Noise and High Frequency Properties of Single-Molecule Transistors

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****NON-TECHNICAL ABSTRACT****The transistor is the underpinning of the Information Age. Over the last sixty years, the transistor has been reduced from several centimeters to a few tens of nanometers, with each device now more than 1000 times smaller than the diameter of a human hair. As sizes are reduced further, quantum effects become critically important in determining device properties. At the same time, it becomes increasingly difficult to acquire information about the detailed geometry and material quality of the devices. In the last decade the ultimate limit of this scaling has been reached with the development of single-molecule transistors (SMTs), where the critical channel for current is a small molecule 1-2 nm in size. These devices are excellent tools for examining the physics of conduction at the nanoscale, including the origins of dissipation and the importance of electron-electron interactions. This award supports a project with the goal of extending SMT studies beyond electrical conduction to include measurements of electrical noise. Noise, in the form of fluctuations in the current through the device, is predicted to provide valuable information about both vibrational and magnetic processes within SMTs. Two graduate students will be trained in state-of-the-art nanofabrication methods and will use both low- and high-frequency techniques to measure the noise in SMTs under various conditions, thus preparing them for future academic or industrial careers. If successful the research results will provide new insights into the physics relevant to future technologies, while the work itself will open the door to further new measurements, including the detection and manipulation of single electron spins. ****TECHNICAL ABSTRACT****Single-molecule transistors (SMTs) have been developed over the last decade, and have been outstanding tools for examining the physics of conduction at the nanometer scale. SMTs are highly quantum mechanical systems where electron-electron, electron-vibrational, and spin-based interactions can all be strong. One persistent challenge in understanding such structures is the limited information available through DC characterization of electronic conduction. Higher frequency measurements of conduction as well as shot noise can provide much deeper insight into the roles of electron-vibrational and strong correlation effects. Shot noise in particular gives information about the correlations between electron tunneling events. This award supports a project to use both low- and high-frequency methods to measure shot noise in SMTs under various conditions. In SMTs containing unpaired electrons, shot noise will be used to test the theoretical prediction that the effective charge of the electron is modified to a fractional value when transport takes place via the Kondo process. These measurements will lay the groundwork for the eventual development of high frequency ?RF-SMTs? and possible single-molecule electron spin resonance. This program will provide state-of-the-art training of two graduate students in nanoscale science fabrication and measurement techniques thereby preparing them for future careers in academic or industrial research.