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.

人们在铅笔芯中发现的块状石墨是由数百层碳原子堆叠而成。正是这种简单的原子结构使得石墨在轻轻摩擦另一个表面时很容易沉积，因为石墨层可以自由地相互滑动。最近发现，这一过程甚至产生单原子层，即只有一个原子厚的微小碳片。这种扁平的碳同素异形体被称为石墨烯，自其发现以来引起了巨大的关注。它表现出与广泛的设备应用和基础研究问题相关的大量新的电子、机械和光学特性。电子界对石墨烯特别感兴趣，因为它结合了高迁移率、高透明度和承载非常高电流密度的能力。最近，英国气象标准机构国家物理实验室（NPL）表明，石墨烯可以在低温和高磁场下用作电阻标准，因为它显示出量子霍尔效应，并具有非常精确的霍尔电阻平台。然而，石墨烯尚未与目前用于校准电阻器的半导体材料竞争，这可能是由于无序程度所致。该项目的第一个目标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的无序性，从而提高量化的精度。此外，我们的表征结果应该有助于那些生长石墨烯层的人开发生产更优质材料的技术。石墨烯的导电能力无法打开和关闭，除非将其图案化为宽度小于5纳米，因此目前它不适合数字电子中的晶体管等应用。然而，双层石墨烯由一层一层的两层组成，可以使用垂直电场使其绝缘。我们项目的第二部分旨在利用这种行为来控制电子穿过石墨烯时所采取的路径。具体来说，我们的目标是将电子沿着小的传导路径引导到电子陷阱（称为量子点）中，并在那里进行定位。然后，使用高频，我们将一次一个地对单个电子通过点进行计时。其效果是产生一个电流，该电流等于电子上的电荷乘以我们通过点计时的频率。这开启了产生明确电流的可能性，该电流可用作校准科学仪器和对自然基本常数进行非常精确的测量的标准。此外，因为我们使用金属电极的电场来定义量子点，所以限制电势应该非常平滑，并且电荷载流子从该电势的散射应该是镜面的。结果，电子将穿过狭窄的通道而不会发生反向散射。这种行为尚未在石墨烯中出现，可能是因为迄今为止设计的器件具有粗糙的边缘和大量具有复杂散射特性的无序性。通过使用双层门控器件，我们应该能够消除这种散射并增加石墨烯量子点的自旋寿命，从而开启使用铅笔芯作为量子计算机基础的诱人前景。

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.

Reading and writing charge on graphene devices

石墨烯设备的读写充电

• DOI: 10.1063/1.4732802
• 发表时间: 2012
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: Connolly M