Purification of silicon powder by the formation of thin porous layer followed by photo-thermal annealing

ABSTRACT: Porous silicon has been prepared using a vapor-etching based technique on a commercial silicon powder. Strong visible emission was observed in all samples. Obtained silicon powder with a thin porous layer at the surface was subjected to a photo-thermal annealing at different temperatures under oxygen atmosphere followed by a chemical treatment. Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) results indicate that silicon purity is im-proved from 99.1 to 99.994 % after annealing at 900 degreesC.     

Investigation of Strongly Hydrophobic and Thick Porous Silicon Stain Films Properties

Silicon - Porous silicon (PSi) structures with strong hydrophobicity have been achieved by chemical etching of p-type silicon substrates in a solution based on hydrofluoric acid solution (HF) and...     

Nanoporous Silicon Microcavity Based Fuel Adulteration Sensor

Fuel adulteration is a very common practice in several countries around the world. This paper reports the use of porous silicon as a sensor for the detection of adulteration of petrol and diesel by kerosene. Porous silicon has some very useful properties such as high sensitivity, small size, high surface-to-volume ratio, bio-compatibility and compatibility with silicon IC technology which make it suitable for sensing purposes. The main objective of this work is to develop an optical sensor to detect the level of adulteration in a fuel sample using a porous silicon microcavity (PSMC). Reflectance measurements are used to detect the concentration of kerosene, which is the most commonly used adulterant for petrol and diesel, in the fuel sample. The core principle on which the sensing is based is that a change in the effective refractive index of the microstructure due to the introduction of the fuel in the pores leads to a change in the reflectance spectrum of the structure. The same sensor is used for the detection of adulteration in petrol as well as in diesel. The sensing process is reversible, thus making the sensor reusable.     

Characterization of superhydrophobic a-C:F thin film deposited on porous silicon via laser ablation of a PTFE target

Fluorinated amorphous carbon (a-C:F) thin films are deposited on both flat silicon and porous silicon (PS) surfaces via laser ablation of a polished polytetrafluoroethylene (PTFE). Porous silicon (PS) is prepared by anodic etching of p-type silicon wafers in HF based solution. The film deposited on the flat silicon surface exhibits a highly hydrophobic state with water contact angle (WCA) of ~ 146°. In comparison, the surface of film deposited on PS layer shows a roll-off superhydrophobic state, where the water droplet is seen to roll off without wetting its surface with contact angle hysteresis of ~ 4.5°. Micro-Raman results show that the graphite domain of the film deposited on PS has higher disorder level and lower average gain size. The effect of substrate porosity on chemical composition of deposited films has been investigated by using both Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). It is found that the porous substrate improves the incorporation of the fluorine into the film. Atomic force microscopy (AFM) results revealed that the film deposited on PS has higher surface roughness and lower grain size as compared to the film deposited on flat silicon surface.     

Porous Silicon Nitride Ceramics Prepared by Reduction–Nitridation of Silica

A new method for preparing porous silicon nitride ceramics with high porosity had been developed by carbothermal reduction of die-pressed green bodies composed of silicon dioxide, carbon, sintering additives, and seeds. The resultant porous silicon nitride ceramics showed fine microstructure and uniform pore structure. The influence of SiO₂ particle size and sintering process (sintering temperature and retaining time) on the microstructure of sintering bodies was analyzed. X-ray diffractometry demonstrated the formation of single-phase β-Si₃N₄ via the reaction between silicon dioxide and carbon at high temperature. SEM analysis showed that pores were formed by the banding up of rod-like β-Si₃N₄ grains. Porous Si₃N₄ ceramics with a porosity of 70–75%, and a strength of 5–8 MPa, were obtained.     

Free-Standing Porous Silicon Film Produced by a Pulsed Anodic Etching of n+-Silicon Substrate in an HF: HCl: C2H5 OH: H2O2:H2O Electrolyte: Characterization and Adsorption of Colchicine

Silicon - Porous silicon (PSi) has been established as a promising candidate for a variety of applications in many fields of science and technology. Currently, free-standing PSi is receiving an...     

