Methods to Determine Electrical Conductance of Single-Molecule Junctions
In this chapter, three major experimental methods, i.e., a break junction (BJ) method, an electromigration (EM) method, and an ultrahigh-vacuum low-temperature scanning tunneling microscopy (UHV-LT-STM), to measure electrical properties of single-molecule
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Methods to Determine Electrical Conductance of Single-Molecule Junctions Ryo Yamada
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. Keywords Break junction • Electromigration • Scanning tunneling microscope • Statistical analysis • Conductance histogram • Two-dimensional histogram • Cross-correlation analysis • Distance modulation
2.1 Introduction One of the great challenges in single-molecule electronics is the preparation of single-molecule junctions. In the early stages of experimental studies, metal contacts were deposited on top of monolayers prepared on metal surfaces by Langmuir-Blodgett and self-assembly techniques to investigate the charge transport through monolayers [1]. Other techniques including nano-pore technique [2],
R. Yamada () Graduate School of Engineering Science, Osaka University, Osaka, Japan e-mail: [email protected] © Springer Science+Business Media Singapore 2016 M. Kiguchi (ed.), Single-Molecule Electronics, DOI 10.1007/978-981-10-0724-8_2
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metal-nanoparticle contact [3–5], and cross wire contact [6] were developed. Although interesting characteristics of the single-molecule and monolayer junctions were reported, these techniques suffered low yield of working device and reproducibility. The poor reproducibility is attributed not only to the difficulty of experimental procedure itself but also to the nature of single-molecule junctions that have a wide variety of structures and flexibility. A mechanical break junction method enabled researchers to obtain a large number of experimental results on the electrical conductance of the single-molecule junctions and to discuss results on both the statistics and the detailed static measurements on a single-molecule junction [
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