Correlation of Photoluminescence and Bandgap Energies with Nanocrystal Sizes in Porous Silicon

We have measured the crystallite sizes, the bandgap energies, and the photoluminescence (PL) energies in porous silicon (PSi) samples having a wide range of porosities and kept in different ambient conditions. The dependence of the bandgap energy on the crystallite size agrees with theory. For PSi samples exposed to air and containing crystallites smaller than 5 nm, the PL intensity increases by several orders of magnitude and the PL peak energy shifts from the near infrared to the red, in agreement with the quantum confinement model for the PL. For crystallites smaller than 3 nm, there is a Stokes shift between the excitonic bandgap and PL energies, which increases to several hundreds of meV for sizes 2 nm, indicating that, in PSi exposed to air, the PL is not due to free excitons. Before exposure to air, very high porosity PSi samples emit at shorter wavelengths than after exposure to air, suggesting that the Stokes shift depends on the surface chemistry.     

Electroluminescence from porous silicon formed by photoetching in an HF/I<Subscript>2</Subscript> solution

We demonstrate the formation of a light-emitting porous silicon (PSi) layer by photoetching in an HF/I₂ solution. The use of a Xe lamp makes possible a large and homogeneous PSi layer on an n-type Si(100) wafer. An insulating layer has been formed on the PSi layer by chemical oxidation in an acidic solution. These techniques are used to fabricate electroluminescent (EL) devices of metal/insulator/semiconductor (MIS) type. It is shown that the present device is superior with respect to emission efficiency to the conventional Schottky- or metal/semiconductor-type device.     

Thermal and combustion behavior of phosphorus–nitrogen and phosphorus–silicon retarded epoxy

A novel trizine ring-based phosphorus–nitrogen flame retardant, 1,3,5-tris(3-(diphenylphosphoryl)propyl)-1,3,5-triazinane-2,4,6-trione (PN), was synthesized by the reaction of diphenylphosphine oxide and triallyl isocyanurate with triethylborane as catalyst. Chemical structure of the target compound was confirmed by Flourier transform infrared spectrum, nuclear magnetic resonances, matrix-assisted laser desorption/ionization time-of-flight mass spectrum measurements. The newly developed PN was used in the flame retardancy of o-cresol novolac epoxy/phenolic novolac hardener system. For comparison, another analogous phosphorus–silicon flame retardant, [(1,1,3,3-tetramethyl-1,3-disiloxanediyl)-di-2,1-ethanediyl]-bis(diphenylphosphine oxide) (PSi), was also applied in the same system. Experimental results revealed that PN showed superior flame retardant efficiency to that of PSi. In addition, the incorporation of flame retardants was in favor of the char formation during the thermal degradation process of epoxy thermosets. With the same flame retardant content, the char residue of epoxy thermosets with PSi was higher than that of epoxy thermosets with PN at 750 °C. Cone calorimeter results indicated that PN contributed to gas phase flame retardancy while PSi was more likely to take part in flame retardancy in the condense phase. X-ray photoelectron spectroscopy data revealed that the binding energies of phosphorus changed in different ways in PN and PSi after combustion. This implied that phosphorus exhibited different combustion behaviors when combined with nitrogen or silicon.     

Porous silicon nanoparticles for cancer photothermotherapy

The in vitro cell tests and in vivo animal tests were performed to investigate the feasibility of the photothermal therapy based on porous silicon (PSi) in combination with near-infrared (NIR) laser. According to the Annexin V- fluorescein isothiocyanate Apoptosis assay test results, the untreated cells and the cells exposed to NIR laser without PSi treatment had a cell viability of 95.6 and 91.3%, respectively. Likewise, the cells treated with PSi but not with NIR irradiation also had a cell viability of 74.4%. Combination of these two techniques, however, showed a cell viability of 6.7%. Also, the cell deaths were mostly due to necrosis but partly due to late apoptosis. The in vivo animal test results showed that the Murine colon carcinoma (CT-26) tumors were completely resorbed without nearly giving damage to surrounding healthy tissue within 5 days of PSi and NIR laser treatment. Tumors have not recurred at all in the PSi/NIR treatment groups thereafter. Both the in vitro cell test and in vivo animal test results suggest that thermotherapy based on PSi in combination with NIR laser irradiation is an efficient technique to selectively destroy cancer cells without damaging the surrounding healthy cells.     

