Highly stable atom-tracking scanning tunneling microscopy

In this article, we propose a technique for highly stabilized atom-tracking control of a scanning tunneling microscope (STM) tip by referring to an atomic point on a regular crystalline surface. Our aim is to prevent jumping of the STM tip to neighboring atoms and to use it even in a noisy environment. Graphite crystal, whose lattice spacing is approximately 0.25 nm, was utilized as the reference. To improve the performance of the tracking controller against external disturbances, the influence of a disturbance on the STM under various environmental conditions was compared experimentally with the frequency response of the open-loop tracking system. The atom-tracking conditions required to avoid jumping of the STM tip are proposed and applied to the design of the tracking controller by referring to the results of the comparison. The new tracking controller consists of integrator, tracer, and limiter units. The integrator unit is designed to eliminate the steady-state error due to thermal drift. A phase-lag...