Porous Silicon Surface Research Articles

Porous Silicon for Accumulation and Generation of Hydrogen

Porous silicon layers have been formed by electrochemical anodization of [Formula: see text]- and [Formula: see text]-type Si substrates. The volume of hydrogen desorbed from the surface of porous silicon after the anodic treatment was measured to be as large as 4[Formula: see text]wt.%. Regeneration of hydrogen can be achieved by porous silicon reanodization.

Growth of ZnO Microstructure on Porous Silicon

In this study, Zinc Oxide (ZnO) microstructures were grown on porous silicon (PS) using chemical bath deposition (CBD) method by varying the growth time. The field emission scanning electron microscopy (FESEM) revealed the morphology and sized of ZnO. The X-ray diffraction (XRD) spectra indicate the high quality growth of ZnO on PS surface. Raman analyses revealed the peaks shift of E2(High), characterized wurtzite lattice and indicates good crystallinity of ZnO.

Investigation of Light Trapping from Porous Silicon Surface for the Enhancement of Silicon Solar Cell Performance

Investigation of Light Trapping from Porous Silicon Surface for the Enhancement of Silicon Solar Cell Performance

Morphology, chemical and electrical properties of CdO Nanoparticles on porous silicon

In this paper, CdO nanoparticles prepared by pulsed laser deposition techniqueonto a porous silicon (PS) surface prepared by electrochemical etching of p-type silicon wafer with resistivity (1.5-4Ω.cm) in hydrofluoric (HF) acid of 20% concentration. Current density (15 mA/cm2) and etching times (20min). The films were characterized by the measurement of AFM, FTIR spectroscopy and electrical properties.
 Atomic Force microscopy confirms the nanometric size.Chemical components during the electrochemical etching show on surface of PSchanges take place in the spectrum of CdO deposited PS when compared to as-anodized PS.
 The electrical properties of prepared PS; namely current density-voltage characteristics under dark, show that the pass current through the PS layer is more than that obtained from the CdO/PS/Si which is related to increasing junction resistivity that come from increasing in depletion width.

Spatially Controlled Surface Modification of Porous Silicon for Sustained Drug Delivery Applications

A new and facile approach to selectively functionalize the internal and external surfaces of porous silicon (pSi) for drug delivery applications is reported. To provide a surface that is suitable for sustained drug release of the hydrophobic cancer chemotherapy drug camptothecin (CPT), the internal surfaces of pSi films were first modified with 1-dodecene. To further modify the external surface of the pSi samples, an interlayer was applied by silanization with (3-aminopropyl)triethoxysilane (APTES) following air plasma treatment. In addition, copolymers of N-(2-hydroxypropyl) acrylamide (HPAm) and N-benzophenone acrylamide (BPAm) were grafted onto the external pSi surfaces by spin-coating and UV crosslinking. Each modification step was verified using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, water contact angle (WCA) measurements, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). In order to confirm that the air plasma treatment and silanization step only occurred on the top surface of pSi samples, confocal microscopy was employed after fluorescein isothiocyanate (FITC) conjugation. Drug release studies carried out over 17 h in PBS demonstrated that the modified pSi reservoirs released CPT continuously, while showing excellent stability. Furthermore, protein adsorption and cell attachment studies demonstrated the ability of the graft polymer layer to reduce both significantly. In combination with the biocompatible pSi substrate material, the facile modification strategy described in this study provides access to new multifunctional drug delivery systems (DDS) for applications in cancer therapy.

Preparation and Characteristics Study of Polystyrene/Porous Silicon Photodetector Prepared by Electrochemical Etching

Novel doped polystyrene (PS)/porous silicon (PSi) heterojunction photodetector prepared by solution cast and electrochemical techniques is proposed here. The structural and optical properties of polystyrene film and porous silicon surface were investigated using X-ray diffraction (XRD), scanning electron microscope, Fourier transformed infrared (FT-IR), and UV–Vis spectrophotometer. XRD data confirmed that the PS film was amorphous in nature and the porous silicon was nanocrystalline. The optical properties showed that the average optical transmittance and the optical energy gap of PS film were 80% and 3.2 eV, respectively. The electrical properties revealed that the electrical resistivity and mobility of the doped polystyrene film were 3 × 104 Ω cm and 4.5 × 10−5 cm2 V−1 s−1, respectively. Photoluminescence PL of porous silicon was investigated. Dark I–V characteristics revealed that the PS/PSi heterojunctions prepared with an etching time of 5 min exhibited better-rectifying properties than that of PS/PSi heterojunction prepared at 10 min. The figures of merit of the photodetectors such as spectral responsivity, external quantum efficiency, and detectivity were investigated and compared with Au/PSi Schottky photodetectors. Minority carrier lifetime of the photodetectors was measured using open circuit voltage decay method.

