新型量子霍尔电阻样品计量应用研究

采用AsGa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。     

基于石墨烯量子点的多相催化剂（英文）

石墨烯量子点作为纳米炭家族中独特的一员,由于其高比表面、丰富的表面化学反应位点和高电荷转移性能,已成为全解水和金属-空气电池等领域中的重要催化剂。了解石墨烯量子点在多相催化中的催化机理有助于合理设计高性能石墨烯量子点基催化剂。本文综述了近年来石墨烯量子点基多相催化剂的合成、改性及在全解水、金属-空气电池等领域应用的研究进展。讨论了目前石墨烯量子点基催化剂研究中存在的问题,并对设计高性能石墨烯量子点基催化剂的前景进行了展望。     

计量院研制成功量子化电学基准

本刊讯量子化电学基准有两项 ,约瑟夫森量子电压基准和量子化霍尔电阻基准。我院的约瑟夫森量子电压基准 ,１９９８年获国家科技进步二等奖。量子化霍尔技术难度很大 ,近期经科技人员努力 ,突破了难关 ,取得了良好结果。２０００年计量院完成了“量子化霍尔电阻基准”课题的研制工作 ,并在同年１０月与日本电子综合技术研究所（ＥＴＬ）进行了双边比对 ,比对结果两国１Ω电阻量值的差别为１ ３ｎΩ。根据日本专家估计 ,用１Ω实物电阻作为可运输标准进行此种双边比对时 ,其不确定度约为±５ｎΩ。中、日两国的此项比对结果在国际上已发表的…     

石墨烯量子点的制备及应用研究进展

石墨烯量子点是一种新型的零维碳纳米材料,不同于常规碳材料,因其具有量子局限效应和边缘效应,在催化、检测、生物医学以及传感器等化工领域显示出重要的应用价值。因此,石墨烯量子点的制备以及应用研究迅速成为石墨烯研究领域的热点之一。综述了石墨烯量子点的制备以及应用研究的发展现状,探讨了现今该领域亟待解决的问题以及今后的发展趋势和前景。     

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。     

我国实现米级单晶石墨烯的制备

<正>石墨烯是典型的二维轻元素量子材料体系,具有优越的量子特性。科学界在石墨烯体系中观察到了许多量子现象和量子效应,石墨烯已经成为凝聚态物理研究领域的重要量子体系,在未来量子信息、量子计算和量子通讯等领域具有广泛的应用前景。     

石墨烯/量子点复合材料的研究进展

石墨烯/量子点复合材料因其具有优异的性能,近年来已成为国内外研究的热点。着重介绍了石墨烯/量子点复合材料的制备方法和应用进展。     

石墨烯材料在水处理方面的研究进展

石墨烯具有独特的结构和优异的物理、化学性能,其作为水处理材料的应用前景值得期待。本文介绍了石墨烯、氧化石墨烯及还原氧化石墨烯材料与水处理相关的主要性能,对石墨烯及其衍生物吸附重金属离子及有机物的研究及进展进行了综述,分析了相关的研究机理及主要影响因素;对各种石墨烯复合材料在水处理方面的研究逐一进行了介绍,包括磁性及非磁性石墨烯复合材料、石墨烯光催化复合材料;最后对该研究领域存在的问题及面临的挑战进行了分析,并对该领域研究发展趋势进行了展望。     

石墨烯晶畴尺寸的可控生长及其对材料电学性能的影响

采用化学气相沉积技术(CVD)在铜箔衬底上实现了石墨烯单晶畴的可控生长,并用两步生长法制备了不同单晶畴尺寸的多晶石墨烯连续膜。利用光学显微镜和拉曼光谱仪对石墨烯的形貌和结构进行了表征。通过对转移到SiO2衬底上石墨烯连续膜的霍尔测试发现,石墨烯晶畴尺寸变化对其连续膜的电学性能影响显著。石墨烯连续膜的晶畴尺寸越大,其方块电阻越小,载流子迁移率越高。     

石墨烯量子点的制备及其生物应用

石墨烯量子点(GQDs)作为石墨烯材料的衍生物, 在兼顾了石墨烯优良特性的同时, 又依靠量子限域效应和边界效应而具备了光致发光(PL)等石墨烯所不具备的性质, 而且在细胞毒性、生物相容性等方面也有更好的表现。近年来, GQDs的制备方法日趋多样化, 通常将其分为Top-down和Bottom-up两种方法。随着GQDs在生物医学领域应用的不断深化, 对其形貌和尺寸控制也提出了更高的要求, 因此本文对Bottom-up法等一些有希望精确控制GQDs形貌和尺寸的方法进行了重点介绍, 并对各种方法的优缺点进行了对比。目前GQDs的生物应用主要包括生物成像、生物传感器、药物输运和抗菌剂等, 本文对其各种应用分别进行了介绍, 并结合各种应用对GQDs的要求给出了制备方法的建议。文章最后还指出了GQDs研究中存在的问题及发展方向。     

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.     

