Silver-assisted Chemical Etching Research Articles

Erratum to: Enhancement of silicon nanowire opto-electric properties by combining acid vapor etching and lithium pore-filling

In this paper, we report a novel method combining acid vapor etching (AVE) and Lithium (Li) pore-filling aiming to enhance the opto-electrical properties of silicon nanowires (SiNWs). Images provided by both scanning and transmission electron microscopies (SEM and TEM) show that, the silver-Assisted Chemical Etching (Ag-ACE) method provides uniform and vertically aligned SiNWs with smooth sidewalls. AVE treatment leads to the formation of thin porous silicon (pSi) layer covering the initially solid SiNW sidewalls without affecting their initial length. The as-prepared porous SiNWs (pSiNWs) exhibit a quite strong photoluminescence (PL) band centered on 2 eV. An additional immersion of pSiNWs in LiBr aqueous solution leads to a significant change in the surface chemistry and a stable PL emission with fourfold increase in the intensity. The total reflectivity decreases with Li concentration and reaches 1% in the visible range. Simultaneously, the minority carrier lifetime (τeff) of pSiNWs is enhanced from 1.48 to 7.1 µs due to the formation of a stable passivation layer and the saturation of dangling bands. The dark I–V measurement shows a significant decrease of the series resistance from 340 to 85 Ω.

Gold nanoparticles modified porous silicon chip for SALDI-MS determination of glutathione in cells

The gold nanoparticles (Au NPs) modified porous silicon chip based surface assisted laser desorption/ionization mass spectrometry (SALDI-MS) was developed to capture and analyze glutathione (GSH) in cells. With silver-assisted chemical etching, Ag nanoparticles (Ag NPs) were generated and deposited on the silicon surface and the nanopores were etched on silicon substrate. Then Au NPs were in-situ synthesized on the ridges of silicon nanopores. This Ag-Au NPs modified porous silicon surface could specially capture and enrich thiol compounds through Au-S binding, and it could also function as matrix to assist ionization for SALDI-MS. The silicon chip was array patterned for high throughput SALDI-MS detection. GSH and cysteine could be distinguished without the interference from matrix signals. This approach was successfully applied to preconcentration and detection of GSH in Caco-2 cells. The GSH alterations in cells under drug stimulation were investigated. This invented silicon chip showed great potential for more efficient analysis of small thiol biomarkers in complex biological samples.

Effect of Silver-Assisted Chemical Vapor Etching on morphological properties and silicon solar cell performance

In this work, we report a novel, simple and reproducible etching technique named Silver-Assisted Chemical Vapor Etching method (Ag-ACVE). It consists to expose Ag-loaded silicon substrates to vapors emanating from HF/H2O2 hot solution. The surface treatment performed with this method aims to enhance both optical and electrical properties of conventional silicon solar cells. SEM images of Ag-ACVE treated samples exhibit the appearance of porous micro-cavity like-structure for short etching duration. For long etching duration, sporadic and curved silicon nanowires (SiNWs) were formed. A kinetic study of the vapor etching reaction revealed a relatively high etching rate. Furthermore, the dimension of the micro-cavities increased as a function of the H2O2 molar ratio. UV–Visible measurement showed a significant decrease of the total reflectivity versus the molar ratio. Whereas, at the same time the minority carrier life time was significantly enhanced and as a result the solar cell performance was improved.

The Preparation of Silicon Nanowires Using Metal-Assisted Chemical Etching

The preparation of silicon nanowires by metal catalytic chemical etching has the advantages of low cost and simple operation. This study attempts to use a silver-assisted chemical etching to prepare silicon nanowires. In the process of experiment we change the corrosive liquid concentration of corrosion and corrosion time to compare these factors on the surface topography of silicon nanowires in the preparation. The experimental results were observed by optical microscope and electron microscope. The experiment shows that in the process of etching, etching time of CLSM has had a huge impact, if etching time is short, the sample cannot generate silicon nanowires, while a long etching time will cause silicon erode up, finally dissolved in the etching liquid. The wafer surface surface morphology of honeycomb like, and the result shows that when the corrosive liquid concentration is 0.02mol/L and the corrosive time is four works better, formed the length 100-200nm and the line diameter 100μm and more uniform silicon nanowires.

Nanotextured Si Solar Cells on Microtextured Pyramidal Surfaces by Silver-assisted Chemical Etching Process

We investigated nanotextured Si solar cells using the silver-assisted chemical etching process. The nanotexturing process is very sensitive to the concentration of chemical etching solution. The high concentration process results in a nanowire formation for the nanosurfaces and causes severe surface damage to the top region of the micropyramids. These nanowires show excellent light absorption in photoreflectance spectra and radiative light emission in photoluminescence spectra. However, the low concentration process forms a nano-roughened surface and provides high minority carrier lifetimes. The nano-roughened surfaces of the samples show the improved electrical cell properties of quantum efficiency, conversion efficiency, and cell fill factor due to the reduction in the formation of the over-doped dead layer.

