Seminar Abstracts
Fall 2009
Single Molecule Charge Transfer and Localization at Interfaces
Eric Borguet
Department of Chemistry, Temple University, 130 Beury Hall, 1901 North 13th
Street, Philadelphia, PA 19122, USA
Charge transfer through and between molecules is central to many important
processes in chemistry. In particular, studying the conductivity of single
molecules can contribute to a better understanding of charge transfer
through molecules, and also help develop better molecular wires and other
building blocks of molecular electronics, light harvesting devices, etc. We
will discuss the results of a number of different experimental approaches
designed to understand these processes at the single molecule level. We
measure the conductivity of molecules using the STM break-junction method
that utilizes repeatedly formed circuits where one or a few molecules are
trapped between two electrodes, at least one of which has nanoscale
dimensions. The statistical analysis of thousands of measurements yields
the conductance of single molecules. Of particular interest is the role of
the molecule-electrode contact, which we have investigated using especially
designed linker groups, in conjugated organic oligomers, as well as Peptide
Nucleic Acids (PNA).[1-3] Experiments to probe charge transfer between
molecules is made possible because STM can distinguish between oxidized and
reduced porphyrin species on electrodes so that two-dimensional charge
diffusion can be observed.[4]
1. Conjugated Thiol Linker for Enhanced Electrical Conduction of
Gold-Molecule Contacts, Alexei V. Tivanski, Yufan He, Eric Borguet, Haiying
Liu, Gilbert C. Walker and David H. Waldeck, Journal of Physical Chemistry
B, 109(12); 5398-5402 (2005).
2. Optimizing Single Molecule Conductivity of Conjugated Organic
Oligomers
with Conjugated Carbodithioate Linkers, Yangjun Xing, Tae-Hong Park,
Ravindra Venkatramani, Shahar Keinan, David N. Beratan, Michael J. Therien,
and Eric Borguet (submitted).
3. Charge Transfer through Single Stranded Peptide Nucleic Acid
Composed
of Thymine Nucleotides, Amit Paul, Richard M. Watson, Paul Lund, Yangjun
Xing, Kathleen Burke, Yufan He, Eric Borguet, Catalina Achim, and David H.
Waldeck, Journal of Physical Chemistry C, 112(18); 7233-7240 (2008).
4. Dynamics of Porphyrin Electron Transfer Reactions at the
Electrode-Electrolyte Interface at the Molecular Level, Y. He and E.
Borguet, Angewandte Chemie International Edition, 46(32), 6098-6101 (2007).
Eric Garfunkel
Department of Chemistry
Rutgers University, Piscataway, New Jersey
The materials changes that the electronics industry is implementing in the core “gate” region of transistors are the result of a decade of focused research. In this presentation we first give an overview of the materials chemistry and structure issues that are at the center of the current changes in semiconductor device production. We then present results of the composition and electronic structure of interfaces critical for future nanoelectronic devices, focusing on novel metal electrodes, high-K dielectrics, and high mobility semiconductors (e.g. TiN/HfO2/Ge). We show high resolution chemical profiling results, discussing reactivity and interdiffusion between layers. In one set of studies, we use isotopic labeling methods to demonstrate how oxygen reacts and diffuses within films, as oxygen stoichiometry is critical to understanding device defects. We then present results of the electronic structure, including energy band alignment, at individual interfaces in these structures. Fermi level pinning, dielectric defects, and other issues will be discussed for the Ge and III-V substrate materials. The interplay between interface chemistry and nanoelectronic device properties is elucidated. Finally, we outline related results on nanowire and organic interfaces as they pertain to transistor, photovoltaic and sensor applications.
National Science Foundation and Semiconductor Research Corporation support are gratefully acknowledged.