中国计量科学研究院建成的量子化霍尔电阻标准

国际计量委员会推荐 ,1990年 1月 1日起在世界范围内启用量子化霍尔电阻标准代替使用了几十年的电阻实物基准。中国计量科学研究院经过十几年的努力 ,于 2 0 0 3年建成了量子化霍尔电阻标准。自主研制了能满足实际量值传递工作要求的量子化霍尔器件 ,并建成了高精度的低温电流比较仪 ,以把量子化霍尔电阻量值传递到日常检定工作中使用的十进位电阻。课题成果中有多项独创性的成就。目前所建量子化霍尔电阻标准的不确定度为 10 -10 量级 ,达到国际领先水平。     

中国计量科学研究院建成量子化霍尔电阻标准

国际计量委员会推荐，1990年1月1日起在世界范围内启用量子化霍尔电阻标准代替使用了几十年的电阻实物基准。中国计量科学研究院经过十几年的努力，在2003年建成了量子化霍尔电阻标准。课题组自主研制了能满足实际量值传递工作要求的量子化霍尔器件，并建成了高精度的低温电流比较仪，以把量子化霍尔电阻量值传递到日常检定工作中使用的十进电阻值。课题成果中有多项独创性的成就。目前所建量子化霍尔电阻标准的不确定度为10^-10量级，达到国际领先水平。     

Degradation of GaAs/AlGaAs Quantized Hall Resistors With Alloyed AuGe/Ni Contacts

Careful testing over a period of 6 years of a number of GaAs/AlGaAs quantized Hall resistors (QHR) made with alloyed AuGe/Ni contacts, both with and without passivating silicon nitride coatings, has resulted in the identification of important mechanisms responsible for degradation in the performance of the devices as resistance standards. Covering the contacts with a film, such as a low-temperature silicon nitride, that is impervious to humidity and other contaminants in the atmosphere prevents the contacts from degrading. The devices coated with silicon nitride used in this study, however, showed the effects of a conducting path in parallel with the 2-dimensional electron gas (2-DEG) at temperatures above 1.1 K which interferes with their use as resistance standards. Several possible causes of this parallel conduction are evaluated. On the basis of this work, two methods are proposed for protecting QHR devices with alloyed AuGe/Ni contacts from degradation: the heterostructure can be left unpassivated, but the alloyed contacts can be completely covered with a very thick (> 3 μm) coating of gold; or the GaAs cap layer can be carefully etched away after alloying the contacts and prior to depositing a passivating silicon nitride coating over the entire sample. Of the two, the latter is more challenging to effect, but preferable because both the contacts and the heterostructure are protected from corrosion and oxidation.     

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.     

Comparison of the quantized Hall resistance and ohm NRC

A report is given of the progress towards the establishment of a quantized Hall resistance (QHR) measurement system suitable for maintaining the NRC (National Research Center of Canada) representation of the ohm. A system using a cryogenic current comparator bridge is described and compared to the previously reported 15 T, 20-mK potentiometric system. General problems concerning the use of the quantized Hall resistance to realize a representation of the ohm are discussed     

Enhancing the Quantum Anomalous Hall Effect by Magnetic Codoping in a Topological Insulator

The quantum anomalous Hall (QAH) effect, which has been realized in magnetic topological insulators (TIs), is the key to applications of dissipationless quantum Hall edge states in electronic devices. However, investigations and utilizations of the QAH effect are limited by the ultralow temperatures needed to reach full quantization—usually below 100 mK in either Cr‐ or V‐doped (Bi,Sb)₂Te₃ of the two experimentally confirmed QAH materials. Here it is shown that by codoping Cr and V magnetic elements in (Bi,Sb)₂Te₃ TI, the temperature of the QAH effect can be significantly increased such that full quantization is achieved at 300 mK, and zero‐field Hall resistance of 0.97 h/e² is observed at 1.5 K. A systematic transport study of the codoped (Bi,Sb)₂Te₃ films with varied Cr/V ratios reveals that magnetic codoping improves the homogeneity of ferromagnetism and modulates the surface band structure. This work demonstrates magnetic codoping to be an effective strategy for achieving high‐temperature QAH effect in TIs.     

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.     

金属-绝缘体颗粒膜的巨霍尔效应研究进展

介绍了金属-绝缘体颗粒膜巨霍尔效应的研究背景及样品的制备与测量，总结了近年来该领域的研究进展和应用前景，最后对研发应用中存在的问题和趋势提出了自己的看法。