Synthesis of colloidal solutions with silicon nanocrystals from porous silicon

In this work, we have obtained colloidal solutions of Si nanocrystals (Si-ncs), starting from free-standing porous silicon (PSi) layers. PSi layers were synthesized using a two-electrode Teflon electrochemical cell; the etching solution contained hydrogen peroxide 30%, hydrofluoric acid 40% (HF), and methanol. The anodizing current density was varied to 250 mA cm^-2, 1 A cm^-2, and 1.2 A cm^-2. Thus obtained, PSi was mechanically pulverized in a mortar agate; then, the PSi powders were poured into different solutions to get the final Si-ncs colloidal solutions. The different optical, morphological, and structural characteristics of the colloidal solutions with Si-ncs were measured and studied. These Si-ncs colloidal solutions, measured by photoluminescence (PL), revealed efficient blue-green or violet emission intensities. The results of X-ray diffraction (XRD) indicate that the colloidal solutions are mainly composed of silicon nanocrystallites. The result of UV–vis transmittance indicates that the optical bandgap energies of the colloidal solutions varied from 2.3 to 3.5 eV for colloids prepared in methanol, ethanol, and acetone. The transmission electron microscopy (TEM) images showed the size of the nanocrystals in the colloidal solutions. Fourier transform infrared spectroscopy (FTIR) spectra showed different types of chemical bonds such as Si-O-Si, Si-CH₂, and SiH _x , as well as some kind of defects.

PACS

61.46Df.-a; 61.43.Gt; 61.05.cp; 78.55.-m; 81.15.Gh     

Conduction and Luminescent Properties of Wet Porous Silicon

Carrier transport and photoluminescence-quenching mechanisms in reverse-biased p-type porous silicon in contact with an aqueous electrolyte are investigated. Concerning transport mechanisms investigation, experiments are based on the study of the photo-induced current as a function of the porous layer thickness. The liquid-impregnated porous silicon skeleton is found under equipotential conditions. Transport of electrons (supplied by the substrate) in porous silicon is shown to be dominated by a diffusion process. Photoluminescence-quenching is investigated by using a reverse-biased p-type porous silicon illuminated at 365 and 809 nm simultaneoulsy. The first illumination generate photoluminescence and the second supplies carriers in the substrate. A progressive photoluminescence-quenching has been observed, under a constant applied voltage, by increasing progressively the electron concentration in the porous layer. This original experiment allows to reject the hypothesis of an electric-field-induced separation of carriers as the photoluminescence-quenching mechanism in wet porous silicon, while it strongly supports the mechanism based on Auger recombination.     

Preparation of Pyramids Structured Silicon as a Support for Nano Sized Zero Valent Iron Particles for Nitrate Removal from Water

In this study, pyramids structured silicon (PSi) has been made from metallurgical grade silicon powder with wet alkaline etching and then chemically activated with nano zero valent iron (NZVI) to eliminate nitrate. The NZVI/PSi composite was characterized by scanning electronic microscopy (SEM), X-ray diffraction(XRD), X-ray fluorescence spectrometer (XRF), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and UV–Vis spectrophotometry. The size of NZVI particles was between 30–100 nm coated on PSi without clustering of the NZVI particles due to the electromagnetic attraction forces. The synergistic effect of NZVI/PSi composites obviously increased remarkably nitrate removal efficiency than NZVI alone. Chemical reduction of nitrate by zerovalent iron in water requires acidic pH conditions but NZVI/PSi composite can reduce nitrate in water in the pH range of 2–7. Also, removal of nitrate complete in 20 min by NZVI/PSi composite that was shorter than NZVI in 120 min. Above all, this composite completely was separated from solution with external magnetic field.     

