XRD-Studies of SiC/Si layers on carbon substrates

Structural investigations of thin films of SiC, SiC with free silicon and various titanium suicides (TiSi₂, TiSi and Ti₅Si₃) are described. The crystal phases have been identified using X-ray diffractometry. The growth of reaction products from surface reactions between silicon and deposited titanium can be observed.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Carbon-containing nano-titania prepared by chemical vapor deposition and its visible-light-responsive photocatalytic activity

Ultraviolet and visible-light-responsive titania was synthesized and employed in the NO_x photomineralization. A thermal decomposition reaction of titanium isopropoxide was carried out with a metal-organic chemical vapor deposition (MOCVD), enabling continuous production of TiO₂ nanoparticles. Carbon-containing titanium dioxide with the anatase phase prepared at 500 °C under nitrogen atmosphere exhibited high photocatalytic activity for NO oxidation under visible-light illumination. Experimental results indicate that up to 48% removal of NO_x can be achieved in a continuous flow type of reaction system under visible-light illumination (green LED). The chamber temperature in this MOCVD process plays an important role in lattice structure formation, and also affected TiO₂ carbon content. The carbonaceous species on the TiO₂ surface, shown by X-ray diffractometry (XRD), and Raman, UV–vis, and X-ray photoelectron spectroscopies (XPS), is important to the visible-light absorption and visible-light-catalytic mineralization of NO_x.     

Thermal transformations of titanium slag of high titania content

Titanium raw materials play important role as a source of titanium and titanium dioxide. The investigation of the rate of oxidation and phase transformation of titanium slag in static air atmosphere by use of thermogravimetry (TG) and X-ray diffractometry (XRD) were presented. The investigation were carried out for three different particle size fractions to determine influence of this parameter on rate of reaction. To estimate kinetic parameters was used the kinetic model of contracting volume. The value of kinetic parameters show that influence of heating rate and particle size on rate of reaction is not so large. The thermogravimetric investigations of the oxidation of titanium slag in air atmosphere shown that reaction proceeds in two stages. The XRD investigation shown that titanium slag has the pseudobrookite structure and its diffraction pattern is very close to the diffractogram of magnesium titanate MgTi₂O₅ and iron magnesium titanium oxide (Fe-Mg-Ti-O). At elevated temperature the structure of slag transforms to the ferric pseudobrookite structure and excess titanium dioxide forms the rutile phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

XPS study on the use of 3-aminopropyltriethoxysilane to bond chitosan to a titanium surface

Chitosan, a biopolymer found in the exoskeletons of shellfish, has been shown to be antibacterial, biodegradable, osteoconductive, and has the ability to promote organized bone formation. These properties make chitosan an ideal material for use as a bioactive coating on medical implant materials. In this study, coatings made from 86.4% de-acetylated chitosan were bound to implant-quality titanium. The chitosan films were bound through a three-step process that involved the deposition of 3-aminopropyltriethoxysilane (APTES) in toluene, followed by a reaction between the amine end of APTES with gluteraldehyde, and finally, a reaction between the aldehyde end of gluteraldehyde and chitosan. Two different metal treatments were examined to determine if major differences in the ability to bind chitosan could be seen. X-ray photoelectron spectroscopy (XPS) was used to examine the surface of the titanium metal and to study the individual reaction steps. The changes to the titanium surface were consistent with the anticipated reaction steps, with significant changes in the amounts of nitrogen, silicon, and titanium that were present. It was demonstrated that more APTES was bound to the piranha-treated titanium surface as compared to the passivated titanium surface, based on the amounts of titanium, carbon, nitrogen, and silicon that were present. The metal treatments did not affect the chemistry of the chitosan films. Using toluene to bond APTES on titanium surfaces, rather than aqueous solutions, prevented the formation of unwanted polysiloxanes and increased the amount of silane on the surface for forming bonds to the chitosan films. Qualitatively, the films were more strongly attached to the titanium surfaces after using toluene, which could withstand the ultrahigh vacuum environment of XPS, as compared to the aqueous solutions, which were removed from the titanium surface when exposed to the ultrahigh vacuum environment of XPS.     

Atomic layer deposition of the titanium dioxide thin film from tetraethoxytitanium and water

Using the methods of Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction in the geometry of the grazing beam, and Fourier transform infrared spectroscopy, we studied the chemical composition and structure of thin films of titanium dioxide formed by atomic layer deposition from tetraethoxytitanium and water. It is shown that the films obtained are characterized by a high stoichiometry of composition and by amorphous or polycrystalline structure of the anatase modification, depending on the number of reaction cycles. Using a model of the process of atomic layer deposition that takes into account the size and number of ligands of the reacting molecules, we calculated the amount of titanium dioxide deposited in a single reaction cycle.     

