Bildungsbedingungen und Struktur dünner Bi1−xSbx-Schichten

Thin polycrystalline Bi_1−xSb_x films in oriented state were deposited by flash evaporation techniques and by catode sputtering. In dependence on the conditions of formation the structure of these films was analysed by means of transmission electron microscopy, electron diffraction and electron beam microanalysis. Estimating the orientation, quality of surface and largeness of the average diameter of the crytallites the flash evaporation technique is superior to the catode sputtering under the experimental conditions chosen in this investigation. The Bi:Sb proportion does not change in comparison with the target, material of the source respectively, during the formation of the film.     

Untersuchung der Volumenstruktur dünner Bi1–xSbx-Schichten

The cross-sectional structure of evaporated Bi_1–xSb_x film has been investigated using electron microscopy and a replica technique. The conditions of film formation were varied by using different hydrocarbon partial pressures. After formation the films were annealed at 150°C. The cross-sectional structure is supposed to be columnary. This is in good agreement with the 〈00.1〉 texture. Grain coarsing during annealing is mainly influenced by the hydrocarbon concentration of the film. The upper part of the film shares most of the hydrocarbons. The correlation between surface- and cross-sectional structure disappeares by formation of an oxid layer.     

缓冲层厚度对Ge/Si多层膜的影响

采用离子束溅射技术,通过改变Si缓冲层厚度,在p型Si衬底生长了一系列的Ge/Si多层膜样品.利用Raman光谱、X射线小角衍射以及原子力显微镜等分析测试技术,研究了多层薄膜的结晶、膜层结构、表面形貌等性质.结果表明:通过引入缓冲层,在一定程度上可以提高颗粒的结晶性;随着缓冲层逐渐沉积,来自界面态的影响有了明显的减弱,且多层膜结构的生长得到有效改善.红外吸收光谱实验表明多层膜的吸收特性与其周期结构密切相关,因此可以通过改变缓冲层厚度的方法,实现对多层薄膜红外吸收特性的调制.     

石墨烯及石墨烯/氮化硼的电子结构特性研究

化学气相沉积法生长的单层石墨烯具有卓越的力学、热学和电学特性,成为新一代纳米器件的首选材料。对石墨烯电子特性的理论研究有利于推动纳米器件的发展与应用。本文基于密度泛函理论与非平衡格林函数相结合的方法,系统地研究了石墨烯及石墨烯/氮化硼的电子结构特性。结果表明,在高对称K点,带隙为零。在50~400 K范围内,由于费米面的电声子散射作用,单层石墨烯的迁移率随着温度增加呈现显著下降趋势。此外,通过对不同层间距的石墨烯/氮化硼结构的能带、态密度、电子密度等特性分析,发现随着层间距增加,能带间隙减小,导带与价带间的能量差减小。随着原子个数的增加,石墨烯/氮化硼超胞结构与原胞结构的带隙开度变化规律一致,这对石墨烯基器件的结构设计具有一定的指导意义。     

Influence of ensembles of gold nanoparticles on the growth of ZnO on the sapphire (0001) surface

Gold is deposited on sapphire (0001) substrates by vacuum sputtering to form an ensemble of nanoparticles on the surface. Then the substrates are transferred to a magnetron sputtering chamber to be heated to 650°C and coated by a ZnO layer. The resulting layers are investigated by scanning electron microscopy, atomic force microscopy, electron diffraction, and photoluminescence. It is established that the Au sublayer ensures a higher quality of the ZnO structure and enhances photoluminescence. The differences in the morphology of ZnO structures is explained by the Au aggregation during substrate heating before ZnO deposition.     

