Porous Silicon Research Articles

Quantitative analysis of niobium in electropolishing solution by laser-induced breakdown spectroscopy using porous silicon

This is the first report that applied LIBS to the analysis of electropolishing solution. Quantitative analysis of Nb dissolved in the solution was demonstrated by using porous silicon as the sample loading substrate.

A zero-gap silicon membrane with defined pore size and porosity for alkaline electrolysis.

Porous separators are a key component in alkaline water electrolyzers and are significant sources of overpotential. In this paper, porous silicon separators were fabricated by etching precise arrays of cylindrical pores into silicon substrates through lithography. Chemical stability of the silicon-based separators is ensured through the deposition of a silicon nitride layer. Platinum or nickel were vapor-deposited directly on the faces of the separator to complete a zero-gap configuration. Separator porosity (ε) was varied by changing the pore diameter and the pore spacing. These well-controlled porous silicon zero gap electrodes (PSi-ZGEs) were used to study the trade-off between separator resistance and gas-crossover at different porosities. It was found that separator resistances comparable to commercially used Zirfon UTP 500 were achieved at much lower ε. Gas crossover remained within the explosive limits for ε ≤ 0.15%. The PSi-ZGEs achieved stable performance at 100 mA cm-2 for 24 hours without significant surface damage in the alkaline electrolyte. In the broad perspective, the current work can pave the path for the development of ionomer-free separators for alkaline water electrolysis which rely on the separator geometry to limit gas-crossover.

High-areal capacity Si architecture as an on-chip anode for lithium-ion batteries

Silicon is one of the most promising anode materials for Li-ion batteries, especially to meet the growing demand for energy storage in the form of microbatteries for mobile and autonomous devices. However, the development of such batteries is hindered by mechanical and electrochemical failures resulting from massive Si volume expansion and continuous growth of the solid electrolyte interphase. In this study, we propose a novel on-chip anode architecture using rapid thermal annealing on porous silicon. The structure consists of a densified silicon layer on top of an isotropic structure of a porous layer. We demonstrate that this structure enhances both electrochemical and mechanical stabilities, achieving an areal capacity of 9 mAh cm−2 over more than 200 cycles with a high Coulombic efficiency near 100%.

Performance of high sensitive heterojunction CuS/porous silicon photodetector

In this work, copper sulfide (CuS) nanostructure was deposited on a porous silicon wafer for the visible light by spray pyrolysis method. Through this, a series of devices were suggested as a part of the deposit concentration of CuS on n-type porous silicon. Simultaneously, the physical features of the attained film were illustrated. FESEM exhibited that the average nanoparticle diameter increased with the concentration of CuS at orientation (100) and was found to be 47.84 nm, 56.36nm and 71.32nm, while the average diameter at (111) orientation was found to be 37.64 nm, 41.46nm, 55.22 nm of 0.1, 0.3 and 0.5M respectively. In addition to the atomic force microscope (AFM) showed the roughness and uniformity of the CuS/PSi fabricated decreased with increasing concentration of CuS, In detail, the attained photo-responsivity and specific detectivity were observed to be 210 mW/A, 340 mW/A and 3×1010 Jones, 4.2×1010 Jones at orientation (100 )using concentration of 0.1M and 0.5M respectively . On the other hand, the photo-responsivity and specific detectivity were observed to be 260 mW/A, 380 mW/A and 1.8 ×1010 Jones, 4.5×1010 Jones at orientation (111) using concentrations of 0.1M and 0.5M respectively. The presented work shows a substitutional system for an economical and environmentally friendly optoelectronic scheme. The photo-responsive considered to be in a positive linear relationship with the used concentration.

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

Enhancing Solid-state Hydrogen Storage Properties of Lithium Hydride through Thermodynamic Tuning with Porous Silicon Nanowires

Solid-state hydrogen storage technology ensures a safer storage method, eliminating the risks of leaks, boiling losses, and explosions in commercial applications. Based on earlier findings, alloying LiH with silicon (Si)...

