Characterization of charge transport in molecular scale electronic devices has to date shown exquisite sensitivity to specifics of device fabrication and preparation. Thus, intrinsic molecular band structure has been problematic to extract from published results. Here we demonstrate cross-platform device characterization for the metal-insulator-metal (M-I-M) tunneling through a large bandgap alkanethiol self-assembled monolayers (SAMs).
Electronic charge transport is investigated for various-length alkanethiol SAMs using three different characterization methods, in which lateral areas span the nanometer to the micrometer scale. In each method, the measured current-voltage characteristics are analyzed with metal-insulator-metal tunneling models. Transport parameters are determined where possible and compared across methods, as well as to previously reported values. Advantages and limitations of these various methods for characterizing molecular junctions are briefly discussed.
We also perform inelastic electron tunneling spectroscopy (IETS) on alkanedithiol nanoscale devices. The IETS spectrum of the octanedithiol device clearly shows vibrational signatures of an octanedithiolate bonded to gold electrodes. The pronounced IETS peaks correspond to vibrational modes perpendicular to the junction interface, which include the Au-S and C-C stretching modes and CH2 wagging mode. The observed peak intensities and peak widths are in good agreement with theoretical predictions.
Takhee Lee received a B.S. and M.S. degree in physics at Seoul National University, Seoul in Korea in 1992 and 1994, respectively. Then, he attended Purdue University in 1995 and obtained a Ph.D. degree in Physics in 2000. His Ph.D. thesis is Electronic properties of Au nanoclusters/semiconductor structures with low resistance interfaces (advised by Prof. Ron Reifenberger). Since 2000, he has been in the Department of Electrical Engineering at Yale University as Postdoctoral Associate (supervised by Prof. Mark Reed). His current research interest is focused on molecular nanotechnology. Specific research interests are (1) characterize the electrical and structural properties of nanostructures involving single molecules, nanoparticles, and their arrays and (2) assemble these "nano-building blocks" (such as molecules, nanoparticles) into electronic devices.
MSEE 239, Purdue University, West Lafayette, IN