped channel layer on (010) semi-insulating β-Ga2O3 substrates are demonstrated. β-Ga2O3 fin channels with smooth sidewalls are produced by the plasma-free metal-assisted chemical etching (MacEtch) method. A specific on-resistance (Ron,sp) of 6.5 mΩ·cm2 and a 370 V breakdown voltage are achieved. In addition, these MacEtch-formed FinFETs demonstrate DC transfer characteristics with near zero (9.7 mV) hysteresis. The effect of channel orientation on threshold voltage, subthreshold swing, hysteresis, and breakdown voltages is also characterized. The FinFET with channel perpendicular to the [102] direction is found to exhibit the lowest subthreshold swing and hysteresis.