The research in our lab is the application of molecular spectroscopic
methods to the study of surface adlayers and ODMR:
Disorder-to-Order Transitions in Adlayer Molecules on Al2O3 (0001).
Molecules were vacuum deposited onto a cold surface, thereby creating an
amorphous adlayer. The surface was then heated and the disorder-to-order
transition observed by monitoring the emission from the photoexcited molecules.
Subtle changes in the molecular environment during the transition were
observed to cause dramatic changes in the spectrum and the intensity.
In naphthalene and benzophenone molecules, the intensity decreased due
to thermally enhanced nonradiative processes. In other molecules,
such as cycloalkanones, the intensity increased due to enhanced spin-orbit
interaction due to molecular aggregation.
Multiple Trap Sites in 2-Indanone Single Crystals. The second
area of research is the characterization of trap sites in 2-indanone by
a method known as optically detected magnetic resonance (ODMR). In
ODMR, the energies of the sublevels in the phosphorescent triplet state
is detected by slowly sweeping the frequency corresponding to the resonant
energies. Since the population in the sublevels is determined by
the individual population and decay kinetics, it is not equal in the three
sublevels. Hence, the perturbation of the population by the presence
of the resonant field can be detected by changes in the emission intensity.
In the case of 2-indanone, deuteration of the hydrogens on the
a-carbon gives rise to a multiple trap sites in the single crystal.
With the help of Dr. David Marten and his students, several specific a-deuterated
2-indanone were synthesized. The traps were then definitively assigned
and characterized.