Production Of Porous Silicon Research Articles

The total use of rice husk to create highly porous silicon and sulfur-doped activated carbon for the fabrication of high-performance silicon-anode lithium-ion capacitors

The promising advantages between the high energy density of lithium-ion batteries and the high power density of supercapacitors are hybridized to construct lithium-ion capacitors (LICs). The high capacity of anode materials is challenging for high-performance LICs. Simultaneously, the quest for sustainable and environmentally friendly energy storage materials has attracted attention. In this work, rice husk was treated with alkaline to separate silica and biochar, followed by magnesiothermic reduction and thermal activation to produce porous silicon (PSi) and sulfur-doped activated carbon (SAC), respectively. The PSi had high porosity for accommodating volumetric expansion during cycling, resulting in outstanding rate capability and cycling stability, whereas the SAC had a high surface area with micro- and mesopores (2511 m2 g−1), a high degree of graphitization, and excellent electrochemical performance. For the fabrication of half-cell lithium-ion batteries, PSi gave a specific capacity of 1005.3 mAh g−1 between 0.01 and 2 V, while SAC provided a specific capacity of 108 mAh g−1 (2.0–4.5 V), and showed a better electrochemical stability than the both commercial silicon and activated carbon. When a full-cell LIC was fabricated, the optimized P-Si//SAC LIC had a high energy density of 107 Wh kg−1 at a power density of 163 W kg−1 and a capacitance retention of 81.3 and 61.8% between a potential range of 2.0–4.5 V after 1000 and 3000 charge-discharge cycles, respectively. This study not only turned agricultural waste into valuable, high-performance LICs but also made significant progress toward the creation of environmentally responsible, long-lasting, and sustainable energy storage systems.

Production of porous silicon from silicon wafer waste for Li-ion batteries via low load metal assisted catalytic etching

Silicon (Si) is recognized as a superior anode material in lithium-ion batteries (LIBs) compared with graphite, which is currently used. Despite the high theoretical capacity (3579 mAh g−1) of Si, designing Si-based materials is challenging because of its large volume change (280%) during the charging and discharging processes. Mesoporous structured silicon (PSi) is a promising solution for overcoming the volume expansion issue of Si-based anodes. This study proposes the feasibility of using Si wafer waste to produce porous Si materials as anodes for LIBs. By varying the etching parameters, Si particles with various porosities and surface areas were produced and electrochemically tested. The sample with low porosity (28%) and low surface area (37 m2g-1) exhibited the best rate performance and cycling stability. In addition, this sample showed the highest initial Coulombic efficiency (ICE) value of 84% and exhibited stable cycling performance for 135 cycles at 0.2 C with a capacity limit of 500 mAh g−1. Furthermore, the PSi/graphite composites were prepared with Si contents ranging from 10 to 30 wt%. The composite with 30 wt% Si delivered a reversible capacity of 1053 mAh g−1 with an ICE of 88% and a capacity of 351 mAh g−1 after 100 cycles.

A novel proton-exchange porous silicon membrane production method for μDMFCs.

This study introduces a new production method to use as a porous silicon-based proton exchange membrane for μDMFCs. In this respect, EIS, fuel crossover test, and fuel cell performance test at the μDMFC sample cell are performed at room temperature on a porous silicon-based membrane that was produced for passive mode μDMFC as a proton exchange membrane. The reason for performing the fuel crossover test is to ensure the silicon opened pores along the silicon wafer and to examine the fuel permeability of the membrane. The fuel crossover test shows that the fuel cell provides energy for about 60 min with a 50 mL fuel. EIS reveals proton permeability of proton exchange membrane. The calculated value of the conductivity of the membrane is 0.0016 S/cm. OCV of the system is 0.4V, whereas values (with highest power density is 0.1 mW/cm²and with the highest current density is 0.39 mA/cm²) are low. However, porous silicon is not a natural proton conductor. Hence, these values can be increased by different ways such as porous silicon functionalized, or serial connection of fuel cells. On the other hand, the value of OCV is consistent with the previous studies. In sum, this study presents a simple, cost-effective, and short time-consuming method for the production of porous silicon as proton-conducting membrane behavior.

