Exploring the electrical conductance of single molecules via mechanically controllable break junctions

In this thesis we use a mechanically controllable break junction technique to
measure the electric transport properties of single molecules. This technique
allows to control the distance between two atomic sized contacts, matching
the size of a molecule. Via an implemented liquid cell we are further
able to investigate molecules in a controlled liquid environment. We start
with a study on “simple” test molecules, as octanedithiol or bipyridine, to
obtain a better understanding on metal-molecule-metal junctions. To overcome
molecular fluctuations, we introduce a robust statistical analysis of
repeatedly formed molecular junctions. We then move on and compare the
conductance of four different conjugated oligomers. Finally, we show the
immobilization of new switchable molecules, which incorporates the previously
studied conjugated molecules.
This thesis is structured as follows:
• Chapter 1 gives a brief introduction on mechanically controllable break
junctions, basic theory on electron transport through single atoms as
well as molecules and a quick look into data analysis by histograms.
• Chapter 2 describes the fabrication process of a break junction as
well as the setup which we built to measure molecules in a liquid
environment.
• In Chapter 3 we present a single molecule measurement of bipyridine
and octanedithiol and on this basis a robust statistical analysis without
any data selection.
• Chapter 4 shows a comparison of conductance of four conjugated
oligomers at the single molecule level.
• In Chapter 5 we demonstrate the immobilization of a newly synthesized
molecule with the potential of a molecular switch in the break junction.