Facile and Efficient Gas-Phase Pressure-Controlled Thermal Functionalization of Nanocrystalline Porous Silicon with 1-Hexene

Substitution of hydrogen at porous silicon (PSi) surface by organic groups can be done via thermally activated hydrosilylation reactions in which PSi is left for several hours into liquid alkenes at temperatures typically over 100°C. For alkenes whose boiling points are below 100°C (e.g. 1-heptene and shorter molecules), the process suffers from high reagent boiling and evaporation. Gas-phase hydrosilylation is an alternative when using short molecules. It has not been as extensively studied, and was mainly done in plasma reactors with silicon nanocrystals. Here we present a new method for facile gas-phase thermally-activated hydrosilylation in PSi, but using liquid solutions as reagent (1-hexene was used here). PSi and liquid alkene are loaded at room temperature into a chamber which is then closed and heated up to a temperature greater than the alkene boiling point. The effects of process temperature, time and pressure were investigated by means of Fourier transform infrared spectroscopy. The maximum theoretical derivatization efficiency was achieved with optimized parameters. The derivatization was uniform across the PSi layer depth. PSi luminescence was effectively stabilized by the process. The new gas-phase method presented here is facile, requires very small amount of liquid reagent, and is useful for attachment of short molecules to PSi or other materials surface.

A Mini Review: Recent Advances in Surface Modification of Porous Silicon.

Porous silicon has been utilized within a wide spectrum of industries, as well as being used in basic research for engineering and biomedical fields. Recently, surface modification methods have been constantly coming under the spotlight, mostly in regard to maximizing its purpose of use. Within this review, we will introduce porous silicon, the experimentation preparatory methods, the properties of the surface of porous silicon, and both more conventional as well as newly developed surface modification methods that have assisted in attempting to overcome the many drawbacks we see in the existing methods. The main aim of this review is to highlight and give useful insight into improving the properties of porous silicon, and create a focused description of the surface modification methods.

Synthesis of graphene on porous silicon for vapor organic sensor by using photoluminescence

In this work, ultra-sensors of chemical solvents vapor were fabricated for chloroform, n-Hexane and Ethanol via modified porous silicon (PS) surface by the reduction of graphene oxide (rGO) layer. The rGO was conducted by electrochemical exfoliation of graphite electrodes with electrolyte solution at PH = 4.6. Then porous silicon (PS) was prepared by employing electrochemical etching (ECE) method using silicon (Si) p-type at different etching current density J = 2, 4 and 6 mA/cm2with constant HF concentration of 15%, and time of etching of 15 min. The reduction graphene oxide competition with PS was studied as vapors organic sensor, morphological, structural, and surface bond configuration were characterized by Atomic Force Microscopic (AFM), X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) respectively, then the Photoluminescence (PL) quenching was measured by using sensor test system with three types of organic chemical solvents n-Hexane, chloroform and ethanol with nitrogen gas mixing, where they were prepared for testing humidity sensor towards the different organic solvents. The results revealed that the reduction graphene oxide layer on surface of PS lead to intensity increase of the PL, and modified the quality of PS sensor for chemical vapor.

