Tools
-
- Print Version
-
Font Size:
Summer Research Opportunities in Walter Smith's research group, Summer 2008
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 try to gain insights into the conduction mechanisms
in this nanomaterial by measuring the photoconductivity as a function
of gate voltage. The gate is a third electrode, positioned near the nanowires
but not quite touching them. By applying a voltage to the gate, we can
move the energy levels of the quantum states in the nanowires relative
to those of the wires used to bring the electrical current in and out
(the “bias” electrodes), and so can map out the level structure of the
nanowires. Preliminary experiments have shown that the gate voltage produces
quite unexpected results for this system, of a character never before
observed.
In a second project, we will work in collaboration with the groups of
Karin Akerfeldt in chemistry and Rob Fairman in biology. They are synthesizing
a different type of nanowire, which combine peptides (short protein segments)
with porphyrins. Using peptides gives us greater control of the structure
which results from self-assembly of the building blocks, while the porphyrins
should provide photoelectronic activity.