Scanning tunneling spectroscopy on organic molecules

Andre Paul Labonte, Purdue University

Abstract

Scanning Tunneling Spectroscopy was performed on a number of organic molecules. Current-Voltage response, I(V), and dynamic conductance, dI/dV, data were collected using new systematic techniques. The new techniques are understood in terms of known theories and provide a means by which a scanning tunneling microscope (STM) can perform reproducible two-terminal electrical measurements on an organic film. In particular, STS clearly discerns the relative conductivity (resistivity) of organic films. The I(V) and dI/dV data collected demonstrate that the conductivity of organic molecules may be changed in a variety of ways, including: altering molecular endgroups, altering morphology, a chemical doping event, altering the orientation of an internal component of the molecule. It has also been demonstrated that organic molecules can exhibit conducting, semiconducting and insulating behaviors. Through measurements performed on the dI/dV data, a table of conduction gaps and Ef-HOMO has been tabulated for the molecules studied. In certain instances (see Chapter 7), molecular resistances have been estimated from the I(V) data. In summary, this body of work firmly establishes that STS provides a useful tool in the study of the electrical properties of molecular films. Additionally, it has been shown that organic molecules exhibit a broad range of electrical behaviors and that these behaviors can be controllably altered.

Degree

Ph.D.

Advisors

Reifenberger, Purdue University.

Subject Area

Condensation|Molecules|Analytical chemistry

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