Single Electron Tunneling

This is a brief review of some recent developments inexperiments and theory of the Coulomb blockade phenomenon. Weconcentrate on electron tunneling through semiconductorquantum dots and normal-metal nanoparticles. The linearconductance and non-linear I–V characteristics are sensitivenot only to the charging energy, but also to smaller energyscales. These are the spacing between discrete energy levelsof intra-dot electron excitations, and the width these levelsacquire due to the electron escape to leads through thejunctions. At sufficiently low temperatures, or at not-so-small junction conductances, the many-body phenomena, such asKondo effect, become observable in the dot-lead system. Kondoeffect yields an additional fine energy scale to the problem.We discuss a simple theoretical model incorporating theseenergy scales, and its relation to the experimentalobservations.     

Tunneling Through a Single Quench-condensed Cluster

Quench-condensed bismuth films of 3–5 nm thickness have beenused as a cluster source to prepare Single ElectronTransistors (SET) based on a single cluster with high chargingenergy. We used electron-beam defined shadow evaporation masksto pattern 10 nm wide constrictions in these films. Byincremental depositions through these masks controlled by insitu sample conductance measurements, we obtained a SETgeometry for clusters with charging energies up to 90 meV. Ourexperiment showed that the SET geometry can be achieved inevery sample preparation run, despite the apparent randomnature of cluster formation in granular films. The resultingcharging energy of the transistor varied from experiment toexperiment. Its value, however, was always higher than 10 meV.     

基于单片机的宽带高精度频率计设计

介绍一种基于单片机的宽带高精度变闸门频率测试法,并给出该方法的测试原理及软、硬件组成.本设计以AT89C51单片机为测频的核心器件,用单片机的软件控制程序取代复杂的外计数电路,从而达到简化电路,提高测量精度的目的.总体看来,该设计具有结构简单,功能齐全,使用方便的特点.     

基于测试频响函数的结构连接参数识别方法

构造了半刚性结构连接单元，并应用于结构连接参数识别的模型中。利用子结构法建立的组合结构有限元模型和不完备的组合结构的测试频响函数，导出了连接子结构参数识别方法。提出了基于子矩阵因子法求解变量系数矩阵的通用方法。并将参数识别归结为求解非线性最小二乘问题，应用信赖域法克服了最小二乘求解初值选取范围过小的问题。最后利用仿真算例对上述方法进行了验证，结果表明该方法可行且具有一定的实用性。     

通用逻辑门电路的SET实现及应用

通用逻辑门具有更强的逻辑功能,相比传统逻辑门更适合作为阵列逻辑单元。单电子晶体管（SingleElectronTransistor,SET）被认为是众多纳米电子器件中的强有力竞争者。为了拓展SET的应用,减少逻辑综合所用逻辑门的种类,提出了通用逻辑门的SET电路实现方案,设计出基于sET的通用逻辑门树形结构的全比较器等电路,用Hspicer软件对所设计的电路进行仿真,结果表明,该电路具有正确的逻辑功能,为SET通用逻辑门的进一步研究应用奠定了基础。     

Novel Hybrid Voltage Controlled Ring Oscillators Using Single Electron and MOS Transistors

This paper proposes two kinds of novel hybrid voltage controlled ring oscillators (VCO) using a single electron transistor (SET) and metal-oxide-semiconductor (MOS) transistor. The novel SET/MOS hybrid VCO circuits possess the merits of both the SET circuit and the MOS circuit. The novel VCO circuits have several advantages: wide frequency tuning range, low power dissipation, and large load capability. We use the SPICE compact macro model to describe the SET and simulate the performances of the SET/MOS hybrid VCO circuits by HSPICE simulator. Simulation results demonstrate that the hybrid circuits can operate well as a VCO at room temperature. The oscillation frequency of the VCO circuits could be as high as 1 GHz, with a -71 dBc/Hz phase noise at 1 MHz offset frequency. The power dissipations are lower than 2 uW. We studied the effect of fabrication tolerance, background charge, and operating temperature on the performances of the circuits     

Tunneling Conductance Dependence of the Tunneling Spectra in Bi2Sr2CaCu2O8

We have measured the tunneling spectra in Bi₂Sr₂CaCu₂O₈ with a scanning tunneling microscope(STM) at various tip-sample distances by changing the tunneling conductance in a controlled manner. When the tunneling conductance is increased from 1×10^–9 to 1×10^–5 S, the spectra do not show changes in particular. However, the gap value decreases steeply and the asymmetric back ground density of states turns inverted V-shaped one above 6×10^–4 S. The changes in the tunneling spectra at the high tunneling conductances are explained by the enhancement of the local carrier density induced by the pressure that the STM tip applied to the sample.     

Tunneling Rates of Electron Pumping in the R-SINIS Transistor

We consider the influence of the electromagnetic fluctuations on the transport properties of a hybrid single electron transistor, consisting of superconducting electrodes and a normal-metal island, when operated as a turnstile. We derive the analytic expressions for the rates near the thresholds of single electron tunneling, Andreev reflection, and Cooper-pair–electron cotunneling processes. These results show that the dissipative on-chip impedance suppresses the rates of the undesirable higher-order tunneling processes much stronger than the single electron tunneling which can therefore be utilized to increase the accuracy of such a device in quantum metrological applications.     

