Porous Silicon Structures Research Articles

Manufacturing lithium-ion anodes from silicon recovered from end-of-life solar panels

With the rapid growth of solar energy, the recycling or re-use of used solar panels has become a key issue. Recycling high-value photovoltaic silicon from solar cells is an important step towards achieving “carbon neutrality.” In this paper, an efficient and high-value recycling strategy is employed to convert recycled silicon from discarded solar cells into lithium-ion anode materials. In this case, the recycled PV silicon is etched with hydrofluoric acid (HF) to create a porous silicon structure. This structure is designed to withstand the expansion stress of the electrodes. After surface modification with citric acid and carbon nanotubes to enhance the electrical conductivity of the recycled silicon and buffer the electrode from stress expansion during lithium storage and release, lithium difluorooxalate borate was added to pre-treat the surface of the recycled photovoltaic silicon through heat treatment. This process creates a robust and fast lithium-ion conductive interface enriched with LiF, Li2C2O4, LiBO2, and Li2B4O7. Density Functional Theory (DFT) calculations were performed to investigate the electronic structure of the synthesized materials, revealing their remarkable electronic conductivity and atomic bonding characteristics. When used as an anode for Li-ion batteries, W-pSi@C/CNTs exhibited high initial coulombic efficiency with stable cycling, demonstrating a capacity of 2040 mAh/g at 0.2 A/g for 200 cycles. In addition, this high-value recycling will help promote the development of renewable energy in an economically and environmentally sustainable manner.

Diverse energy laser ablation in liquid for indium oxide nanoparticles on porous silicon: enhancing photodetector performance

Abstract The fabrication and analysis of a photodetector using copper oxide nanoparticles (In2O3-NPs) embedded in a porous silicon (PS) structure are detailed in this study. One method used to create In2O3 NPs was pulsed laser ablation in ethanol (PLAL), while another was photo-assisted electrochemical etching to create a porous silicon substrate. The optical, structural, and electrical features of In2O3-NPs/PS devices are investigated, with a particular emphasis on their variations with laser energy. After successfully applying In2O3 nanoparticles onto PS, the X-ray diffraction analysis revealed the presence of distinct peaks that correlate to a copper cubic structure. Using field emission scanning electron microscopy, the researchers determined that the particles had a spherical shape. Absorption increased with increasing laser intensity, and the In2O3-nanocolloids showed clear surface plasmon resonance peaks between 570 and 590 nm in wavelength range. Band gaps of 3.5, 3.4, 3.2, and 3.1 eV were found for the In2O3-NPs generated at 500, 600, 700, and 800 mJ of laser energy, according to the optical properties. According to the optoelectronic properties of the In2O3-NPs/PS photodetector, it was built with an energy level of 700 mJ and had a maximum responsivity of 0.2766 A/W at 650 nm. The In2O3NPs/PS devices discussed in this study have excellent photodetecting performance because they integrate In2O3-NPs with PS.

Temporary changes in current flow mechanisms in erbium-doped porous silicon

The paper discusses the basic mechanisms of conductivity in silicon MIS structures. The object of the study is porous silicon doped with an erbium impurity of an aqueous solution of erbium nitrate Er(NO3)3 • 5H2O by temperature annealing in a diffusion furnace at a temperature of 800°C for 1 hour. Comparative characteristics of the current-voltage and capacitance-voltage dependences are presented, describing the regular changes in the mechanisms of current flow and charge capture in the samples under study. The results of the work qualitatively and quantitatively describe the temporary change in the electrical characteristics of porous silicon, which can be taken into account by technologists for better understanding the mechanisms of current transfer in luminescent structures of porous silicon with erbium ions, as well as in the study and manufacture of light-emitting diodes based on it.

