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 low-pass filter is utilized as the tracer unit to compensate for the dominant disturbance due to vibration/acoustic noise with a frequency lower than the cutoff frequency, fco, of the open-loop tracking system. To improve the phase margin condition of the controller at fco and to suppress the disturbance with a frequency higher than fco, the limiter is designed to include a phase-lead high-pass filter and a saturator whose output is less than one-half of the lattice spacing. The performance of the stabilizing technique, which is to combine the new tracking controller with enhanced STM stiffness, was evaluated using internal/external artificial disturbance generators. The experimental results show that the proposed method has a high capability for maintaining atom-tracking control without any jumping of the STM tip, even in a noisy environment.

In this paper, we demonstrate a technique for highly stable atom-tracking control of a scanning tunnelling microscope (STM) tip by referring to an atomic point on a regular crystalline surface. We also demonstrate an atomic encoder using ‘atom-by-atom’ step control along a crystalline axis. A graphite crystal, whose lattice spacing is approximately 0.25 nm, was utilized as the reference material. To enhance the stability of the atom-tracking control in the presence of external disturbances, a robust controller, consisting of an integrator, a tracer and limiter units, was developed. Experimental results show that the proposed method has high capability for maintaining the atom-tracking control without any jumping of the STM tip to adjoining atoms, even in a noisy environment. This method was also applied to atom-step control of the STM tip by referring to a specific crystalline axis. Atom-stepping control along a crystalline axis over a range of 200 atoms and at a rate of 10 atoms s−1 was performed and demonstrated without missing the atomic array.

No abstract

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 (or atomic array) on a regular crystalline surface. Graphite crystal, whose lattice spacing is approximately 0.25 nm, was utilized as the reference. To enhance stability of the atom-tracking control against external disturbances, a new atom-tracking controller, which consists of integrator, tracer and limiter units, was developed. The integrator unit is designed to eliminate the steady-state error due to thermal drift. A phase-lag low-pass filter is utilized as the tracer unit to compensate the disturbance due to vibration/acoustic noise. To improve the phase margin of the controller, the limiter unit consists of a phase-lead high-pass filter and a saturator whose output is less than one-half of the lattice spacing. The performance of the stabilized technique, which is to combine the new tracking controller with enhanced STM stiffness, was evaluated using internal/external artificial disturbance generators. The experimental results show that the proposed method has a high capability for maintaining atom-tracking control without any jumping of the STM tip to neighboring atoms, even in a noisy environment. The method was also applied to atom-stepping control of the STM tip by referring to some crystalline axis. The atom-stepping control atom by atom along the crystalline axis over a range of 200 atoms, at a rate of 10 atoms/sec, was performed without missing the atomic array.