Fabrication and characterization of c-Si/porous-Si/CdS/ZnxCd1-xO heterojunctions for applications in nanostructured solar cells

Solar cells based on c-Si/porous-Si/CdS/ZnxCd1-xO heterojunctions were synthesized by depositing CdS films on c-Si/porous-Si (PS) substrates by electrochemical deposition (ED). PS layers with systematically varied pore diameter (8-45 nm) and were fabricated on p-type c-Si wafers using electrochemical etching. The window layers of ZnxCd1-xO with several Zn concentrations(x=0.2; 0.4; 0.5 and 0.6) were also deposited on the CdS buffer layers by ED. The photoelectrical properties of heterojunctions were studied as functions of PS pore size and Zn content in ZnxCd1-xO. The optimal pore size and Zn contents were found to be 10 nm and x=0.6, respectively. These yielded a solar cell sample exhibiting an efficiency of 9.9%, the maximum observed in this study. Full Text: PDF ReferencesM.A.Green. "Limiting efficiency of bulk and thin-film silicon solar cells in the presence of surface recombination", Progress in Photovoltaic 7, 327 (1999). CrossRef P.Papet, O. Nichiporik, A. Kaminski et al. "Pyramidal texturing of silicon solar cell with TMAH chemical anisotropic etching", Solar Energy Materials and Solar Cells 90, 2319 (2006). CrossRef P. Vitanovet et al. "High-efficiency solar cell using a thin porous silicon layer", Thin Solid Films 297, 299 (1997). CrossRef L. Santinacci et al. "Electrochemical and optical characterizations of anodic porous n-InP(1 0 0) layers", Electrochim. Acta 56, 878 (2010). CrossRef V.Lehmann. "The Physics of Macropore Formation in Low Doped n‐Type Silicon", J. Electrochem. Soc. 140, 2836 (1993). CrossRef Bisi O et al. "Porous silicon: a quantum sponge structure for silicon based optoelectronics", Surface Science Reports 38, 1 (2000). CrossRef A.I. Raid et al. Applied Nanoscience 7, 9 (2016). CrossRef M.A. Naser et al. "Characteristics of Nanostructure Silicon Photodiode using Laser Assisted Etching", Procedia Engineering 53, 393 (2013). CrossRef D.H. Oh et al. J. Ceram. Process. Res. "Effects of a H2SO4 treatment on the optical properties in porous Si layers and electrical properties of diode devices fabricated with a H2SO4 treated porous Si layer", 9, 57 (2008). DirectLink H. Foll et al. "Formation and application of porous silicon", Materials Science and Engineering R 280, 1 (2002). CrossRef P. Granitzer et al. "Porous Silicon—A Versatile Host Material", Materials 3, 943 (2010). CrossRef G. Korotcenkov, Porous Silicon: From Formation to Application (Taylor and Francis Group, CRC Press, Boca Raton, USA, 2016). DirectLink V.Y. Yerokhov. "Porous silicon in solar cell structures: a review of achievements and modern directions of further use", Renewable and Sustainable Energy Rev. 3, 291 (1999). CrossRef A. Ramizy et al. "New optical features to enhance solar cell performance based on porous silicon surfaces", Appl. Surf. Science 257, 6112 (2011). CrossRef F. Ruske et al. "Large area ZnO:Al films with tailored light scattering properties for photovoltaic applications", Thin Solid Films 515, 8695 (2007). CrossRef Y. Alivov et al. "Observation of 430 nm electroluminescence from ZnO/GaN heterojunction light-emitting diodes", Appl. Phys. Lett. 83, 2943 (2003). CrossRef G.V. Lashkarev et al. "Properties of zinc oxide at low and moderate temperatures", Low Temp. Phys. 37, 289 (2011). CrossRef P.M. Devshette et al. "Growth and physical properties of ZnxCd1−xO thin films prepared by spray pyrolysis technique", J. of Alloys and Compunds 463, 576 (2008). CrossRef Y. Caglar et al. "Morphological, optical and electrical properties of CdZnO films prepared by sol–gel method", J. Phys. D: Appl. Phys. 42, 065421 (2009). CrossRef A. Abdinov et al. "Photosensitivity of p,n-Si/n-Cd1−xZnxS heterojunctions manufactured by a method of electrochemical deposition", Thin Solid Films 480-481, 388 (2005). CrossRef A Abdinov et al. "Investigation of electrodeposited p-Si/Cd1 − xZnxS1 − ySey heterojunction solar cells", Thin Solid Films 511-512,140 (2006) CrossRef J.B. Orhan et al. "Nano-textured superstrates for thin film silicon solar cells: Status and industrial challenges", Sol. Cells 140, 344 (2015). CrossRef H.Ch. Alan et al. "Light management of tandem solar cells on nanostructured substrates", J. Photon. Energy 7, 027001 (2017) CrossRef