Dynamic magnesiothermic reduction of various silica to porous silicon structures for lithium battery anodes

A dynamic magnesiothermic reduction (DMR) of various silica having different size and porosity is conducted to study the effects of silica properties on the ⅰ) DMR reaction kinetics, ⅱ) properties of resulting porous silicon (pSi) microparticles, and ⅲ) performances of pSi/C composites as anodes in lithium batteries. A DMR kinetic study using the Ginstling–Brounstein diffusion model shows that the smaller the silica particle size, the higher the reduction rate and the lower the apparent activation energy. Irrespective of silica properties, all the resulting pSi particles have mesoporous structures. The pSi particles comprise interconnected small primary silicon nanoparticles (approximately 30–40 nm in diameter) to render similar particle morphologies to those of the parent silica. Owing to these appealing features of pSi particles, pSi/C composites exhibit excellent cycling performance for over 200 cycles and high rate capabilities, whereas SiMP/C (prepared with a non-porous silicon microparticles) loses most of its capacity in early cycles owing to high resistance build-up during cycling. Overall, the DMR of silica precursors of several micrometers or less in size (preferably porous precursors) are desirable for the production of high-purity pSi microparticles for use in high-capacity and stable anodes for advanced lithium batteries.

Mitigation of Volumetric Expansion in Silicon Anodes via Engineered Porosity: Electrochemical Performances and Stress Distribution Implication

To overcome the significant volume expansion issue encountered by traditional silicon anodes in lithium‐ion batteries, this study employs chemical etching techniques to treat aluminum–silicon alloys of various ratios, successfully preparing three types of porous silicon electrode materials with different pore structures. Through a series of electrochemical tests, this article investigates the role of porous silicon structures in improving electrode performance. The results demonstrate that the porous silicon anodes exhibit superior cycle stability and rate capability compared to traditional solid silicon anodes. This confirms the effectiveness of the porous structure in mitigating the significant volume expansion during the charge and discharge process of silicon materials and in preventing premature electrode failure, thereby significantly enhancing the electrode's cycle life. Remarkably, the porous silicon with a high porosity rate shows exceptionally outstanding performance. Additionally, using computer simulations, this study also models the impact of changes in pore size within the porous silicon material at different states of charge and discharge on the stress distribution at the particle center and surface. These experimental and simulation results jointly provide strong empirical evidence for applying porous silicon materials as high‐performance anode materials for lithium‐ion batteries and offer essential guidance for future stress analysis and electrode design of porous silicon electrode materials.

Fabrication of humidity monitoring sensor using porous silicon nitride structures for alkaline conditions

Porous silicon nitride structures were fabricated for a humidity sensor. The porous silicon structures were fabricated by the metal-assisted chemical etching process, and the conformal silicon nitride thin film was deposited by the atomic layer deposition process. The optimized porous sensor with the 10 nm-thick silicon nitride thin film had a hydrophilic surface and compared to other sensors, had an excellent humidity sensing response. Especially, it showed a superior humidity sensing response at 1 kHz with fast response and recovery times of 13.3 s and 12.4 s, respectively, were observed. Based on the electrochemical impedance spectroscopy results, the equivalent circuits and humidity sensing mechanism were discussed. The chemical stability of the silicon nitride was characterized using Tafel analysis in alkaline electrolytes. Additionally, the sensor's humidity sensing capabilities were tested under cement-embedded conditions.

Enhancing light trapping efficiency: Germanium-coated porous silicon structures for optimal antireflection performance

Porous silicon structures are effective in trapping light due to the abundance of pores on their surface, finding widespread use in optical applications like photoelectric conversion, photon collection, and detection. We have successfully created micro-porous silicon with exceptionally high antireflection performance through electrochemical etching using different concentrations of silver catalysts. Results show that this germanium coated porous silicon structure has a smaller range of pore sizes, leading to a reduced reflectivity of 2.6 % under light radiation with wavelengths. To understand the antireflective mechanism further, we explored the surface reflectivity of porous silicon structures by coating the germanium metal on the porous structure. Importantly, germanium coated porous silicon structures with high surface quality and well-preserved pore integrity are identified as beneficial for achieving lower reflectivity in the incident light wavelength range of 300–1200 nm. These findings are significant for the design of porous silicon antireflective materials.

