Growth and characterization of new oxide and fluoride crystals for optical applications

High quality oxide and fluoride single crystals for optical applications have been grown by the Czochralski technique. Lattice parameter investigation of grown Gd₃Yb _x Ga_5−x O₁₂ suggested that this crystal will be a superior material as substrate for optical isolators with large Faraday effect. Growth conditions of (La,Sr)(Al,Ta)O₃ single crystals are discussed. These crystals have excellent lattice matching with GaN, a promising material for optoelectronic devices. Ce-doped fluoride single crystals—LiCaAIF₆, LiYF₄ and BaLiF₃—have been grown for solid state UV laser applications. Growth results and optical characterization are discussed.     

Growth of titanium oxide overlayers by thermal oxidation of titanium

This paper describes a theoretical model for the growth of titanium oxide by thermal oxidation of titanium. It is shown that this model can explain the formation of layers of different oxides of titanium and the changes in these layers with variations in the conditions of oxidation. Some experimental X-ray diffraction results which support the model are also given.     

Formation and composition of titanium oxinitride nanocrystals synthesized via nitridizing titanium oxide for nonvolatile memory applications

Formation and composition analyses of titanium oxinitride nanocrystals (NCs) fabricated via treating a magnetron co-sputtered thin film of titanium and silicon dioxide with a rapid thermal annealing in nitrogen ambient were demonstrated for nonvolatile memory applications. Phase separation characteristics with different annealing conditions were examined by transmission electron microscopy and chemical bonding characteristics were confirmed by X-ray photon emission spectra. It was observed that a blanket layer composed mainly of titanium oxide was still present as annealing temperature was increased to 700 °C, associated with the thermodynamically stable phase of titanium oxide. Furthermore, a higher thermal treatment of 900 °C induced formation of a well-separated NC structure and caused simultaneously partial nitridation of the titanium oxide, thereby forming titanium oxinitride NCs. A significant capacitance-voltage hysteresis in threshold voltage shift at 1 V was easily achieved under a small sweeping voltage range of + 2 V/−2 V, and a memory window retention of 2.2 V was obtained after 10⁷ s by extrapolation under a 1 s initial-program/erase condition of + 5 V/−5 V, respectively.     

Synthesis and characterization of vanado titanium silicate molecular sieves with MEL structure

A series of vanadotitanium silicates was synthesized by a hydrothermal method. The MEL structure of these synthesized zeolites is clearly evidenced by X-ray diffraction spectroscopy. An advanced study with framework i.r., u.v.-vis, n.m.r., e.p.r., SIMS, and EDS indicates that atoms of both vanadium and titanium are simultaneously and homogeneously incorporated into the framework of the zeolite. In addition, the e.p.r. experiment also shows this zeolite to have redox properties.     

钒掺杂二氧化钛薄膜制备与材料特性分析

以钛酸四丁酯和乙酰丙酮钒（Ⅲ）为主要原料,采用溶胶-凝胶法制备了钒掺杂二氧化钛薄膜,利用XRD、紫外-可见吸收光谱、FT-IR及XPS等表征手段,将其与未掺杂二氧化钛薄膜进行了材料特性对比研究。结果表明两种薄膜均为锐钛矿结构,引入钒后二氧化钛的禁带宽度由3.28eV减小至3.15eV,吸收带边红移至可见光范围;XPS分析证实制备的钒掺杂二氧化钛薄膜中钒以四价和五价两种氧化价态存在,可能在二氧化钛禁带中引入较深的杂质能级而引起价带顶向禁带拓展,从而产生引起禁带宽度变窄效应,扩展了二氧化钛带边光吸收。理论分析还表明,钒掺杂引起的深能级杂质在二氧化钛晶界处易于形成有效的陷阱俘获光生空穴,从而抑制光生载流子的复合,尤其适于用作光催化材料。     

Growth and characterization of silicon nitride films for optoelectronics applications

Silicon nitride (Si₃N₄) films have been deposited by thermal-CVD system and characterized by the ellipsometry, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy dispersive analysis of X-ray (EDAX). The present paper reports the effect of deposition temperature on the physical and optical properties of deposited Si₃N₄ films. The stress of the film has been observed to be tensile in nature and it is found to be decreased by increasing the deposition temperature through ellipsometric study. The increase in refractive index of the film has been observed with increasing deposition temperature. The Si–H, N–H and Si–N–Si stretching characteristic peaks of Si₃N₄ films have been observed with significant intensities by using FTIR spectroscopy. The peak positions of Si–N–Si stretching absorption band and the corresponding full width at half maxima (FWHM) have also been analyzed. The FWHM observed to be increasing on corresponding increase in the deposition temperature, which indicates the improvement in the deposited films quality. However, films deposited in the temperature range of 780–850 °C, have some amount of H contents. The total H concentration in the films decreases with corresponding increase in deposition temperature, which reveals that the densification of deposited films increases on increasing the deposition temperature. The SEM and EDAX have been used to carry the morphological and compositional analysis of the deposited films, respectively.     