Influence of doping elements on the formation rate of silicon nanowires by silver-assisted chemical etching

Metal-assisted chemical etching (MACE) has gained great interest for the preparation of vertically aligned silicon nanowires (SiNWs); however, the process mechanism has not yet been identified. In this study, the influence of doping elements on the formation rate of SiNWs prepared by silver-assisted chemical etching was investigated. Two n-type silicon substrates, bulk silicon and silicon-on-insulator (SOI) samples, containing different dopant concentrations (from 1011 to 1019atomscm−3) and species (phosphorous and arsenic), were considered. The SiNW formation rates increase with dopant concentration and are influenced by the dopant species. The use of SOI samples allowed highlighting the remarkable loss of the starting device layer in conventional process conditions, never previously observed; such occurrence limits the most achievable SiNW length. The study of the gas evolution both from bulk and SOI samples allowed for the first time the in situ H2 detection as well as to identify one definite overall process reaction.

Fluorinion transfer in silver-assisted chemical etching for silicon nanowires arrays

Uniform silicon nanowires arrays (SiNWAs) were fabricated on unpolished rough silicon wafers through KOH pretreatment followed by silver-assisted chemical etching (SACE). Density functional theory (DFT) calculations were used to investigate the function of silver (Ag) at atomic scale in the etching process. Among three adsorption sites of Ag atom on Si(100) surface, Ag(T4) above the fourth-layer surface Si atoms could transfer fluorinion (F−) to adjacent Si successfully due to its stronger electrostatic attraction force between Ag(T4) and F−, smaller azimuth angle of FAg(T4)Si, shorter bond length of FSi compared with FAg. As F− was transferred to adjacent Si by Ag(T4) one by one, the Si got away from the wafer in the form of SiF4 when it bonded with enough F− while Ag(T4) was still attached onto the Si wafer ready for next transfer. Cyclic voltammetry tests confirmed that Ag can improve the etching rate by transferring F− to Si.

Silver-assisted chemical etching on silicon with polyvinylpyrrolidone-mediated formation of silver dendrites.

Metal-assisted chemical etching (MaCE) on silicon (Si)-mediated by polyvinylpyrrolidone (PVP)-is systematically investigated herein. It is found that the morphologies and crystallographic natures of the grown silver (Ag) dendrites can be significantly modulated, with the presence of PVP in the MaCE process leading to the formation of faceted Ag dendrites preferentially along the (111) crystallographic phase, rather than along the (200) phase. Further explorations of the PVP-mediated effect on Si etching are also revealed. In contrast to the aligned Si nanowires formed by MaCE without PVP addition, only distributed nanopores with sizes of 200 to 400 nm appear on the Si surfaces in the presence of PVP. The origin of surface polishing on Si in the PVP-mediated MaCE process can be attributed to the distinct transport pathway of holes supplied by the Ag(+) ions, where the holes are injected directly into the primary Ag seeds, rather than through Ag dendrites, thus leading to the isotropic etching of the Si surface.

A new approach to fabricating silicon nanowire/poly(3, 4-ethylenedioxythiophene) hybrid heterojunction solar cells

The silicon/poly(3, 4-ethylenedioxythiophene) core/shell organic/inorganic nanowire array (SiNWs/PEDOT) hybrid heterojunction solar cells are successfully fabricated by silver-assisted chemical etching method and vapor phase polymerization processes. The SiNWs/PEDOT hybrid solar cell shows that the performance is improved greatly and an excellent power conversion efficiency of 3.23% is achieved, which is as seven times as large as that of the planar cell without the nanowire structure. In addition, the studies of the reflectance, the I-V curve and the external quantum efficiency show that the great enhancement of performance for the SiNWs/PEDOT cell is due to the fact that the Si/PEDOT core/shell nanowire structure is successfully fabricated by vapor phase polymerization method, resulting in a high light trapping effect, a large junction area and an enhancement of the carrier collection efficiency.

Nanopore-type black silicon anti-reflection layers fabricated by a one-step silver-assisted chemical etching

An effective and economical fabrication process for the synthesis of nanopore-type "black silicon", that significantly decreases reflectivity of silicon wafer surfaces, is reported using a room temperature one-step Ag-assisted chemical etching method. The effects on the surface morphology and the corresponding surface reflectivity of the concentration of the silver catalyst (500, 50, and 5 μM), the HF and H2O2 concentration in the silicon etchant, the HF : H2O2 ratio, and etching time have been investigated. Lower reflectivity is a balance between sufficient silver catalyst to create large numbers of nanopores on a silicon surface and excessive silver that brings deeply etched channels that would potentially short-circuit a solar cell junction. The lowest relative effective reflectivity (0.17% over a range of 300-1000 nm) occurs with a silver ion concentration of 50 μM, however, with the silver ion concentration decreases to 5 μM surfaces with a low relative effective reflectivity (2.60%) and a short nanopore length (<250 nm) can be obtained with 10 minute etching time, indicating that this method can be used as a simple (one-pot), low cost (low silver concentration), energy efficient (room temperature), method for the synthesis of anti-reflection layers for silicon-based solar cell applications.

