Kinetics and mechanism of oxidation of silicon nitride bonded silicon carbide ceramic

Thermogravimetry (TG) has been used to study the oxidation of a commercial silicon nitride bonded silicon carbide (SNBSC) ceramic. The oxidation was studied in air and carbon dioxide atmospheres between 800 and 1300°C. TG/mass spectrometry (MS) shows that the silicon nitride bonding phase oxidises first. The kinetics follow a multi-stage mechanism with diffusion control. Carbon dioxide was found to be a more powerful oxidant than air at temperatures above 1050°C.     

Chemically assisted ion beam etching of silicon and silicon dioxide using SF6

A chemical flux of sulfur hexafluoride (SF₆) in conjunction with low-energy Ar-ion bombardment has been used for chemically assisted ion beam etching (CAIBE) of silicon and silicon dioxide. The study has shown a large degree of independent control over the selectivity and anisotropy in dry etching. The total etch rate could be controlled by varying either the Ar-ion milling parameters or the chemical flux of SF₆. Etch rate enhancement of 7–8 for silicon and 3–4 for silicon dioxide have been obtained over pure physical etching.     

Quantum confinement effect in electroluminescent porous silicon

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Immobilization of thiabendazole-specific monoclonal antibodies to silicon substrates via aqueous silanization

Monoclonal antibodies specific for thiabendazole were immobilized to silicon, silicon dioxide, stoichiometric silicon nitride, and silicon-rich silicon nitride surfaces. This work provides the foundation for the development of a homogeneous sensor system for rapid detection and quantification of thiabendazole residues in produce and animal tissue. Immobilization was performed via aqueous silanization of the substrate followed sequentially by treatment with glutaraldehyde and contact with antibody solution in the presence of detergent. Surfaces were challenged with thiabendazole-horseradish peroxidase conjugate in an ELISA format to estimate immobilized antibody load. A stable and reproducible surface loading of 2 x 10¹¹ antibodies/cm² was obtained only after surfaces received postimmobilization treatments to remove nonspecifically adsorbed antibody. No difference in surface loading was noted when using 30% hydrogen peroxide rather than nitric acid for silanol activation. Little difference was noted among the antibody loadings achieved on the various silicon substrates. Bound antigen-enzyme conjugate was eluted with 0.1N acetic acid and reproducible surface activity was measured for up to four consecutive antigen challenges. Immobilized antibody surfaces were stabilized with 2% sucrose, dehydrated at 37‡C and stored in vacuum or stored at 4‡C in phosphate buffered saline containing 0.01% sodium azide without significant loss of activity.     

Effect of current density on morphological,structural and optical properties of porous silicon

The morphology of porous silicon (PS) layers produced by electrochemical etching of n-type (100) silicon (Si) at different low current densities was studied using SEM, image J analysis and WSxM software. From FTIR spectroscopy analysis, the Si dangling bonds of the as-prepared PS layer have large amount of Hydrogen to form weak Si–H bonds. From Raman analysis, a full width half maximum (FWHM) of the Raman peak was gradually increased with increased current density, shifted towards lower energies due to reduce of crystallite size, the crystallite size in the PS varied from 63 nm to 20 nm depending on the current density. The optical response of the PS layer has been performed by the absorbance and Photoluminescence was studied experimentally in the visible range. The optical absorption and photo luminescence in PS is due to excitonic recombination between the defect states as well as on the surface of nanocrystals, and this was attributed to the presence of silicon hydride species which are confirmed by FTIR spectra. The red shift was observed in absorbance and Photoluminescence due to decrease in the size of Si crystallites and growth of Si=O bonds. The contact angle varied from 76° to 120.1°. From the wettability studies, the surface nature of the PS was converted from hydrophilic to hydrophobic when the current density increased.     

Surface oxidation of high-surface-area silicon carbide: FT-IR studies

The surface of ultrafine silicon carbide powders, prepared by a laser-driven gas-phase reaction was studied as a self-supporting disk by FT infrared spectrometry. After evacuation silicon and carbon atoms located at the surface give rise tovSiH andvCH bands. When heating in oxygen, subtraction spectra showed features which could be strictly correlated with a progressive growth of a silica layer: SiH and CH bands were replaced by new bands characteristic of amorphous silica and the typical band of surface silanol groups on silica (3745 cm^–1) simultaneously increased.     