Synthesis and characterization of type-II textured tungsten disulfide thin films by vdWR process with Pb interfacial layer as texture promoter

The growth of type-II textured tungsten disulfide (WS₂) thin films by solid state reaction between the spray deposited WO₃ and gaseous sulfur vapors with Pb interfacial layer has been studied. X-ray diffraction (XRD) technique is used to measure the degree of preferred orientation ‘S’ and texture of WS₂ films. Scanning electron microscopy (SEM) and transmission electron microscopy techniques have been used to examine the microstructure and morphology. The electronic structure and chemical composition were studied using X-ray photoelectron spectroscopy (XPS). The use of Pb interfacial layer for the promotion of type-II texture in WS₂ thin films is successfully demonstrated. The presence of (0 0 3 l), (where l=1, 2, 3, …) family of planes in the XRD pattern indicates the strong type-II texture of WS₂ thin films. The crystallites exhibit rhombohedral (3R) structure. The large value of ‘S’ (1086) prompts the high degree of preferred orientation as well. The stratum of crystallites with their basal plane parallel to the substrate surface is seen in the SEM image. The EDS and XPS analyses confirm the tungsten to sulfur atomic ratio as 1:1.75. We purport that Pb interfacial layer enhances type-II texture of WS₂ thin films greatly.     

Fabrication and characterization of ‘self-binding’ nanocrystalline SnO2 powder based thick film ethanol sensor

Sensing response of ‘self-binding’ nanoparticles of tin dioxide powder deposited on alumina substrate has been investigated. The nanocrystalline SnO₂ powder has been derived from stannic chloride. It has been prepared through fine crystallization in liquid phase. SnO₂ powder has been characterized using SEM, TEM and XRD techniques, which reveal that the average crystallite size is of 12 nm. The slurry blobs deposited on alumina substrate of the powder-thus-prepared have been studied for sensing response to ethanol at various temperatures and concentrations. The observations reveal that the material prepared is ‘self-binding’ and is very sensitive even without catalyst.     

Spectroscopic ellipsometry studies of reactively sputtered nitrogen-rich GaAsN films

Nitrogen-rich GaAsN thin films have been deposited at 500 °C by reactive rf sputtering of GaAs target in argon-nitrogen atmosphere. The arsenic content of the films was varied by changing the nitrogen percentage in the sputtering atmosphere and the As/Ga ratio in the films was estimated by X-ray fluorescence measurements. Spectroscopic ellipsometry measurements have been carried out on these films and the measured ellispometric spectra were fitted with theoretical spectra generated by using suitable model sample structures. From the best fit parameters of the dispersion model, band-gap values and variation of refractive index and extinction coefficient as a function of wavelength have been obtained for films deposited with different percentages of nitrogen in the sputtering atmosphere. The films deposited with 12% to 100% nitrogen in the sputtering atmosphere, which are of hexagonal GaN, exhibit GaN-like optical properties, though effects due to excess arsenic in amorphous phase are seen in the films deposited with less than 40% nitrogen. The films deposited with 5% to 12% nitrogen in sputtering atmosphere are dominantly polycrystalline GaAs_xN_1−x (x ≈ 0.01 to 0.08) and exhibit variations in optical parameters, which are consistent with their structure and composition. The films deposited with less than 5% nitrogen in sputtering atmosphere are arsenic-rich and amorphous.     

Real structure of the ZnO epitaxial films on (0001) leucosapphire substrates coated by ultrathin gold layers

The real structure of ZnO films formed by magnetron sputtering on (0001) leucosapphire substrates coated by an ultrathin (less than 0.7 nm) Au buffer layer has been studied by high-resolution microscopy. It is shown that modification of the leucosapphire substrate surface by depositing ultrathin Au layers does not lead to the formation of Au clusters at the film–substrate interface but significantly improves the structural quality of ZnO epitaxial films. It is demonstrated that the simplicity and scalability of the technique used to modify the substrate surface in combination with a high (above 2 nm/s) film growth rate under magnetron sputtering make it possible to obtain high-quality (0001) ZnO epitaxial films with an area of 5–6 cm².     

Preparation of hollow dipyramid TiO2 with truncated structure using an oxidation/etch method and its gas‐sensing properties

Hollow dipyramid titanium dioxide with truncated structure was synthesized by a facile hydrothermal approach in an aqueous solution of hydrofluoric acid and hydrogen peroxide. The critical oxygen from the decomposition of hydrogen peroxide has been investigated in detail. X‐ray diffraction and Raman measurements show that the main phase is anatase titanium dioxide, accompanied by a small amount of rutile titanium dioxide. The formation mechanism is proposed based on oxygen release, oxidation, etching and hydrolyzation. The sensing properties of such a hollow dipyramid titanium dioxide sensor show that the desirable sensing characteristics with a sensitivity of about 2.1 towards 5 ppm ethanol gas at 200 °C could be obtained.     

