Structural Properties Of Porous Silicon Research Articles

دراسة الخصائص التركيبية للسيليكون المسامي وتطبيقاتها كأجهزة استشعار حرارية

تم استخدام طريقة الحفر الضوئي الكهروكيميائي (PECE) لإنشاء عينات pSi على رقائق السيليكون من النوع (Si) n. بأستخدام وقت الحفر (12 و 22 دقيقة) في التجربة مع الحفاظ على المعلمات الأخرى (10 مللي أمبير / سم2 كثافة التيار وحمض HF بتركيز 75٪). تمت دراسة تغير السعة والمقاومة مع زيادة درجة الحرارة وانخفاضها للعينات المحضرة عند ترددات 10 و 20 كيلو هرتز. ، تم التحقق من صحة عرض المسام والعمق والمسامية باستخدام الفحص المجهري الإلكتروني (SEM). تم تأكيد تكوين السيليكون المسامي من خلال أنماط حيود الأشعة السينية (XRD) ، وأنخفض حجم البلورة ، وكشفت أطياف التلألؤ الضوئي (PL) أن قمم الانبعاث تركزت عند q2 من 28.5619 ° و 28.7644 ° لوقت حفر 12 و 22 دقيقة على التوالي. تظهر دراسة السعة والمقاومة أثناء زيادة درجة الحرارة وانخفاضها لكلتا أوقات الحكة بوضوح أن pSi المحضر كمستشعر حراري يعمل بشكل أفضل وبانتقائية أكثر لمدة 20 دقيقة من وقت الحفر.

Influence of different etching methods on the structural properties of porous silicon

PurposePorous silicon (Si) was fabricated by using three different wet etching methods, namely, direct current photo-assisted electrochemical (DCPEC), alternating CPEC (ACPEC) and two-step ACPEC etching. This study aims to investigate the structural properties of porous structures formed by using these etching methods and to identify which etching method works best.Design/methodology/approachSi n(100) was used to fabricate porous Si using three different etching methods (DCPEC, ACPEC and two-step ACPEC). All the samples were etched with the same current density and etching duration. The samples were etched by using hydrofluoric acid-based electrolytes under the illumination of an incandescent lamp.FindingsField emission scanning electron microscopy (FESEM) images showed that porous Si etched using the two-step ACPEC method has a higher porosity and density than porous Si etched using DCPEC and ACPEC. The atomic force microscopy results supported the FESEM results showing that porous Si etched using the two-step ACPEC method has the highest surface roughness relative to the samples produced using the other two methods. High resolution X-ray diffraction revealed that porous Si produced through two-step ACPEC has the highest peak intensity out of the three porous Si samples suggesting an improvement in pore uniformity with a better crystalline quality.Originality/valueTwo-step ACPEC method is a fairly new etching method and many of its fundamental properties are yet to be established. This work presents a comparison of the effect of these three different etching methods on the structural properties of Si. The results obtained indicated that the two-step ACPEC method produced an etched sample with a higher porosity, pore density, surface roughness, improvement in uniformity of pores and better crystalline quality than the other etching methods.

Sodium effects on the electronic and structural properties of porous silicon for energy storage

Sodium effects on the electronic and structural properties of porous silicon for energy storage

Structural properties of porous silicon obtained with laser photoetching assisted by computerized numeric control

This study presents the preparation of porous silicon (PS) using the photoetching technique. The light source was a laser with a 405 nm wavelength. Hydrofluoric acid, hydrogen peroxide, and ethanol were used in the process. An approach to forming PS in a selected area was also studied, in which a computational control of the laser movement was developed. A laser allows for the formation of PS in short period of time using n-type crystalline silicon (c-Si) as a substrate. Photosynthesized PS shows similar characteristics (physical and chemical) to anodized PS. Raman scattering showed a broadening of the peak centered at 525 cm−1, this behavior is related to the formation of PS. Micro-Fourier transform infrared spectroscopy showed bands related to Si-H wagging and SiH2 bending vibrations, these types of bonds were generated during the porosification process. The morphologic characteristics were defined by scanning electron microscopy (SEM) and revealed that the porous structures depend on the potency of the laser used. The topography of the surface confirms PS formation. SEM analysis demonstrated that pores with diameters of 60 and 300 nm can be obtained. Energy-dispersive x-ray spectroscopy showed an increase in oxygen in the PS due to the oxidation process following photoetching. The x-ray diffraction showed that this type of etching eliminates the induced tension in the c-Si grain edges due to PS formation.

