Rod-like β-FeSi2 phase grown on Si (111) substrate

Pure Fe with coverage of 0.5-2.0 nm was deposited on Si (111) 7×7 surfaces by reactive deposition epitaxy (RDE) in an integrated ultrahigh vacuum (UHV) system. Transmission electron microscopy (TEM) confirmed that the as-deposited epitaxial phase exhibits rod-like and equilateral triangular morphology. The as-deposited phase was identified as c-FeSi₂ by electron diffraction and high-resolution transmission electron microscopy. It was found that there exists lattice distortion in epitaxial c-FeSi₂ phase. Upon annealing at 1073 K, the metastable c-FeSi₂ transforms into equilibrium β-FeSi₂ phase, the latter inherits completely the morphology of c-FeSi₂ phase. Based on RDE and subsequent annealing, a new fabrication technique to grow rod-like semiconducting β-FeSi₂ on a Si substrate has been proposed in the present work.     

包渗法制备硅化物涂层的结构形貌及形成机理

采用包渗法在C-103铌合金基体上制备MoSi2涂层,通过X射线衍射、扫描电镜和能谱分析等手段研究涂层表面、截面形貌以及氧化后涂层结构变化,并分析硅化过程中涂层的形成机理。研究结果表明：包渗法制备硅化物涂层是通过反应扩散形成的,硅化过程服从抛物线规律;该涂层为复合结构：MoSi2相为主体层;以NbSi2相为主、并含少量Nb5Si3相的两相为过渡区;Nb5Si3相为扩散层。在高温氧化环境下,涂层表面生成致密的非晶氧化层,有效地阻止了氧向涂层内扩散。     

Quantitative differential thermal analysis of polymorphic transformations in LaGe1.8 and SmSi2

The possibility of using quantitative differential thermal analysis to investigate phase transformations is examined. The temperature, enthalpy, and entropy of polymorphic transformations in LaGe_1.8 and SmSi₂ are determined: T_tr = 724 K, Δ_trH = 1635 ± 79 J · mole⁻¹, Δ_trS = 2.3 ± 0.1 J · mole⁻¹ · K⁻¹ (LaGe_1.8); T_tr = 658 K, Δ_trH = 1384 ± 69 J · mole⁻¹, Δ_trS = 2.1 ± 0.1 J · mole⁻¹ · K⁻¹ (SmSi₂). __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 72–78, 2007.     

Research of the influence of thermohydrogen treatment on microstructural evolution and hardness of Ti600 alloy

研究了热氢处理对Ti600合金组织演变和硬度的影响. 结果表明: 热氢处理后,在Ti600合金中析出具有四方结构的硅化物粒子S3(0.357% H)和六方结构的硅化物粒子S1(0.497% H). 在氢的质量分数为0.357%和0.497%的试样中均发现有面心立方(fcc)的氢化物, 并且随着氢含量的提高氢化物表现出明显细化的趋势.Ti600合金的硬度随着氢含量的提高而提高, 其主要原因是氢化物、硅化物粒子以及晶格缺陷的存在.     

ZnCl2-assisted Synthesis of ZnSe Polycrystal

A chemical-assisted element direct-reaction method is developed to synthesize ZnSe compound semiconductor material at a relatively low temperature (～1000 C). ZnSe polycrystal was obtained in the closed-tube systems with Zn-Se, Zn-Se-Zn(NH3)2Cl2, Zn-Se-NH4Cl and Zn-Se-ZnCl2. The as-synthesized samples were tested by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and analyzed by thermodynamic numerical method. The results demonstrate that the synthesis efficiency is higher than 99.96% for Zn-Se-ZnCl2 system at around 1000 C for 3 weeks. It also exhibits that not only temperature, but also low apparent ratio of volume and surface area of the source materials and higher ZnCl2 content are required to achieve high synthesis efficiency. A SeCl transporting reaction synthesis process is proposed based on the thermodynamic analysis.     

