Stabilization for Atomic Tracking Control of the Scanning Tunneling Microscope Tip by Referring Regular Crystalline Surface

摘要

To improve the performance of the atomic tracking control against the outer disturbance, an effect from the surrounding disturbance was evaluated by monitoring a power spectrum of the tunneling current without a XY raster scanning. The dominant disturbance is located in the area whose frequency is lower than 100 Hz. The new tracking control algorithm and the enhancement of the STM stiffness were employed as the stabilization technique. The new control algorithm consists of tracer and limiter units. The tracer was designed to compensate the disturbance whose frequency is lower than 100 Hz. On the other hand, for the disturbance whose frequency is higher than 100 Hz, the limiter was designed to restrict a displacement amplitude of its output within less than a half of the lattice spacing on the crystalline surface. The enhancement of the STM stiffness is also employed for suppressing a disturbance whose frequency is higher than 100 Hz. To evaluate the stabilization technique, the artificial lateral disturbances were applied to the system. By varying the amplitude and the frequency of the artificial sinusoidal disturbance as experimental parameters, a maximum controllable amplitude for a specific frequency were determined, and the performance comparison between the new technique and the conventional PI controller with normal stiffness was made. The results show the new technique can compensate the disturbance of larger amplitude and higher frequency than the conventional method. The atomic tracking control can be made even at daytime with the new technique. The results show the feasibility of the positioning control with atomic resolution using the stabilized atomic tracking control by referring atomic point and array on regular crystalline surface.