Adsorption of Thin Liquid Helium Films on Cs Measured via Photoelectron Tunneling

The alkali metals Cs and Rb are the only surfaces which are not wetted by superfluid ⁴ He below a certain temperature. In our experiments, using the photoelectron tunneling method, we can highly resolve the growth of the non-wetting thin-film state of ⁴ He on a quench-condensed Cs surface. It turns out that far from coexistence there is little adsorption of helium. In contrast, close to coexistence a rapid growth up to two monolayers of helium is observed, but the surface is still non-wet under the usual convention.     

一种新型单频激光干涉系统的研究

这种单频激光干涉系统采用共光路设计布局,通过偏振分束器以及1/4波长片等光学器件对干涉条纹进行空间移相,提取相位依次相差90°的三路干涉输出信号,进行比较放大,解决了常规单频激光干涉仪中的光强“零漂”问题。利用共模抑制技术,提高了干涉系统的测量稳定性和重复性。采用光程差放大技术,提高了干涉系统的分辨力。     

Electrical Methods of Monitoring and Strengthening Electron Devices

The conditions for resonance oscillations of the current and the electromagnetic field to occur in metal-dielectric-metal structures when acted upon by a constant external electric field are determined, taking into account the electron emission in the dielectric from microprotuberances on the surface of the metal electrodes. A physical model of self-excited wave processes which occur in the initial reversible stage of electric breakdown of a thin dielectric layer is formulated.     

制造纳米电子器件的技术途径

目的 为发展纳米电子年及纳米电子学技术寻找有效途径。方法 对目前制造纳米电子器件的主要途径,例如基于三束的光刻加工技术、分子组装与纳米微粒排列技术、扫描力探针加工技术等进行了概略的介绍。讨论了各种方法所存在的优势与限制。结果 对基于分子组装与纳米光刻的纳料制造技术给予很大的重视。结论 认为综合若干种技术之长可能是我们目前实现特定纳料器件制造的有效途径。     

Pressure Dependence of UO2 Melting Measured by Double-Pulse Laser Heating

The melting point of uranium dioxide was measured as a function of isostatic pressure in an autoclave filled with helium up to 0.25 GPa. Containerless laser surface-heating was applied to measure the melting point by thermal arrest measurements during sample cooling. Precise control of the cooling rate, aimed at a precise determination of the freezing plateau, was obtained with a two-pulse method, where two Nd:YAG high power laser pulses are mixed within the same optical fiber and then focused on the sample surface. Calibration of the power of the two pulses permits the measurement of the melting point with very low uncertainty (0.5%). The measured melting slope of UO₂ is 170 and 200 KGPa^–1, a value which is markedly higher than that predicted by the Clausius–Clapeyron equation, which expresses this slope in terms of the enthalpy of fusion and the melting expansion. Possible reasons for this discrepancy are discussed.     

Beam Current Dependence of SEM Electron Probe Diameter

A method has been developed for measuring the dependence of the electron probe diameter d in a scanning electron microscope SEM on the beam current J. The relationship for the CAMSCAN CS-44 SEM is d(J) ~ J ^1/4, whereas electron probe formation theory gives d(J) ~ J ^3/8; the reasons for these differences are considered.     

Doping Dependence of Superconducting Energy Gap of NCCO Observed by Tunneling Spectroscopy

In order to clarify the electron-hole symmetry in cuprates, Nd_2–x Ce _x CuO₄ (NCCO) thin films were fabricated for various Ce concentrations and conductance spectra were measured by tunneling spectroscopy. Since the superconductivity appears even at x=0.095, thin film samples have an advantage over single crystals for studying the electronic states in underdoped region. It is shown that the amplitude of superconducting energy gap was almost 7–11 meV in the whole superconducting range. Comparing with hole-doped cases, the energy gap of NCCO is relatively insensitive to the doping concentration.     

Frequency Dependence of Second-Harmonic Generation in Lamb Waves

The frequency dependence of the second-harmonic generation in Lamb waves is studied theoretically and numerically in order to examine the role of phase matching for sensitive evaluation of material nonlinearity. Nonlinear Lamb wave propagation in an isotropic plate is analyzed using the perturbation technique and the modal decomposition in the neighborhood of a typical frequency satisfying the phase matching. The results show that the ratio of the amplitude of second-harmonic Lamb mode to the squared amplitude of fundamental Lamb mode grows cumulatively in a certain range of fundamental frequency for a finite propagation distance. It is also shown that the frequency for which this ratio reaches maximum is close but not equal to the phase-matching frequency when the propagation distance is finite. This feature is confirmed numerically using the finite-difference time-domain method incorporating material and geometrical nonlinearities. The fact that the amplitude of second-harmonic mode becomes high in a finite range of fundamental frequency proves robustness of the material evaluation method using second harmonics in Lamb waves.     

Phase Identification in a Scanning Electron Microscope Using Backscattered Electron Kikuchi Patterns

Backscattered electron Kikuchi patterns (BEKP) suitable for crystallographic phase analysis can be collected in the scanning electron microscope (SEM) with a newly developed charge coupled device (CCD) based detector. Crystallographic phase identification using BEKP in the SEM is unique in that it permits high magnification images and BEKPs to be collected from a bulk specimen. The combination of scanning electron microscope (SEM) imaging, BEKP, and energy dispersive x-ray spectrometry holds the promise of a powerful new tool for materials science.