Waveguide writing by CO2 laser annealing on sputtered silica film

We present a novel method for creating refractive-index structures in sputtered silica film using CO₂ laser annealing. The silica film was prepared by radio frequency magnetron sputtering on silica substrate. Deposited film with the refractive-index 0.8% higher than that of the silica substrate was realized, with a propagation loss of 0.4 dB/cm. The refractive-index of the silica film could be reduced by CO₂ laser annealing, enabling the formation of cladding structure for 2-D waveguide.     

Bilayered Super-Structures of Antiferroelectric Mesogens

Abstract

Crystal structures of two antiferroelectric mesogens, TFMHPBC and MHPBC-10, were analysed by an X-ray diffraction method. In both crystals, mesogen molecules formed a herringbone structure which was essentially the same as that proposed for the antiferroelectric liquid crystal phase. Because of the crystallographic 2₁-symmetry along the b-axis, only the b-axis component of the dipole moment remains in a smectic layer. Since the dipole moment in the next layer has the same magnitude but the opposite direction, both crystals show no dipole moment as a whole. These structural features observed in their crystal states seem to be conserved in their antiferroelectric liquid crystal phases which are just above their crystal phases.     

Characterization of reactive DC magnetron sputtered TiAlN thin films

Thin films of about 1μm Titanium Aluminum Nitride (TiAlN) were deposited onto mild steel substrates by reactive direct current (DC) magnetron sputtering using a target consisting of equal segments of titanium and aluminum. X‐ray diffraction (XRD) analysis showed that the TiAlN phase had preferred orientations along 111 and 200 with the face‐centered cubic structure. Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM) analyses indicated that the films were uniform and compact. Photoluminescence (PL) spectra reveal that TiAlN thin films are of good optical quality. Laser Raman studies revealed the presence of characteristic peaks of TiAlN at 312.5, 675, and 1187.5 cm^–1. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Rf-sputtered FeO films: Vapor species control in non-crystalline solid formation

It is shown that iron oxide films prepared by rf-sputtering display a wide variation in structure, composition, and film properties, depending upon the sputtering process parameters. We demonstrate that for Fe₂O₃ composition films non-crystalline solid (NCS) formation is controlled not only by substrate temperature but also by the vapor species in the vapor → solid transformation. The evidence indicates that the vapor species from an Fe₃O₄-sputtered target are primarily “molecules”. A qualitative model of the NCS formation is presented.     

Hydrothermal synthesis of MoO3 nanobelt‐graphene composites

A composite of graphene sheets decorated with molybdenum trioxide (MoO₃) nanobelts has been fabricated via a facile and efficient hydrothermal route in the presence of NaCl. The structure, morphology of these promising composites were investigated by means of field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), Raman spectroscopy and thermogravimetric (TG) analysis. FESEM and TEM studies suggest the presence of uniform crystalline MoO₃ nanobelts and graphene sheets in as‐prepared hybrid materials. XRD and Raman results confirm the reduction of graphite oxide (GO) sheets to graphene sheets accompanying by the formation of MoO₃ nanobelts. Moreover, thermal properties of GO and MoO₃ nanobelt‐graphene composites reveal that thermal stability of the obtained MoO₃ nanobelt‐graphene composites is obviously higher than that of GO due to the transformation of GO sheets to highly stable graphene sheets in the hybrids. This work could provide new insights into the fabrication of high quality MoO₃‐graphene hybrid nanomaterials and facilitate their potential applications in different fields. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

圆筒式柱面磁控溅射靶的磁场设计与仿真研究

为探究一种可实现向心溅射的圆筒式柱面磁控阴极靶,需要对靶装置内的磁场分布进行研究,进一步讨论靶结构参数对其磁场分布的影响规律。本文根据磁控靶的结构与工作原理,利用COMSOL Multiphysics有限元分析软件中AC/DC接口,对靶进行三维模型构建、划分网格和仿真计算。通过改变靶内磁体形状尺寸、磁轭形状以及结构排布,对靶面磁场的分布进行规律探究。最终确定新型圆筒式柱面磁控溅射阴极靶内的磁场结构参数,结果表明结构靶面磁场分布均匀且大小满足溅射要求的磁感应强度(20~50 mT),平行靶面均匀磁场区域达35%~40%左右。通过这类靶磁场结构的研究,为设计优化磁控阴极靶提供依据。     