Ni(Pt)Si硅化物温度稳定性的研究

对比研究了夹层结构N i/P t/N i分别与掺杂p型多晶硅和n型单晶硅进行快速热退火形成的硅化物薄膜的电学特性。实验结果表明,在600~800°C范围内,掺P t的N iS i薄膜电阻率低且均匀,比具有低电阻率的镍硅化物的温度范围扩大了100~150°C。依据吉布斯自由能理论,对在N i(P t)S i薄膜中掺有2%和4%的P t样品进行了分析。结果表明,掺少量的P t可以推迟N iS i向N iS i2的转化温度,提高了镍硅化物的热稳定性。最后,制作了I-V特性良好的N i(P t)S i/S i肖特基势垒二极管,更进一步证明了掺少量的P t改善了N iS i肖特基二极管的稳定性。     

基于数学建模要求下先进的提拉法控制系统研制

提出了在开发一种先进的直拉法晶体生长控制系统中占据重要地位的设备及工艺特征的下位机模型;分析所采集到的实验数据,揭示出控制中的重要问题,由此开发了一种新的控制结构;该模型是建立在常规控制结构和提出新的控制结构性能对比的基础上。     

Transistor Paint: Environmentally Stable N‐alkyldithienopyrrole and Bithiazole‐Based Copolymer Thin‐Film Transistors Show Reproducible High Mobilities without Annealing

New solution processable 4‐(2‐hexyldecan)‐4H‐bisthieno[2,3‐d:3′,2′‐b]pyrrole and 4,4′‐dialkyl‐2,2′‐bithiazole‐based copolymers (PBTzDTPs) are synthesized with excellent FET performance. These novel copolymers have considerable potential in printable electronics as they have high charge carrier mobilities, excellent air stability, good solution processibility, and no requirement for post‐deposition thermal annealing, all requirements for this field of application. The thin film transistors fabricated from PBTzDTPs achieve field effect mobilities as high as 0.14 cm² V^?1 s^?1 with current on/off ratios up to 10⁶ without thermal annealing. In addition, the devices exhibit stable performance in air, showing no significant degradation over 60 days. Moreover, the polymers described here provide an excellent example of the systems in which higher mobility performance does not require higher crystalline, long‐range ordered structures. Such a system appears to be particularly promising for rapid fabrication techniques, where kinetic conditions usually prevent the development of long‐range order.     

Insight into the vacancy effects on mechanical and electronic properties of Tantalum Silicide

The effects of the vacancies on the structural stability, elastic constants, elastic moduli, brittle-to-ductile transition and electronic properties of Tantalum Silicide (TaSi₂) are investigated in detail by first-principles calculations. The values of vacancy formation energy confirm that the perfect TaSi₂ and TaSi₂ with different atomic vacancies can exhibit the structural stability at ground state. It is found that Ta atom vacancies are more stable than Si atom vacancies in TaSi₂ with vacancies. The elastic constants and elastic moduli describe the mechanical behavior for TaSi₂ and TaSi₂ with vacancies. The different atomic vacancies weaken the elastic stiffness for TaSi₂. But the values of B/G confirm that the brittle-to-ductile transition occurs with different atomic vacancies for TaSi₂. Although these vacancies make the shear and volume deformation resistance of TaSi₂ weaker, they obviously improve the brittle behavior of TaSi₂. The difference charge density and electronic structures are calculated to discuss and analyze the structural stability and mechanical properties for the perfect TaSi₂ and TaSi₂ with vacancies.     

Processing of High‐Density Magnesia Spinel Electro‐Conducting Ceramic Composite and its Oxidation at 1400°C

Dense conductive ceramic composites of MgAl₂O₄ and MoSi₂ were processed using combustion synthesis under‐load methodology. The starting reactants were blends of MoO₃, SiO₂, MgO, and Al powders. The study revealed that to obtain dense composite with homogeneous microstructure, 30 wt. % of MoSi₂, 18.5 μm Al average particle size, and 175 MPa load are required. The produced dense composite was found to have a low apparent porosity (<1.0 vol. %), moderate density 4.61 g/cm³, and low electrical resistivity 0.3 Ωcm. The dense composite exhibited excellent thermodynamic stability between its phases at 1400°C in open atmosphere.