Theoretical Study of a Porous Silicon Cavity Based on Second Harmonic Waves Formed by Ferroelectric Crystals for Wide Range Multiphysical and Chemical Measurement

Theoretical Study of a Porous Silicon Cavity Based on Second Harmonic Waves Formed by Ferroelectric Crystals for Wide Range Multiphysical and Chemical Measurement

Pore-spanning membranes as a tool to investigate lateral lipid membrane heterogeneity.

Over the years, it has become more and more obvious that lipid membranes show a very complex behavior. This behavior arises in part from the large number of different kinds of lipids and proteins and how they dynamically interact with each other. In vitro studies using artificial membrane systems have shed light on the heterogeneity based on lipid-lipid interactions in multicomponent bilayer mixtures. Inspired by the raft hypothesis, the coexistence of liquid-disordered (ld) and liquid-ordered (lo) phases has drawn much attention. It was shown that ternary lipid mixtures containing low- and high-melting temperature lipids and cholesterol can phase separate into a lo phase enriched in the high-melting lipids and cholesterol and a ld phase enriched in the low-melting lipids. Depending on the model membrane system under investigation, different domain sizes, shapes, and mobilities have been found. Here, we describe how to generate phase-separated lo/ld phases in model membrane systems termed pore-spanning membranes (PSMs). These PSMs are prepared on porous silicon substrates with pore sizes in the micrometer regime. A proper functionalization of the top surface of the substrates is required to achieve the spreading of giant unilamellar vesicles (GUVs) to obtain PSMs. Starting with lo/ld phase-separated GUVs lead to membrane heterogeneities in the PSMs. Depending on the functionalization strategy of the top surface of the silicon substrate, different membrane heterogeneities are observed in the PSMs employing fluorescence microscopy. A quantitative analysis of the heterogeneity as well as the dynamics of the lipid domains is described.

Construction of honeycomb porous silicon as a high-capacity and long-life anode toward Li-ion batteries

Honeycomb porous Si is purposefully designed as a promising material to effectively alleviate the volume expansion of Si-based anodes toward advanced Li-ion batteries.

Utilization of microdroplets as optical lenses for surface-enhanced Raman spectroscopy (SERS) enhancement on localized silver nanoparticle-decorated porous silicon substrates

We demonstrate the use of a microdroplet as an optical lens positioned on a localized silver nanoparticle-decorated porous silicon (LocAg-PS) surface for enhanced surface-enhanced Raman spectroscopy (SERS) analysis.

Multi-walled carbon nanotube network on porous silicon for humidity sensing

Multi-walled carbon nanotube network on porous silicon for humidity sensing

Unlocking the secrets of porous silicon formation: insights into magnesiothermic reduction mechanism using in situ powder X-ray diffraction studies.

The magnesiothermic reduction of SiO2 is an important reaction as it is a bulk method that produces porous Si for a wide range of applications directly from SiO2. While its main advantage is potential tunability, the reaction behavior and final product properties are heavily dependent on many parameters including feedstock type. However, a complete understanding of the reaction pathway has not yet been achieved. Here, using in situ X-ray diffraction analysis, for the first time, various pathways through which the magnesiothermic reduction reaction proceeds were mapped. Further, the key parameters and conditions that determine which pathways are favored were determined. It was discovered that the reaction onset temperatures can be as low as 348 ± 7 °C, which is significantly lower when compared to previously reported values. The onset temperature is dependent on the size of Mg particles used in the reaction. Further, Mg2Si was identified as a key intermediate rather than a reaction byproduct during the reduction process. Its rate of consumption is determined by the reaction temperature which needs to be >561 °C. These findings can enable process and product optimization of the magnesiothermic reduction process to manufacture and tune porous Si for a range of applications.

Transmission and Absorption of Bilateral Porous Silicon with Macropores or Nanowires

Transmission and Absorption of Bilateral Porous Silicon with Macropores or Nanowires

Controlled synthesis and characterization of porous silicon nanoparticles for dynamic nuclear polarization.

