Co元素对硬质合金基底金刚石涂层膜基界面结合强度的影响

采用基于密度泛函理论的第一性原理平面波赝势方法, 研究了硬质合金刀具基底黏结相Co元素对金刚石涂层膜基界面结合强度的影响机理. 借助Materials Studio软件建立了WC/Diamond膜基界面模型和WC-Co/Diamond膜基界面模型, 采用CASTEP仿真软件计算了WC/Diamond膜基界面模型和WC-Co/Diamond膜基界面模型的最优稳定结构. 通过仿真计算, 获得了WC/Diamond膜基界面模型和WC-Co/Diamond膜基界面模型的界面结合能、电荷密度图及Mulliken重叠布居数. 经对比分析后发现, 硬质合金基底中磁性元素Co的存在能转移金刚石涂层膜基界面处W元素及C元素的电荷, 从而使膜基界面处的原子因失电荷而相斥, 这直接导致了金刚石涂层膜基界面间距变大, 使得金刚石涂层膜基界面结合能降低.     

高密度氦相变的分子动力学研究

采用分子动力学方法结合对关联函数分析计算了0–1000 K范围内氦的固–液相变曲线, 与实验数据的对比显示, 在0–500 K之间与实验数据符合很好, 500 K以上还没有相应的实验数据. 另外, 计算了钛金属中不同尺寸氦泡的压强, 并与高密度氦的固–液相变曲线进行了对比. 结果显示, 在低温条件下, 随着温度的降低, 钛晶体中可能会出现固态氦泡; 在300 K以上不会存在固态氦泡.     

温度对超薄铜膜疲劳性能影响的分子动力学模拟

用嵌入原子势的分子动力学方法模拟了温度对超薄铜膜疲劳性能的影响. 通过模拟, 首先给出了超薄铜膜的总能及应力随循环周次的变化曲线; 根据叠加经验式得出的叠加量随循环周次变化曲线, 判断出各种恒定温度下超薄铜膜的疲劳寿命. 由 200–400 K温度范围内超薄铜膜的疲劳寿命-温度变化曲线, 可以发现存在两个温度区域: 在约370 K以下, 超薄铜膜的疲劳寿命随温度升高缓慢增加, 而在约370 K以上增加较快. 建立了模型并用位错演化机制解释了超薄铜膜疲劳寿命的温度依赖关系. 关键词： 分子动力学 疲劳 温度效应 位错     

1.5μm处CO2与CO高温线强的实验分析与理论计算

本文在采用乘积近似方法计算二氧化碳、一氧化碳分子总的配分函数(其中分子的振动配分函数采用谐振子近似, 转动配分函数采用非刚性转子模型, 并考虑了离心扭曲修正)的基础上, 利用所得配分函数和振动跃迁矩平方的实验值以及Herman-Wallis系数, 计算了1.5 μm 附近二氧化碳30012–00001跃迁带和一氧化碳3–0跃迁带在300–6000 K温度范围内部分温度下的吸收线强; 为验证计算方法和结果的准确性, 在基于可调谐二极管激光吸收光谱技术搭建的高温测量系统中, 对300–800 K温度范围内部分谱线线强进行了测量, 并把计算结果、测量结果及HITRAN数据库中对应数据进行了对比, 发现相对偏差小于3%, 证明了本方法的有效性, 同时计算及测量所得高温线强数据可对HITRAN数据库进行有效的校正和补充.     

金属钛中氦团簇融合的分子动力学模拟

运用分子动力学方法研究了金属钛中氦的扩散聚集行为.在300—800K的温度范围内,模拟了钛基底中氦团簇之间的融合过程.研究发现,温度的升高会加快氦团簇的融合.在300—800K,融合后的氦团簇在所模拟的时间尺度内三维结构保持不变.模拟结果还表明,常温下氦团簇之间的吸引力是导致氦团簇融合的重要因素. 关键词： 氦团簇 团簇融合 分子动力学模拟     

硅功能化石墨烯热导率的分子动力学模拟

采用Tersoff势函数与Lennard-Jones势函数,结合速度形式的Verlet算法和Fourier定律,对单层和两层硅功能化石墨烯沿长度方向的导热性能进行了正向非平衡态分子动力学模拟.通过模拟发现,硅原子的加入改变了石墨烯声子的模式、平均自由程和移动速度,使得单层硅功能化石墨烯模型的热导率随着硅原子数目的增加而急剧地减小.在300 K至1000 K温度变化范围内,单层硅功能化石墨烯的热导率呈下降趋势,具有明显的温度效应.对双层硅功能化石墨烯而言,少量的硅原子嵌入,起到了提高热导率的作用,但当硅原子数目达到一定数量后,材料的导热性能下降.     

