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Haverford College
Departments of Physics and Astronomy
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Summer Research Opportunities in Walter Smith's research group, Summer 2011

I expect to hire up to four undergraduates for research this summer.

A few years ago, my research group, in collaboration with a group from the chemistry department, discovered a remarkable phenomenon: when acid is added to a solution of a carefully chosen porphyrin molecule (the photoactive part of chlorophyll), it self assembles into beautifully straight nanowires, which display an impressive array of photoelectronic behaviors. In the dark, the wires are insulating. When light and voltage are applied, they begin conducting, i.e. a current begins to flow. With continued illumination, the current grows over periods of up to several hours! If the light is removed for a few minutes and then reapplied, the current still flows at a high level, indicating a “memory” of the slow growth period. If instead the applied voltage is reduced to zero, with illumination still applied, the sample generates a current in a direction opposite the previously-applied voltage; thus the sample acts as a solar cell with trainable polarity.

This summer, we will explore the photoelectronic properties of related self-assembled nanowires, in which the porphryin is combined with other materials, including peptides and inorganic nanotubes, to provide additional control of the structure. (The work with peptides is done in collaboration with the groups of Karin Akerfeldt in chemistry and Rob Fairman in biology.)

We will also continue to develop electron beam lithography at Haverford. This method, based on our Scanning Electron Microscope, allows us to create metal patterns in any desired geometry, with feature sizes down to 50 nm. We will use this to create electrode patterns for the work on self-assembled nanowires.

For all projects, you will learn how to image samples with the atomic force microscope, and conduct current-voltage measurements of the samples as a function of the wavelength and duration of illumination.

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