有机硅单体BMSB合成物的高分辨质谱定性分析及UPLC/TUV定量检测

以实验室自制1,4-二(甲氧二甲基硅烷基)苯[1,4-Bis(methoxydimethylsilyl)benzene,BMSB]为研究对象,Waters高分辨UPLC-TOFMS为分析测试手段,建立了针对有机硅合成单体体系的定性、定量分析方法,并把该方法应用于合成工艺优化,制得了较高品质的BMSB。     

The Energy-Band Structure of Porous Silicon Studied with Photoluminescence Excitation and Photoacoustic Spectroscopy

Porous silicon has been studied with photoluminescence, photoluminescence excitation, and photoacoustic spectroscopy. From the luminescence data, an energy-level diagram related to the luminescence is constructed. The diagram is confirmed in detail by the photoacoustic spectra. The results are discussed with the conclusion that they are in good agreement with the surface-band oxyhydride-like emitter, which recently has been established as the source for the photoluminescence from porous silicon.     

Porous silicon microcavities: synthesis, characterization, and application to photonic barcode devices

ABSTRACT: We have recently developed a new type of porous silicon we name as porous silicon colloids. They consist of almost perfect spherical silicon nanoparticles with a very smooth surface, able to scatter (and also trap) light very efficiently in a large-span frequency range. Porous silicon colloids have unique properties because of the following: (a) they behave as optical microcavities with a high refractive index, and (b) the intrinsic photoluminescence (PL) emission is coupled to the optical modes of the microcavity resulting in a unique luminescence spectrum profile. The PL spectrum constitutes an optical fingerprint identifying each particle, with application for biosensing.In this paper, we review the synthesis of silicon colloids for developing porous nanoparticles. We also report on the optical properties with special emphasis in the PL emission of porous silicon microcavities. Finally, we present the photonic barcode concept.     

Development of a technique to prepare porous materials from glasses

A new technique to prepare porous materials has been developed for recycling of used glasses. Porous materials were produced from used glass powders by hydrothermal reaction of glass powders with water at low temperatures followed by calcination at high temperatures for expansion. The new technique does not require additional vesicants such as calcium carbonate, silicon carbide, and organic polymers that have been used in the ordinary method. In this process, the water incorporated into the glass structure by hydrothermal treatment acts as a vesicant. When the hydrothermally treated glass was heated at high temperatures around 700 °C, water was released as vapor from the softened glass to form pores. The obtained porous materials had different pore structures that were determined by the sizes of raw glass particles. Crystallization occurred during the calcination of the hydrothermally treated glass powder.     

Surface and interface analysis of nanostructured porous silicon layers fabricated at low temperatures from highly doped silicon substrate: application in optical filters

The influence of low temperature of the electrolyte on the surface and interface of porous silicon and its application in optical devices has been studied. Porous Si–bulk Si interface profile was observed by means of the high resolution SEM images. At low temperatures, a decrease in the interface roughness and an increase in the pore size has been observed. These results were used to fabricate optical filters for UV and visible regions at low temperatures. As compared to the filters fabricated at room temperature an increased optical response is reported for the filters formed at low temperature.     

Electron emission properties of cold cathodes based on porous silicon layer processed by electrochemical oxidation and high-pressure water vapor annealing

Journal of Porous Materials - Porous silicon (PS) layers were processed by electrochemical oxidation (ECO) and high-pressure water vapor annealing (HWA) after they were prepared on n+-type silicon...     

Microstress in Reaction‐Bonded SiC from Crystallization Expansion of Silicon

Microstress in reaction‐bonded silicon carbide (RBSiC) has been measured using piezo‐Raman spectroscopy. Compressive microstresses as high as 2 GPa exist in the silicon phase and tensile microstresses as high as 2.3 GPa exist in the SiC phase of RBSiC. This is much larger than expected for thermoelastic microstress from coefficient of thermal expansion mismatch would provide. Instead the microstresses arise from the crystallization of liquid silicon. During the reaction bonding process, not all of the silicon reacts to form SiC and there is liquid free silicon. The phase transformation of the free silicon from liquid to solid has a large volume expansion, which results in large residual microstress within the silicon and SiC phases of RBSiC.     