Optimizing of Gold Nanoparticles on Porous Silicon Morphologies for a Sensitive Carbon Monoxide Gas Sensor Device

A set of carbon monoxide (CO) gas sensors based on porous silicon (PSi)/gold nanoparticle (AuNP) hetro structures were fabricated. Different forms of PSi surface morphologies were studied as a substrate for growth of AuNPs. Simple dipping process of PSi in hydrogen tetrachloroaurate (III) solution (HAuCl4) at fixed concentrations of 10−2 M/3.5 HF was used to synthesize AuNPs. The n-type PSi was equipped through photo-electrochemical etching process at current density value of 10 mA/cm2 under illumination condition of 530-nm wavelength and laser illumination intensity of 20 to 80 mW/cm2. Three different forms of PSi morphology, meso, macro, and double layers with pore shapes and sizes, were prepared. The structural and surface morphology properties of PSi-based substrate before and after deposition of AuNPs were investigated through studying of scanning electron microscopy (SEM), photoluminescence (PL), and X-ray diffraction (XRD). The electrical property (J-V) was carried out in primary vacuum and CO at low pressure. The results show that PSi surface morphologies strongly influenced the AuNP sizes and hence the sensor performance. It was found that decrease the AuNP sizes could be occasioned in high and fast current response.

Porosity and roughness determination of porous silicon thin films by genetic algorithms

The problem of determining the porous silicon (PSi) optical constants, thickness, porosity, and surface quality using just reflectance data is board employing evolutionary algorithms. The reflectance measurements were carried out of PSi films over crystalline silicon (c-Si) substrate, and the fitting procedure was done by using a genetic algorithm (GA). The PSi is treated as a mixture of c-Si and air. Therefore, its effective optical constants can be correlated with the porosity through effective medium approximation (EMA). The results show that genetic fitting has a good match with the experimental measurements (near UV–vis reflectance) and the thickness obtained by scanning electron microscopy (SEM).

Chip-based SALDI-MS for rapid determination of intracellular ratios of glutathione to glutathione disulfide

Alterations in the ratio of glutathione (GSH) to glutathione disulfide (GSSG) reveal the cell living state and are associated with a variety of diseases. In this study, an Au NPs grafted nanoporous silicon chip was used for surface assisted laser desorption ionization-mass spectrometry (SALDI-MS) detection of GSH. Due to the bond interaction between thiol of GSH and Au NPs modified on the chip surfaces, GSH could be captured from the complex cellular lysate. Meanwhile, the composite nanostructures of Au NPs grafted porous silicon surface presented good desorption/ionization efficiency for GSH detection. The GSH levels in different tumor cells were successfully detected. Chip-based SALDI-MS was optimized for quantification of intracellular GSH/GSSG ratio changing under drug stimulation in liver tumor cells, GSSG was reduced to GSH by reductant of tris(2-carboxyethyl)phosphine (TCEP) and isotope-labeling GSH was as an internal standard. It was found that the increasing concentration of drug irinotecan and hypoxia culture condition caused the rapid consumption of GSH and a decrease of GSH/GSSG ratio in liver tumor cells. The developed SALDI-MS method provided a convenient way to accurately measure and rapidly monitor cellular GSH value and the ratios of GSH/GSSG.

Optimization of Porous Silicon Conditions for DNA-based Biosensing via Reflectometric Interference Spectroscopy.

Objective Substantial effort has been put into designing DNA-based biosensors, which are commonly used to detect presence of known sequences including the quantification of gene expression. Porous silicon (PSi), as a nanostructured base, has been commonly used in the fabrication of optimally transducing biosensors. Given that the function of any PSi-based biosensor is highly dependent on its nanomorphology, we systematically optimized a PSi biosensor based on reflectometric interference spectroscopy (RIS) detecting the high penetrance breast cancer susceptibility gene, BRCA1. Materials and Methods In this experimental study, PSi pore sizes on the PSi surface were controlled for optimum filling with DNA oligonucleotides and surface roughness was optimized for obtaining higher resolution RIS patterns. In addition, the influence of two different organic electrolyte mixtures on the formation and morphology of the pores, based on various current densities and etching times on doped p-type silicon, were examined. Moreover, we introduce two cleaning processes which can efficiently remove the undesirable outer parasitic layer created during PSi formation. Results of all the optimization steps were observed by field emission scanning electron microscopy (FE-SEM). Results DNA sensing reached its optimum when PSi was formed in a two-step process in the ethanol electrolyte accompanied by removal of the parasitic layer in NaOH solution. These optimal conditions, which result in pore sizes of approximately 20 nm as well as a low surface roughness, provide a considerable RIS shift upon complementary sequence hybridization, suggesting efficient detectability. ConclusionWe demonstrate that the optimal conditions identified here makes PSi an attractive solid-phase DNA-based biosensing method and may be used to not only detect full complementary DNA sequences, but it may also be used for detecting point mutations such as single nucleotide substitutions and indels.

