Microdetermination of silicon dioxide on the surface by sensors based on perfluorinated proton-conducting membranes

A microdetermination method of silicon dioxide on the silicon surface is studied. In this method, a thin SiO₂ layer is dissolved in an aqueous solution of hydrofluoric acid and then the resulting solution is analyzed with sensors based on perfluorinated proton-conducting membranes. Quantitative determination of silicon dioxide remaining on the silicon surface in a quantity as low as 1 × 10^?6 mol is demonstrated to be feasible.     

Formation of titanium oxide films on the surface of porous silicon carbide

The influence of rapid thermal annealing (RTA) on the properties of a titanium film on the surface of porous silicon carbide is considered. It is shown that an increase in the RTA temperature to 900°C stabilizes the phase composition of the forming titanium oxide over the film, which is identified as rutile. Due to the formation of titanium oxide nanoclusters under the action of RTA, an additional photoluminescence band arises near 2.5 eV. Based on Auger spectrometry data, a multilayer model to calculate the optical parameters of titanium oxide films covering porous silicon carbide is suggested.     

Hypersonic surface waves in 2D titanium nanostructure on silicon

The non‐destructive method of Brillouin spectroscopy was applied to investigate the vibrations of 2D titanium nanoislands. Simulations realized by the Finite Element Method permitted determination of the dispersion relations of the surface waves propagating in the island structure and silicon substrate as well as the width of the frequency gap for the system studied. 3D maps of unit cell deformation for the structure with nanoislands for individual modes were obtained. The Brillouin experiment is shown as an excellent tool for direct experimental determination of the presence of eigenvibrations and the frequency gap in phononic structures in the GHz range.

     

Shadow-casted ultrathin surface coatings of titanium and titanium/silicon oxide sol particles via ultrasound-assisted deposition

Ultrasound-assisted deposition (USAD) of sol nanoparticles enables the formation of uniform and inherently stable thin films. However, the technique still suffers in coating hard substrates and the use of fast-reacting sol–gel precursors still remains challenging. Here, we report on the deposition of ultrathin titanium and titanium/silicon hybrid oxide coatings using hydroxylated silicon wafers as a model hard substrate. We use acetic acid as the catalyst which also suppresses the reactivity of titanium tetraisopropoxide while increasing the reactivity of tetraethyl orthosilicate through chemical modifications. Taking the advantage of this peculiar behavior, we successfully prepared titanium and titanium/silicon hybrid oxide coatings by USAD. Varying the amount of acetic acid in the reaction media, we managed to modulate thickness and surface roughness of the coatings in nanoscale. Field-emission scanning electron microscopy and atomic force microscopy studies showed the formation of conformal coatings having nanoroughness. Quantitative chemical state maps obtained by x-ray photoelectron spectroscopy (XPS) suggested the formation of ultrathin (<10 nm) coatings and thickness measurements by rotating analyzer ellipsometry supported this observation. For the first time, XPS chemical maps revealed the transport effect of ultrasonic waves since coatings were directly cast on rectangular substrates as circular shadows of the horn with clear thickness gradient from the center to the edges. In addition to the progress made in coating hard substrates, employing fast-reacting precursors and achieving hybrid coatings; this report provides the first visual evidence on previously suggested “acceleration and smashing” mechanism as the main driving force of USAD.     

Enhancement of deposition rate of titanium silicon oxide films on silicon using hexafluorotitanic acid by nitric acid

The deposition of titanium silicon oxide films on silicon using hexafluorotitanic acid and boric acid as sources is much enhanced by nitric acid incorporation. The deposition delay time is almost zero. The structure of the films is titanium silicon oxide examined by Fourier transform infrared spectrometer. By current-voltage measurement, the leakage current of the as-deposited film with a thickness of 458 Å is about 7.78×10^-6 Å/cm² at the electrical field of 1 MV/cm. By capacitance-voltage measurement, the effective oxide charge of the as-deposited film is 6.31×10¹⁰ cm^-2. The static dielectric constant and refractive index are about 13 and 1.98, respectively. Compared with that without nitric acid incorporation, the lower effective oxide charge is from a sharp interface due to in-situ etching of nitric acid. The higher leakage current is from the higher deposition rate and the higher dielectric constant is from higher titanium content. PACS 77.84.-s     

Application of crystalline silicon surface oxidation to silicon heterojunction solar cells

