Development of Noncontact Mode Scanning Force/Tunneling Microscopy

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Simultaneous measurement of atomic force and tunneling current will offer new opportunity to investigate the mechanical and electronic properties on the surface on an atomic scale. However, so far, simultaneous measurement of atomic force and tunneling current has not been achieved on atomic scale. This is due to the following three main reasons : (i) It is much difficult to measure weak attractive atomic force with a good signal-to-noise (SIN) ratio. (ii) It is much difficult to develop the clean and sharp conducting tip with atomic scale. (iii) It is much difficult to reduce the cross-talk between the atomic force and tunneling current.In this project, we constructed noncontact mode scanning atomic force/tunneling microscope (noncontact AFM/STM) to detect atomic force and tunneling current simultaneously on atomic scale. Atomic force measurement is based on frequency modulation (FM) detection method. The high sensitive atomic force measurement was realized by improving the displacement sensor and FM demodulator. Novel technique to fabricate the clean and sharp conducting Si cantilevers was developed, in which the argon ion sputtering method was used. Also, new technique to measure the atomic force and tunneling current without the cross-talk was developed, which is based on the frequency and time domain method. Measurement conditions for simultaneous measurement of atomic force and tunneling current were investigated theoretically and experimentally.