Morphological and Structural Properties of Porous Silicon (PSi)

This study includes the effect of the etching time on the morphology of the surfaces produced using the electrochemical method of silicon ( p-type), where it was found that the etching leads to increase the porosity layer of silicon. The production of nanocrystalline structures and control of their production conditions is the first step to control the properties of the devices. These are very important applications for the etching of renewable energy.

Morphological and Structural Properties of Porous Silicon (PSi)

This study includes the effect of the etching time on the morphology of the surfaces produced using the electrochemical method of silicon ( p-type), where it was found that the etching leads to increase the porosity layer of silicon. The production of nanocrystalline structures and control of their production conditions is the first step to control the properties of the devices. These are very important applications for the etching of renewable energy.

Porous silicon based CO2 sensors with high sensitivity

Porous silicon (PS) has been an attractive material for bio-chemical sensors. Pore volume and surface area of the porous silicon are key parameters for the sensor applications. Its large surface area for the applications and compatibility with silicon-based technologies has been the driving force for this technology development. The carbon dioxide (CO2) gas is one of the most important greenhouse gases that cause global warming and air pollution. For this reason, detection of CO2 gas in living environment is essential. In this study, luminescence and electrical properties of the PS under different carbon dioxide levels and detection mechanisms were investigated. PS are fabricated by anodic etching in hydrofluoric acid based solution in a double anodization cell. The surface bond configurations and structural properties of PS were monitored by Fourier Transmission Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM), respectively. The experimental results suggested that the PS surface very sensitive to CO2 gas and can be used for CO2 sensing.

The effect of etching time on structural properties of Porous silicon at the room temperature

Nano-porous silicon (PS) layers have been prepared by electrochemical etching of (100) silicon wafer in the solution of hydrofluoric acid (HF) and ethanol (C2H5OH). In this paper, XRD and FTIR confirm the formation of PS.The size of crystallites in the porous Si layers was found from XRD, which isaround ∼2.4 nm. The evolution of morphology of PS as a function of etching time is imaged using SEM. The average pore-diameter has been calculated from the image j software, which is in the range of 238-1117nm. The Raman spectrareveal that the peak intensities sharply increase with etching time due to presence of nancrystals on the surface of PS.It was observed that the peak of Raman signal was around ∼520.5cm-1. Luminescence studies revealedthat the strong photoluminescence emission was observed at about ∼660nm.It possesses a broad red emission band on the surface of PS due to the growth of Si=O bonds and the formation of silicon hydrides (SiHx), which is caused to trapped electron states at the interface between the crystalline Si and SiO2.

The Effect of Gamma Irradiation on the Structural Properties of Porous Silicon

Porous silicon layers (PSi) were prepared from p-type silicon wafer by using electrochemical cell with etching time 20 min, current 30 mA and fixed electrolyte solution HF:C2H5OH (1:4). The effect of increase of γ-ray intensity (50Gy and 100Gy) on the structural properties of porous silicon has been studied using SEM, AFM, XRD and Raman spectrum. The SEM images before irradiation shows high density and randomly distributed of pores that cover all of the surface which have different size and spherical shape. After irradiation by 50Gy, the pores seems more obvious, discriminate and larger diameters. The initial elementary pores on the PSi surface decrease with the increasing of radiation intensity to 100Gy, as a result of formation of new pores with in the initial layer of Psi. The AFM images show that the roughness of the samples increase with irradiation. XRD spectrum before irradiation did not show clearly any featured peaks while the spectra after irradiation show the presence of different peaks but the most important distinctive was peaks at ( 2θ = 28.12) which give indication that the structure is cubic. An extremely symmetric band shape were recognized from Raman spectra of the samples after and before irradiation.