新型酞菁的光致发光性质研究

研究了2,3-四-(2-异丙基一5-甲基苯氧基)氢酞菁在10,77,177和300 K下石英衬底上的浇铸膜和单晶硅衬底上真空镀膜(约200 nm厚)在300 K下光致发光光谱.氢酞菁的浇铸膜光致发光光谱在上述温度下均出现荧光发射和磷光发射峰,在177和300 K下出现了1 673 nm激基缔合物峰.该峰的出现与分子抗聚集能力的强弱有关,在300 K激基缔合物峰比在177 K下的峰强,从氢酞菁分子结构特点讨论了形成激基缔合物的原因.随着温度的升高,可以观察到荧光发射峰渐渐减弱而激基缔合物峰变强.由于浇铸膜和真空镀膜的酞菁分子聚集态不同导致了斯托克司位移的差异,真空镀膜的发光峰峰值在1 140 nm左右,与酞菁浇铸膜的峰值差别较大.浇铸膜的发光峰的半高宽为300 nm,而真空镀膜发光峰的半高宽为100 nm左右.     

相变材料热物理性质的分子动力学模拟

为从微观尺度探寻相变材料的热物性变化机理, 本文采用分子动力学的方法, 构建了由正二十二烷组成的无定形结构的相变材料体系, 采用周期性边界条件以及COMPASS力场对相变材料的比热以及导热系数进行了模拟, 并对纯正二十二烷进行了DSC测试. 结果表明, 模拟所得的相变材料热容与文献实验值的偏差是6.5%, 熔点与DSC实验值的偏差是0.98%. 当温度为288–318 K时, 相变材料的导热系数在0.1–0.4 W·m^-1·K^-1 范围内波动, 且随着压力增大略呈下降趋势. 关键词： 扩散系数 比热 导热系数 分子动力学     

上海光源低温波荡器永磁铁在低温下的磁特性研究

用综合物性测量系统测试了国产Nd₂Fe₁₄B (N50M)永磁铁在低温下(10–300 K)的M-H和M-T. 获得了N50M剩磁B_r和内禀矫顽力H_ci在低温下的变化图, 对其取向度和三维磁化强度进行了分析研究. 结果表明, N50M在80–150 K发生强烈自旋再取向效应, B_r在120–130 K出现峰值, H_ci随温度下降呈线性增加. 在130 K, B_r和H_ci分别比常温(300 K)增加15.6%和220%, 达到1.65 T和3638 kA/m. 在150–300 K, 随温度下降, N50M宏观取向度与外磁场均匀性逐步改善, 但在80–235 K, 微观外磁场均匀性恶化.实验研究发现, 235 K附近, N50M垂直取向方向呈现“剩余磁化强度跳跃”. 研究结果为上海光源Ⅱ期低温波荡器及其他高精度低温永磁仪器与设备的物理设计提供了参考. 关键词： 低温波荡器 2Fe₁₄B永磁铁')" href="#">Nd₂Fe₁₄B永磁铁 低温 磁特性     

纳米多晶铜微观结构的分子动力学模拟

基于EAM镶嵌原子势函数,采用分子动力学模拟了零温下纳米多晶铜的微观结构.首先用Voronoi几何方法构造了5个纳米多晶铜数值模型,在300K弛豫50ps并退火至0K.然后分析零温下弛豫模型的径向分布函数、原子能量、配位数、原子Voronoi体积、以及本征应力分布 关键词： 纳米多晶铜 微观结构 分子动力学     

Yield strength temperature dependence of tungsten nanosized crystals: experiment and simulation

Regularities of the temperature effect on yield strength of nanosized tungsten crystals are ascertained. Experimental values of the yield strength of nanoneedles in the direction [1?1?0] are obtained using the high-field technology at the temperature range 17,4–862 K. It is found that in this range, decrease in strength of tungsten nanoneedles is about 30%. So low, compared with ordinary single crystals, susceptibility of nanoneedles’ strength to change in temperature is due to specific feature of mechanism of transition from elastic to plastic deformations in defect-free nanocrystals. To analyse this mechanism, molecular dynamic simulation of tensile of tungsten nanowire over the temperature range 3–2400 K has been utilized. The thermal fluctuation model of the temperature effect on the strength of nanosized crystals is offered.     

Mechanical Properties of Ni-Coated Single Graphene Sheet and Their Embedded Aluminum Matrix Composites

The effects of Ni coating on the mechanical behaviors of single graphene sheet and their embedded Al matrix composites under axial tensionare investigated using molecular dynamics (MD) simulation method. Theresults show that the Young's moduli and tensile strength of grapheneobviously decrease after Ni coating. The results also show that the mechanical properties of Al matrix can be obviously increased by embedding asingle graphene sheet. From the simulation, we also find that the Young'smodulus and tensile strength of the Ni-coated graphene/Al composite isobviously larger than those of the uncoated graphene/Al composite. Theincreased magnitude of the Young's modulus and tensile strength ofgraphene/Al composite are 52.27 and 32.32 at 0.01 K, respectively,due to Ni coating. By exploring the effects of temperature on the mechanicalproperties of single graphene sheet and their embedded Al matrix composites, it is found that the higher temperature leads to the lower critical strain and tensile strength.     