We study the effect of ultra-thin oxide (SiO_x) layers inserted at the interfaces of silicon heterojunction (SHJ) solar cells on their open-circuit voltage (V_OC). The SiO_x layers can be easily formed by dipping c-Si into oxidant such as hydrogen peroxide (H₂O₂) and nitric acid (HNO₃). We confirm the prevention of the undesirable epitaxial growth of Si layers during the deposition of a-Si films by the insertion of the ultra-thin SiO_x layers. The formation of the SiO_x layers by H₂O₂ leads to better effective minority carrier lifetime (τ_eff) and V_OC than the case of using HNO₃. c-Si with the ultra-thin SiO_x layers formed by H₂O₂ dipping, prior to deposition of a-Si passivation layers, can have high implied V_OC of up to ∼0.714 V.     

Technology of polishing of titanium surface using the fiber-laser radiation

The effect of the radiation of the pulsed fiber laser on the surfaces of cylindrical samples made of the VT16 titanium alloy is studied. It is demonstrated that the irradiation at appropriate parameters of the laser radiation in the inert-gas (argon) atmosphere leads to an increase in the microhardness of the surface layer and a decrease in the surface roughness of the irradiated samples by a factor of five in comparison with the roughness of the original samples.     

In vitro investigation of anodization and CaP deposited titanium surface using MG63 osteoblast-like cells

The aim of the present study was to investigate surface characteristics in four different titanium surfaces (AN: anodized at 270 V; AN-CaP: anodic oxidation and CaP deposited; SLA: sandblasted and acid etched; MA: machined) and to evaluate biological behaviors such as cell adhesion, cell proliferation, cytoskeletal organization, and osteogenic protein expression of MG63 osteoblast-like cells at the early stage. Surface analysis was performed using scanning electron microscopy, thin-film X-ray diffractometry, and a confocal laser scanning microscope. In order to evaluate cellular responses, MG63 osteoblast-like cells were used. The cell viability was evaluated by MTT assay. Immunofluorescent analyses of actin, type I collagen, osteonectin and osteocalcin were performed. The anodized and CaP deposited specimen showed homogeneously distributed CaP particles around micropores and exhibited anatase type oxides, titanium, and HA crystalline structures. This experiment suggests that CaP particles on the anodic oxidation surface affect cellular attachment and spreading. When designing an in vitro biological study for CaP coated titanium, it must be taken into account that preincubation in medium prior to cell seeding and the cell culture medium may affect the CaP coatings. All these observations illustrate the importance of the experimental conditions and the physicochemical parameters of the CaP coating.It is considered that further evaluations such as long-term in vitro cellular assays and in vivo experiments should be necessary to figure out the effect of CaP deposition to biological responses.     

Electroless deposition of platinum on proton-conductive perfluorinated membranes modified with ethylene diamine

Perfluorinated, non-hydrolysed, carbon-chain flat-sheet membranes were treated with ethylene diamine (EDA) to investigate the influence of EDA-treatment on the process of the Pt deposition on these membranes. The electrical resistances of the modified membranes were also measured, to determine the degree of modification of the membranes. Pt-containing membranes were characterised using SEM to compare the profile of the Pt deposition on Pt-containing membranes that were not modified. Dielectric analysis (DEA) was used to investigate the dipole and ion mobility of hydrolysed EDA-modified membranes. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998     

Anchoring of alkyl chain molecules on oxide surface using silicon alkoxide

Chemical states of the interfaces between octadecyl-triethoxy-silane (ODTS) molecules and sapphire surface were measured by X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) using synchrotron soft X-rays. The nearly self-assembled monolayer of ODTS was formed on the sapphire surface. For XPS and NEXAFS measurements, it was elucidated that the chemical bond between silicon alkoxide in ODTS and the surface was formed, and the alkane chain of ODTS locates upper side on the surface. As a result, it was elucidated that the silicon alkoxide is a good anchor for the immobilization of organic molecules on oxides.     

