Electrode contact study for SiGe thin film operated at high temperature

A study on the electrode contact of the sputtered SiGe thin film is reported for application of devices working at high temperature. Surface morphological characterization with optical microscope and AFM (atomic force microscope) together with the electrical characterization by TLM measurements (transmission line method) were performed before and after aging at 500 °C for 24 h using various sputtered multilayer electrodes, Ti/Au/Ti, Ta/Pt/Ta and Ti/Pt/Ti, on 300-nm B-doped SiGe thin film deposited by magnetron sputtering and furnace crystallisation at high temperature. After aging at 500 °C for 24 h, the Ti/Au/Ti multilayer electrodes seriously degraded to be non-ohmic contact, showing rough surface morphology. The Ti/Pt/Ti metal layers showed the lowest specific contact, resistivity before and after aging, 1.46 × 10⁻³ Ω cm² and 1.68 × 10² Ω cm² respectively.     

Electronic structure calculations for inhomogeneous systems: Interfaces,surfaces, and nanocontacts

The article gives an introduction into the application of density functional theory (DFT) to inhomogeneous systems. To begin with, we describe the interplay of specific materials at interfaces, resulting in structure relaxation and modifications of the chemical bonding. We address interfaces between YBa₂Cu₃O₇ and a normal metal, in order to quantify the intrinsic interface charge transfer into the superconductor. Moreover, we study the internal interfaces in a V₆O₁₃ battery cathode and the effects of ion incorporation during the charging and discharging process. The second part of the article deals with the influence of surfaces on the nearby electronic states. Here, we investigate a LaAlO₃/SrTiO₃ heterostructure in a thin film geometry. We particularly explain the experimental dependence of the electronic states at the heterointerface on the surface layer thickness. Afterwards, surface relaxations are studied for both the clean Ge(001) surface and for self‐assembled Pt nanowires on Ge(001). In the third part, we turn to atomic and molecular contacts. We compare the properties of prototypical Al nanocontact geometries, aiming at insight into the chemical bonding and the occupation of the atomic orbitals. Finally, the local electronic structure of a benzene‐1,4‐dithiol molecule between two Au electrodes is discussed as an example for a molecular bridge.     

The effect of a surface layer capping p-InGaN/p-GaN superlattices on the contact to p-GaN

In this study, the influence of the surface layer (p-InGaN or p-GaN) capping p-InGaN/p-GaN superlattices (SLs) on the contact to p-type GaN was investigated. It was found that the specific contact resistance (_ρc)$\left({\rho }_c\right)$ to p-type GaN is lower when using p-InGaN as the surface layer. The lowest value of _ρc${\rho }_c$ was 1.99×10⁻⁴ Ω cm² at room temperature. It was also found that low temperature growth of the p-GaN layers in the SLs is beneficial for lowering the ohmic contact resistance. Unlike Ni/Au deposited directly on p-GaN (without the strained p-InGaN/p-GaN SLs), Ni/Au deposited on p-InGaN/p-GaN SLs produces ohmic behavior even before annealing.     

Experimental studies of influence of the turbulent flow structure on temperature distribution in a compact heat exchanger

Results of experimental investigation of temperature distribution over the surface of a complex heat exchanger (the Frenkel packing type) are presented. Measurements were carried out in the air flow between two sheets with triangular corrugations directed at 90° to each other. Measurements were carried out by the microthermocouples glued on the heated outer surface. The effect of Reynolds numbers, a gap between corrugated sheets, and substitution of one corrugated sheet by the smooth one on temperature distribution over the heat exchanger surface in the turbulent air flow is analysed. According to the performed experiments, there is a significant effect of a gap and applied perturbations on the type of temperature distribution over the perimeter of a heated cell.     

Laterally inhomogeneous barrier analysis of the methyl violet/p-Si organic/inorganic hybrid Schottky structures

In this work, we have investigated the electrical characteristics, such as current-voltage (I-V) and capacitance-voltage (C-V) measurements, of identically prepared crystal violet/p-Si Organic/Inorganic (OI) Schottky structures formed by evaporation of organic compound solution to directly p-Si semiconductor substrate. It has been seen that the crystal violet organic dye thin film on the p-Si substrate has exhibited a good rectifying behavior. The barrier heights (BHs) and ideality factors of all devices have been calculated from the electrical characteristics. Although the diodes were all identically prepared, there was a diode-to-diode variation: the effective barrier heights ranged from 0.6 ± 0.1 to 0.8 ± 0.1 eV, and the ideality factor from 1.6 ± 0.4 to 3.5 ± 0.4. The barrier height versus ideality factor plot has been plotted for the OI devices. Lateral homogeneous BH was calculated as a value of 0.7 eV from the observed linear correlation between BH and ideality factor, which can be explained by laterally inhomogeneities of BHs. The values of barrier height and acceptor doping concentration yielded from the reverse bias C-V measurements ranged from 0.7 ± 0.1 to 1.3 ± 0.1 eV and from (4.7 ± 0.8) × 10¹⁴ to (8.1 ± 0.8) × 10¹⁴ cm⁻³, respectively. The mean barrier height and mean acceptor doping concentration from C-V characteristics has been calculated 1.0 eV and 5.9 × 10¹⁴ cm⁻³, respectively. It has been seen that the mean BH value of 0.7 eV obtained for the Al/methyl violet/p-Si contact is significantly larger than BH values of the conventional Al/p-Si Schottky diodes. Thus, modification of the interfacial potential barrier for metal/Si diodes has been achieved using a thin interlayer of the methyl violet organic semiconductor; this has been ascribed to the fact that the methyl violet interlayer increases the effective barrier height by influencing the space charge region of Si.     