Behavior of titanium diboride nanofilms and nanopowders in hydrochloric acid solutions

We have studied the behavior of TiB₂ nanofilms and nanopowders in HCl solutions of various concentrations (1.2 to 12.0 mol/L). The TiB₂ films were grown by nonreactive magnetron sputtering in an additional magnetic field or without it. The TiB₂ powder was prepared by reacting fine-particle titanium and boron in a Na₂B₄O₇ ionic melt. The samples were characterized by X-ray diffraction, electron microscopy, energy dispersive X-ray spectroscopy, and atomic force microscopy. The reactions with the acid solutions were studied by atomic absorption spectroscopy. The results demonstrate that a magnetic field applied during the sputtering process improves the corrosion resistance of the films. Titanium diboride powders consisting of rounded particles are shown to have the highest resistance to dissolution in hydrochloric acid.     

非晶型超疏水和超亲水TiO2薄膜的制备与表征

通过溶胶-凝胶法, 以载玻片为基底制得非晶型纳米TiO₂薄膜, 用SEM、 XPS、 XRD和接触角测量仪研究了薄膜的微观形貌、 表面元素、 晶型结构及薄膜的疏水性, 用Wenzel、 Cassie 理论对纳米TiO₂薄膜的润湿性进行了理论分析。结果表明, 经紫外光照射16 h后, 薄膜表面由超疏水性变为超亲水性, 接触角接近0°。薄膜表面合适的粗糙度和低表面能材料表面修饰的协同作用使其表现出良好的超疏水性。     

Growth and characterization of some novel crystals for nonlinear optical applications

The advent of high intensity lasers coupled with the recent advances in crystal technology has led to rapid progress in the field of nonlinear optics. This article traces the history of materials development that has taken place over the past forty odd years and dwells on the current status in this important area. The materials aspect is discussed under three classes viz. inorganic, organic and semiorganic crystals. In the end, some of the crystal growth work that has been carried out in author’s laboratory is presented.     

Synthesis and characterization of stable iron-iron oxide core-shell nanoclusters for environmental applications

Iron-iron oxide core-shell nanoclusters are of great interest due to their potential applications as a remedy for environmental contamination. We report the room-temperature synthesis of core-shell iron-iron oxide nanoclusters using our novel cluster deposition system. Various types of measurements such as Transmission Electron Microscopy, X-ray Diffraction, X-ray Photon Spectroscopy, and Electron Energy Loss Spectroscopy are conducted in characterizing nanoclusters. Stable, monodispersive iron-iron oxide core-shell nanocrystals are identified.     

Growth and applications of superconducting and nonsuperconducting oxide epitaxial films

Growth and characterization of high-temperature-superconducting YBa₂Cu₃O₇ and several metallic-oxide thin films by pulsed laser deposition is described here. An overview of substrates employed for epitaxial growth of perovskite-related oxides is presented. Ag-doped YBa₂Cu₃O₇ films grown on bare sapphire are shown to giveT _c=90 K, critical current >10⁶ A/cm² at 77 K and surface resistance =450μΩ. Application of epitaxial metallic LaNiO₃ thin films as an electrode for ferroelectric oxide and as a normal metal layer barrier in the superconductor-normal metal-superconductor (SNS) Josephson junction is presented. Observation of giant magnetoresistance (GMR) in the metallic La_0·6Pb_0·4MnO₃ thin films up to 50% is highlighted.     

Synthesis and characterization of cadmium titanium oxide powders by sol-gel technique

Uniform crystals of CdTiO₃ orthorhombic phase have been preapred by Sol-Gel method using titanium butoxide and cadmium acetate. For the first time the sample has been characterised detailedly to confirm the formation of pure single phase of CdTiO₃. It is observed that the sample sintered at 500°C for 5 h showed complete formation of the single phase of CdTiO₃ by X-ray diffraction technique. X-ray photoelectron spectroscopy measurement has been carried out for the bulk CdTiO₃ sintered at 500 °C for 5 h, which showed 20% of Cd, 20% of Ti and 60% of O indicating stoichiometric CdTiO₃. Surface morphology studies by scanning electron microscopy showed uniform crystals of CdTiO₃. The purity of the compound has also been checked by Energy Dispersive X-ray method indicating the absence of foreign ions apart from that, the ratio of Cd : Ti has been calculated and found to be 1 : 1 indicating the stoichiometric CdTiO₃.     