响应面方法的硅刻蚀工艺优化分析（英）

利用响应面分析方法优化了用于压力传感器硅敏感芯体的刻蚀操作条件。主要考虑了温度、KOH浓度和腐蚀时间三个操作参数,将它们的范围分别设定为40~60 ℃,0.4~0.48 mol/L 和 5~12.5 h,并设定各向异性腐蚀速率为响应值。通过建立二次方模型,分析这些参数的单独影响以及多个操作条件之间对腐蚀速率的相互交叠作用。分析结果表明:模型可以精确预测99%的响应值,相比于腐蚀时间,溶液浓度和工作温度对刻蚀速率的影响更为明显。     

响应面方法的硅刻蚀工艺优化分析（英）

利用响应面分析方法优化了用于压力传感器硅敏感芯体的刻蚀操作条件。主要考虑了温度、KOH浓度和腐蚀时间三个操作参数,将它们的范围分别设定为40~60 ℃,0.4~0.48 mol/L 和 5~12.5 h,并设定各向异性腐蚀速率为响应值。通过建立二次方模型,分析这些参数的单独影响以及多个操作条件之间对腐蚀速率的相互交叠作用。分析结果表明：模型可以精确预测99%的响应值,相比于腐蚀时间,溶液浓度和工作温度对刻蚀速率的影响更为明显。     

Fabrication of nanostructured silicon surface using selective chemical etching

A two-stage process based on selective chemical etching induced by metal nanoclusters is used to fabricate nanostructured surfaces of silicon plates with a relatively low reflectance. At silicon surfaces covered with silver nanoclusters, the SERS effect is observed for rhodamine concentrations of about 10^–12 M. At certain technological parameters, the depth of the nanostructured layer weakly depends on the conditions for the two-stage etching, in particular, etching time. Under otherwise equal conditions for etching, the rate of the formation of textured layer in the p-type silicon is two times greater than the formation rate in the n-type silicon.     

Electro-spark alloying using graphite electrode on titanium alloy surface for biomedical applications

In order to improve the biomedical properties of a titanium alloy surface, electro-spark surface alloying was carried out using a graphite electrode in air, in a nitrogen gas atmosphere and in silicone oil. The morphology and microstructure of the strengthened layers were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The hardness distributions as a function of depth were measured by a micro-hardness tester. Corrosion resistance capacities of the modified layers were evaluated using potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). In addition, wear resistance and corrosive wear properties in a simulated body fluid (SBF) were studied with a pin-on-disk tribometer. Alloyed layers, completely covering the substrate surface and about 40 μm thick mainly composed of the TiC phase and with strong metallurgical bonding and adhesion to the substrate, were obtained. This can markedly improve hardness and wear resistance of the surface layer of the substrate. In comparison to coatings prepared in air and nitrogen gas atmospheres, the coating produced in silicone oil media exhibits a denser and more perfect surface structure. The wear resistance in air and corrosive wear resistance in SBF solution is the best for the coating produced in silicone oil. For instance, the wear rate in air with a GCr15 steel ball counterpart is reduced by a factor of 29 compared with the original titanium alloy and the corrosive wear rate in SBF solution with a corundum ball can decrease by a factor of 13.8. Simultaneously, the effect of electron-spark surface alloying of the titanium alloy surface on biocompatibility and biological activity was also investigated. The electron-spark surface strengthened layer treated in silicone oil shows good biocompatibility and biological activity, and can help cell attachment to the substrate surface.     

Low-temperature operation of H2/O2 fuel cells using proton-conducting glasses containing heteropolyacid

Proton-conducting glasses doped with heteropolyacid were synthesized, and their structural characterization has been investigated. The structural analysis shows that proton-conducting glasses have been thermally, chemically, and mechanically stable. The average pore size (∼2–3 nm) and specific surface areas were investigated by the BET method. The phosphotungstic acid based on glasses as electrolyte showed better electrochemical behavior at low temperature. The maximum power density value of 15.5 mW/cm² was achieved with H₂ fed in anode and O₂ fed in cathode sides. Fuel-cell performance at 30 °C under humidified condition is expressed as both maximum power density and current density by electrochemical behavior.     

Laser damage of silicon solar cells with different surface states

An experimental study of the damage of Si solar cells due to Q-switched ruby laser radiation has been made. Four kinds of specimen with different surface states were used in order to examine how the damage depends on the surface state: (a) chemically etched to a mirror finish, (b) mechanically polished by a 0.5 m Al₂O₃ powder, (c) chemically etched, but rough, (d) coated with SiO on the (c) surface. The threshold power densities, at which a change in the photo-current occurs, were for the specimens (a) to (d) respectively 60 MW cm^–2, 20 MW cm^–2, 30 MW cm^–2 and 9 MW cm^–2. Attenuations of the photo-current of the specimens, a, c and d were observed over the whole range of wavelength 500 to 1000 nm. For the b cell, however, increase of the photo-current was observed mainly in the short wavelength region.     