Si nanoparticles (NPs) have been actively developed as a hyperpolarized magnetic resonance imaging (MRI) contrast agent with an imaging window close to one hour. However, the progress in the development of NPs has been hampered by the incomplete understanding of their structural properties that correspond to efficient hyperpolarization buildup and long polarization decays. In this work we study dynamic nuclear polarization (DNP) of single crystal porous Si (PSi) NPs with defined doping densities ranging from nominally undoped to highly doped with boron or phosphorus. To develop such PSi NPs we perform low-load metal-assisted catalytic etching for electronic grade Si powder followed by thermal oxidation to form the dangling bonds in the Si/SiO2 interface, the Pb centers. Pb centers are the endogenous source of the unpaired electron spins necessary for DNP. The controlled fabrication and oxidation procedures allow us to thoroughly investigate the impact of the magnetic field, temperature and doping on the DNP process. We argue that the buildup and decay rate constants are independent of size of Si crystals between approximately 10 and 60 nm. Instead, the rates are limited by the polarization transfer across the nuclear spin diffusion barrier determined by the large hyperfine shift of the central 29Si nuclei of the Pb centers. The size-independent rates are then weakly affected by the doping degree for low and moderately doped Si although slight doping is required to achieve the highest polarization. Thus, we find the room temperature relaxation of low boron doped PSi NPs reaching 75 ± 3 minutes and nuclear polarization levels exceeding ∼6% when polarized at 6.7 T and 1.4 K. Our study thus establishes solid grounds for further development of Si NPs as hyperpolarized contrast agents.

Stable "snow lantern-like" aggregates of silicon nanoparticles suitable as a drug delivery platform.

Nanomedicine is a growing field where development of novel organic and inorganic materials is essential to meet the complex requirements for drug delivery. This includes biocompatibility, suitability for surface modifications, biodegradability, and stability sufficient to carry a drug payload through various tissues for the desired timespan. Porous silicon nanoparticles (pSi NP) are shown to have several beneficial traits in drug delivery in addition to a porous structure to maximize drug loading. The conventional synthesis of pSi NP using electrochemical etching is costly, time-consuming and requires large quantities of highly toxic hydrofluoric acid (HF). As such this research attempted a novel method to address these limitations. Mesoporous silicon nanoparticles were prepared by centrifugal Chemical Vapor Deposition (cCVD) without the use of HF. This process generated aggregates consisting of multiple primary particles fused into each other, similar to snowballs fused together in a snow-lantern (snowball pyramid). Our results demonstrated that the cCVD Si particles were versatile in terms of surface chemistry, colloidal stability, degradability, minimization of acute in vitro toxicity, and modulation of drug release. Dynamic light scattering, scanning electron microscopy, and cryogenic nitrogen adsorption isotherm measurements confirmed the overall size (210 nm), morphology, and pore size (14-16 nm) of the prepared materials. Agglomeration in phosphate-buffered saline (PBS) was minimized by PEGylation by a two-step grafting procedure that employed a primary amine linker. Finally, the release rate of a model drug, hydrocortisone, was evaluated with both PEGylated and pristine particles. Conclusively, these snow-lantern cCVD Si particles do indeed appear suitable for drug delivery.

Improved solar cell efficiency of titanium dioxide on porous silicon using pulsed laser deposition at different laser wavelengths

In this study, a Q-switched Nd:YAG laser with specific parameters, including a pulse repetition rate of 6 Hz, a pulse duration of 10 nm, a wavelength of 532 nm, and a laser fluence of 237.47 J cm−12, was employed to fabricate highly crystalline TiO2 nano-films. These nano-films exhibited a narrow energy band gap of 3.24 eV and showcased favorable surface morphology, characterized by a roughness of 2.38 nm. A solar cell device was produced by creating porous silicon (PSi) and applying titanium dioxide films onto the PSi, achieving a notable conversion efficiency of 8.733%. To investigate the impact of different parameters on the resulting TiO2 nano-films, a range of laser fluences (ranging from 131.93 to 263.85 J cm−12) and three distinct laser wavelengths (1064 nm, 532 nm, and 355 nm) were employed during the pulsed laser deposition (PLD) process. These experiments aimed to grow TiO2 films on both quartz and silicon (Si) substrates.