Field-effect transistor based on reduced graphene oxide � porous silicon structure for application in selective gas sensors

Field-effect transistor based on reduced graphene oxide � porous silicon structure for application in selective gas sensors

Porous Silicon and Silicon Nanotubes with Embedded FePt Nanoparticles Investigated by High Temperature Magnetic Measurements

Porous silicon (PSi) and silicon nanotubes (SiNTs) are presented as a platform for filling with FePt nanostructures. The difference of the magnetic characteristics between the two systems is figured out. Furthermore, the FePt filled templates are compared with the same template materials filled with Ni/Co by electrodeposition.The porous silicon is produced by anodization of a highly doped n-type silicon wafer in a 10 wt% HF solution. The produced morphology offers separated pores of about 50 nm and a mean distance between the pores of 50 nm. The SiNTs are fabricated in using an array of ZO wires as template, subsequent silicon deposition and finally etching off the ZO. The inner diameter of the tubes and also the wall thickness can be tuned by the fabrication process. In this work SiNTs with comparable inner diameter to the PSi structure and a wall of about 10 nm are used (1). FePt nanoparticles (NPs) are deposited electroless inside the pores and the tubes, respectively whereat the molar ratio of Fe is varied. For this purpose a 3 component solution consisting of H2PtCl6, Fe(NO3)3 and citric acid is used, whereas the ratio of the components is modified.The varying magnetic response of the different composite systems, porous silicon and silicon nanotubes is investigated. PSi/FePt shows a higher coercivity and remanence than SiNTs/FePt and thus a higher hard magnetic performance. The variation of the coercivities between SiNTs/FePt and PSi/FePt is about 57%.Considering the FePt deposits with different molar ratio of Fe the coercivities vary in a range of 5% in the case of both template types. Comparing FePt loaded samples with Co loaded samples in all cases an increase of the coercivity and of the remanence is observed for FePt, whereat in the case of PSi as template material the increase is significantly stronger than in the case of SiNTs samples. Figure 1 shows the comparison of the hysteresis of PSi and SiNTs filled with FePt NPs.The influence of high temperatures on the nanocomposite samples is of interest, as well as the high temperature magnetic behavior. Therefore, beside low temperature and room temperature magnetic measurements, the magnetic behavior of the samples is investigated at high temperatures up to 1273 K.(1) K. Rumpf, et.al, ECS Transactions 98 (2020) 37

Nanopores limited domain and PVA film used to assist the SERS property of gold nanoparticle arrays

The combination of nanopores and noble metal nanoparticles has been the focus of research in recent years, and their synergistic effect enabled the substrate exhibit excellent SERS property. In this paper, the array porous silicon structures embedded with gold nanoparticles have been prepared by using the polystyrene (PS) microsphere template assisted gold annealing process and metal assisted chemical etching techniques (AuNPs@nanopore). Polyvinyl alcohol (PVA) thin film was introduced as a molecular adsorption layer to be spin coated on the surface and formed composite structure (AuNPs@nanopore @PVA) to enrich more detection molecules. Through the SERS analysis of different depths of gold nanoparticles by Rhodamine 6G (R6G) probe molecules, the optimal etching time, that is, the optimal depth that gold nanoparticles should be in, was determined. Under the etching time of 2 min, the AuNPs@nanopore @PVA structure base with pore depth of 245 nm and diameter of gold nanoparticles of 181 nm showed high sensitivity, high uniformity and the best SERS property. It can realize the low concentration detection of 10−10 mol/L R6G molecule and 10−11 mol/L methylene blue (MB) molecule, and the enhancement factor is up to 1.20 × 107. The substrate can also be used to detect the pesticide thiabendazole molecule, the detection limit of 10−8 mol/L.