Irreversible capacity of the amorphous silicon thin-film electrodes

Irreversible processes accompanying the lithium incorporation into amorphous thin-film silicon are investigated. It is shown that the irreversible processes occurred during the cathodic polarization result in the formation of passive film at the silicon surface. The passive film at silicon is close, in its composition, to the passive film at carbonaceous materials. However, unlike the carbonaceous electrodes, no effect of electrolyte composition on the irreversible capacity of the silicon electrodes is observed.     

Allergen microarrays on high-sensitivity silicon slides

We have recently introduced a silicon substrate for high-sensitivity microarrays, coated with a functional polymer named copoly(DMA-NAS-MAPS). The silicon dioxide thickness has been optimized to produce a fluorescence intensification due to the optical constructive interference between the incident and reflected lights of the fluorescent radiation. The polymeric coating efficiently suppresses aspecific interaction, making the low background a distinctive feature of these slides. Here, we used the new silicon microarray substrate for allergy diagnosis, in the detection of specific IgE in serum samples of subjects with sensitizations to inhalant allergens. We compared the performance of silicon versus glass substrates. Reproducibility data were measured. Moreover, receiver-operating characteristic (ROC) curves were plotted to discriminate between the allergy and no allergy status in 30 well-characterized serum samples. We found that reproducibility of the microarray on glass supports was not different from available data on allergen arrays, whereas the reproducibility on the silicon substrate was consistently better than on glass. Moreover, silicon significantly enhanced the performance of the allergen microarray as compared to glass in accurately identifying allergic patients spanning a wide range of specific IgE titers to the considered allergens.     

Enhancing antireflection property of silicon through direct picosecond laser surface texturing

Crystalline silicon was laser surface textured by picosecond pulsed laser to enhance its antireflection property. The influence of laser scan speed and number of passes in fabricating the uniform surface microtexture were evaluated. Surface texture so generated was investigated and a grid of spherical domes and cavities, with nanoripples in the order of incident laser wavelength spread over it was observed. Reflectivity of bare silicon was greater than 40% and was significantly reduced well below 2% upon laser texturing, over a wavelength range of 400 to 700 nm. Antireflecting surface is an essential requirement for more efficient performance of devices for optical and photovoltaic application.     

Fabrication and chemical surface modification of nanoporous silicon for biosensing applications

In this work, porous silicon (PS) films with varied porosity (68–82%) were formed on the p-type, boron-doped silicon wafer (100) by the electrochemical anodisation in an aqueous hydrofluoric acid and isopropyl alcohol solution at different current densities (I _d) ranging from 20–70 mA cm^?2, respectively. Biofunctionalisation of the PS surface was carried out by chemically modifying the surface of PS by the deposition of 3-aminopropyltriethoxysilane thermally leading to high density of amine groups covering the PS surface. This further promotes the immobilisation of immunoglobulin (human IgG and goat anti-human IgG binding) on to the PS surface. Formation of nanostructured PS and the attachment of antibody–antigen to its surface were characterised using photoluminescence (PL), Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy techniques, respectively. The possibility of using these structures as biosensors has been explored based on the significant changes in the PL spectra before and after exposing the PS optical structures to biomolecules. These experimental results open the possibility of developing optical biosensors based on the variation of the PL position of the PL spectra of PS-based devices.     

Microstructure and surface roughness of graphite‐like carbon films deposited on silicon substrate by molecular dynamic simulation

Molecular dynamics simulations are performed on the atomic origin of the growth process of graphite‐like carbon film on silicon substrate. The microstructure, mass density, and internal stress of as‐deposited films are investigated systematically. A strong energy dependence of microstructure and stress is revealed by varying the impact energy of the incident atoms (in the range 1–120 eV). As the impact energy is increased, the film internal stress converts from tensile stress to compressive stress, which is in agreement with the experimental results, and the bonding of C‐Si in the film is also increased for more substrate atoms are sputtered into the grown film. At the incident energy 40 eV, a densification of the deposited material is observed and the properties such as density, sp³ fraction, and compressive stress all reach their maximums. In addition, the effect of impact energy on the surface roughness is also studied. The surface morphology of the film exhibits different characteristics with different incident energy. When the energy is low (<40 eV), the surface roughness is reduced with the increasing of incident energy, and it reaches the minimum at 50 eV. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and modification of silicon nanosheets and other silicon nanomaterials