The Influence of Immersion of Porous Silicon in Aqueous Solutions of Fe(NO3)3 on Photoluminescence during Long Storage

The interaction of porous silicon (PS) with aqueous solutions of Fe(NO3)3 with different molar (M) concentrations causes introduction of iron ions into silicon pores (PS–Fe), formation of adsorbed iron coatings with different thicknesses, and an increase in the stability of PS layers, which is important for development of device structures based of PS. To treat PS layers with solutions by the immersion method, it is necessary to determine how this affects the spectral composition and intensity of photoluminescence (PL), as well as the kinetics of PL changes during long storage under atmospheric conditions. Upon treatment of freshly prepared PS by immersion into in a Fe(NO3)3 aqueous solution, it was found that, after short-term storage (up to 5 days) of the PS samples, the PL intensity increases by 7.5 and 3–3.6 times at low (0.2 M) and high (0.7–0.8 M) concentrations of Fe(NO3)3, respectively, compared to the PL intensity of an untreated PS layer. After long-term storage (4 months), the PL intensity of PS–Fe samples with concentrations of 0.1–0.2 and 0.7–0.8 M was observed to considerably increase (by 8–18 times) with unchanged position of the PL peak with respect to untreated PS. However, at the Fe(NO3)3 concentration of 0.3 М, the PL intensity decreases and the PL peak shifts to the blue, which is explained by incomplete coverage of the PS surface by an adsorbed iron layer. The kinetics of PL spectra during long-term storage is analyzed, and a model is proposed to explain the PL intensity and spectral composition.

Study of photoluminescence quenching in porous silicon layers that using for chemical solvents vapor sensor

In this work chemical vapor sensors for Ethanol, chloroform and n-Hexane were fabricated by porous silicon (PS). PS samples were prepared by electrochemical etching (ECE) method with different current density J = 2, 4 and 6 mA/cm2 and etching time 15 min and HF concentration 15%. Ordered porous silicon p-type (111) is thoroughly studied as an The structure, chemical composition and surface bond configuration of PS layer has been characterized by X-ray diffraction (XRD), Atomic Force Microscopic (AFM) and a Fourier Transform Infrared Spectroscopy (FTIR) and Photoluminescence (PL) quenching measurement were conducted using mixture nitrogen gas and vapor of n-Hexane, chloroform and ethanol, where prepared to test the sensor response towards the chemical organic solvents. The results refer to the PS surface is good sensing for chemical vapor. It's were also found that a higher PL quenching value for Ethanol compared with the value of n-Hexane and chloroform vapors.

In situ study of porous silicon thin films thermal oxidation by pulsed laser photoacoustics

Passivation is of remarkable importance for porous silicon (PSi) applications to guarantee the chemical stability of its high surface area through time. Thermal oxidation is one of the most common methods to passivate the surface of PSi. In order to better understand the oxidation process, here we performed an in situ study by using pulsed laser photoacoustics. During the thermal oxidation, the photoacoustical signal was measured each 1 °C from 70 °C to 900 °C. The measurements were analyzed by standard correlation, and the significant signal changes were related to the presence of different surface species. We have found temperatures, where the photoacoustical signal changes drastically, that can be related to the absorption and desorption of chemical species in the surface. Species identification where made through Fourier-transform infrared spectroscopy-attenuated total reflection analysis of the PSi samples, at temperatures around where these notorious modifications on the surface were observed.

