Environmental photostability of SF(6)-etched silicon nanocrystals

We report on the long-term environmental stability of the photoluminescent (PL) properties of silicon nanocrystals (SiNCs). We prepared sulfur hexafluoride (SF(6)) etched SiNCs in a two-stage plasma reactor and investigated their PL stability against UV irradiation in air. Unlike SiNCs with hydrogen-passivated surfaces, the SF(6)-etched SiNCs exhibit no photobleaching upon extended UV irradiation despite surface oxidation. Furthermore, the PL quantum yield also remains stable upon heating the SF(6)-etched SiNCs up to 160?°C. The observed thermal and UV stability of SF(6)-etched SiNCs combined with their PL quantum yields of up to ～50% make them attractive candidates for UV downshifting to enhance the efficiency of solar cells. Electron paramagnetic spin resonance indicates that the SF(6)-etched SiNCs have a lowered density of defect states, both as-formed and after room temperature oxidation in air.     

Osteoblast-like cell response to calcium phosphate coating chemistry and morphology on etched silicon surfaces

Being able to control the behaviour of osteoblast-like cells on a surface may provide a genuine insight into the material surface characteristics and help in creating a successful coating/cell interface. The possibility of creating a micro-environment that can induce proliferation, differentiation and mineralisation of bone cells in vitro, by successfully combining both chemistry and topography of a micro-fabricated substrate is an area that requires a multi-disciplinary approach. Utilising sputter deposition, a process that lends itself to high processability, in conjunction with photolithography allowing for the creation of highly repeatable etched surfaces, we aim to provide a successful combination of chemistry and topography. Correlating the substrate conditions with resultant osteoblast biological function and activity can ultimately be used with a view to modulating the behavior of osteoblast-like cells in vitro.     

Improved thrombogenicity on oxygen etched Ti6Al4V surfaces

Thrombus formation on blood contacting biomaterials continues to be a key factor in initiating a critical mode of failure in implantable devices, requiring immediate attention. In the interest of evaluating a solution for one of the most widely used biomaterials, titanium and its alloys, this study focuses on the use of a novel surface oxidation treatment to improve the blood compatibility. This study examines the possibility of using oblique angle ion etching to produce a high quality oxide layer that enhances blood compatibility on medical grade titanium alloy Ti6Al4V. An X-ray photoelectron spectroscopy (XPS) analysis of these oxygen-rich surfaces confirmed the presence of TiO₂ peaks and also indicated increased surface oxidation as well as a reduction in surface defects. After 2 h of contact with whole human plasma, the oxygen etched substrates demonstrated a reduction in both platelet adhesion and activation as compared to bare titanium substrates. The whole blood clotting behavior was evaluated for up to 45 min, showing a significant decrease in clot formation on oxygen etched substrates. Finally, a bicinchoninic acid (BCA) total protein assay and XPS were used to evaluate the degree of key blood serum protein (fibrinogen, albumin, immunoglobulin G) adsorption on the substrates. The results showed similar protein levels for both the oxygen etched and control substrates. These results indicate that oblique angle oxygen etching may be a promising method to increase the thrombogenicity of Ti6Al4V.     

Formation of carbon subnanosize masking coatings on silicon (100) in low-pressure microwave plasma

Self-organization of nanosize domains in deposition of submonolayer carbon coatings on silicon (100) in a low-pressure microwave plasma has been revealed by scanning atomic-force and electron microscopy. It is shown that the nanosize carbon-containing domains can be used as masking coatings to obtain 3D low-dimensional systems on single-crystal silicon (100) by highly anisotropic plasma-chemical etching.     

{7 6 6} Oriented V-groove surfaces on Br2–CH3OH etched (1 0 0) GaAs wafers

Etched V-grooves on (1 0 0) gallium arsenide crystal surfaces produced using various compositions of bromine-in-methanol etchant are bounded by sidewall surfaces, presumably of Ga atoms, aligned along the original {7 6 6} position of the bulk crystal as determined by optical and electron microscope observations. The measurements are tentatively explained by rotational surface reconstruction of Ga-deficient, rehybridized {1 1 1} planes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation of surface roughness on etched glass surfaces

Roughening the surface of solar cells is a common practice within the photovoltaic industry as it reduces reflectance, and thus enhances the performance of devices. In this work the relationship between reflectance characterized by the haze parameter, surface roughness and optical properties was investigated. To achieve this goal, model samples were prepared by hydrofluoric acid etching of glass for various times and measured by optical microscopy, spectroscopic ellipsometry, scanning electron microscopy, and atomic force microscopy. Our investigation showed that the surface reflectance was decreased not only by the roughening of the surface but also by the modification of the depth profile and lowering of the refractive index of the surface domain of the samples.     