Silicon nanomaterials and nanostructures exhibit different properties from those of bulk silicon materials based on quantum confinement effects. They are expected to lead to the development of new applications of silicon, in addition to wide use in semiconductor devices. Aside from industrial interest, intriguing issues of academic interest still remain with respect to the origins of their characteristic properties. Zero- and one-dimensional crystalline silicon nanomaterials have been synthesized, to date, by using many methods and there has been rapid progress in size control and modification procedures. However, there have been only a few examples of silicon nanomaterials with atomic-order thickness akin to carbon nanomaterials, such as two-dimensional silicon nanosheets. Moreover, mass production of silicon nanomaterials with relatively low cost is not easily achievable, due to the typically severe conditions required for fabrication, such as high temperature and ultralow pressure. Recently, we have developed a soft synthetic method for silicon nanosheets with chemical surface modification in a solution process. This review provides methods for the synthesis and modification of silicon nanosheets and other silicon nanomaterials with examples of their potential applications.     

和频光谱研究油酸包覆的Fe3 O4 纳米颗粒

采用红外-可见和频振动光谱研究了表面包覆油酸分子的Fe3O4纳米颗粒, 得到了2种实验构型(构型1: 可见光入射角63°, 红外光入射角55°; 构型2: 可见光入射角45°, 红外光入射角55°)和3种偏振组合(ssp, ppp, sps)下的和频振动光谱, 比较了2种实验构型下和频光谱的特征, 通过偏振分析方法对各个光谱峰进行了归属.     

Dependence of the reactivity of alkyl-doped silicon dioxide layers on the character of Si-O-Si bonding

Using MM2 molcular mechanics simulation and MNDO/PM3 semiempirical methods we show that the most probable mechanism of surface modification of alkyl-doped silicon dioxide layers in plasma is the interaction with CH₃ groups. Detachment of the hydrogen atom causes a change in the character of Si-O-Si bonding, which results in an increase in the number of Si-O-Si groups with an angle in a range of 144° to 146°. Subsequent treatment in ammonia plasma leads to pore sealing through the formation of -CH-Si-O-Si-O-Si-O-Si- chains. The mechanism proposed provides a good explanation to FTIR experimental spectra and to changes in the reactivity of porous layers after treatment in helium plasma.     

Intrinsically stable dispersions of silicon nanoparticles

Stable suspensions of silicon nanoparticles (SiNP) were fabricated by dispersion in 1-butanol as well as ethanol without the application of an additive. In order to achieve an in-depth insight into the stabilizing mechanism, the particle-particle interactions need to be considered. In this respect the total interaction energy of the silicon nanoparticles in 1-butanol and ethanol was calculated for three model systems according to the DLVO theory: (1) two solid silicon spheres, (2) two spheres with a silicon core and an amorphous silicon dioxide shell, and (3) two spheres with a silicon core, an amorphous silicon dioxide shell and a monolayer of adsorbed solvent molecules. The results of the calculations are evaluated and discussed with regard to experimental data obtained by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), high resolution transmission electron microscopy (HRTEM), and zeta potential measurements.     

Asymmetric [Nafion®]/[silicon oxide] hybrid membranes via the in situ sol-gel reaction for tetraethoxysilane

Asymmetric silicon oxide composition profiles along a direction perpendicular to the plane of Nafion® sulfonate films were created via in situ sol-gel reactions for one-sided tetraethoxysilane permeation, as verified by EDAX/ESEM. For K⁺ form membranes, we propose the existence of an IR spectral signature of molecular branches in addition to those characteristic of linear and cyclic fragments in the silicon oxide phase. The molecular structure of the silicon oxide phase is more interconnected than linear in K⁺ form membranes. For H⁺ form membranes, there appears to be an increasing degree of molecular linearity within the silicon oxide phase with increasing uptake. IR spectra indicate that molecular connectivity on the permeated side is lower, on the average, than that on the nonpermeated side. The inverse relationship between gas permeability and upstream pressure in steady-state helium gas transmission experiments suggests the dual-mode sorption of gases, which is in harmony with the multiphasic nature of these membranes. © 1996 John Wiley & Sons, Inc.     