Photoelectron spectroscopy study of the K-covered ZnO(1 0 1̄ 0) surface; annealing-induced changes in the electronic structure and the chemical composition

The electronic structure and the chemical composition of the K-covered ZnO(1 0 1̄ 0) surface at temperatures between 300 and 1200 K are investigated by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Adsorption of K on ZnO(1 0 1̄ 0) at room temperature results in the formation of a two-dimensional disordered K overlayer and induces 0.2 eV downward bending of the substrate’s bands going from the bulk to the surface. Upon annealing the K-covered surface, initial downward bending turns to upward bending with maximum bending of 0.5 eV at 700-800 K. The thermally induced migration of the bulk O atoms and the resultant increase in the number of the O atoms on the surface is responsible for upward bending on the annealed surface. The accumulated O atoms interact with the predeposited K atoms on the surface to form non-stoichiometric K-O complexes with the O/K atomic ratio being 1.6-1.8 in the temperature range between 600 and 1000 K.     

空位在金刚石近(001)表面扩散的分子动力学模拟

用分子动力学方法模拟了空位在金刚石近(001)表面的扩散过程,研究了温度对空位扩散的影响.结果表明,当温度为1000K左右时,位于近表面第二层上的空位开始向表面运动;当温度在1400—2000K时,空位完全扩散到表面.这与实验结果和其他计算结果符合得很好.同时发现,温度为1400—1800K时,空位的扩散经历了两次迁移运动,其分别对应了均方位移图中的两个极大值.在不施加任何约束的条件下得到了空位的动态扩散路径,空位在金刚石近(001)表面的扩散势垒约为042eV.并探讨了一定温度下空位数目增多及其不同排列 关键词： 金刚石 空位 扩散 分子动力学     

Stress analysis at the interface between Ni-P coating and SiCp/Al substrate of space mirror

This paper investigates the mechanical properties at the interface of the coating-substrate system, which comprises the electroless nickel-phosphorus (Ni-P) coating and the aluminum matrix composite substrate reinforced by the silicon carbide particles (SiC_p/Al), and is used for the space mirror. To estimate the adhesion of Ni-P coating on SiC_p/Al substrate, the scratch adhesion testing has been performed by drawing a spherically tipped diamond indenter with a radius of 200 μm over the coated surface. The influence of the coating thickness on the interfacial stress induced by the inertial accelerations, temperature gradients and thermal soaks has been evaluated by simulation analysis based on the finite element method. The results of the scratch testing indicate that the adhesion strength of Ni-P coating to SiC_p/Al composite is more than 3.0 GPa. Compared the maximum value of the interfacial stress obtained by simulation analysis with results of the scratch testing, it is can be seen that the mirror has enough safety margin. Furthermore, the most significant conclusion that can be drawn from this work is that the coating thickness should not exceed 45 μm in order to ensure the performance and reliability of Ni-P coating and SiC_p/Al substrate system for space applications.     

Size and temperature dependence of the tensile mechanical properties of zinc blende CdSe nanowires

The effect of size and temperature on the tensile mechanical properties of zinc blende CdSe nanowires is investigated by all atoms molecular dynamic simulation. We found the ultimate tensile strength and Young?s modulus will decrease as the temperature and size of the nanowire increase. The size and temperature dependence are mainly attributed to surface effect and thermally elongation effect. High reversibility of tensile behavior will make zinc blende CdSe nanowires suitable for building efficient nanodevices.     

Analysis of the current-transport mechanism across a CVD diamond/silicon interface

This work presents a study on the mechanism of injection and charge transport through a CVD diamond/n⁺-Si interface. The current-voltage-temperature characteristics of CVD diamond/silicon heterojunctions measured in the temperature range 119-400 K have been interpreted according to thermionic theory and thermionic field-emission theory. This junction shows deviations from the ideal thermionic theory current model, suggesting the presence of surface states, thin-layer depletion and/or non-homogeneity in the diamond/silicon interface. The T₀ anomaly has been used to explain the behaviour of the ideality factor with temperature. At very low temperatures tunnelling may occur because the E₀₀ values for these junctions are close to the value expected by thermionic field-emission theory. The usual activation-energy plot deviates from linearity at low temperatures. This deviation has been corrected supposing a ln(J_S/T²) versus 10³/nT plot. Under these conditions the Richardson constant is found to be 0.819 A cm⁻² K⁻², which is close to the theoretical value of 1.2 A cm⁻² K⁻². Field-emission device is a promising application for diamond/silicon structure.     

Dynamic Jahn Teller interactions at fluorine in diamond

Two distinct TDPAD signals associated with¹⁹F implanted into diamond have been observed. One of these (site 1) remains steady over a considerable range of temperature, whereas the other signal (site 2) disappears at around 800 K. Since no other TDPAD signals appear with the disappearance of this signal, it is suggested that the temperature dependence relates to a thermal dynamic averaging of the quadrupole interaction at one of the fluorine sites because of a dynamic Jahn Teller effect.