Single-electron effects observed with a low-temperature STM

We have used a low-temperature scanning tunnelling microscope to study the effect of the Coulomb charging energy on the tunnelling behaviour of low capacitance point-contact junctions. The tunnelling I-V characteristics between a tungsten tip and various materials, such as stainless steel, aluminium, carbon and YBa₂Cu₃O_7-δ, show a quadratic behaviour at low voltages and a displaced asymptotic behaviour at high voltages. The I-V characteristics can be quantitatively understood using the model of single-electron tunnelling induced by the Coulomb blockade. The capacitances of this type of point-contact tunnel junctions are in the 10^?18 F range, and are adjustable by varying the distance between tip and surface. These capacitances are at least two orders of magnitude lower than can presently be achieved by electron lithography. In a series configuration of two low-capacitance tunnel junctions, with an isolated small particle as a common electrode, we have observed the so-called Coulomb staircase, due to the quantization of the charge on a single small particle. The experimental results are in good agreement with semi-classical Monte-Carlo simulations. The low capacitance of an STM assembly can cause a serious complication in the interpretation of low temperature spectroscopic data. We will discuss the implications for the measurements on superconductors, and for the case of inelastic tunnelling spectroscopy.     

Low Temperature Properties and Superconductivity of LuB12

We have investigated the low temperature properties of LuB₁₂ by measuring its magnetic susceptibility, heat capacity, and electrical resistivity, as well as by point-contact spectroscopy using both the spear-anvil type technique and mechanically controllable break junctions. Our specific heat measurements and point - contact spectroscopy results indicate that LuB₁₂ is a simple weak-coupling BCS-type superconductor with T_C ≈ 0.4 K, a superconducting energy gap of 2 Δ ≈ 0.12 meV, and a very small critical field B_C ≈ 1 mT. From the dU/dI(U) characteristics in the superconducting state, the energy gap 2Δ, the critical current I_C and the Andreev-reflection excess current I_ex as a function of normal-state point contact resistance R_N have been determined. At low R_N all three parameters are strongly suppressed, possibly due to the self-magnetic field. At contacts with large R_N the model of resistively and capacitively shunted Josephson junctions (RCSJ) allowed us to estimate the superconducting current plasma frequency and the Josephson coupling energy. Moreover, from the d²U/d I²(U) spectra in the normal state the (point-contact) electron-phonon interaction function and the characteristic phonon energies of LuB₁₂ have been determined.     

点啮合球锥滚子弧面凸轮机构及应用

在线啮合圆锥滚子弧面凸轮机构的基础上，根据点啮合理论原理，设计出一种新型的球锥形滚子，使其和原来由圆锥滚子创成的弧面凸轮形成点啮合。并在此基础上设计出了一种新型的球锥滚子弧面凸轮转位工作台。     

点接触齿面滑动率计算方法及其对交错轴渐开线斜齿轮传动的应用

推导出点接触齿轮副齿面滑动系数的计算公式,并分别针对齿轮副的不同组合形式,计算交错轴渐开线斜齿圆柱齿轮传动的滑动系数,绘制该齿轮副的滑动曲线。通过算例,研究了交错轴渐开线斜齿圆柱齿轮副滑动系数的特性。     

六轴联动数控齿轮加工机床加工点啮合齿面的包络逼近原理

提出了一种在六轴联动数控机床上加工点啮合齿面的新加工方法。该方法源于微分几何中通过空间曲线的Darboux-Frenet标架沿设计（理论）齿面上的一条指定接触迹线运动来描述曲面微分结构的思想,所展成的齿面与设计（理论）齿面沿指定的接触迹线有二阶切触且在接触迹线以外的区域与设计（理论）齿面之间具有指定（最小）误差,能完全控制齿面上每一个啮合点的啮合特性。利用六轴联动数控齿轮加工机床的万能运动功能,按被加工齿面预定的啮合特性确定刀具相对工件的运动。实例验证了方法的精确性和可行性。     

Interfacial Superconductivity on the Topological Semimetal Tungsten Carbide Induced by Metal Deposition