Enhanced photocatalytic reduction of Cr(VI) on silver nanoparticles modified mesoporous silicon under visible light

The development of visible-light photocatalysts with desirable material characteristics and efficient performance is an existing challenge for photocatalysis community. Herein, we report on the synthesis of silver nanoparticles (AgNPs) modified porous silicon (PSi) nanopowder and its effective use in the photo-reduction of hexavalent chromium Cr(VI) to trivalent Cr(III) under direct visible light irradiation in the presence of citric acid. The PSi was prepared via simple stain etching of Si microparticles in HF/HNO₃ aqueous solution, followed by the deposition of AgNPs onto PSi by the immersion plating technique. The developed photocatalyst composed of PSi with <20 nm mesoporous structure, decorated with crystalline 15-50 nm AgNPs. Photocatalytic experiments using unmodified Si microparticles, either PSi or sonicated one, indicated inactive catalytic behavior toward the photo-reduction of Cr(VI). Remarkable photo-reduction efficiency (97.4%) was achieved after 180 minutes irradiation using the AgNPs/PSi sample. The efficient photo-reduction capability of AgNPs/PSi photocatalyst is attributed to the enhanced separation between photo-generated electrons and holes (e⁻-h⁺) enabling better utilization of light, as revealed from the photoluminescence measurement. Additionally, the presence of citric acid in solution promoted greatly the photo-reduction reaction as it acted as a hole scavenger, suppressing further the rate of e⁻-h⁺ recombination through rapid consumption of photo-generated holes. Excellent reusability of the current photocatalyst was evidenced by performing cyclic five runs with minimal reactivity loss. Results of synthesis, characterization, photocatalytic activity and reaction mechanism are thoroughly addressed and discussed.     

Synthesis of layered hierarchical porous SnO<Subscript>2</Subscript> for enhancing gas sensing performance

Layered hierarchical porous SnO₂ (LHP-SnO₂) have been synthesized by a two-step method, in which pure SnO₂ nanoparticles(NPs) with the diameter about 3.2 nm were prepared firstly through a hydro-thermal method, and then LHP-SnO₂ were prepared by utilizing polystyrene (PS) microspheres as a template and SnO₂ NPs as a precursor. The as-prepared sample consisted of porous SnO₂ layers, in which each layer presents a three-dimensional random arrangement of macropores with average pore diameter of about 260 nm. The Nitrogen adsorption–desorption analysis implied that the sample was characterized with large surface area of 140.67 m²/g and extensive micropores and mesopores structure. Compared with pure SnO₂ NPs, the LHP-SnO₂ exhibited an obvious improvement in gas sensing properties. These results indicate that the layered hierarchical porous structure possess potential application in sensing materials.     

烟煤地下气化半焦对模拟废水中苯酚的脱除

以鹤壁烟煤地下气化半焦为脱除剂,对苯酚模拟废水进行脱除实验研究。采用扫描电镜、低温氮气物理脱除仪和红外光谱仪对半焦的表面特性、孔结构和表面官能团进行表征,进一步考察了半焦投加量、震荡时间、实验温度对模拟废水苯酚脱除的影响。实验结果表明:气化半焦具有微孔(小于2nm)和层状结构,微孔孔径主要分布在1~5nm之间,表面有较丰富的含氧官能团;在模拟废水苯酚浓度为100mg/L、水焦比为10:1、震荡时间为2h、脱除温度为40℃时,半焦对苯酚的脱除率和吸附容量分别为65%和0.66mg/g,气化半焦的孔结构特性和表面含氧官能团对苯酚脱除有积极作用;半焦对模拟废水中苯酚的吸附为多分子层物理吸附,其Freundlich吸附等温式为Q=0.0546C^0.6286。     

