I have been
working with Dr. Vora (Department of Physics and Astronomy) in his optics
laboratory since the fall of 2014. A significant portion of our efforts focus
on materials characterization, or the process of investigating the properties of
various materials and the way their behaviors change under different
conditions, such as temperature. Our primary methods of exploration are through
absorption, photoluminescence (PL), and Raman spectroscopy, each of which
provide a unique opportunity to probe the material’s underlying structure and
study intermolecular interactions. As an optics lab, we rely heavily on a few
essential pieces of equipment, including a spectrometer, which takes in a beam
of light (typically from a laser) and uses a diffraction grating to disperse
the light across a silicon CCD chip; a liquid Nitrogen-cooled camera, which
contains the CCD chip and sends “images” of the dispersed light to our computer
for analysis; and a cryostat, which is capable of cooling samples to
temperatures as low as 4K.
Over the past two years, I
have conducted experiments on a range of 2D and nanomaterials, including
transition metal dichalcogenides (TMDs) and single-walled nanotubes (SWNTs).
However, my primary responsibility has been the study of charge transfer (CT)
crystals. Unlike atomic crystals (which are the crystals you probably learned
about in chemistry class), CT crystals are formed by stacks of repeating donor
and acceptor molecules. This unique arrangement gives way to emergent physics
that go beyond the constituent molecules. In addition, controlling certain
features of the CT crystal – for example, by modifying the choice of donor and
acceptor or adjusting the molecular packing – can have a significant impact on
its optoelectronic properties. Ultimately, our goal is to identify CT crystals
that can act as semiconductors and would be useful for applications in organic
electronic devices.
I initially received a
traditional URSP grant from OSCAR to study these materials in the summer of
2015. Experiments continued over the course of the 2015-16 school year, and I
was fortunate enough to be the benefactor of additional funding – this time an
intensive URSP grant – to carry on with my work throughout the summer of 2016. At
the outset of this project, we identified one donor-acceptor pair (PTZ-TCNQ, or
phenothiazine-tetracyanoquinodimethane) as a particularly promising candidate.
Most recently, our goal has been to determine the importance of stoichiometry,
or the ratio of donor and acceptor molecules, on the optoelectronic properties
that manifest in the CT crystals. Through a collaboration with Georgetown
University, we have been able to examine five novel stoichiometries using PL
and Raman spectroscopy. These measurements are crucial to understanding which
of the stoichiometries support charge transfer and allow ambipolar conductivity
– in other words, which combinations of molecules are preferential for use in
organic electronics.
Working in a physics lab for
two consecutive years has been an interesting experience, to say the least. I
have been extremely fortunate to have the opportunity to contribute to so many
different aspects of the research process, from constructing the lab and
designing software to taking measurements and analyzing the results – and of
course, learning a lot along the way!