Change of diffused and scattered light with surface roughness of p-type porous Silicon

Porous silicon samples were prepared by electrochemical etching method for different etching times. The structural properties of porous silicon (PS) samples were determined from the Atomic Force Microscopy (AFM) measurements. The surface mean root square roughness (σ rms) changes as function of porosity were studied, and the influence of etching time on porosity and roughness was studied too. UV-Vis-NIR Spectrophotometer with integrating sphere accessory used to measure the specular reflectance (Rspec) and scattered light (Dsca) for all samples. Changes of scattered light intensity with σ rms were studied. Theoretical and measured values were compared and they were almost the same.

Near infrared photoluminescence properties of porous silicon prepared under the influence of light illumination

Porous silicon (PS) has been prepared by anodic etching of boron doped silicon under the influence of monochromatic light illumination. The optical properties of the PS samples have been investigated using temperature dependent photoluminescence (PL) spectroscopy. An overall enhancement of the infrared luminescence yield is caused by the light illumination. In the visible spectral range, changes at the low energy side of the broad PL band were observed. In the near infrared spectral range, a new PL band at 850 nm, which is strongly correlated with light illumination, was detected. The new PL band disappears once blue light is used, whereas an increase in its intensity is observed, when the etching is performed under the illumination of light with wavelengths close to the band gap. By increasing the temperature, the 850 nm transition band grows at the expense of the main near infrared transition at 1100 nm. The recombination characteristics of this PL band are indicative of its extrinsic nature. The macroscopic morphology shows strong dependence on the wavelength of the illumination light. Photoassisted preparation could provide a tool for the control of the optical and structural properties of PS.

Impact of Thermal Oxidation on the Adsorptive Properties and Structure of Porous Silicon Particles

A combination of gas and probe molecule adsorption from aqueous solution have been applied to determine the adsorptive and structural properties of porous silicon (pSi) particles as a function of thermal oxidation in the range 473−1073 K. Gaseous nitrogen adsorption has shown a decrease in the BET specific surface area, mesopore volume, and diameter due to the increasing molecular volume of the oxidized silicon layer within the pores. Methylene blue was used as an adsorbate to establish the apparent surface area of pSi particles in aqueous solution and has shown adsorption capacity independent of oxidation in the range of 473−873 K. Comparable adsorption capacities at low oxidation temperatures are due to methylene-blue-induced oxidation which has been established by X-ray photoelectron spectroscopy, while increased adsorption at high temperatures is due to increased surface silanol concentrations. Comparisons between the nitrogen- and methylene-blue-determined surface areas demonstrate a difference in the adsorptive properties of gas and solution phase molecules onto pSi. These differences can be attributed to the different adsorption mechanisms, that is, physisorption for nitrogen and electrostatic attraction for methylene blue. Nitrogen and methylene blue adsorption probe different features of pSi, demonstrating modification of the structural and adsorptive properties with oxidation as well as highlighting the improved characterization that can be obtained from the combination of solution and gas phase adsorption.

Highly explosive nanosilicon‐based composite materials

AbstractWe present a highly explosive binary system based on porous silicon layers with their pores filled with solid oxidizers. The porous layers are produced by a standard electrochemical etching process and exhibit properties that are different from other energetic materials. Its production is completely compatible with the standard silicon technology and full bulk silicon wafers can be processed and therefore a large number of explosive elements can be produced simultaneously. The application‐relevant parameters: the efficiency and the long‐term stability of various porous silicon/oxidizer systems have been studied in details. Structural properties of porous silicon, its surface termination, the atomic ratio of silicon to oxygen and the chosen oxidizers were optimized to achieve the highest efficiency of the explosive reaction. This explosive system reveals various possible applications in different industrial fields, e.g. as a novel, very fast airbag igniter. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Porous silicon upon multicrystalline silicon: Structure and photoluminiscence

Ultrathin porous silicon layers have been stain-etched upon multicrystalline silicon (multi-Si) substrates. We studied optical and structural properties of porous silicon by photoluminescence, photo-luminescence excitation, reflection, atomic force microscopy and scanning tunnel microscopy methods. It was observed that the thickness of porous silicon did not exceed 20 nm. The photoluminescence method has shown that photoluminescence spectra of porous silicon of different grains have shown that they differ insignificantly (∼10%) in intensity. It was found that por-Si layers with optimal antireflection characteristics was obtained during etching time 7 min. In the paper the comparison of the reflection characteristics of investigated samples por-Si with industrial antireflection coating is presented.

