Room-temperature growth of high-purity titanium nitride by laser ablation of titanium in a nitrogen atmosphere

Thin films of titanium nitride (TiN) were deposited on glass substrates by KrF excimer laser ablation of titanium over a very broad nitrogen pressure range with different target–substrate distances at room temperature. The as-deposited TiN thin films were analyzed by X-ray diffraction and transmission electron microscopy. It was found that the as-deposited thin films are normally a mixture of TiN and metallic titanium, and the TiN-to-Ti ratio of the as-deposited thin film depends on both the nitrogen pressure and the target–substrate distance. High-purity TiN thin films can be obtained only in a very narrow deposition parameter range. A compound parameter (the product of the nitrogen pressure and the target–substrate distance) is proposed to optimize the deposition of high-purity TiN thin films, and the possible mechanism is also discussed. It was also revealed that the as-deposited TiN thin films are polycrystalline with an average grain size of about 20 nm.     

室温直流磁控溅射氮化钛薄膜研究

利用直流磁控溅射在室温下沉积出性能优良的氮化钛薄膜,研究了N2流量和偏压对氮化钛薄膜性能和结构的影响,并采用扫描隧道显微镜(STM)技术对其表面形貌进行了较为详细的研究.结果表明,随着N2流量的增加,薄膜的结构从四边型混合结构转变为面心立方 NaCl型结构,最后变为无定型结构,薄膜结构的变化也使薄膜的硬度随之发生变化;施加负偏压不仅能让薄膜中缺陷减少,使膜层变得更致密,而且还能优化氮化钛晶粒,从而获得性能优良的薄膜.从TiN薄膜的表面形貌图可知,薄膜表面平整,缺陷很少,晶粒排列非常致密,且空位及表面缺陷较少.     

Depletion of charge carriers in electronic polycrystalline silicon

Silicon Si is the material of choice for reliable and low-cost different applications in nano- and optoelectronics, from integrated circuits (IC) to TFTs and flat-panel displays. Some processes taking place in polycrystalline Si samples of finite length; for example, carrier depletion, is of particular interest. Until now processes of carrier depletion were studied only for monocrystalline Si and Ge. Here, we report for the first time the results of the studies carried out in polycrystalline Si specimens of n-type conductivity at room temperature in order to clarify the effect of crystal structure on electric field-induced properties. Samples with columnar and grain type of crystal structure were chosen for simplest non-destructive electric investigations. It was shown that depletion of carriers was observed in samples of columnar crystal structure; at the same time, specimens of grain type structure showed a synthetic mechanism: exclusion+tunneling of carriers through intergranular boundaries. The effect of heat treatment of the samples under 900 and 1100 °C on the described properties was also studied. The experimental results are numerically modeled, and a summary of investigations seems to be useful for future applications of polycrystalline Si.     

Effect of stochastically anisotropic morphology on the mechanical behavior of microbeams

In many Micro-Electro-Mechanical-Systems (MEMS) applications such as polysilicon microstructures, the size of the basic element (grain), compared with the structure’s scale, is not negligible. In these cases, the random microstructure causes statistical dispersion of its response to load, experimentally observed by many researchers. The accompanying calculations, which generally treat the material as homogeneous and isotropic, do not model the structures properly. In this work, we analytically study the relations between morphological properties and the generalized displacements of statically determinate beams, frequently used in MEMS. The analysis includes shear deformation effects, material and structural couplings such as shear and bending deformations due to normal forces, and nonisotropic effects. The governing equations are presented in a special tensorial form, which enables finding analytical expressions for the mean and covariance matrix of the generalized deflections in terms of well defined morphological parameters and their statistics.     

In situ wear studies of surface micromachined interfaces subject to controlled loading

Friction and wear are major limiting factors for the development and commercial implementation of devices fabricated by surface micromachining techniques. These tribological properties are studied using a polycrystalline silicon nanotractor device, which provides abundant, quantitative information about friction and wear at an actual microelectromechanical system (MEMS) interface. This in situ approach to measuring tribological properties of MEMS, combined with high-resolution atomic force microscope (AFM) images of wear tracks, provides insight into the effects of different MEMS surface processing on wear. In particular, monolayer coatings have a significant positive effect, while surface texturing does not strongly affect performance.     

聚晶金刚石复合片（PDC）放电修磨的实验研究

耐磨性是衡量PDC好坏的首要指标。通过实验验证：大规准高能量的放电会对聚晶金刚石层产生破坏,但是通过合理选用电规准,分级设置加工深度和相适应的脉冲参数,可以兼顾放电效率、表面粗糙度和对金刚石层的不良影响。通过对PDC的精细放电,放电后经过铸铁盘抛光,以及与纯粹机械研磨、铸铁盘抛光三者的磨耗比的对比,结果显示三者的耐磨性没有明显区别。     

Micromechanical modeling of the work-hardening behavior of single- and dual-phase steels under two-stage loading paths

Work-hardening behavior of single-phase steel and dual-phase steel which is made of hard martensite surrounded by soft ferrite is analyzed by using an elastoplastic crystal plasticity model in conjunction with the incremental self-consistent model. Two-stage loading paths consisting of uniaxial tension, unloading and subsequent uniaxial tension/compression for various directions are applied. Bauschinger effect and transitional re-yielding behavior, which depends on the direction of the second loading path, are predicted and analyzed with respect to the distribution of the residual resolved shear stresses within the material. These features, which are caused by the inhomogeneity of the residual stress field, are especially pronounced in the case of the dual-phase steel because of the strong mechanical contrast between ferrite and martensite phases.     

Hydrogen passivation of defects in polycrystalline silicon solar cells

The investigations of hydrogen passivation of defects in polycrystalline silicon produced by the Czochralski method have been carried on. The results presented give evidence that it is advisable to use this material to create cheap effective solar cells.     

Investigation of foreign particles in polycrystalline silicon using infrared microscopy

The presence of SiC and SiNO particles in as-grown polycrystalline silicon has been investigated using infrared (IR) microscopy. These foreign particles were also characterized using electron beam induced current measurements, and scanning electron microscopy together with energy dispersive spectrum analyses. These performance-degrading inclusions were found to be distributed throughout the bulk of the material and varied in size from several microns to about 20 μm. In addition to the observation of the foreign particles, the feasibility of using IR microscopy as a characterization tool was also demonstrated.