Tailoring of a γ-Alumina Membrane with a Bimodal Pore Size Distribution for Improved Permeability

Porous γ-alumina with a bimodal pore size distribution has been developed by adding nanosized polystyrene beads to boehmite sol as templating units. The primary pore diameter is in the range of 4–6 nm and the secondary pore diameter is ca. 50 nm with minor pore shrinkage. The unsupported γ-alumina with different porous structures are characterized using thermogravimetric analysis, Fourier transform infrared spectra, X-ray diffraction, N₂ adsorption/desorption, and transmission electron microscopy. γ-alumina with a bimodal porous structure shows reduced transport resistance compared with γ-alumina with a unimodal porous structure in the dye adsorption test. Although the thickness of γ-alumina thin layer increases when more secondary pores are generated, a γ-alumina membrane with a bimodal pore size distribution shows diminution of transport resistance in the water permeability study also.     

Correlations of electrochemical behavior, microstructure and chemical composition of porous silicon

Porous silicon (PSi) layers were prepared by anodic polarization of heavily doped n-type Si in hydrofluoric acid-ethanol solutions under varying current densities and etching time. PSi nanocrystallites formed were examined under a high-resolution transmission electron microscope and analyzed by the broadening and red shifting of characteristic Si Raman band. The Raman data were used to calculate the average sizes and distortion angles of crystallites. The chemical compositions of PSi were studied by Fourier transform infrared spectroscopy, and the amounts of Si hydrides and oxides present on PSi were semi-quantitatively evaluated through the integrations of the corresponding bands. The polarity of Si-H and Si-O bonds caused apparent lattice distortions. The chemical species formed on the steps and (1 1 1) surface of PSi nanocrystallites were well distinguished in infrared bands. The amount of Si_ySiH_x species per unit PSi thickness was found to decrease linearly with the increasing current density. The observed relationships among the electrochemical behavior, microstructure and composition are discussed, and a simplified nanocrystallite model is suggested.     

多孔硅——聚合物PFTD复合膜的光致发光研究

文章采用直接浸泡法在多孔硅中嵌入了新型共轭有机聚合物聚[4-（N,N-二甲基胺丙氧基）苯-4,4’-二苯胺-9,9-二辛基芴-4,7-二噻吩-2-基-2,1,3-苯并噻二唑]（PFTD）,对比研究了多孔硅,PFTD/多孔硅,PFTD/硅以及PFTD在甲苯溶液中的光致发光特性。实验结果表明：PFTD/多孔硅复合膜光致发光强度要明显强于PFTD/硅,同时由于聚合物在固态时有效共轭程度增加导致PFTD/多孔硅复合膜的荧光光谱相对于甲苯溶液中的红光聚合物光谱有所红移。     

铝高压阳极氧化膜微观形貌影响因素的研究

探讨了混合酸体系中电解质浓度与氧化参数对铝高压阳极氧化膜微观形貌的影响。结果表明,磷酸、草酸和成膜添加剂的浓度对氧化膜的孔径和孔的形貌有显著影响,随着电解质浓度的增加,氧化膜的孔径增大,变化范围为250~500 nm,孔形貌从圆形变为规则六边形结构;较高的峰值电流密度导致氧化膜的外边缘破裂;铝高压阳极氧化膜的纵截面照片表明,混合酸体系中的铝高压阳极氧化膜呈现双层结构;厚的多孔层和薄的致密层,孔道垂直于致密层和铝基底,且互相平行。     

Porous silicon Bloch surface and sub-surface wave structure for simultaneous detection of small and large molecules

A porous silicon (PSi) Bloch surface wave (BSW) and Bloch sub-surface wave (BSSW) composite biosensor is designed and used for the size-selective detection of both small and large molecules. The BSW/BSSW structure consists of a periodic stack of high and low refractive index PSi layers and a reduced optical thickness surface layer that gives rise to a BSW with an evanescent tail that extends above the surface to enable the detection of large surface-bound molecules. Small molecules were detected in the sensor by the BSSW, which is a large electric field intensity spatially localized to a desired region of the Bragg mirror and is generated by the implementation of a step or gradient refractive index profile within the Bragg mirror. The step and gradient BSW/BSSW sensors are designed to maximize both resonance reflectance intensity and sensitivity to large molecules. Size-selective detection of large molecules including latex nanospheres and the M13KO7 bacteriophage as well as small chemical linker molecules is reported.     