Controlled and Fast Fabrication for P-Type Porous Silicon Structures with a High Aspect Ratio by Electrochemical Etching

Controlled and Fast Fabrication for P-Type Porous Silicon Structures with a High Aspect Ratio by Electrochemical Etching

Morphological, Structural, Optical and Electrical Characterization of TiO2 and Porous Silicon Structures Working as a Promising Breathing Detector

Morphological, Structural, Optical and Electrical Characterization of TiO2 and Porous Silicon Structures Working as a Promising Breathing Detector

Theoretical and Experimental Study of Optical Losses in a Periodic/Quasiperiodic Structure Based on Porous Si-SiO2

This study investigates the reduction of optical losses in periodic/quasiperiodic structures made of porous Si-SiO2 through a dry oxidation process. Due to their unique optical properties, these structures hold great promise for various optoelectronic applications. By carefully engineering the composition and geometry of the structures, we fabricate periodic/quasiperiodic structures on a quartz substrate using an electrochemical anodization technique and subsequently subject them to dry oxidation at two different temperatures. The structure exhibits two localized modes in the transmission and reflection spectra. Unoxidized and oxidized structures’ complex refractive index and filling factors are determined theoretically and experimentally. Optical characterization reveals that the porous Si-SiO2 structures exhibit lower absorption losses and improved transmission than the pure porous silicon structures. Additionally, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) confirm the presence of porous Si-SiO2 and reduced silicon content. Our study demonstrates that dry oxidation effectively decreases Rayleigh scattering losses, leading to enhanced optical performance and potential applications in efficient optoelectronic devices and systems based on silicon. For instance, periodic/quasiperiodic structures could soon be used as light-emitting devices inside the field of optoelectronics, adding photoluminescent nanoparticles to activate the localized modes.

Porous silicon structures passivated with 10-undecenoic acid for possible ethanol sensing

Multifunctional sensing platforms are useful for classifying and quantifying different analytes. This work presents a simple optical sensor based on porous silicon film modified using open-air pyrolysis with 10-undecenoic acid. The fabricated structure was characterized using vis-NIR reflectance spectroscopy and the functional groups were identified using Fourier transform infrared spectroscopy. With respect to the control, the proposed undecenoic acid passivated porous silicon nanostructured film has been tested as reusable ethanol sensor in water.

Enhancing the specific capacitance of a porous silicon-based capacitor by embedding graphene combined with three-dimensional electrochemical etching

A porous silicon-based capacitive structure with high specific capacitance is fabricated by three-dimensional electrochemical etching. As well as conventional planar electrochemical etching in two dimensions on the surface of a silicon chip, the lateral side walls of trenches engraved by a laser beam are also etched (third dimension). Platinum is deposited on both sides of the porous silicon film to create a capacitive structure that allows for stable measurement of the equivalent permittivity and specific capacitance of the trench-structured, layered porous silicon material. To eliminate the large parasitic effect due to the high roughness and air gaps between the metal layer and the porous silicon layer, nano-scale graphene is embedded into the surface pores of the porous silicon to enable good contact. After preliminary experiments, an etching approach based on a continuously decreasing current is adopted to obtain a strong porous silicon structure with long silicon pillars. Various laser engraving patterns were compared to determine the effect of three-dimensional etching. The results show that the increase in specific capacitance due to the laser trenches is positively correlated with the extent of lateral etching. The proposed method is suitable for improving the equivalent permittivity of the porous silicon layer without changing the device geometry or electrochemical etching parameters, and is also compatible with Si-VLSI technology.

Ultrahigh porosity photoluminescent silicon aerocrystals with greater than 50% nanocrystal ensemble quantum yields

