Abstract
The manufacture of integrated circuits with single-molecule building blocks is a goal of molecular electronics. While research in the past has been limited to bulk experiments on self-assembled monolayers, advances in technology have now enabled us to fabricate single-molecule junctions. This has led to significant progress in understanding electron transport in molecular systems at the single-molecule level and the concomitant emergence of new device concepts. Here, we review recent developments in this field. We summarize the methods currently used to form metal-molecule-metal structures and some single-molecule techniques essential for characterizing molecular junctions such as inelastic electron tunnelling spectroscopy. We then highlight several important achievements, including demonstration of single-molecule diodes, transistors, and switches that make use of electrical, photo, and mechanical stimulation to control the electron transport. We also discuss intriguing issues to be addressed further in the future such as heat and thermoelectric transport in an individual molecule.
Highlights
Miniaturization of electronics devices has been progressed rapidly owing to the advanced silicon technology for integrating billions of silicon-based building blocks in a millimeter-scale chip
Electron transport in this single-molecule junction is characterized by charge injection barriers at the electrode-molecule interfaces, which is determined by energy alignment between the electrode Fermi level and a single discrete energy level of the molecule; either the highest occupied molecular orbital (HOMO) or the lowest unoccupied molecular orbital (LUMO) levels
We review three types of break junction techniques used for fabricating single-molecule junctions: scanning probe microscopy (SPM) break junction, micro-fabricated mechanically-controllable break junction (MCBJ), and electromigration break junction (EBJ)
Summary
Miniaturization of electronics devices has been progressed rapidly owing to the advanced silicon technology for integrating billions of silicon-based building blocks in a millimeter-scale chip. Unlike the energy-band dispersion relation of bulk materials, the energy levels are quantized in an individual molecule anchored to electrodes Electron transport in this single-molecule junction is characterized by charge injection barriers at the electrode-molecule interfaces, which is determined by energy alignment between the electrode Fermi level and a single discrete energy level of the molecule; either the highest occupied molecular orbital (HOMO) or the lowest unoccupied molecular orbital (LUMO) levels. We summarize the technical approaches to form singlemolecule junctions with an emphasis on their advantages for fabricating stable molecular bridges It covers essential spectroscopic techniques incorporated in many single-molecule electron transport measurements that exploit inelastic electron-phonon interactions for revealing the presence of a target molecule in the electrode gap. In the final part of this paper, we discuss the potential use of single-molecule thermoelectric devices
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