Development of fast high-sensitivity scanning charge microscope

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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.