Formation of the geometrically controlled carbon coils by manipulating the additive gas (SF6) flow rate

Carbon coils could be synthesized using C2H2/H2 as source gases and SF6 as an incorporated additive gas under the thermal chemical vapor deposition system. The nickel catalyst layer deposition and then hydrogen plasma pretreatment were performed prior to the carbon coils deposition reaction. The flow rate and the injection time of SF6 varied according to the different reaction processes. Geometries of carbon coils developed from embryos to nanosized coils with increasing SF, flow rate from 5 to 35 sccm under the short SF6 flow injection time (5 minutes) condition. The gradual development of carbon coils geometries from nanosized to microsized types could be observed with increasing SF6 flow rate under the full time (90 minutes) SF6 flow injection condition. The flow rate of SF6 for the coil-type geometry formation should be more than or at least equal to the flow rate of carbon source gas (C2H2). A longer injection time of SF6 flow would increase the size of coils diameters from nanometer to micrometer.     

六氟化硫（SF6）气体的快速定量分析方法

本方法通过配置有气体定量环、5分子筛填充柱及电子捕获检测器(ECD)的气相色谱仪,实现了对SF6的定量分析。为节省单个样品的分析时间,方法优化了载气流速、色谱柱温度、进样和反吹时间等实验参数,实现了SF6的快速测量。为保证方法的可靠性,实验考察了分析方法的检测限、准确度及精密度。以上测量结果表明,此定量分析方法快速、简单及可靠。     

Si(111)衬底上生长GaN晶绳的研究

利用热壁化学气相沉积在Si(111)衬底上获得GaN品绳，采用傅里叶红外吸收谱(FTIR)、扫描电子显微镜(SEM)、选区电子衍射(SAED)、X射线衍射(XRD)和光致发光谱(PL)对晶绳进行组成、结构、形貌和光学特性分析。初步结果证明：在Si(111)衬底上获得择优生长的六方纤锌矿结构的GaN晶绳。SEM显示在均匀的薄膜上出现φ6μm的晶绳，FTIR显示GaN薄膜的主要成分为GaN同时含有少量的C污染，由XRD和SAED的综合分析得出晶绳呈六方纤锌矿单晶结构，PL测试表明晶绳呈现不同于GaN薄膜的发光特性。     

Effect of porous silicon stain etched on large area alkaline textured crystalline silicon solar cells

This work shows the effects of porous silicon stain etched on alkaline textured antireflection coatings of large area monocrystalline silicon solar cells. The texturization process has been produced by immersion of the silicon wafers in different carbonate-based solutions. The porous silicon layers were formed by stain etching in a HNO₃/HF aqueous solution before or after the texturization process. We study the effects of different alkaline and acidic solutions and the etching times on the solar cell parameters and the surface reflectance of the device. We have found that the average reflectance of the surface is lowered when the porous etching is combined with the texturization in the alkaline solution. However, the solar cell characteristics are not improved.     

Effect of a new low pressure SF6 plasma sterilization system on polymeric devices

A low pressure RF remote plasma, with low temperature, was used as new sterilization system. This system was designed especially for thermo-sensitive materials. SF₆ plasma has been found to totally inactivate all investigated microorganisms within three minutes. The effect of the SF₆ plasma treatment (soft conditions) and following the aging on three polymers films has been investigated.The evolution of surface after plasma treatment was studied by several techniques. FTIR was used to follow the degradations and changes in the bulk polymers. The SEM images showed the etching and grafting on the polymers surfaces. The decreasing of the wettability in the treated surfaces indicates an increasing in surface hydrophobicity. The decreasing of C and O atoms on the surface and the developing of non-polar sites (F functionalities) were observed by XPS analysis. The surface modifications were found to be permanent.     