Porous Silicon Studied with Time-Resolved Photoluminescence

Porous silicon has been studied with time-resolved photoluminescence, and growth as well as decay curves have been measured at several detection energies, with sample temperatures between 10 and 300 K. In the decay curves, three components are mainly observed, a small one which is very fast, with time scales of the order of nanoseconds or faster, the main component having time scales of the order of milliseconds, and a very small, very slow component, with time scales of the order of seconds. The main components can in most—but not all—cases be fitted well with stretched exponentials containing two fitting parameters. Of these, it comes out that the parameter accounting for disorder or the like depends only little upon detection energy and temperature, whereas the parameter accouting for the development in time decreases substantially for increasing temperature. The results are discussed.     

Sensitivity of Porous Silicon Photoluminescence to Low Concentrations of CH4 and CO

In this paper we report the sensitivity of porous silicon photoluminescence (PL) to diluted mixtures of methane and carbon monoxide in synthetic air. We also investigate the separate effect of synthetic air, purified nitrogen and relative humidity on both photoluminescence and conductance (G). Porous silicon samples have been prepared from n-type silicon substrates. We find that PL intensity and G decrease in synthetic air with respect to their values in N₂. Presence of carbon monoxide reduces the PL intensity while methane provokes the opposite behaviour. The dependence of the PL spectra on methane and carbon monoxide concentrations has been investigated. The observed effects can be related to gas induced modifications in porous surface and suggest that porous silicon can be employed in gas sensor technology.     

多孔碳化硅陶瓷的原位氧化反应制备及其性能

以SiC为陶瓷骨料,Al2O3作为添加剂,通过原位氧化反应制备了Sic多孔陶瓷,并对其氧化反应特性及性能进行了研究.结果表明:在1 300～1 500℃,随烧结温度的升高,SiC的氧化程度增加,SiC多孔陶瓷的强度逐渐增加,但开口孔隙率有所降低.莫来石相在1 500℃开始生成·当烧结温度升高到1 550℃时,莫来石大量生成,得到了孔结构相互贯通且颈部发育良好的莫来石结合SiC多孔陶瓷;由于在SiC颗粒表面上覆盖了致密的莫来石层,SiC的氧化受到抑制,开口孔隙率因而升高,SiC多孔陶瓷的强度因莫来石的大量生成而增加.由平均粒径为5.0um的SiC,并添加20%(质量分数)Al2O3,经1 550℃烧结2h制备的SiC多孔陶瓷具有良好的性能,其抗弯强度为158.7MPa、开口孔隙率为27.7%.     

Light Emission from Highly Reflective Porous Silicon Multilayer Structures

Porous silicon photoluminescence and electroluminescence can be controlled by periodically modulating the material porosity to form high quality multilayer stacks and microcavities. Important issues not yet fully addressed are (a) the precise role played by this microstructuring, given that the luminescence is distributed throughout the entire structure and that the low porosity layers are highly absorbing at short wavelengths, and (b) whether the quality of such microcavities could be sufficient to support lasing. Using both experimental and theoretical techniques, the emission and reflection properties of different porous silicon single and multilayer structures have been investigated in order to understand further and exploit the nature of light propagation within them.     

登革病毒反向遗传学技术的研究进展

登革病毒(dengue virus,DENV)是流行于世界范围内的重要虫媒病毒之一,近年来其传播范围的不断扩大给疾病防控带来了极大困难。反向遗传学技术作为一种重要手段,广泛应用于RNA病毒的相关研究,自1991年第1次成功构建DENV感染性克隆以来,明显加速了DENV相关领域的研究。本文总结了DENV反向遗传学技术的构建策略及技术突破,为DENV致病机制研究及疫苗研发提供新思路。     

ZnO-porous silicon nanocomposite for possible memristive device fabrication

Preliminary results on the fabrication of a memristive device made of zinc oxide (ZnO) over a mesoporous silicon substrate have been reported. Porous silicon (PS) substrate is employed as a template to increase the formation of oxygen vacancies in the ZnO layer and promote suitable grain size conditions for memristance. Morphological and optical properties are investigated using scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. The proposed device exhibits a zero-crossing pinched hysteresis current-voltage (I-V) curve characteristic of memristive systems.     

Optical,Morphological, and Structural Properties of Tablets Obtained from Porous Silicon

Silicon - Porous silicon (PS) is a material with a great interest due to its optical (photoluminescent) and chemical (reactive surface) properties, for this reason, it is important to find new ways...