Structural properties of porous media

Structural properties of porous silicon are investigated theoretically. Distribution functions of pore sizes were introduced and expressions for the surface and volume porosities of the material are obtained. The suggested models allow one to calculate the specific surface area and its dependence on porosity. A model for macroporous silicon with a nanoporous layer on the pore walls is suggested also. An attempt is done to describe analytically the observed phenomenon of the specific surface area decrease at higher porosities.

Enhanced photoluminescence and structural properties of porous silicon formed in hydrofluoric–hydrochloric solutions

The experimental results reported here made it possible to demonstrate the determining role of the surface chemical composition of Si nanocrystals in ensuring the stability of the physical and chemical properties of porous Si. The performed Fourier transform infrared spectroscopic investigations have shown the appearance of bonded oxygen at the porous silicon surface just after preparation of samples in HCl-modified electrolyte.

Surface relaxation effects on the properties of porous silicon

In this article, surface relaxation and its effects on the electronic and structural properties of porous silicon are studied by using the total-energy pseudopotential formalism within the density-functional theory. Our model is based on a 32-atom supercell, where columns of atoms are removed and saturated with hydrogen atoms. Samples with 4.4%, 13.6%, 16.8%, 28.9%, and 41.3% porosity are analyzed in detail. The results show a clear expansion of the system along the pore direction as the porosity increases. Moreover, this expansion is very sensitive to the hydrogen-atom concentration and a linear dependence is observed. The dependence of the band gap and the effective mass on the porosity are also analyzed. Here, the hydrogen-atom number and pore shapes are observed to play a fundamental role.

Luminescence and structural properties of porous silicon with ZnSe intimate contact

The incorporation of ZnSe into luminescent porous silicon layers (PSL) by electrochemical co-deposition of Zn and Se is described by focusing on the critical parameters related to the specific nature of porous silicon. The PSL photoluminescence is monitored during the growth of ZnSe to reveal the effects of the process on the optical properties of the structure, allowing an in-situ characterization of the growth. The structure and chemical composition of the resulting nanostructures are investigated by transmission electron microscopy (TEM) and chemical microanalysis which show homogeneous incorporation of ZnSe inside the porous matrix with no segregation. Crystallization of ZnSe by subsequent thermal annealing is also studied and preliminary characterizations of the electrical properties of the resulting nanocomposite structures are presented.

Si 29 nuclear magnetic resonance of luminescent silicon

Nuclear magnetic resonance of Si29 is used to study structural properties of porous silicon and siloxene. Evidence for changes in the chemical shift of porous silicon due to quantum confinement could not be observed. A hydride phase exhibiting a chemical shift of −75 ppm versus tetramethyl silane (TMS) is found in both porous silicon and siloxene. In as-prepared Wöhler siloxene, a chemical shift of −83 ppm versus TMS is assigned to threefold coordinated Si atoms forming a planar polysilane.

Control of structure and optical anisotropy in porous Si by magnetic-field assisted anodization

The effects of an applied magnetic field during anodization on the structural and optical isotropy of luminescent porous silicon (PS) are investigated. The PS layers are prepared by anodizing p-type Si wafers in HF solutions with an external magnetic field of 0–1.7 T applied perpendicular to the Si surface. It is shown that the photoluminescence intensity of PS significantly increases with increasing magnetic field. This effect is accompanied by an increase in both the porosity and the optical isotropy without affecting the surface chemical composition. The structural uniformity in the PS layer and at the PS-substrate interface are also improved. These results suggest that an external magnetic field during anodization regulates the supply of holes from the substrate and produces well-controlled optical and structural properties of PS.