Enhanced photodetection performance of vanadium pentoxide nanostructures deposited on porous silicon substrate via pulsed laser deposition

Enhanced photodetection performance of vanadium pentoxide nanostructures deposited on porous silicon substrate via pulsed laser deposition

Porous silicon microparticles as efficient carriers for immunologic adjuvants

In this work we report a first-time combination of porous silicon (pSi) particles with the immunologic adjuvant Pam3CSK4, a TLR 1/2 agonist, as a tool for immunotherapy. pSi is a sponge-like biocompatible and biodegradable nanomaterial with high porosity, large surface-to-volume ratio and tunable surface, suitable for drug delivery applications. This study provides, by means of live-cell confocal microscopy, an insight about the time course of the interaction of free Pam3CSK4 vs vectorized by pSi microparticles with human dendritic cells (DCs). We found a delay in the ingestion of the agonist when carried by pSi microparticles. These findings were supported by the observation of the morphological changes related to the activation of DCs that occurred with a 5 h difference when treated with the vectorized ligand.These results provide the first demonstration of pSi as a conceivable candidate to deliver Pam3CSK4 to DCs paving the way towards immunotherapy practice.

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

Metal Filled Nanostructured Silicon a Platform to Interlink Magnetism and Optics

This presentation deals with the utilization of nanostructured silicon (porous silicon and silicon nanotubes) for deposition of various metals, especially magnetic ones, within the pores/tubes. The novel magnetic properties of the semiconducting/magnetic composites which arise due to the nanoscopic size of the used materials are investigated with respect to optical and magnetic on-chip applications.Porous silicon is fabricated by anodization of a silicon wafer in an aqueous hydrofluoric solution. The morphology of the porous structures depends on the doping density of the used wafer and on the applied current density as well as the electrolyte concentration. The ferromagnetic metals are deposited within the porous structures electrochemically in using the corresponding metal salt solution as electrolyte. A modification of the electrochemical parameters results in adjustable size and shape of the deposits. Ni and Co, both metals are electrodeposited within the nanostructured silicon in using aqueous NiSO4 and CoSO4 solutions by applying a current density between 10 and 20 mA/cm2 and a frequency between 0.05 and 0.2 Hz.One of our key topics is luminescent porous silicon loaded with magnetic metals to enhance the photoluminescence, with the final aim to influence/control the optical properties by a magnetic field. The metal deposits affect the optical properties but also give rise to specific magnetic behavior (1). Due to the metal filling of the porous silicon the photoluminescence is blue-shifted and furthermore an increase of the intensity is observed. The influence of the magnetic metal filling on the optical properties (photoluminescence, decay time) is discussed, and the magnetic characterization of the nanocomposites is presented.A further issue, the deposition of hard and soft magnetic materials within the nanostructures, aiming in the fabrication of arrays of permanent nanomagnets is presented (2). Here the investigation of the magnetic behavior of bi-metal nanostructures within nanostructured silicon with the aim to exploit the magnetic properties of both metals and gain control of the exchange coupling between the two metals especially with respect to their volume ratio is discussed. Furthermore, a variation of the structure size and the proximity of the metal deposits modify the exchange coupling and thus the energy product. Nanocomposite systems with an energy product as high as possible should be achieved to give rise to on-chip applications using permanent nanomagnets, especially arranged in arrays.(1) P. Granitzer, et al, Frontiers in Physics, 8 (2020) 121(2) K. Rumpf, et.al, Phys. Stat. Sol. A, 217 (2020) 1901040