Analysis of crystalline phases in airborne particulates by grazing incidence X-ray diffractometry

Amounts of crystalline phases of airborne particulates collected on a silicon wafer (10 x 10 mm) using a high-volume air sampler were analyzed by grazing incidence X-ray diffractometry (GIXD). Airborne particulates were classified into five size ranges (1.09-10.5 microm) with a cascade impactor attached on the sampling ports of the high-volume air sampler. GIXD was used throughout this analysis to obtain better sensitivity for small amounts of airborne particulates on the silicon wafer. Calibration standards on the silicon wafer for the diffractometric determination were prepared by the suspension droplet method of the crystalline standards dispersed in cyclohexane. Analytical lines were (020) for gypsum, (101) for quartz, (104) for calcite, (200) for halite, and (110) for sal ammoniac. The sample and the calibrating standards were heated at 350 degrees C for 2 h to avoid mutual interference with gypsum (041 and 221) when calcite and halite were determined. The GIXD method enables us to determine 0.23-13.2 microg of gypsum, quartz, calcite, halite and sal ammoniac in 0.110-0.233 mg of airborne particulates on the silicon wafer.     

Multi-electron transfer in composite phthalocyanine thin films: structure and electrochromic properties

Both sequentially deposited double-layered and codeposited composite thin films were prepared by using two kinds of phthalocyanines. The structure and the electrochromic property of these thin films were compared with those of simple phthalocyanine films. The structures of the films were analyzed by scanning electron microscopy (SEM), X-ray diffrction (XRD) and electron spin resonance (ESR) spectra. From the viewpoint of morphology and crystallinity, codeposited thin films have the same structure as the simple one, having sharp peaks at ca. 2θ=7.0° in the XRD pattern and narrow crystal grains in SEM photographs. ESR measurements have revealed that phthalocyanine molecules disperse very well in the codeposited thin films in a molecular level in comparison with the physical mixture of phthalocyanine powders. This high dispersibility of the molecules in the codeposited thin films can play a role to improve the reversibility in the electrochromism. Thus, the reversibility of the phthalocyanine, which shows irreversible electrochromism in the simple film form, can be improved by the codeposition with another phthalocyanine with reversible electrochromism. In contrast, sequentially deposted double-layered thin film gives completely different results. The electrochromism of the double-layered film depends on the property of the simple phthalocyanine thin film which is in contact with the substrate.     

X-ray microanalysis of thin film layered specimens containing light elements

Analysis of thin film layers on bulk substrates is carried out using a technique based on the (z) model of the depth distribution of X-ray emission. Both the composition and thickness of individual layers can be determined provided that the same element is not present in more than a single layer.The application of this method to the analysis of thin titanium-boron nitride bilayers on silicon or molybdenum substrates is discussed. X-ray intensities were measured by energy dispersive spectroscopy with a windowless or ultra thin window detector. The thickness of a 10 nm titanium layer could be estimated to within about ±1 nm, which is comparable with the depth resolution attainable by Auger sputter profiling.     

Depth-profiling of vertical sidewall nanolayers on structured wafers by grazing incidence X-ray flourescence

The Physikalisch-Technische Bundesanstalt (PTB), Germany's national metrology institute, developed an alignment strategy to specify elemental depth profiling in vertical sidewall layers on structured wafers. For this purpose, PTB's irradiation chamber for 200 mm and 300 mm silicon wafers was used to combine total-reflection X-ray fluorescence (TXRF) and grazing incidence XRF (GIXRF) techniques by employing monochromatized undulator radiation of the BESSY II electron storage ring. 3-D test structures were fabricated to develop an optimal alignment strategy allowing for depth profiling in such nanolayers. The test structures consisted of silicon bars with widths/spacings either in the μm or in the nm range. In order to be able to differentiate the sidewalls more easily from the remainder of the structures, they were provided with an additional silicon nitride layer. Four structure types of different bar width and density parameters on two 200 mm silicon wafers were investigated. The alignment procedure developed in the present work consists of three main steps and allows for distinct excitation of multiple sidewalls of one kind. Information about depth-dependent sidewall contamination, layer thickness and composition can be obtained by this approach. First results obtained on these test structures demonstrate the application potential of this new technique. In principle, depth-dependent chemical speciation should also be possible using GIXRF in combination with near edge absorption X-ray fine structure (NEXAFS).     

