Alloyed contacts to thick,large area semiconductor devices

Severe damage has been found to occur in silicon when the conventional alloying technique is used to form contacts to very thick samples of large area. The usual alloying procedure has been modified by the use of separate silicon spacers to apply pressure to the alloying foil. This modified technique combined with the use of an improved alloying jig which provides positive control of the temperature gradient, has enabled satisfactory contacts to be formed on samples up to 22 mm diameter and 4 mm thick.     

煤块冲击破碎粒度的分形特征

煤块冲击破碎后的粒度分布具有分形特征,根据分形理论建立了煤块冲击破碎粒度的分形模型,对不同矿区的煤块进行冲击破碎试验。在不同试验条件下对冲击破碎后煤块的筛下质量累积概率进行函数拟合,拟合结果表明分形模型能够很好地描述煤块冲击破碎后的粒度分布特征,粒度分形维数是评价煤块冲击破碎效果的重要参数。采用Matlab软件建立了粒度分形维数与试验参数之间的二次方模型,该模型的预测结果与试验结果的平均误差为2.51%,满足预测误差要求,为控制煤块冲击破碎后的产品粒度分布提供了理论依据。     

Lithography-free in situ Pd contacts to templated single-walled carbon nanotubes

We report a metalization technique for electrically addressing templated vertical single-walled carbon nanotubes (SWNTs) using in situ palladium (Pd) nanowires. SWNTs are synthesized from an embedded catalyst in a modified porous anodic alumina (PAA) template. Pd is electrodeposited into the template to form nanowires that grow from an underlying conductive layer beneath the PAA and extend to the initiation sites of the SWNTs within each pore. In this way, individual vertical channels of SWNTs are created, each with a vertical Pd nanowire back contact. Further Pd deposition results in annular Pd nanoclusters that form on portions of SWNTs extending onto the PAA surface. Two-terminal electrical characteristics produce linear I-V relationships, indicating ohmic contact in the devices.     

TiO_2纳米管半导体特性与光电催化动力学研究

通过阳极氧化法在有机溶液中制备TiO2纳米管阵列,随着氧化时间的不同,TiO2纳米管阵列呈现各异的形貌。通过光电流测试,考察了不同氧化时间和施加不同电压下的Ti/TiO2纳米管阵列光电极的光电化学响应,阳极氧化6h表面规整纳米管阵列并施加偏压0.1V光电流响应最强。通过测试Mott-Schott-ky曲线,计算不同氧化时间的TiO2纳米管阵列的半导体载流子浓度、平带电位、空间电荷层宽度和能带弯曲量等特征参数,理论上提出了TiO2纳米管阵列生长机理。在光电催化降解无机氨氮的实验中,所得到的电化学阻抗谱(EIS)表明,外加偏压0.1V时,TiO2纳米管阵列电极的光电催化活性最强,同时通过拟合电路分析可知,光电催化降低了电极界面的反应阻抗,加速了光生载流子的转移,在TiO2纳米管阵列电极/溶液界面Helmholtz层中发生的氧化还原反应是整个光电催化反应的速率控制步骤。     

The asymmetric heat conduction of semiconductor rectifiers

We offer a survey of existing literature dealing with the problem of asymmetric heat conduction of semiconductor rectifiers, and we present the experimental results achieved by the authors of this article.     

Low-temperature semiconductor resistance thermometer with heat conductor

A 0.5–100 K GaAs thermometer with a toroidal element and a heat conductor improving the thermal contact and mechanical strength is described. At 4.2 K the reproducibility is 10 mK and the thermal resistance is about 10⁴ KW⁻¹ for P ≈ 10⁻⁶ W.     

Synthesis in situ of nanosize silver sulphide semiconductor particles in reverse micelles

Control of the size of silver sulphide semiconductor particles in functionalized reverse micelles was achieved by changing the water content and intermicellar interactions. Opposite to what it is generally observed in reverse micelles, the size of the crystallites varies linearly with water content from 2 to 10 nm. By changing the intermicellar potential, the size distribution slightly decreases and the stability of the particles with time increases.     