Metallization of DNA on silicon surface

New simple way for silver deoxyribonucleic acid (DNA)-based nanowires preparation on silicon surface was developed. The electrochemical reduction of silver ions fixed on DNA molecule provides the forming of tightly matched zonate silver clusters. Highly homogeneous metallic clusters have a size about 30 nm. So the thickness of nanowires does not exceed 30–50 nm. The surface of n-type silicon monocrystal is the most convenient substrate for this procedure. The comparative analysis of DNA metallization on of n-type silicon with a similar way for nanowires fabrication on p-type silicon, freshly cleaved mica, and glass surface shows the advantage of n-type silicon, which is not only the substrate for DNA fixation but also the source of electrons for silver reduction. Images of bound DNA molecules and fabricated nanowires have been obtained using an atomic force microscope and a scanning ion helium microscope. DNA interaction with silver ions in a solution was examined by the methods of ultraviolet spectroscopy and circular dichroism.     

Effects of controlled surface treatment on titanium dioxide electrode nanostructure for dye-sensitized solar cells

A stable surface treatment for the nanoporous TiO₂ electrode of dye-sensitized solar cells (DSCs) has been developed via sol-gel processing of titanium(IV) isopropoxide (TiP), enabling controllable performance improvements, which has been hitherto unachievable. A systematic study of the electrode chemistry and morphology was performed to examine the mechanisms by which the treatment contributes to enhancement in DSC performance. The electrode exhibited a linear increase in mass with TiP concentration and a corresponding reduction in porosity. The increase in nanoparticle diameter resulted in the increase in surface area without altering the surface chemistry, leading to an increase in dye loading. Current–voltage characteristics and incident photon-to-electron conversion efficiencies (IPCE) were analyzed. A linear increase in the short-circuit photocurrent was measured with TiP concentration, increasing by 30 % for a 4 mM TiP treatment, which resulted in a corresponding efficiency gain of 23 %. This was found to primarily result from a controllable increase in the charge collection efficiency, via a 30 % faster electron transport time and a 19 % increase in the electron lifetime. The results elucidate the underlying physical mechanisms for improvement in DSC performance by surface treatment.     

Bioactive modification of silicon surface using self-assembled hydrophobins from Pleurotus ostreatus

A crystalline silicon surface can be made biocompatible and chemically stable by a self-assembled biofilm of proteins, the hydrophobins (HFBs) purified from the fungus Pleurotus ostreatus. The protein-modified silicon surface shows an improvement in wettability and is suitable for immobilization of other proteins. Two different proteins were successfully immobilized on the HFBs-coated chips: the bovine serum albumin and an enzyme, a laccase, which retains its catalytic activity even when bound on the chip. Variable-angle spectroscopic ellipsometry (VASE), water contact angle (WCA), and fluorescence measurements demonstrated that the proposed approach in silicon surface bioactivation is a feasible strategy for the fabrication of a new class of hybrid devices.     

XPS surface analysis of monocrystalline silicon solar cells for manufacturing control

X-ray photoelectron spectroscopy (XPS) has been applied to surfaces of silicon wafers in the different stages of the assembly line for large-scale monocrystalline silicon solar cell manufacturing (ISOFOTON, Malaga, Spain). XPS results have shown that a considerable amount of carbon is present on the pyramidal-textured monocrystalline silicon surface. This amount decreases slightly but is still present after the process of phosphor diffusion (p-n junction), as well as after subsequent calcination in humid air for SiO₂ film formation (passivation). This amount of carbon may be buried during the process of CVD coating an anti-reflection TiO₂ film. After calcination of the film in order to obtain the TiO₂ rutile phase, an even higher amount of carbon is detected on the TiO₂ anti-reflection coating surface. This indicates that not all organics from the tetra-isopropile ortho-titanate (TPT) precursor were released from the film. Furthermore, in this case phosphor is found in excess on the SiO₂ wafer surface (dead layer) and also on the rutile TiO₂ surface, indicating that an extra phosphor diffusion from the bulk silicon through the TiO₂ film has taken place during calcination. These results demonstrate how thermal treatments applied in the solar cell manufacturing assembly line can influence and may change the intended compositional distribution. These treatments may also introduce defects that act as recombination centres for charge carriers in the solar cell device. Received: 13 September 2000 / Accepted: 10 January 2001 / Published online: 3 May 2001