Von Punktkontakten zu Nano-Elektro-Mechanischen Systemen (NEMS) : Herstellung und Charakterisierung von Ein-Atom-Kontakten

Abstract

The study of adjustable atomic contacts is made possible by the use of break-junctions. A break-junction is constituted of a metallic conductor, aluminum or gold for example, which has been deposited on a substrate. This conductor locally possesses an underetched constriction forming a suspended bridge. When bending the substrate this constriction can be stretched in a controlled way. By this means, the stretching of the conductor can be adjusted in such a way, that a contact made of single atoms is stabilized.This research work is subdivided into two parts. On the one hand, single aluminum break-junctions made on bronze substrates were studied at very low temperatures. Using the phenomenon of multiple Andreev reflections we conclude that aluminum, in contrast to gold, does not form monoatomic chains longer than a dimer. A single electron transistor (SET) structure was also characterized at very low temperatures. On the other hand, a system composed of one or two break-junctions on a monocrystalline silicon membrane was developed and characterized at room temperature.This system forms a nano-electro-mechanical-system, named NEMS, integrable in silicon technology. Membranes of a thickness of just 340 nm, were fabricated out of SOI substrates. The mechanical static and dynamic properties of these membranes were studied. Several stable mechanics based on the use of a tip mounted on a piezo were developed. These allow us to address each break-junction on a common membrane individually, both at room temperature and at very low temperature. The effect of laser light on the conductance of a break-junction, which leads to a conductance increase, was studied. The influence of the substrate can be excluded through the use of silicon membranes. The conductance variation is associated with the phenomenon of photoassisted transport. In this work break-junctions initially designed for fundamental physics were integrated on silicon membranes allowing them to be used as electromagnetic sensors.