Origin of Mosaic Structure Obtained During the Production of Porous Silicon with Electrochemical Etching

So far, while producing porous silicon (PSi) with anodic etching of silicon in an aqueous solution of hydrofluoric acid, many researchers (including us) have obtained the crack-into-pieces (or mosaic) structure. Most of the authors believed that the cause of this structure is the collapse and the cracking of the porous, especially highly porous, silicon layer which took place during the drying of PSi after fabrication. However, our study showed that the mosaic structure was formed right during the course of silicon anodization at high anodic current density. Furthermore, our study also showed that at high anodic current density the real silicon etching has been replaced by the growth of a silicon oxide layer. This is a layer of another substance that grows on silicon, so when the layer is too thick (which is obtained when the anodic current density is too high and/or the anodization time is too long) it will crack, creating mosaic pieces. When the silicon oxide layer is cracked, the locations around the cracks will be etched more violently than elsewhere, creating trenches. Thus, the mosaic structure with mosaic pieces emerged between the trenches has formed.

Laser-Induced Fluorescence of Wet Porous Silicon as Laser-Induced Fluorescence of H<sub>3</sub>O<sup>+</sup>

This article presents a theoretical model based on previously published chiropractic theories and clinical experience. The thesis proposes a comparison of specific dynamically diagnosed manipulative procedure with non-specific statically determined mobilization. The proposed mechanism also theoretically provides a means by which one can determine areas of segmental motion-disturbance necessitating specific correction, as well as identifying areas where adjusting might be contraindicated. Theoretical considerations based on the model are then used to predict consequences of such procedures on hypermobility, fixation, correction efficacy, and side effects. Since the predictions can be tested experimentally, the model provides a basis for researching chiropractic theories and clinical options.

Fabrication of antireflective layers on silicon using metal-assisted chemical etching with in situ deposition of silver nanoparticle catalysts

Ag particle-assisted chemical etching of silicon wafers in HF/H2O2 is of interest for its potential to produce antireflective layers for solar cells. In this work, Ag films containing both nanoscale (d<100nm) and microscale (d<1μm) particles were deposited through the silver-mirror reaction on planar p-Si(111), planar p-Si(100) and p-Si(100) pre-etched in KOH/isopropanol to produce pyramidal textures. Subsequently, these wafers were subjected to metal-assisted chemical etching (MacEtch) in 1:1:1 (v:v:v) HF(49%):H2O2(30%):EtOH solutions, to produce porous silicon (PSi) containing both micro- and nanoscale roughness features. The resulting surfaces exhibit morphologies that evolve with processing conditions, especially the absence/presence of pyramidal textures and the time the structure is subjected to MacEtch. Under optimal conditions excellent anti-reflection behavior is observed with surface reflectivities being reduced below 10% for either p-Si(100) or p-Si(111) surfaces. For p-Si(100) better results (R∼5%) were obtained for 30min KOH/isopropanol pre-etch than for either no pre-etch or longer (60min) pre-etch. The influence of the reductant on Ag particle deposition on p-Si(111) was studied, and MacEtch catalyzed by Ag produced from acetaldehyde reductant produced surfaces with lower reflectivities than those with glucose reductant.

Porous silicon biosensor for detection of variable domain of heavy-chain of HCAb antibody

In this paper, we produce porous silicon (PSi) by electrochemical etching, and it is the first time to evaluate the performance of label-free porous silicon biosensor for detection of variable domain of heavy chain of heavy-chain antibody (VHH). The binding of hen egg white lysozyme (HEWL) and VHH causes a red shift in the reflection spectrum of the biosensor. The red shift is proportional to the VHH concentration in the range from 14 g·ml−1 to 30 g·ml−1 with a detection limit of 0.648 ng·ml−1. The research is useful for the development of label-free biosensor applied in the rapid and sensitive determination of small molecules.

Structural, optical and electrical characterization of porous silicon prepared on thin silicon epitaxial layer

Silicon-on insulator (SOI) wafers, consisting of 22 μm thick p-type silicon epitaxial layer grown on 280 μm thick n-type (1 1 1) silicon substrate, were electrochemically etched in hydrofluoric acid (HF) to produce porous silicon (PS) samples. The pores of different size and different depth were obtained by etching at different time duration, from 10 to 80 min, using the constant concentration of 48% HF in ethanol solution. The structural and optical properties of porous layers were investigated by Raman, FTIR and photoluminescence (PL) spectroscopy, and scanning electron microscopy. SEM images showed high density of micrometer-sized pores whose morphology and density depended on the etching duration. For all samples the observed PL peak is in the visible spectral range. The intensity of the PL peak was increased with the etching time. The exception was the epitaxial layer of the sample etched for 80 min. It showed the strong decrease in the PL peak intensity. For this sample the insulator layer was completely etched out and the epitaxial layer was detached from the substrate. Fine nanometer-sized pores with the strong photoluminescence were observed in the substrate layer. The fine silicon nanostructure was confirmed by the broadening and the red-shift of crystalline silicon TO(Γ) vibrational band that indicates a strong phonon confinement.