Analysis of protein folds using protein contact networks

Proteins are important biomolecules, which perform diverse structural and functional roles in living systems. Starting from a linear chain of amino acids, proteins fold to different secondary structures, which then fold through short- and long-range interactions to give rise to the final three-dimensional shapes useful to carry out the biophysical and biochemical functions. Proteins are defined as having a common ‘fold’ if they have major secondary structural elements with same topological connections. It is known that folding mechanisms are largely determined by a protein’s topology rather than its interatomic interactions. The native state protein structures can, thus, be modelled, using a graph-theoretical approach, as coarse-grained networks of amino acid residues as ‘nodes’ and the inter-residue interactions/contacts as ‘links’. Using the network representation of protein structures and their 2D contact maps, we have identified the conserved contact patterns (groups of contacts) representing two typical folds — the EF-hand and the ubiquitin-like folds. Our results suggest that this direct and computationally simple methodology can be used to infer about the presence of specific folds from the protein’s contact map alone.      

粉末热压扩散与应力场耦合的力学模型

以弹性接触应力场为初始条件,建立了热压条件下球形颗粒表面扩散与应力场耦合的力学模型. 引入包含表面能项级数形式的应力函数,以描述随时间演化的表面扩散过程及扩散对应力场演化的影响. 而应力场通过改变化学势梯度,又会促进(或阻止)表面扩散结合的进程.利用该模型分析了压力、温度和界面区应力场演化对致密化参数的影响. 比较了满足粘着或非粘着对结合宽度和应力分布的影响,将考虑粘着的弹性接触应力场作为初始条件,分析了弹性变形和表面扩散共同驱动的粉末冶金热压烧结致密化规律.      

Critical oscillations of mass–spring systems due to nonsmooth friction

Critical values of the parameters governing the dynamics of simple systems appear when Coulomb friction is not regularized. We explore such systems using a method based on the fact that under constant or analytical data the trajectory exists, is unique and is also sufficiently regular. In fact these properties justify elementary analytical computations on successive time intervals where the condition used to connect the solution from one interval to the other is due to the regularity. Although the systems are simple the dynamics turn out to be quite complex and thus furnish an interesting benchmark for contact dynamics numerical codes. Among other possible applications we choose to present here how to use a mass–spring chain with Coulomb friction to slow down in a progressive and regular manner an oncoming mass with a given initial velocity.     

基于轮轨蠕滑机理的货车车轮磨耗寿命预测

为对货车车轮磨耗寿命进行预测,在SIMPACK中建立车辆-轨道多体动力学模型,基于轮轨半赫兹接触理论和Zobory车轮磨耗模型编制车轮磨耗数值仿真程序.对C80型货车等在环形线和大秦线上运行时的车轮磨耗行为进行仿真,并根据实测结果和仿真结果对Zobory车轮磨耗模型进行修正,最后利用修正后的Zobory模型对C80型货车在国内某重载线路上运行时的车轮磨耗寿命进行预测.结果表明:车辆在环形线和大秦线上运行时,仿真得到的车轮磨耗分布范围以及圆周磨耗深度和轮缘厚度随运行里程的变化趋势均与现场实测结果较为接近,但车轮圆周磨耗率分别为实测结果的1.394 ～1.842倍和2.172 ～3.658倍,主要原因是仿真中采用了轮轨半赫兹接触理论,考虑了弹性剪切变形对滑动速度的影响,并且国内货车采用的CL60钢的硬度大于国外BSll钢的硬度;C80型货车在国内某重载线路上运行时,利用修正后的Zobory模型仿真得到的车轮段修磨耗寿命为39×105 km,运用磨耗寿命为65×105 km,与现场统计结果较为吻合.     

考虑接触界面材料微观结构与势能参数的滑动摩擦计算研究

根据独立振子模型的能量耗散机理,提出了在无磨损界面摩擦中,利用通用界面粘附能量函数计算滑动时接触界面势能的变化从而计算摩擦力和摩擦系数的方法,建立摩擦力和摩擦系数与金属材料表面能与微观结构参数的关系,并利用已有的实验数据进行计算.结果表明,摩擦力与金属材料的表面能基本呈线性关系,与比例参数呈线性负相关关系,与晶格常数基本无关.计算结果与粘附理论公式以及超高真空原子力显微镜试验结果吻合较好.