Electrochemical characteristics of bundle-type silicon nanorods as an anode material for lithium ion batteries

In order to prepare bundle-type silicon nanorods, a silver-assisted chemical etching technique was used to modify a 1.6μm silicon thin film, which was deposited on Cu foil by Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition. The bundle-type silicon nanorods on Cu foil were employed as anodes for a lithium secondary battery, without further treatment. The electrochemical characteristics of the pristine silicon thin film anodes and the bundle-type silicon nanorod anodes are different from one another. The electrochemical performance of the bundle-type silicon nanorod anodes exceeded that of the pristine Si thin film anodes. The specific capacity of the bundle-type silicon nanorod anodes is much higher than 3000mAhg−1 at the first charge (Li insertion) cycle. The coulombic efficiency of bundle-type silicon anodes was stable at more than 97%, and the charge capacity remained at 1420mAhg−1, even after 100 cycles of charging and discharging. The results from the differential voltage analysis showed a side reaction at around 0.44–0.5V, and the specific potential of this side reaction decreased after each cycle. The apparent diffusion coefficients of the two anode types were in the range of 10−13–10−16cm2s−1 in the first cycle. In subsequent charge cycles, these values for the silicon thin film anodes and the silicon nanorod bundle anode were approximately 10−12–10−14 and 10−13–10−15cm2s−1, respectively.

Tailoring Broadband Antireflection on a Silicon Surface through Two-Step Silver-Assisted Chemical Etching

Combined nanostructure arrays with tailored structural profiles are presented (see picture, GN: graded nanostructure). These arrays exhibit a sharp decrease in reflectivity when submitted to strong sunlight irradiation, showing great potential for diverse applications, such as optical and electro-optical devices and other antireflection designs.

Fabrication and characterization of polycrystalline silicon nanowires with silver-assistance by electroless deposition

Single crystal silicon wafers are widely used as the precursors to prepare silicon nanowires by employing a silver-assisted chemical etching process. In this work, we prepared polycrystalline silicon nanowire arrays by using solar-grade multicrystalline silicon wafers. The chemical composition and bonding on the surface of silicon nanowire arrays were characterized by Fourier Transform Infrared spectroscope, and X-ray photoelectron spectroscope. The photoluminescence spectra of silicon nanowires show red light emissions centered around 700nm. Due to the passivation effect of Si dangling bonds by concentrated HNO3 aqueous solution, the photoluminescence intensities are improved by 2 times. The influences of surface chemical states on the wettability of silicon nanowire arrays were also studied. We obtained a superhydrophobic surface on the as-etched silicon nanowire arrays without surface modification with any organic low-surface-energy materials, and realized the evolution from superhydrophobicity to superhydrophilicity via surface modifications with HNO3 solutions.

Preparation of Photoluminescent Silicon Nanowires Based on Multicrystalline Silicon Wafers

Single crystal silicon (sc-Si) wafers are widely used as the precursors to prepare silicon nanowires (SiNWs) by employing a silver-assisted chemical etching process. In this work, we obtained SiNWs arrays using multicrystalline silicon (mc-Si) wafers. Firstly, silver nanoparticles were deposited on the textured solar-grade mc-Si wafer by a galvanic displacement process; secondly, the SiNWs arrays were formed by a silver-assisted chemical etching process conducted in a HF-H2O2 aqueous solution. The etching process indicated that the growth of SiNWs is independent on the orientation of the Si wafer. TEM images showed that the SiNWs have rough and nanoporous structures on the top side along axial directions. The photoluminescence (PL) spectrum of SiNWs showed a broad visible emission centred around 700 nm, which is attributed to the emission properties of silicon nanocrystallites in SiNWs. This work may contribute to the development of SiNWs in application including optoelectronic devices, solar energy conversion devices, chemical sensors, and lithium secondary batteries, etc.

Fabrication of silver-coated silicon nanowire arrays for surface-enhanced Raman scattering by galvanic displacement processes

Silver-coated silicon nanowire (SiNW) arrays were prepared utilizing galvanic displacement processes consisting of three steps: galvanic displacement deposition of silver particles using a HF–AgNO 3 or NH 4F–AgNO 3 aqueous solution; formation of SiNW arrays by a silver-assisted chemical etching process conducted in the HF–H 2O 2 aqueous solution; deposition of silver particles on the SiNW arrays from the NH 4F–AgNO 3 aqueous solution. The effects of the morphology of pre-deposited silver particles and deposition solution on the formation of silver-coated SiNW arrays were discussed. Surface-enhanced Raman scattering (SERS) performances have been studied using Rhodamine 6G (R6G) probe molecules on the silver-coated SiNW substrates.