新型量子霍尔电阻样品计量应用研究

采用As Ga砷化镓系材料研制了多种结构的新型量子霍尔电阻样品,介绍了该样品的特点及应用领域。使用常温电流比较仪和低温电流比较仪,用过渡比对法对新型的量子霍尔电阻与标准量子霍尔电阻样品进行了双重测量比对验证,在实验室内测量结果的相对偏差小于4×10^-8,验证了新型的量子霍尔电阻样品和测量系统的准确度满足当前计量应用需求。     

石墨烯在计量科学中的应用

石墨烯是一种具有奇异特性的新型材料,它由单层碳原子构成六方蜂巢状二维结构。因其具有独特的电子能带结构而显示相对论电子学特性,石墨烯是迄今为止人类发现的最理想的二维电子系统,具有丰富而新奇的物理特性。综述了石墨烯的结构、特性、制备方法及其可能的工业应用,结合现代计量科学进展,对石墨烯在量子计量基准中的应用前景进行了展望。     

基于量子化霍尔电阻考核的国家电阻基准的稳定性

报告了自1990年以来通过与量子化霍尔电阻比对考核的国家直流电阻（实物）基准的长期漂移率及偏差。结果表明2001年以来,国家直流电阻（实物）副基准的漂移率为-0．0551μΩ／a,主基准的漂移率为-0．0808μΩ／a;2006年10月25日,国家直流电阻（实物）基准复现的电阻量值较量子化霍尔电阻的相对偏差为＋0．677mm,预计2007年1月1日需要修正-0．69μΩ／a。     

启用量子化霍尔电阻基准时国内直流电阻量值的修正

报告了2003年以来采用量子化霍尔电阻(QHR)监测的原国家电阻基准的长期漂移率;通过直流电阻副基准分别与QHR和原主基准比对,确定了原主基准相对于QHR的偏差.2008年1月1日启用QHR新基准时,溯源到原基准的直流电阻及相关量值的修正量为-0.70 μΩ/Ω,该修正量的不确定度为0.05 μΩ/Ω,涉及到一等及其以上各级电阻计量标准.     

量子化霍尔电阻国家标准的研究

中国计量科学研究院在2003年建成了量子化霍尔电阻标准装置。成功研制了系统的核心器件—量子化霍尔器件。并通过对低温电流比较仪系统及运行过程的研究,发现了氦气气压波动引起的冻结磁通蠕动导致的附加噪声是限制系统不确定度的主要原因。进而提出了一种新型的气压滤波器,消除了这些干扰因素。还改进了电路动态特性,改善了前馈补偿环节,把匝数比提高了8倍,信噪比也因而提高了8倍。完成的量子化霍尔电阻标准装置的综合不确定度为2.4×10-10(k=1)。     

中国的量子化霍尔电阻标准

1988年10月举行的国际计量委员会(CIPM)第77次会议决定,从1990年1月1日起在世界范围内启用量子化霍尔电阻标准。中国计量科学研究院从1987年起也开始了建立量子化霍尔电阻标准的研究课题,该项标准现已建成,用量子化霍尔效应复现的10kΩ和1kΩ电阻量值的不确定度为2.2×10~(-8)。     

石墨烯量子点在生物医学中的研究进展

石墨烯量子点是石墨烯超家族的衍生物,与高维度石墨烯相比,具有良好的生物相容性,较低的细胞毒性及较好的化学修饰性。自发现以来,石墨烯量子点的应用领域被逐渐地拓宽。其中石墨烯量子点的生物应用主要包括生物成像、生物传感器、药物运输、基因载体、抗菌抗病毒及肿瘤的光动力治疗研究等。主要介绍了近几年有关石墨烯量子点生物相容性及其在生物医学研究的进展,并对其发展前景进行了展望。     

量子化霍尔电阻基准获国家科技进步一等奖

1月8日。由中国计量科学研究院张钟华院士领导的课题组研制的“量子化霍尔电阻基准”在人民大会堂召开的“国家科学技术奖励大会”上荣获国家科技进步一等奖。     

Temperature Dependence of the Hall and Longitudinal Resistances in a Quantum Hall Resistance Standard

We present detailed measurements of the temperature dependence of the Hall and longitudinal resistances on a quantum Hall device [(GaAs(7)] which has been used as a resistance standard at NIST. We find a simple power law relationship between the change in Hall resistance and the longitudinal resistance as the temperature is varied between 1.4 K and 36 K. This power law holds over seven orders of magnitude change in the Hall resistance. We fit the temperature dependence above about 4 K to thermal activation, and extract the energy gap and the effective g-factor.     

