Scanning probe microscopy of the quantum Hall effect and charge pumping in graphene for meterological applications

用于计量应用的石墨烯量子霍尔效应和电荷泵的扫描探针显微镜

• 批准号: EP/I029575/1
• 负责人: Charles Smith
• 金额: $ 44.57万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2011
• 资助国家: 英国
• 起止时间: 2011 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FI029575%2F1
• 关键词: Scanning; probe; microscopy; quantum; Hall

The bulk graphite which one finds at the core of a pencil is composed of many hundreds of layers of carbon atoms stacked on top of one another. It is this simple atomic architecture which makes graphite so easy to deposit when gently rubbed against another surface because the layers are free to slide over one another. It was discovered recently that this process even produces single atomic layers, i.e., tiny flakes of carbon which are only one atom thick. This flat allotrope of carbon is called graphene and has created enormous excitement since its discovery. It exhibits a remarkable number of new electronic, mechanical, and optical properties relevant to a wide range of device applications and fundamental research questions. The electronics community is particularly attracted to graphene because it combines high mobility, high transparency, and the ability to carry very high current densities. Recently the UK's meterological standards agency, the National Physical Laboratory (NPL), has shown that graphene can be used at low temperatures and at high magnetic fields as resistance standard as it shows the quantum Hall effect with very accurate plateau in the Hall resistance. Graphene is not yet competitive with the semiconducting material currently used to calibrate resistors, however, probably due to the level of disorder. The first objective of this project is to use low temperature scanning probe microscopy and chemical functionalisation to characterise and then reduce the disorder in these layers, thus improving the precision of the quantisation. In addition, the results of our characterisation should help those who grow the graphene layers to develop techniques for producing better quality material. Graphene's ability to conduct electricity cannot be switched on and off unless it is patterned so as to have widths less than 5 nm, so at the moment it is unsuitable for applications such as transistors in digital electronics. However, bilayer graphene, which consists of two layers one above the other, can be made insulating using a vertical electric field. The second part of our project aims to exploit this behaviour to control the path taken by electrons as they travel through graphene. In particular our aim is to channel electrons down small conducting pathways and into electron traps, known as quantum dots , where they are localised. Then, using high frequencies we will clock single electrons through the dot one at a time. The effect is to produce a current that is equal to the charge on the electron times the frequency that we clock them through the dot. This opens up the possibility of producing a well defined current that could be used as a standard for calibrating scientific instruments and for making very precise measurements of the fundamental constants of nature. In addition, because we are defining our quantum dots using the electric field from metal electrodes, the confinement potential should be very smooth and the scattering of the charge carriers off this potential should be specular. As a result, electrons will go through narrow channels without back scattering. This behaviour has not been seen in graphene yet, probably because devices designed so far have rough edges and a great deal of disorder with complex scattering properties. By using the bilayer gated devices we should be able to get rid of this scattering and increase the spin lifetime in graphene quantum dots, thereby opening up the tantalising prospect of using pencil lead as the basis for a quantum computer.

在铅笔核心上发现的散装石墨由数百层二层碳原子组成。正是这种简单的原子体系结构，当在另一个表面上轻轻摩擦时，石墨使石墨如此易于沉积，因为这些图层可以自由滑动彼此。最近发现，这个过程甚至会产生单个原子层，即只有一个原子厚的碳的微小薄片。这种平坦的碳的同素碳被称为石墨烯，自发现以来就引起了巨大的兴奋。它表现出与广泛的设备应用和基本研究问题相关的大量新电子，机械和光学特性。电子界特别吸引了石墨烯，因为它结合了较高的移动性，高透明度和携带非常高电流密度的能力。最近，英国的仪表标准机构国家物理实验室（NPL）表明，石墨烯可在低温下和高磁场上用作电阻标准，因为它显示了量子厅效应，并在大厅阻力中具有非常准确的高原。石墨烯尚未与目前用于校准电阻器的半导体材料竞争，但是，可能是由于疾病的水平。该项目的第一个目的是使用低温扫描探针显微镜和化学功能化来表征并减少这些层中的疾病，从而提高定量的精度。此外，我们的表征结果应有助于那些种植石墨烯层的人，以开发生产更好质量材料的技术。除非对宽度小于5 nm的宽度进行图案，否则不能打开和关闭地石墨烯的导电能力，因此目前不适合使用数字电子中晶体管等应用。但是，双层石墨烯由两层在另一层上方组成，可以使用垂直电场进行绝缘。我们项目的第二部分旨在利用这种行为来控制电子通过石墨烯传播的路径。特别是我们的目的是将电子沿小型导电途径降低到电子陷阱，称为量子点，并在其定位。然后，使用高频，我们一次将单个电子通过点。效果是产生等于电子上电荷的电流，乘以我们通过点的频率。这打开了产生定义明确的电流的可能性，该电流可用作校准科学仪器的标准，并非常精确地测量自然的基本常数。此外，由于我们使用金属电极的电场定义了量子点，因此限制电势应该非常光滑，并且电荷载体的散射从该电位上应很坦率。结果，电子将通过狭窄的通道而不会散射。这种行为尚未在石墨烯中看到，可能是因为到目前为止设计的设备具有粗糙的边缘和许多具有复杂散射特性的疾病。通过使用双层门控设备，我们应该能够摆脱这种散射并增加石墨烯量子点中的自旋寿命，从而打开使用铅笔铅作为量子计算机的基础的诱人前景。

项目成果

Evidence for formation of multi-quantum dots in hydrogenated graphene.

• DOI: 10.1186/1556-276x-7-459
• 发表时间: 2012-08-16
• 期刊: Nanoscale research letters
• 作者: Chuang C;Puddy RK;Connolly MR;Lo ST;Lin HD;Chen TM;Smith CG;Liang CT
• 通讯作者: Liang CT

Magnetic-field-induced charge redistribution in disordered graphene double quantum dots

• DOI: 10.1103/physrevb.92.155408
• 发表时间: 2015-05
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: K. Chiu;M. Connolly;A. Cresti;J. Griffiths;G. Jones;C. Smith

Tilted potential induced coupling of localized states in a graphene nanoconstriction

• DOI: 10.1103/physrevb.83.115441
• 发表时间: 2011-03-23
• 期刊: PHYSICAL REVIEW B
• 影响因子: 3.7
• 作者: Connolly, M. R.;Chiu, K. L.;Smith, C. G.
• 通讯作者: Smith, C. G.

Experimental evidence for Efros-Shklovskii variable range hopping in hydrogenated graphene

• DOI: 10.1016/j.ssc.2012.02.002
• 发表时间: 2012-05-01
• 期刊: SOLID STATE COMMUNICATIONS
• 影响因子: 2.1
• 作者: Chuang, Chiashain;Puddy, R. K.;Liang, C. -T.
• 通讯作者: Liang, C. -T.

Single-particle probing of edge-state formation in a graphene nanoribbon

石墨烯纳米带边缘态形成的单粒子探测

• DOI: 10.1103/physrevb.85.205452
• 发表时间: 2012
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Chiu K