Step-growth synthesis and interfacial friction properties of surface dendron coatings

We report a new procedure for synthesizing self-assembled two-tiered coatings comprised of a tethered carbosilane dendron canopy layer over an alkylsilane sublayer. The sublayer is anchored to a silicon substrate, and the areal density of the canopy can be controlled by changing the concentration of reactive vinyl groups on the sublayer surface. The structure of the dendron layer is characterized by angle-resolved X-ray photoelectron spectroscopy (ARXPS), water contact angle, and ellipsometry. Steric hindrance due to close packing of functional groups has a strong effect on the reaction efficiency, and dendron structure can be obtained only in canopies with low areal densities. Lateral force microscopy (LFM) is used to study interfacial friction and adhesion properties of the coatings. Structural variations in the canopy layer are found to play a crucial role in interfacial friction properties of these coatings.     

Hydrogen Production Using a Molybdenum Sulfide Catalyst on a Titanium-Protected n(+) p-Silicon Photocathode

A low-cost substitute: A titanium protection layer on silicon made it possible to use silicon under highly oxidizing conditions without oxidation of the silicon. Molybdenum sulfide was electrodeposited on the Ti-protected n(+) p-silicon electrode. This electrode was applied as a photocathode for water splitting and showed a greatly enhanced efficiency.     

酞菁氧钛的合成及晶型转化

酞菁氧钛以联环己烷为溶剂，以邻苯二脂及四氯化钛直接反应生成。其优点是便于分离及纯化。同时对各晶型的获得及晶型间的相互转化进行了研究，并以Ｘ－射线粉末衍射及ＦＴ－ＩＲ进行了表征，并记录了不同晶型的酞菁氧钛在室温硫化硅橡胶中的吸收光谱。     

(CH3)3SiCl/SiCl4 azeotrope grows superhydrophobic nanofilaments

We describe the vapor-phase reaction (at room temperature and 40-45% relative humidity) of silicon wafers with the azeotropic mixture of trimethylchlorosilane and tetrachlorosilane. Water contact angle analysis indicates that surfaces become nearly perfectly hydrophobic (thetaA/thetaR > or =176 degrees/> or =176 degrees) after 2 min of reaction. SEM analysis at various reaction times shows the growth of nanofilaments with diameters of approximately 30 nm. X-ray photoelectron spectroscopy of oxidized titanium surfaces that were exposed to the azeotrope vapor indicates that the product is derived from a approximately 10:1 ratio of SiCl4 and (CH3)3SiCl. A mechanism for filament growth is proposed.     

Elaboration and characterisation of yttria psz coatings deposited by RF sputtering on silicon

Yttria stabilised Zirconia coatings on polycrystalline silicon wafers have been performed using physical vapor deposition with negative bias applied to the substrate. The thicknesses determined by ellipsometry were between 45 and 70 nm and the deposition rate was about 0.25 nm per min. Secondary ion mass spectroscopy analyses revealed no interdiffusion of metallic elements between the zirconia coating and silicon substrate. Grazing incidence X-ray diffraction indicates that the coatings are crystallized, but it can not permit to identify all the crystalline phases. The disparity between the experimental and the k-ratios (Pouchou and Pichoir simulation of electron probe microanalysis analyses) showed the usefulness of others techniques to determine coating and interface compositions. Cross sectional transmission electron microscopy observations demonstrate an amorphous layer between the zirconia coating and the substrate with a thickness of 30–120 nm. If it is considered to be an amorphous silicon layer, the PAP simulation based on the ellipsometric thicknesses and an yttria stabilised zirconia density of 4 g/cm³ fits correctly the experimental values.     

环氧倍半硅氧烷的合成研究

由SiO₂(白炭黑)制备了高活性的五配位硅化合物, 并用带环氧官能团的含卤化合物与活性五配位硅作用, 衍生出带有环氧官能团的硅酸酯; 通过环氧化硅酸酯的控制水解反应, 制备出了新型聚合物纳米复合平台——环氧化倍半硅氧烷; 借助X衍射、热分析、红外等现代测试手段, 对合成产物进行了结构表征.     

