Methods to determine electrical conductance of single-molecule junctions

Abstract

In this chapter, three major experimental methods, i.e., a break junction (BJ) method, an electromigration (EM) method, and an ultrahigh-vacuum lowtemperature scanning tunneling microscopy (UHV-LT-STM), to measure electrical properties of single-molecule junctions are explained with some remarkable example of studies. The BJ method is the most widely used technique and explained including statistical analytical methods to analyze data. Studies of molecular switch and temperature dependence are shown as examples of studies based on statistical analysis as well as examples of static current-voltage measurements with external field modulations. Techniques related to the BJ method such as distance modulation and electromechanical response measurements are also introduced. Although the EM method can suffer from several problems, it is still useful to measure electrical gate effects and in the preparation of nanoscale gap electrodes. A novel application of the EM method to create in-plane nano-holes that would open a new application field of the single-molecule measurement techniques is shown. The UHV-LT-STM is capable of forming single-molecule junctions on single-crystal surfaces and manipulating molecules on the surface that enables researchers to study singlemolecule junctions under controlled and well-defined structures and environments.