Interfaces between materials with different electronic ground states have become powerful platforms for creating and controlling novel quantum states of matter, in which inversion symmetry breaking and other effects at the interface may introduce additional electronic states. Among the emergent phenomena, superconductivity is of particular interest. Here, by depositing metal films on a newly identified topological semimetal tungsten carbide (WC) single crystal, interfacial superconductivity is obtained, evidenced from soft point-contact spectroscopy. This very robust phenomenon is demonstrated for a wide range of metal/WC interfaces, involving both nonmagnetic and ferromagnetic films, and the superconducting transition temperatures are surprisingly insensitive to the magnetism of thin films. This method offers an opportunity to explore the long-sought topological superconductivity and has potential applications in topological-state-based spin devices.     

GCr15球-盘点接触摩擦副的滑滚摩擦磨损特性研究

选用GCr15钢盘和GCr15球作为摩擦副,在NGY‐6纳米润滑膜测量仪上开展球‐盘点接触摩擦副在润滑状态下的滑滚摩擦磨损实验,研究不同接触应力、钢球转速、滑滚比等参数对摩擦副的摩擦因数、磨损形貌的影响规律．结果表明：当接触应力和钢球转速一定时,摩擦因数随着滑滚比的增大而逐渐增加后达到稳定状态;当滑滚比一定时,摩擦因数随接触应力的增大而逐渐增大;当钢球转速低于300 r／min时,摩擦因数随着钢球转速的增大而减小;当钢球转速高于300 r／min、接触应力大于0．84 GPa时,摩擦因数随着钢球转速的增大而呈增大趋势．Stribeck曲线表明：当滑滚比为0．01时,摩擦副处于流体动压润滑状态;当滑滚比为0．03时,润滑状态随Sommerfield参数的增加而从边界润滑过渡到混合润滑;当滑滚比分别为0．05、0．1、0．3、0．5时,润滑状态为边界润滑．滑滚比较小时,磨损机制以疲劳磨损为主,随着滑滚比的增大,磨损机制转变为磨粒磨损．     

Singularities of phonon spectra of superconductors observed with point contacts: A theory for dirty S-N contacts

Nonlinearities in the conductance of point contacts between a superconductor and a normal metal are considered for applied voltages larger than the energy gap . The voltage dependence of the conductance and the second derivative of the current-voltage characteristic, resulting from the local electron-phonon interaction in the contact region, are obtained for the case where electrons move diffusively through the contact, their mean free path being much shorter than the contact dimensiond. The conductance nonlinear structure corresponding to peaks of the Eliashberg function is calculated for simple model examples. These results are valid when the inequalityd ²/D<1 holds, where is the electron-phonon coupling constant andD is the electron diffusion coefficient. The second derivative,d ² I/dV ², is obtained for voltages near the values corresponding to Van Hove singularities of the phonon density of states.     

触点式微型光热驱动器设计及实验研究

随着微电机系统(MEMS)在众多领域的广泛应用,各种形式的微型驱动器不断得到发展。介绍微尺度光热膨胀与光热微驱动的原理,设计与加工制作了基本型和优化型触点式微型光热驱动器,开展了光热微驱动的实验研究,证明了光热微驱动的可行性,并验证了优化型触点式微型光热驱动器的优化性能。     

基于FBG的触点式动态压力传感器及其在脉象信息测量中的应用

提出了一种光纤Bragg光栅(FBG)压力传感器和基于 相位产生载波(PGC)的干涉式波长解调相结合的传感器系统,实现脉象波形 信息的探测。设计了一种高灵敏度的触点式FBG动态压力传感器,采用有限元软件分析 了传感器的灵 敏度和频率范围;对基于PGC的干涉式波长解调算法的低频特性进行了优化,实现低至0.2Hz的高分辨率 波长解调,以适应脉象信息测量的需要。实验研究了传感器的压力灵敏度,并进行了脉搏样 本信号的采集。 测试结果表明,传感器灵敏度为750pm/N,频率响应平坦,分辨率优 于1.4×10－6 N·H₂12,能够高保真的还 原脉象信息,为客观化脉诊提供了一种可靠的技术途径。