Gold nanoparticle triggered dual optoplasmonic-impedimetric sensing of prostate-specific antigen on interdigitated porous silicon platforms

A porous silicon (PSi) platform with interdigitated NiCr electrodes has been used for the impedimetric biosensing of prostate specific antigen (PSA), a cancer biomarker. The first step involved the formation of a conductive PSi structure through the ion beam creation of 250 nm deep interdigitated slots, followed by their filling with NiCr electrodes deposited by plasma sputtering. In the second step, a biorecognition interface was formed by modification of the PSi surface with (3-Glycidyloxypropyl)-trimethoxysilane. A sandwich assay was performed in which PSA was first recognized by a surface-anchored antibody and then by a secondary antibody tethered to 100 nm gold nanoparticles (GNPs). The changes in the impedance upon analyte binding at different concentrations have been monitored showing that the PSA concentration exhibits a linear dependence with the series resistance defined from the device equivalent circuit. A limit of detection in the range of 1 ng/mL PSA has been determined. A dark-field study of the PSi surface after the sandwich bioassay allowed an optoplasmonic demonstration of the increasing density of GNPs at higher PSA concentrations, which was confirmed by using scanning electron microscopy. The results confirm the dual optoplasmonic-electric labelling effect of the 100 nm GNPs and their role in an internally controlled detection of PSA.

In Ukrainian

The purpose of this work is to develop a technology for the production of CdS films by chemical surface deposition on porous substrates of nanocrystalline silicon. The possibility of using the heterostructure CdS/porous-Si/p-Si as photovoltaic solar energy converters is considered. The formation of layers CdS was carried out by the method of precipitation in a chemical bath from an aqueous solution. As a template, plates of porous silicon (Si) are used. Nanoporous silicon was obtained by electrochemical etching of single-crystal plates Si (100) of p-type conductivity with a specific impedance of 6 mΩ•cm. For the chemical surface deposition of CdS films, a freshly prepared 0.015 M aqueous solution of cadmium chloride CdCl 2 , 1.5 M solution of thiourea CH 4 N 2 S, and 14.28 M solution of ammonium hydroxide NH 4 OH were used. The process of heating the plates lasted 5 min. The final temperature was 80 °C. The morphology of the porous silicon surface, the cross-section of the resulting CdS/porous-Si/p-Si structures and the chemical composition of the films obtained were investigated using a scanning electron microscope. The chemical composition of the film surface was determined using X-ray spectral microanalysis. According to the results of the conducted studies, it has been found that the thickness of the CdS layer is homogeneous and is 10–30 microns. CdS films have n-type conductivity. X-ray diffractograms of the sample exhibit pronounced peaks at 2θ ≈ 26.5° and at 2θ ≈ 43.3°, which correspond to the hexagonal modification of CdS. There are also intense peaks from the silicon substrate. A solar photocell is produced, which is a heterostructure of n-CdS/porous-Si/p-Si. The value of the efficiency of the received solar cells exceeds 5.4 % of the efficiency value for similar structures of CdS/p-Si under the same conditions for obtaining a conductive film of n-type CdS. Thus, the heterostructures CdS/porous-Si/p-Si produced by the precipitation of CdS layers in a chemical bath from an aqueous solution can be used as the basis of photovoltaic converters for solar energy.

Correlation between structural and optical properties of porous silicon treated with Erbium(III)

This paper highlights a novel passivation approach of porous silicon (pSi) surface through a simple spin coating Erbium (Er) (III) treatment. The effects of Er(III) concentration and annealing temperature on the structural and optical properties of pSi have been investigated. XRD measurements show a significant improvement in the crystallinity of the Er(III) layer and a decrease in the silicon (Si) crystalline size with temperature. Atomic force microscopy (AFM) was used to estimate the surface roughness of the Er-doped pSi layer. Changes of surface chemical composition and spatial distribution of elements in the pSi/Er(III) layer were inspected using Fourier-transform infrared (FTIR) and energy-dispersive X-ray (EDX) spectroscopies. FTIR analysis exhibit a steady enhancing of SiO2 bands accompanied by a dwindling of SiHx bands and the appearance of new bands related to Er–O–Si. Photoluminescence (PL) spectroscopy reveals a sixfold increase in the intensity with the Er(III) concentration and a shift toward the higher energy with the temperature.