Optical and structural analysis of porous silicon coated with GZO films using rf magnetron sputtering

In the production of porous silicon (PS) to optoelectronic application one of the most significant constrains is the surface defects passivation. In the present work we investigate, gallium-doped zinc oxide (GZO) thin films deposited by rf magnetron sputtering at room temperature on PS obtained with different etching times. The X-ray diffraction (XRD), Fourier transform infrared (FTIR) and atomic force microscopy (AFM) analysis have been carried out to understand the effect of GZO films coating on PS. Further, the XRD analysis suggests the formation of a good crystalline quality of the GZO films on PS. From AFM investigation we observe that the surface roughness increases after GZO film coating. The photoluminescence (PL) measurements on PS and GZO films deposited PS shows three emission peaks at around 1.9 eV (red-band), 2.78 eV (blue-band) and 3.2 eV (UV-band). PL enhancement in the blue and ultraviolet (UV) region has been achieved after GZO films deposition, which might be originated from a contribution of the near-band-edge recombination from GZO.

Improved surface sensing of DNA on gas-etched porous silicon

A new gas-based etching process has been used to produce porous silicon (PSi) samples as sensor substrates. The as-etched porous material demonstrated an intense photoluminescence signal at an average wavelength of 658 nm ( σ = 1%). The photoluminescence signal, with a peak wavelength in the range 530–540 nm, was found to increase with the length and concentration of unmodified oligonucleotide probes on surfaces coated with either amino-propyl trimethoxysilane (APTMS) or glycidoxy-propyl trimethoxysilane (GPTMS). The large surface area that characterized this material significantly increased the binding of DNA probes and led to increased sensitivity in target detection. Using fluorescently-labeled DNA, the target capture for sub-micromolar detection on this novel sensor substrate was demonstrated to be 100 times higher than that obtained on non-etched silicon. In a 1 h assay, we were able to detect specifically approximately 3 fmole of a 25mer target oligonucleotide per mm 2 of substrate.

The role of boron impurity in the activation of free charge carriers in layers of porous silicon during the adsorption of acceptor molecules

Infrared-absorption spectroscopy and electron spin resonance are used to study the role of boron impurity in the activation of free charge carriers in layers of porous silicon that have been exposed to nitrogen dioxide acceptor molecules. It is found that the higher the level of doping is for the substrates used in the production of porous silicon, the higher the concentration of free holes that appear as a result of the adsorption of nitrogen dioxide. The experimental results are accounted for by the appearance of donor-acceptor pairs formed by anionic radicals (NO2)− and positively charged defects (dangling silicon bonds) at the surface of the silicon nanocrystals that comprise porous silicon.

Understanding the Origin of Luminescence in Porous Silicon: An Undergraduate Solid-State Chemistry Experiment

We report a modular solid-state chemistry experiment based on the chemical and electrochemical etching of crystalline silicon wafers to produce porous silicon (PSi) layers. Under relatively simple etching conditions, porous silicon exhibits efficient room-temperature photoluminescence (PL) at approximately 680 nm. While the luminescence mechanism is still a source of debate, it is generally agreed that the light emission is due to the spatial confinement of electron-hole pairs in nanometer-scale silicon particles that remain after etching. Using this explanation, students are able to apply a three-dimensional particle-in-a-box solution to Schrodinger's equation to explain the energy of the PL as a function of nanoparticle size. We have also compared PSi surfaces with unetched silicon wafers using atomic force microscopy to demonstrate how surface morphology can influence a material's optical properties. This experiment is a tool for introducing chemistry majors to the fabrication and characterization techniques used to study microelectronic materials and provides a solid-state counterpart to molecular absorption measurements typically used to demonstrate the particle-in-a-box principle