Growth of titanium dioxide films by cluster supersonic beams for VOC sensing applications

We developed and tested gas sensing devices based on TiO/sub 2/ nano-crystalline films produced at room temperature by the novel growth method of cluster beam deposition. The devices show a very good response to ethanol, methanol, and propanol and an overall performance comparable or better to the best devices reported in literature, based on films grown with other techniques. The major advantage of our growth method is that there is no need of the thermal annealing or doping processes usually required to improve sensitivity and reliability of gas sensing devices based on nanostructured thin film. The sensors dynamic response gives a maximum sensitivity for ethanol at about 250/spl deg/C. As the morphological (AFM) and structural (XRD) characterizations of the films show, the high performance of our sensors could only be achieved because their nano-crystalline structure was well controlled by the properties of the cluster precursors in the supersonic beam. We envisage possible further developments in terms of sensitivity and selectivity of gas sensing devices based on films grown by cluster beam deposition.     

Growth and characterization of electrosynthesised zinc oxide thin films

Zinc oxide (ZnO) films have been electrodeposited from an aqueous solution containing 0.1 M zinc nitrate as the electrolyte with pH around 5±0.1. The deposition was carried out by galvanostatic reduction with an applied cathodic current density in the range between 5 and 20 mA cm⁻². The influence of bath composition on the preparation of ZnO films is studied. The effects of zinc nitrate concentration and cathodic current density on the deposition rate of ZnO films were also studied. An optimum current density of 10 mA cm⁻² is identified for the growth of ZnO film with improved crystallinity and optical transmittance. The crystalline structure of the deposits studied by X-ray diffraction reveals the possibility of growing hexagonal ZnO films under suitable electrochemical conditions. The surface morphological studies by scanning electron micrographs revealed the presence of nodular appearance for films deposited at 800 °C bath temperatures.     

Preparation and characterization of selenium incorporated anodic conversion coatings on titanium surfaces for biomedical applications

An anodic spark deposition process was used for preparation of inorganic, glass-ceramic like conversion coatings. The microstructure of the layers was characterized by surface and solid state techniques such as scanning electron microscopy, electron probe microanalysis and Raman spectroscopy. The porous coatings, typically up to 8 μm thick, consist mainly of titanium oxides and amounts of incorporated electrolyte constituents like Se, Ca or P. Beside nano crystalline anatase phases, a mostly amorphous structure is proposed in which network-forming [PO₄] tetrahedras and [TiO₆] octahedras in various degrees of condensation are connected. A drastic modification of the film structure was observed when selenium was incorporated into the glassy oxide structure of the coating. In these cases no nano crystalline phases of titanium oxides or other chemical compounds were detected. First cell culture investigations show a significant improvement of the biological properties. Cell proliferation and TGF-beta-expression of these coatings in comparison with commercial pure titanium (CPT) with native titanium oxide films were examined.     

Growth and characterization of AP-MOCVD iron doped titanium dioxide thin films

Atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) was used to prepare iron doped titanium dioxide thin films. Thin films, between 40 and 150 nm thick, were deposited on Si, SiO₂ and Al₂O₃ substrates using titanium tetra isopropoxide and ferrocene as metal organic precursors. TiO₂ iron doping was achieved in the range of 1–4 at.%. The film morphology and thickness, polycrystalline texture and doping content were studied using respectively scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The influence of growth temperature, deposition time, substrate type and dopant partial pressure were studied. Electrical characterizations of the films were also performed.     

Pyrolytic carbon coating for cytocompatibility of titanium oxide nanoparticles: a promising candidate for medical applications

Nanoparticles for biomedical use must be cytocompatible with the biological environment that they are exposed to. Current research has focused on the surface functionalization of nanoparticles by using proteins, polymers, thiols and other organic compounds. Here we show that inorganic nanoparticles such as titanium oxide can be coated by pyrolytic carbon (PyC) and that the coating has cytocompatible properties. Pyrolization and condensation of methane formed a thin layer of pyrolytic carbon on the titanium oxide core. The formation of the PyC shell retards coalescence and sintering of the ceramic phase. Our MTT assay shows that the PyC-coated particles are cytocompatible at employed doses.     

纳米硅/氧化硅多层膜的电性能及结构研究

用真空蒸发技术和自然氧化法在玻璃衬底上制备纳米级的硅／氧化硅薄膜和多层膜。本文采用三点法测定了常温、低温下的U—I特性，发现常温、低温下纳米量级的硅／氧化硅多层膜具有类似负阻的特性。SEM检测表明，硅／氧化硅多层膜的厚度和称重法所估算的厚度相符，薄膜表面均匀。TEM和XRD观察表明薄膜主要以无序状态存在，局部有晶化现象。