Equivalent Electrical Circuit Representations of AC Quantized Hall Resistance Standards

We use equivalent electrical circuits to analyze the effects of large parasitic impedances existing in all sample probes on four-terminal-pair measurements of the ac quantized Hall resistance R_H. The circuit components include the externally measurable parasitic capacitances, inductances, lead resistances, and leakage resistances of ac quantized Hall resistance standards, as well as components that represent the electrical characteristics of the quantum Hall effect device (QHE). Two kinds of electrical circuit connections to the QHE are described and considered: single-series “offset” and quadruple-series. (We eliminated other connections in earlier analyses because they did not provide the desired accuracy with all sample probe leads attached at the device.) Exact, but complicated, algebraic equations are derived for the currents and measured quantized Hall voltages for these two circuits. Only the quadruple-series connection circuit meets our desired goal of measuring R_H for both ac and dc currents with a one-standard-deviation uncertainty of 10⁻⁸R_H or less during the same cool-down with all leads attached at the device. The single-series “offset” connection circuit meets our other desired goal of also measuring the longitudinal resistance R_x for both ac and dc currents during that same cool-down. We will use these predictions to apply small measurable corrections, and uncertainties of the corrections, to ac measurements of R_H in order to realize an intrinsic ac quantized Hall resistance standard of 10⁻⁸R_H uncertainty or less.     

Comparison of the dimensions of electrical resistance units, supported on the basis of the hall quantum effect, in the All-Russia Research Institute of Metrological Service and the Czech Metrological Institute

VNIIMS (Russia) and CMI (Czech Republic) quantum Hall resistance standards are compared using a VNIIMS portable resistance standard of 1 and 10 kΩ. Conformity is established for the dimensions of units within the limits of relative expanded (k = 2) uncertainty of 10⁻⁷. Translated from Izmeritel’naya Tekhnika, No. 12. pp. 58–61, December, 2008.     

Precision Tests of a Quantum Hall Effect Device DC Equivalent Circuit Using Double-Series and Triple-Series Connections

Precision tests verify the dc equivalent circuit used by Ricketts and Kemeny to describe a quantum Hall effect device in terms of electrical circuit elements. The tests employ the use of cryogenic current comparators and the double-series and triple-series connection techniques of Delahaye. Verification of the dc equivalent circuit in double-series and triple-series connections is a necessary step in developing the ac quantum Hall effect as an intrinsic standard of resistance.     

当代计量科学发展的新趋势

回顾了计量科学在日常生活和科学研究方面的重要性,指出以实物计量基准建立的计量单位制存在的问题.分析了以基本物理常数(真空光速值c0,元电荷e,普朗克常数h,波尔兹曼常数kB和阿伏加德罗常数NA)和原子的物理特性(约瑟夫森效应和量子霍尔效应)进行计量基本单位量子化研究的重要性和紧迫性.介绍了长度、质量、电学量、温度和时间等计量基本单位量子化研究的新趋势.简单介绍了欧盟计量科学研究计划新动向.     

Calculating the Effects of Longitudinal Resistance in Multi-Series-Connected Quantum Hall Effect Devices

Many ac quantized Hall resistance experiments have measured significant values of ac longitudinal resistances under temperature and magnetic field conditions in which the dc longitudinal resistance values were negligible. We investigate the effect of non-vanishing ac longitudinal resistances on measurements of the quantized Hall resistances by analyzing equivalent circuits of quantized Hall effect resistors. These circuits are based on ones reported previously for dc quantized Hall resistors, but use additional resistors to represent longitudinal resistances. For simplification, no capacitances or inductances are included in the circuits. The analysis is performed for many combinations of multi-series connections to quantum Hall effect devices. The exact algebraic solutions for the quantized Hall resistances under these conditions of finite ac longitudinal resistances provide corrections to the measured quantized Hall resistances, but these corrections do not account for the frequency dependences of the ac quantized Hall resistances reported in the literature.     

Science in High Magnetic Fields: What Could Be Learned?

High magnetic fields are one of the most powerful tools available to scientists for the study, modification and control of matter. This includes the knowledge on correlations effects, interaction mechanisms, structural information and understanding of mesoscopic effects. In this context, a review of recent scientific achievements at the Grenoble High Magnetic Laboratory is given to illustrate, on specific examples, the power of the Magnetic Field probe.     

A Problem in AC Quantized Hall Resistance Measurements and a Proposed Solution

In all experiments reported to date the measured values of the ac quantized Hall resistances R_H varied with the frequency of the applied current, and differed significantly from the dc values of R_H, making it difficult to use the ac quantum Hall effect as an absolute impedance standard. We analyze the effects due to the large capacitances-to-shields existing in the sample probes on measurements of R_H to see if this is the source of the problem. Equivalent electrical circuits are utilized; they contain capacitances and leakage resistances to the sample probe shields, longitudinal resistances within the quantized Hall effect devices, and multiple connections to the devices. The algebraic solutions for the R_H values in these circuits reveal large out-of-phase contributions to the quantized Hall voltages V_H that would make it difficult to do accurate measurements with high precision ac bridges. These large out-of-phase contributions could introduce the linear frequency dependences observed in previous R_H measurements. We predict, however, that quadruple-series connections to the quantum Hall devices yield only small out-of-phase contributions to V_H which may allow accurate measurements of the quantity R_H − R_x, where R_x is the longitudinal resistance along the device.