Interfaces can legitimately be called the final frontier
for chemistry – particularly those interfaces that are
highly flexible – liquids,
glasses, and irregular solids.
Yet picturing interactions at such interfaces is critical
for understanding phenomenon ranging from the impact of
human activities on the environment to macromolecular
configuration and transport across cell membranes.
Our current focus is on water at any interface:
The first challenge in probing such interfaces is finding
a technique that distinguishes molecules at the interface
from the much larger concentration in the bulk phases on
either side of the interface. Our primary probe is the
nonlinear optical spectroscopy sum frequency generation, SFG.
SFG combines a visible photon with an infrared photon to
generate the sum of these two. Scanning the infrared
frequency generates a vibrational spectrum of the surface.
With the advent of increasingly reliable light sources, it
is relatively easy to collect SFG spectra. Interpreting
these spectra remains a challenge. Recently, we developed a
methodology termed polarization angle null,
increasing the power of SFG.
Recently, we have applied SFG and PAN to generate the
first molecular-level glimpse of the ice surface –
simultaneously providing a rich picture of this surface and
demonstrating the power of the PAN methodology. We are
currently pulling together the ice work with work with
aqueous nanodrops to unlock the secrets of formation of
clathrates. Clathrates consist of shells of water around
hydrophobic molecules such as methane. It has been estimated
that clathrates in the oceans contain more carbon than all
the oil discovered on Earth. Global warming may render these
clathrates unstable, presenting a run-away mechanism that
could lead to incredibly high temperatures.
Our most applied work focuses on production of clean
water. It has been suggested that shortage of clean water will be a global crisis far
surpassing the oil crisis. Billions of people world wide
currently lack access to safe drinking water. One of the
initiatives aimed at generating safe water uses solar energy
and semiconductor materials, specifically
TiO2, to oxidize
unsafe substances in the water. Semiconductors oxidize
pollutants in the gas phase with near unit efficiency.
Unfortunately, contact with condensed water greatly reduces
Our efforts are aimed at discovering the
mechanism by which water quenches the oxidation reaction
with the goal of modifying the basic substrate to avoid this