Three types of mesoporous silicon flakes were fabricated by anodization in methanoic hydrofluoric acid from the same substrates (heavily doped p-type). Even though anodization current density, rinsing, drying method, and storage condition were the same for all three wafers, the resulting porous silicon (PSi) structures had very different properties. They had very different colors. Two of them showed quite high luminescence quantum yields (QYs), confirmed by very long luminescence lifetimes. The highest QY exceeded 50% for a peak photoluminescence wavelength of ∼750 nm. To date, this QY is the highest obtained for PSi and very importantly for silicon with large mesopores, which is typically not highly efficient (as opposed to silicon with small mesopores and microporous silicon). Large mesopores (>15 nm diameter) facilitate impregnation of various substances into luminescent material, such as metals for plasmonics and drugs for theranostics. The differing luminescent properties were correlated to electrolyte temperature during anodization, and evolution of the electrolyte batch (lowering of active fluoride content and buildup of hexafluorosilicate) used to anodize several wafers, whose effects are often overlooked when mass-producing PSi. Supercritical drying and completion of the slow growth of native oxide passivation in the dark leading to different final partially oxidized PSi structures are also important factors for the high QYs obtained. The highest QY was obtained with the structure having the most isolated Si nanocrystals in an amorphous Si oxide tissue.

Microsecond All-Optical Modulation by Biofunctionalized Porous Silicon Microcavity.

We successfully created a composite photonic structure out of porous silicon (PSi) microcavities doped by the photochromic protein, photoactive yellow protein (PYP). Massive incorporation of the protein molecules into the pores was substantiated by a 30 nm shift of the resonance dip upon functionalization, and light-induced reflectance changes of the device due to the protein photocycle were recorded. Model calculations for the photonic properties of the device were consistent with earlier results on the nonlinear optical properties of the protein, whose degree of incorporation into the PSi structure was also estimated. The successful proof-of-concept results are discussed in light of possible practical applications in the future.

Structure and composition of a composite of porous silicon with deposited copper

Porous silicon is a promising nanomaterial for optoelectronics and sensorics, as it has a large specific surface area and is photoluminescent under visible light. The deposition of copper particles on the surface of porous silicon will greatly expand the range of applications of the resulting nanocomposites. Copper was chosen due to its low electrical resistivity and high resistance to electromigration compared to other metals. The purpose of this research was to study changes in the structure and composition of porous silicon after the chemical deposition of copper. Porous silicon was obtained by the anodisation of monocrystalline silicon wafers KEF (100) (electronic-grade phosphorus-doped silicon) with an electrical resistivity of 0.2 Ohm·cm. An HF solution in isopropyl alcohol with the addition of H2O2 solution was used to etch the silicon wafers. The porosity of the samples was about 70 %. The porous silicon samples were immersed in copper sulphate solution (CuSO4·5H2O) for 7 days. We used scanning electron microscopy, IR spectroscopy, and ultrasoft X-ray emission spectroscopy to obtain data on the morphology and composition of the initial sample and the sample with deposited copper. The chemical deposition of copper on porous silicon showed a significant distortion of the pore shape as well as the formation of large cavities inside the porous layer. However, in the lower part the pore morphology remained the same as in the original sample. It was found that the chemical deposition of copper on porous silicon leads to copper penetrating into the porous layer, the formation of a composite structure, and it prevents the oxidation of the porous layer during storage. Thus, it was demonstrated that the chemical deposition of copper on a porous silicon surface leads to visible changes in the surface morphology and composition. Therefore, it should have a significant impact on the catalytic, electrical, and optical properties of the material.

Analysis of porous silicon structures using FTIR and Raman spectroscopy

Abstract This work deals with the production of porous silicon samples by electrochemical etching method and their analysis using FTIR and Raman spectroscopy. Porous silicon samples were prepared under various conditions, such as etching time and current density. A p-type silicon substrate was used to prepare the porous silicon structures. FTIR spectroscopy was performed to determine the chemical bonds formed during the etching process. The structural properties of the prepared samples were investigated by Raman spectroscopy.

Porous Silicon Fabry-Perot Sensor Fabrication

Porous silicon structures are widely used in gas sensor applications. The reason for this is that the gas holding capacity of the porous structure is quite high. In this study, mesoporous structures were obtained. It has been proven by studies that mesoporous structures are superior to other pore structures in gas retention and gas detection. In addition, fabry-perot structures were obtained by impact etching. SEM images and XPS results of fabry-perot porous structures were obtained.