Scanning tunneling microscopy and spectroscopy study of single electron tunneling in self-assembled molecular nanostructures
Abstract
In this study, an ultrahigh vacuum scanning tunneling microscope (STM) was constructed and used to study the conduction properties of self-assembled molecular nanostructures. The molecular nanostructures were formed by depositing nanometer-size gold clusters on self-assembling monolayer films. The use of self-assembling monolayer films as cluster supports was investigated as a solution to the longstanding problem of reproducibly imaging individual clusters with the STM. Three different self-assembling monolayer (SAM) films were used as supports for gold clusters: 1-octadecanethiol (ODT), 4,4$\sp\prime$-biphenyldithiol (BPD), and $\alpha, \alpha\sp\prime$-xylyldithiol (XYL). Of the three SAM films, XYL films were found to be excellent substrates for scanning tunneling spectroscopy studies of supported clusters. Simultaneous I(V,z) spectroscopy and topography measurements taken over clusters deposited on XYL films revealed reproducible room temperature Coulomb blockade and Coulomb staircase behavior. By fitting a semiclassical double-junction model to the Coulomb blockade and Coulomb staircase data, it was possible to determine the resistance and capacitance values associated with each junction. The model fitting parameters varied as expected due to the changing tip-cluster separation and were consistent with the geometric information in the corresponding STM image. Because of the well-characterized nature of the molecular nanostructures, it was possible to estimate the resistance of a single XYL molecule from the I(V,z) data.
Degree
Ph.D.
Advisors
Reifenberger, Purdue University.
Subject Area
Condensation
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