Development of fast high-sensitivity scanning charge microscope

本项目的目标是研制一种多功能的快速扫描电荷显微镜，它使用单电子晶体管作为电荷传感器，工作在2K。我们引进了低温扫描剪切力显微镜作为电荷显微镜的基本伺服扫描系统。剪切力显微镜使用一根锋利的光纤作为力传感器，光纤固定在传感器头上的石英振荡器上。我们开发了一种在尖端制作单电子晶体管的工艺。该工艺包括利用色散补偿光纤的选择性刻蚀技术对光纤进行锐化处理，并主要通过真空蒸发沉积在锐化光纤的尖端形成双小隧道结。我们还研制了通用的单电子晶体管快速测量电路。电路的主要部分是由运算放大器(运算放大器)组成的电流放大器，它测量被测设备的电导。通常，带偏置电压的电导测量受信号电缆的杂散电容的影响小于带偏置电流的电阻测量。通过使用基于C-MOS的运算放大器(TLC4501)并将放大器放在液氦中靠近传感器的位置，使信号电缆变短，或者使用三轴信号电缆，在信号线电压下用电压跟随器驱动其中间导体，有效地降低杂散电容，进一步降低了信号电缆的杂散电容的影响。遗憾的是，我们在电荷传感器的制造工艺的开发上花费了大量的精力和时间，在项目期间，我们没有成功地集成上述所有元件，并构建了电荷显微镜本身。

The goal of this project is to develop a versatile fast scanning charge microscope which utilizes the single-electron transistor as its charge sensor and works at 2K. We have introduced a low-temperature scanning shear-force microscope as the basic servo scanning system for the charge microscope. The shear force microscope uses as its force sensor a sharpened optical fiber that is fixed on a quartz oscillator on the sensor head. We have developed a fabrication process of a single-electron transistor on the tip of the sharpened optical fiber. The process comprises a sharpening process of an optical fiber by using a selective etching technique of a dispersion- compensation fiber, and a formation of double small tunnel junctions on the tip of the sharpened fiber mostly by means of a vacuum-evaporation deposition.We have also developed versatile fast-measuring circuits of the single-electron transistor. The main part of the circuits is a current amplifier that is composed of an operational amplifier (opamp) and it measures a conductance of a measured device. Generally a conductance measurement with a voltage biasing is less influenced by the stray capacitance of the signal cable than the resistance measurement with a current biasing. We have further reduced the influence of the stray capacitance of the signal cable by using a C-MOS based opamp (TLC4501) and putting the amplifier near the sensor device in liquid He and making the signal cable short, or by using a tri-axial signal cable and driving its middle conductor with a voltage follower at the voltage of the signal line and reducing the stray capacitance effectively.Unfortunately we have spent a lot of effort and time on the development of the fabrication process of the charge sensor, and we have not succeeded in integrating all the elements described above and constructing the charge microscope itself during the period of the project.