Large-scale atom manipulation on an ionic surface and its prospects

Abstract

In this thesis, a technique is developed to manipulate individual atoms on an ionic surface, with great precision and at a large scale, to study the quantum mechanical properties of atomic assemblies on the nanoscale. We use the needle of a scanning tunnelling microscope (STM) to approach missing atoms - vacancies - in a chlorine monolayer on a copper crystal, inducing a neighbouring Cl atom to jump to the vacancy position by ramping up the tunnel current. This procedure is automated - with sometimes up to 99% reliability - to construct a 1 kB memory where each bit is represented by an atom-vacancy pair. The data storage is stable at low temperatures and can be rewritten automatically, leading to an information density of 502 terabits per square inch, or 0.778 bits/nm^2. Atom manipulation is then used to build other one- and two-dimensional structures with varying sizes and atom densities. In artificial crystals made of vacancies, standing wave patterns are observed at certain energies, suggesting that it is possible to tune electronic properties of the material, such as the dispersion, by controlling the local geometry with atomic assembly. In the rest of the thesis, more structures were built by atom manipulation in order to investigate the coupling between assemblies of vacancies that form 'artificial molecules'. Resonances in scanning tunnelling spectroscopy measurements indicate the existence of quantum dots on the apex of the STM tip, of which the properties are explored. The chlorine terminated copper surface is also investigated for its use as a decoupling layer suitable for magnetic adatoms.