Controlling heterojunction abruptness in VLS-grown semiconductor nanowires via in situ catalyst alloying

For advanced device applications, increasing the compositional abruptness of axial heterostructured and modulation doped nanowires is critical for optimizing performance. For nanowires grown from metal catalysts, the transition region width is dictated by the solute solubility within the catalyst. For example, as a result of the relatively high solubility of Si and Ge in liquid Au for vapor-liquid-solid (VLS) grown nanowires, the transition region width between an axial Si-Ge heterojunction is typically on the order of the nanowire diameter. When the solute solubility in the catalyst is lowered, the heterojunction width can be made sharper. Here we show for the first time the systematic increase in interface sharpness between axial Ge-Si heterojunction nanowires grown by the VLS growth method using a Au-Ga alloy catalyst. Through in situ tailoring of the catalyst composition using trimethylgallium, the Ge-Si heterojunction width is systematically controlled by tuning the semiconductor solubility within a metal Au-Ga alloy catalyst. The present approach of alloying to control solute solubilities in the liquid catalyst may be extended to increasing the sharpness of axial dopant profiles, for example, in Si-Ge pn-heterojunction nanowires which is important for such applications as nanowire tunnel field effect transistors or in Si pn-junction nanowires.     

In situ formation of highly conducting covalent Au-C contacts for single-molecule junctions

Charge transport across metal-molecule interfaces has an important role in organic electronics. Typically, chemical link groups such as thiols or amines are used to bind organic molecules to metal electrodes in single-molecule circuits, with these groups controlling both the physical structure and the electronic coupling at the interface. Direct metal-carbon coupling has been shown through C60, benzene and π-stacked benzene, but ideally the carbon backbone of the molecule should be covalently bonded to the electrode without intervening link groups. Here, we demonstrate a method to create junctions with such contacts. Trimethyl tin (SnMe(3))-terminated polymethylene chains are used to form single-molecule junctions with a break-junction technique. Gold atoms at the electrode displace the SnMe(3) linkers, leading to the formation of direct Au-C bonded single-molecule junctions with a conductance that is ～100 times larger than analogous alkanes with most other terminations. The conductance of these Au-C bonded alkanes decreases exponentially with molecular length, with a decay constant of 0.97 per methylene, consistent with a non-resonant transport mechanism. Control experiments and ab initio calculations show that high conductances are achieved because a covalent Au-C sigma (σ) bond is formed. This offers a new method for making reproducible and highly conducting metal-organic contacts.     

Low-temperature specific heat of a semiconductor in a strong magnetic field

We calculate the electronic specific heat of a semiconductor (GaAs) at very low temperatures when subjected to a magnetic field strong enough to make the electron distribution nondegenerate. The transition to nondegeneracy is characterized by a large and rapid increase in the specific heat. For large fields the value approaches that of a one-dimensional nondegenerate gas, after first exceeding this value. Zeeman splitting, even with a very smallg factor (0.32), almost doubles the maximum in the specific heat as a function of field.On leave from Centre de Recherches sur les Très Basses Températures, Grenoble, France.     

Characterization of heat treated wood species

The objective of this work is to investigate the effect of heat treatment on swelling, hardness and surface quality of samples from four species, namely mindi (Melia azedarch L.), mahogany (Swietenia macrophyla), red oak (Quercus falcate Michx.) and Southern pine (Pinus taeda L.). Specimens were exposed to temperature levels of 130 °C and 200 °C for 2 and 8 h. Swelling values of the control and heat treated samples were evaluated by soaking them in water for 2 h. Surface quality and hardness of the species were also determined using a stylus technique and Janka hardness, respectively. Based on the findings in this study dimensional stability of all four types of samples improved with heat treatment. Surface quality of the specimens was also significantly enhanced by exposing them to heat. Micrographs taken from scanning electron microscope revealed that there was some distortion and modification of the cells due to heat treatment. Overall hardness of the samples was adversely influenced by heat treatment. It seems that properties of the species evaluated in this investigation were more pronounced with increasing temperature and time span.     