Microstructural characteristics and crystallographic evolutions of Ga-doped ZnO films grown on sapphire substrates at high temperatures by RF magnetron sputtering

The microstructural characteristics and crystallographic evolutions of Ga-doped ZnO (GZO) films grown at high temperatures were examined by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The GZO films with various film thicknesses were grown on (0 0 0 1) Al₂O₃ substrates at 750 °C by RF magnetron sputtering using a 2 wt% Ga-doped ZnO single target. The (0 0 0 2) ZnO peaks in the XRD patterns shifted to a higher angle with increasing film thickness and an additional (1 0 1¯ 1) ZnO peak was observed in the final stage of film growth. HRTEM showed the epitaxial growth of GZO films in the initial growth stage and the formation of surface protrusions in the intermediate stage due to elastic relaxation. The surface protrusions consisted of {1 0 1¯ 1}, {1 0 1¯ 3}, and {0 0 0 2} planes. After the surface protrusions had formed, a GZO film with many c-axis tilted grains formed due to plastic relaxation, where the tilted grain boundaries had an angle of 62° to the substrate. The formation of the protrusions and c-axis tilted grains was closely related to the strain status of the film induced by Ga incorporation, high-temperature growth and a high film thickness.     

Superlattice-like structure of sputter-deposited amorphous aluminum-heavy element alloys

Al---Zr, Al---Nb, Al---Mo, Al---Ta and Al---W alloys were prepared by DC magnetron sputtering using an Al target with embedded heavy metals disks and substrate rotating around their own central axes and revolving around the central axes of the sputtering chamber. They were examined with X-ray diffraction (XD) of the Cu K, and Al---Ta alloys were also observed by transmission electron microscopy (TEM). Within the diffraction angles, 2τ = 20° ≈ 90°, XD patterns of the examined specimens were all typical of the amorphous structure. However, at the small angle region, 2τ < 10°, a number of sharp diffraction peaks appeared. The lattice spacing obtained from the diffraction peaks was linearly dependent on the inverse of the revolution period of the substrate during the sputter deposition. TEM images showed a layered structure which corresponded to the lattice spacing detected by XD. It is concluded that the superlattice-like structure appearing in the sputter-deposited alloy films arises from the compositional heterogeneity in the sputtered flux of atoms, which comes from the large non-uniformity of the target structure and sputtering conditions.     

Carbon nanocones: A variety of non-crystalline graphite

Previously known graphitic structures of conical shape – whiskers and helical cones – consist of a single wrapped graphene sheet, which gives a rather amorphous tip structure. Carbon nanocones, on the other hand, are nearly perfect sheets, curved by 1–5 pentagonal rings in the otherwise hexagonal network of carbon atoms. However, the resulting loss of periodicity implies electronic properties quite different from those of graphite and nanotubes. Experimental results have so far been limited by restricted access to sample material, but the cones have shown a unique capability of storing hydrogen gas reversibly at normal temperatures. The cones are characterized by large electrostatic dipole moments which will influence future experiments and technological applications. In this paper we study the interplay between topology, geometry and electronic properties, and investigate the magnitude of the dipole moments as a function of size and apex angle of the cones.     

Reduction of tensile stress in GaN grown on Si(1 1 1) by inserting a low-temperature AlN interlayer

We studied the selective growth behaviors of InP through narrow openings (<2 μm) by metal-organic chemical vapor deposition. The lateral overgrowth was observed to be significantly affected by both the opening width and orientation. It was found that the lateral overgrowth length reached the maximum at 60° off [0 1 1] direction. The lateral overgrowth also showed a ‘diffraction-like’ behavior, with the overgrowth length increasing with decreasing opening width. Based on these results, a novel InP/InGaAs heterojunction bipolar transistor (HBT) structure with extrinsic base laterally overgrown on SiO₂ is proposed. The device behaviors of the laterally regrown-base HBT prototypes are demonstrated.