Identifier

etd-07122007-142343

Degree

Master of Science in Electrical Engineering (MSEE)

Department

Electrical and Computer Engineering

Document Type

Thesis

Abstract

The goal of this work is to characterize and to analyze hybrid electronic materials (HEMs) using fluorescence (FL) spectroscopy and conductive probe-atomic force microscopy (CP-AFM) in order to investigate the electrical and optical properties of these materials. Currently, research efforts to characterize novel organic materials for the determination of molecular level transport properties are of great interest.[6] One of the most interesting organic materials is the porphyrin molecule, which exhibits behavior useful for memory applications.[4] Colloidal CdS quantum dots (Q-CdS) capped with dioctyl sulfosuccinate (AOT) and thiol functionalized porphyrin molecules are explored for their potential application to next-generation hybrid electronic systems. Q-CdS capped with AOT self-assembled on various substrates are used to study the effect of electron transport in colloidal quantum dots using FL spectroscopy. In turn, porphyrin molecules chemisorbed onto gold surfaces are used to study the phonon-electron interaction in these molecules due to their metal cations. Maximum fluorescence intensities are obtained at specific angles of incidence, such as 80 and 45 degree with respect to the sample, for Q-CdS and porphyrin molecules, respectively. Emission spectra of Q-CdS absorbed onto different substrates such as gold, GaAs, and mica show a slight but systematic redshift of peak characteristics of spatially confined phonon interactions. The effects of relative quantum dot size, different substrates, and light intensity are discussed in this thesis. As the relative sizes of the quantum dots decrease, the excitonic peaks are slightly blue shifted. In order to study the electron transport mechanism of a single or a few molecules in metal-molecule-metal heterostructures, the electronic characteristics of self-assembled monolayers (SAMs) of n-alkanethiols such as hexanethiol and octanethiol are investigated using CP-AFM. SAMs of alkanethiols on gold surfaces have been shown to form stable surface structures.[21] Studies have shown that thiolated porphyrins readily self-assemble on gold surfaces.[73] The I-V characteristics of self-assembled monothiolated porphyrin molecules on gold substrates are measured under ambient conditions. I-V traces of porphyrin molecules behave sigmoidally according to the Simmons Equation for square barrier tunneling and illustrate that the electron transport mechanism through porphyrin is direct tunneling for the applied bias levels in this study.

Date

2007

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Theda Daniels-Race

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