Real-time atomic encoder using scanning tunnelling microscope and regular crystalline surface

Abstract

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.

Two-dimensional encoder with picometre resolution using lattice spacing on regular crystalline surface as standard

“…Therefore, the two unit lattice vectors of the HOPG crystal can be used, in combination with an STM, as two-dimensional references (or standards) with sub-nanometre resolution or less [7][8][9]. The authors have previously demonstrated atomstep control along the a 1 or a 2 direction on the HOPG crystalline surface over a range of 200 atoms using STM [10]. By this method, counting the unit lattice vector a 1 or a 2 introduces a displacement measurement along the a 1 or a 2 direction, and serial counting of the unit lattice vectors a 1 and a 2 allows for two-dimensional displacement measurement [10].…”

“…The authors have previously demonstrated atomstep control along the a 1 or a 2 direction on the HOPG crystalline surface over a range of 200 atoms using STM [10]. By this method, counting the unit lattice vector a 1 or a 2 introduces a displacement measurement along the a 1 or a 2 direction, and serial counting of the unit lattice vectors a 1 and a 2 allows for two-dimensional displacement measurement [10]. However, it is impossible to realize simultaneous two-dimensional displacement measurement in arbitrary directions.…”