Attachment of functionalized single-walled carbon nanotubes (SWNTs) to silicon surfaces

Single-walled carbon nanotubes (SWNTs) were functionalized by direct fluorination and subsequent reaction with 6-aminohexanoic acid for water-soluble carboxylic acid functionalized SWNTs (AHA-SWNTs). Both of the compounds were used as precursors to attach SWNTs to APTES coated silicon surfaces. AHA-SWNTs in aqueous solution were reacted with APTES self-assembled monolayers (SAMs) with coupling reagents N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS). The surface coverage is a function of concentration of AHA-SWNTs, solvent and coupling method. While for the fluorinated SWNTs (F-SWNTs), direct addition of F-SWNTs to preformed APTES SAMs at 90 degrees C shows essentially no reaction, in contrast to the one-pot reaction of F-SWNTs with APTES molecules in the presence of SWNTs on a silicon substrate. This reaction route provides a convenient method to attach SWNTs to silicon surfaces.     

Formation of (001)-textured grain in (111) polycrystalline silicon film

We report the formation of (001)-textured gains in (111) polycrystalline silicon (poly-Si) by Ni-mediated crystallization of amorphous silicon (a-Si) using a cap layer (MICC). The a-Si precursor deposited by plasma enhanced chemical vapor deposition was dehydrogenated at 550 °C and then crystallized at 580 °C. The (001)-textured grains appear in the network of (111) poly-Si of ∼ 100 μm grains, which was confirmed by the analysis of electron back-scattered diffraction. From the kinetic study of the grain growth, it is found that the nucleation rate of (001) nuclei is higher than that of (111) ones, but the (111) grains grow faster than that of (001) grains.     

Electrical and optical characterization of regrown PHEMT layer structures on etched GaAs surfaces

Selective regrowth, which involves the growth of a device structure, patterning, etching and epitaxial regrowth of another device structure is an important technique for monolithic integration. The nature of the surface before the regrowth is crucial for realizing good quality regrown devices. In this study, the effect of different GaAs surface preparation processes on the electrical and optical characteristics of a regrown pseudomorphic high electron mobility transistor (PHEMT) is studied. Using photoluminescence, Hall, atomic force microscopy and d.c. and microwave measurements on devices, an optimized process sequence has been identified to fabricate PHEMT structures with equivalent characteristics of those grown on epiready wafers.     

Effect of etchant concentration and defects on pyramid formation in TMAH etched silicon

An investigation on the effect of TMAH concentration on the etch rate of silicon, and the influence of etchant concentration, ambient temperature and wafer thermal history on the formation of pyramids at the surface of TMAH etched silicon has been carried out. From the results obtained from this study, we are able to explain the influence of TMAH concentration and ambient temperature on the silicon etch rate and the changes occurring at the silicon surface satisfactorily using the pH theory. However, the results from wafers with different thermal history seem to favour the defects theory. We suggest that in order to explain the etching mechanism of TMAH of silicon satisfactorily, a combination of pH and defects theories is necessary.     

Investigation and interpretation of adsorption on silicon surfaces

A review is given of some experimental investigations of hydrogen adsorption on silicon surfaces by thermodesorption and reflection electron energy loss spectroscopy. The interpretation of REEL adsorbate spectra by application of the dielectric model and the density of states model is discussed. The latter serves for simulation of the adsorbate loss spectra by local densities of states for hydrogen adsorbed on silicon. Further the utility of the LDOS concept to explain the hydrogen spectra is demonstrated.     

Formation of silicon dioxide layers at low temperatures (150-400 °C) by atmospheric pressure plasma oxidation of silicon

The formation of silicon dioxide (SiO₂) layers at low temperatures (150-400 °C) by atmospheric pressure plasma oxidation of Si(0 0 1) wafers have been studied using a gas mixture containing He and O₂. A 150 MHz very high frequency (VHF) power supply was used to generate high-density atomic oxygen in the atmospheric pressure plasma. Oxidation rate, structure, and thickness and refractive index profiles of the oxidized layers were investigated by ellipsometry and infrared absorption spectroscopy. Atomic force microscopy was also employed to observe atomic-scale morphologies of the layer surface and wafer Si surface, after chemical removal of the oxidized layers. It was found that stoichiometric SiO₂ layers were obtained at higher oxidation rates than conventional dry O₂ thermal oxidation and radical oxidation processes, even at a very low substrate temperature of 150 °C. Although thickness variations were observed in the plasma region, the refractive index was independent of both substrate temperature and VHF power. In addition, the SiO₂ surface and SiO₂/Si interface roughnesses were comparable to those obtained in conventional dry oxidation at high temperatures.