Role of poly(diallyldimethylammonium chloride) in selective polishing of polysilicon over silicon dioxide and silicon nitride films

A cationic polymer, poly(diallyldimethylammonium chloride), or PDADMAC (MW ≈ 200,000), at a concentration of 250 ppm was used to enhance polysilicon removal rates (RRs) to ～600 nm/min while simultaneously suppressing both silicon dioxide and silicon nitride RRs to <1 nm/min, both in the absence or in the presence of ceria or silica abrasives during chemical mechanical polishing (CMP). These results suggest that aqueous abrasive-free solutions of PDADMAC are very attractive candidates for several front-end-of-line (FEOL) CMP processes. Possible mechanisms for the enhancement of poly-Si RR and the suppression of oxide and nitride RRs are proposed on the basis of the RRs, contact angle data on poly-Si films, zeta potentials of polishing pads, polysilicon films, silicon nitride particles, and silica and ceria abrasives, thermogravimetric analysis, and UV-vis spectroscopy data.     

Computer-assisted study of silver absorption by porous silicon dioxide nanoparticles

The absorption of silver atoms by porous silicon dioxide particles is studied by the molecular dynamics method. Upon the absorption of silver atoms, (SiO₂)₅₀ nanoparticles do not increase their volume. A particle is divided into two unequal parts by an island shell formed from SiO₂ structural units, which causes anisotropy in the electrical and thermal conductivity of the nanocomposite. IR absorption and emission spectra, Raman spectra, as well as the number of electrons active with respect to IR radiation are calculated. The calculated absorption spectra show the mode corresponding to the stretching vibrations of Si-O surface groups. The addition of silver atoms to nanoparticles can enhance significantly the power of heat radiation emission.     

Surface plasmon resonance on the LB monolayer of solvent-soluble silicon phthalocyanine

Thin films of bis-(p-chlorophenoxy) (tetra-4-nitrophthalocyaninato)silicon, TNPcSi(OPhCl-p)₂, were prepared by using Langmir-Blodgett techniques and the morphology of the film was investigated by AFM (atomic force microscope) analysis. It has been found that the LB films were successfully transferred onto substrates like mica, gold deposited glass, and pure glass with domains aggregated on the substrates. Surface plasmon resonance has been used to investigate the interaction between sulfur dioxide and a monolayer of TNPcSi(OPhCl-p)₂ LB film. It has been found that the monolayer of LB film transferred onto gold deposited glass gave a 0.55° shift of resonant angle and an additional 0.45° shift of resonant angle after exposion in sulfur dioxide\atomospheric ambient for twenty minute. The UV–visible absorption spectrum of the LB films of TNPcSi(OPhCl-p)₂ showed that there is chemical changes in the film after the exposure to the sulfur dioxide ambient. This work has shown a promising application as an optical gas sensor.     

Vibrational sum-frequency-generation (SFG) spectroscopy study of the structural assembly of cellulose microfibrils in reaction woods

The cellulose microfibril assemblies in secondary cell walls of tension wood and compression wood were studied with vibrational sum frequency generation (SFG) spectroscopy. The tension wood contains the gelatinous layer with highly-crystalline and highly-aligned cellulose microfibrils. The SFG spectral features of tension wood changed depending on the azimuth angle between the polarization of the incident IR beam and the preferential alignment axis of the cellulose microfibrils. The SFG spectra of the compression wood did not show any dependence on the azimuth angle, implying that the overall orientation of cellulose microfibrils in compression wood is not highly aligned. Instead, the decrease of cellulose content in compression wood brought about larger separation between cellulose microfibrils, which was manifested as changes in CH₂/OH intensity ratio in SFG spectra. These results implied that SFG spectral features are sensitive to cellulose microfibril alignments and inter-fibrillar separations.