基于MOFs材料的酸性气体传感器应用研究进展

采用化学气体传感器对有害酸性气体进行实时有效的监测具有重要意义.目前的传统材料在灵敏度、选择性和稳定性等方面仍存在很大问题.金属有机框架材料(MOFs)是一种具有多孔结构的有机-无机杂化材料,具有孔隙率结构丰富、孔结构可调节和比表面积大等特点,已成为当今新功能材料研究的热点.MOFs材料的优良特性为解决上述问题提供了很...     

Peptide immobilisation on porous silicon surface for metal ions detection

In this work, a Glycyl-Histidyl-Glycyl-Histidine (GlyHisGlyHis) peptide is covalently anchored to the porous silicon PSi surface using a multi-step reaction scheme compatible with the mild conditions required for preserving the probe activity. In a first step, alkene precursors are grafted onto the hydrogenated PSi surface using the hydrosilylation route, allowing for the formation of a carboxyl-terminated monolayer which is activated by reaction with N-hydroxysuccinimide in the presence of a peptide-coupling carbodiimide N-ethyl-N'-(3-dimethylaminopropyl)-carbodiimide and subsequently reacted with the amino linker of the peptide to form a covalent amide bond. Infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy are used to investigate the different steps of functionalization.The property of peptides to form stable complexes with metal ions is exploited to achieve metal-ion recognition by the peptide-modified PSi-based biosensor. An electrochemical study of the GlyHisGlyHis-modified PSi electrode is achieved in the presence of copper ions. The recorded cyclic voltammograms show a quasi-irreversible process corresponding to the Cu(II)/Cu(I) couple. The kinetic factors (the heterogeneous rate constant and the transfer coefficient) and the stability constant of the complex formed on the porous silicon surface are determined. These results demonstrate the potential role of peptides grafted on porous silicon in developing strategies for simple and fast detection of metal ions in solution.     

多孔陶瓷板红外线燃气灶具燃烧能效特性探究

本文从红外线家用燃气灶的自身结构和燃烧原理出发,分析多孔陶瓷板红外线燃气灶节能高效的特性,并对影响红外线燃气灶热效率的各种因素进行探讨,研究不同灶具标准试验方法、不同测试环境条件,以及使用不同锅具等,与红外线灶热效率的关系。     

Porous Silicon-Based DNA Biosensor for Human Papillomavirus Detection: Towards the Design of Fast and Portable Test

Silicon - We have developed porous silicon (PSi) biosensors for detecting high-risk human papilloma virus 16 and 18, (HPV16 and HPV18), frequently associated with the generation of pre-cancerous...     

Localized Photo-Assisted Electro-Deposition of Zinc Selenide into p-Type Porous Silicon

Electroplating of II-VI semiconductors like ZnSe into porous silicon can be an efficient and low cost method to fill the porous volume with a transparent and conductive material. With n-type porous layers, ZnSe impregnation is more effective near the sample surface because of reaction rate limitations due to diffusion in the electrolyte. In this paper, it is shown that the deposition of ZnSe into p-type porous silicon can be localized in the lower part of the porous layer if the reduction reaction rate is monitored by limiting the charge carrier supply. This can be done by controlling the power of the laser beam which photo-generates the carriers at the bottom of the pores. Studying the porous layer chemical composition by Auger electron spectroscopy confirms that the deposit is localized at the pore bottom, whereas the changes in the chemical composition of the porous silicon surface are analyzed by infra-red spectroscopy.