Transformations in a metal/insulator/semiconductor structure with an amorphous insulator film caused by contacts

The thermodynamic criteria for and structural consequences of interphase interactions at the boundaries of adjacent layers in an Nb/a-Nb₂O₅/MnO₂ (where a indicates amorphous) metal/insulator/semiconductor (MIS) structure were analysed and studied as an example of the behaviour of similar MIS structures. It was shown experimentally that the interaction in the thin insulator film induced a permanent electrochemical breakdown of the MIS structure which was followed by a step-like electrothermal breakdown under certain conditions. The relation between transformations in the ionic and electronic subsystems of the MIS structure at both stages of its relaxation into a state of thermodynamic equilibrium was investigated. A mechanism was proposed for the electroforming of the film, and investigations of the current-controlled negative resistance and bistable memory switching were performed.     

Fractal dimension of the grain boundary fracture in creep-fracture of cobalt-based heat resistant alloys

The effects of grain boundary configuration and creep conditions on the fractal dimension of the grain boundary fracture (D _f) were investigated using commercial cobalt-based heat resistant alloys, namely, HS-21 and L-605 alloys. Creep-rupture experiments were carried out under the initial creep stresses of 19.6–176 MPa in the temperature range from 1089–1422 K in air. The value of D _f was larger in specimens with serrated grain boundaries than in those with straight grain boundaries in the HS-21 alloy under the same creep condition, and the difference in the value of D _f between these specimens was large in the scale range of the analysis which was less than about one grain boundary length. However, there was almost no difference in the value of D _f between the specimens with serrated grain boundaries and those with straight grain boundaries in the L-605 alloy, because there was no obvious difference in the microstructure between these specimens. The value of D _f increased with decreasing creep stress in the scale range of the fractal analysis larger than about one grain boundary length in both HS-21 and L-605 alloys, while the stress dependence of D _f was larger in the HS-21 alloy. The stress dependence of D _f was explained by the stress dependence on the number of grain boundary microcracks linked to the fracture surface. The value of D _f estimated in the scale range smaller than about one grain boundary length showed essentially no stress dependence in both L-605 and HS-21 alloys.     

Structural variations in heat treated low alloy steel forgings

A study has been made of the microstructures of two low alloy Cr–Mo–Ni–V steel forgings in the quenched and tempered condition. Optical metallography of variously etched specimens, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) and X-ray diffraction were used to characterize the tempered martensite microstructures. Variations in prior austenite grain size and martensite lath structure have been related to the observed different carbide distributions. These arise from small differences in composition, mainly vanadium content, and the consequent response to heat treatment. The metallographic results can account for the differences in tensile and fracture toughness properties observed between the two materials as well as between the two ends of the same forging.     

808nm高功率量子阱远结激光器及其电噪声特性

介绍了８０８ｎｍ高功率最子阱远结半导体激光器的结构和器件特性,测试了器件的低步电噪声,讨论了噪声与频率、注入电流及器件质量的关系。结果表明,８０８ｎｍ高功率量子阱远结半导体激光的阈值电流在老化初期随时间的延续而降低,其噪声在低频段主要为１／ｆ噪声,且以阈值附近有量大值,器件噪声与器件质量有一定的相关性。     

Diagnostics of heat removal from semiconductor solar cells by laser thermowave methods

Methods of laser thermowave diagnostics have been used to study the process of heat transfer between a semiconductor solar cell and heat-removal ceramics. A theoretical model is proposed that describes the propagation of thermal waves in these systems with allowance for a layer of solder present between the semiconductor and ceramics. It is shown that, using laser thermowave methods, it is possible to evaluate the thermal properties of solder joint layers and the character of their degradation under the action of working temperature variations.