Experimental Investigation of Charge Transport and Heat Dissipation in Atomic-Scale Junctions.

Nanoscale Transport;Molecular Electronics;Nanoscale Charge Transport;Nanoscale Energy Transport;Mechanical Engineering;Engineering;Mechanical Engineering

Lee, WoochulLiang, Xiaogan ;

University of Michigan

关键词: Nanoscale Transport;    Molecular Electronics;    Nanoscale Charge Transport;    Nanoscale Energy Transport;    Mechanical Engineering;    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/107102/wolee_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Atomic-scale junctions, which comprise a single-molecule or a chain of atoms bridging two metal electrodes, hold great potential for the advancement of technology. These junctions are believed to offer a range of unique properties for creating novel technological applications because quantum mechanical effects persist even at room temperature. I first describe the design and specifications of a custom-made scanning tunneling microscope that enabled the creation of mechanically stable single-molecule junctions at room temperature. With this instrument, I experimentally investigated charge transport in a series of single-molecule junctions, created by trapping single-molecules of hexanedithiol/octanedithiol/decanedithiol between gold electrodes. My results show that single-molecule junctions can be stably trapped for durations in excess of one minute, at least two orders of magnitude longer than what previous work had demonstrated. Next, I experimentally identified the low-bias conductance of single-molecule junctions using statistical analysis and found that the low-bias conductance exponentially decreases with increasing the length of alkanedithiol molecules. I also performed transition voltage spectroscopy in these alkanedithiol single-molecule junctions to determine the energetic separation between the Fermi level and the frontier molecular orbital. Experimental results confirmed that the energetic separation between the Fermi level and the frontier molecular orbital is independent of the length of the alkanedithol molecules. Subsequently, I investigated heat dissipation in atomic-scale junctions resulting from charge transport. Toward this goal, stiff scanning tunneling probes with an integrated nanoscale-thermocouple at the tip are developed. Using this custom-fabricated probe with the scanning tunneling microscope break junction technique, I stably formed Au-Benzenediamine-Au junction, Au-Benzenediisonitrile-Au junction, and Au-Au atomic junctions and measured heat dissipation in the electrodes of atomic-scale junctions with the integrated nanoscale-thermocouple at the tip of the probe. These measurements show that heat dissipation in the electrodes of molecular junctions, whose electronic transmission characteristics are strongly dependent on energy, is asymmetric (that is, heat dissipation in the electrodes is unequal). In contrast, Au-Au atomic junctions, whose electronic transmission characteristics show weak energy dependence, do not exhibit appreciable asymmetry in their heat dissipation. I found that experimental results are consistent with the Landauer formalism for heat dissipation.