Synthesis and Characterization of ZnO Nanowires

Zinc oxide is a wide bandgap (3.37 eV) semiconductor with a hexagonal wurtzite crystal structure. ZnO prepared in nanowire form may be used as a nanosized ultraviolet light-emitting source. In this study, ZnO nanowires were prepared by vapor-phase transport of Zn vapor onto gold-coated silicon substrates in a tube furnace heated to 900 ?C. Gold serves as a catalyst to capture Zn vapor during nanowire growth. Size control of ZnO nanowires has been achieved by varying the gold film thickness…     

Characterization of cationic pillared layer clays

Na-montmorillonite and its Al-, Ti-, Fe-, Cr-, Zr- and Sn-pillared derivatives (pillared layer clays) were prepared and characterized by instrumental methods and a chemical reaction. Structural characterization involved X-ray fluorescence (XRF) analysis, X-ray diffractometry (XRD),²⁹Si and²⁷Al MAS NMR spectroscopies, thermogravimetric (TG) and BET measurements. By the distinctly characteristic shapes of the d₀₀₁ vs. temperature curves two groups could be distinguished, (i) Al-PILC, Ti-PILC, Cr-PILC, Zr-PILC and (ii) Fe-PILC, Sn-PILC, Na-montmorillonite. On montmorillonite isomerization of cyclopropane only occurred while oligomerization followed isomerization over Al-PILC. This latter reaction was attributed to Lewis and (the considerably smaller number of) Br?nsted acid sites whose number, strength and accessibility increased due to pillaring.     

pH-driven assembly of various supported lipid platforms: a comparative study on silicon oxide and titanium oxide

Supported lipid platforms are versatile cell membrane mimics whose structural properties can be tailored to suit the application of interest. By identifying parameters that control the self-assembly of these platforms, there is potential to develop advanced biomimetic systems that overcome the surface specificity of lipid vesicle interactions under physiological conditions. In this work, we investigated the adsorption kinetics of vesicles onto silicon and titanium oxides as a function of pH. On each substrate, a planar bilayer and a layer of intact vesicles could be self-assembled in a pH-dependent manner, demonstrating the role of surface charge density in the self-assembly process. Under acidic pH conditions where both zwitterionic lipid vesicles and the oxide films possess near-neutral electric surface charges, vesicle rupture could occur, demonstrating that the process is driven by nonelectrostatic interactions. However, we observed that the initial rupturing process is insufficient for propagating bilayer formation. The role of electrostatic interactions for propagating bilayer formation differs for the two substrates; electrostatic attraction between vesicles and the substrate is necessary for complete bilayer formation on titanium oxide but is not necessary on silicon oxide. Conversely, in the high pH regime, repulsive electrostatic interactions can result in the irreversible adsorption of intact vesicles on silicon oxide and even a reversibly adsorbed vesicle layer on titanium oxide. Together, the results show that pH is an effective tool to modulate vesicle-substrate interactions in order to create various self-assembled lipid platforms on hydrophilic substrates.     

Effect of substrate surface on dewetting behavior and chain orientation of semicrystalline block copolymer thin films

Three symmetrical semicrystalline oxyethylene/oxybutylene block copolymers (EmBn) were spin-coated on different substrates including silicon, hydrophobically modified silicon, and mica. The effects of surface property on the dewetting behavior of EmBn thin films and the chain orientation of the crystalline block were investigated with atomic force microscopy and grazing incidence X-ray diffraction . The EmBn thin films on silicon exhibit an autophobic dewetting behavior, while ordinary dewetting occurs for the thin films on modified silicon. It was observed that the stems of the E crystals in the first half-polymer layer contacting the mica surface were parallel to the surface, in contrast to the perpendicular chain orientation of the other polymer layers and of the first half-polymer layer on silicon. This is attributed to the strong interaction between the E block and mica, verified by infrared spectra.     

Fabrication and electrochemical investigation of layer-by-layer deposited titanium phosphate/Prussian blue composite films

Composite films of titanium phosphate (TiPS)/Prussian blue (PB) were fabricated by the alternative deposition of TiPS layer and PB nanocrystals. The layer of TiPS was fabricated by adsorption of hydrated titanium from aqueous Ti(SO4)2 solution and subsequent reaction with phosphate groups. The layer of PB nanocrystals was fabricated by sequential adsorption of FeCl3 solution and K4[Fe(CN)6] solution. Regular deposition of TiPS/PB composite films were verified by UV-vis absorption spectroscopy and quartz crystal microbalance measurements. The successful fabrication of the TiPS/PB composite films was further confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. Instead of producing films of TiPS layers alternating with PB nanocrystal layers, the TiPS/PB composite films have a structure in which the interstices of the PB nanocrystal films are filled with TiPS component. TiPS/PB composite films show enhanced electrochemical properties and improved stability in comparison with pure PB films prepared by the multiple sequential adsorption process. TiPS/PB composite films have the capability to catalyze the electrochemical reduction of H2O2 and can be used as a biosensor for detecting H2O2.