B.S., 1979, University of Minnesota
Ph.D., 1985, University of California at Berkeley
Honors and Awards
Editorial Advisory Board, Journal of Physical Chemistry Letters, 2013–15
Chemist of the Year, South Carolina Section of the ACS, 2014
USC Educational Fund Research Award, 2007
Fellow of the American Physical Society, 2000
Sloan Foundation Fellowship, 1992
National Science Foundation Presidential Young Investigator, 1990
Camille and Henry Dreyfus Distinguished Young Faculty Award, 1987
Ultrafast Laser Spectroscopy. The times that are important for molecular processes are fast. Single-collision
times in solids and liquids are near 0.1 ps; sound waves transmit conformational changes
across protein in 10 ps; solar energy captured by a semiconductor nanoparticle persists
no longer than a few 10's of ns. If we want to understand the macroscopic behavior
of materials in terms of molecular properties, experiments on ultrafast time scales
Although these times are natural for molecular processes, they cannot be measured
by standard techniques. Ultrafast lasers are needed. In our laboratory, pulses with
durations as short as 50 fs and with peak intensities in the 10 gigawatt range are
used to investigate these processes. These pulses are only 15 microns in length and
contain a only a few cycles of the electric field. Using these pulses, we observe
events as fast as the breaking of a chemical bond or of a single collision in solution.
Multidimensional Kinetics for Complex Dynamics. Molecules in complex materials often do not have a well-defined rate; the dynamics
spread over a wide time range. Either local heterogeneity or complex relaxation pathways
can be responsible. We have pioneered multidimensional kinetics as a way to disentangle
these possibilities. For ultrafast lasers, a sequence of six pulses (called a MUPPETS
experiment) has been developed to measure 2D kinetics. For single-molecule measurements
and computer simulations, 2D and 3D correlation methods are being developed. These
techniques can measure the relaxation within a specific subpopulation, extract the
distribution of subpopulations, and find the rate of exchange between subpopulations.
Our interest is not confined to a single material. We seek problems where the complexity
of the system demands new insights from advanced methods. Current and future interests
include (but are not limited to):
Energy Pathways in Nanostructures. Semiconducting nanostructures offer great promise for harvesting solar energy, but
no two nanostructures are ever identical at the atomic level. Lattice defects, variation
in surface structure and misplaced passivating molecules are common. They greatly
affect energy flow, but are difficult to detect in structural measurements. MUPPETS
offers a means to measure the different fates of energy in different particles within
a real sample.
Ionic Liquids. Organic, ionic liquids possess unusual macroscopic properties that make them exceptionally
useful in new laboratory and commercial applications. Our 2D analysis of computer
simulations suggest that some of these properties arise from short-lived heterogeneity
at the molecular level. New MUPPETS experiments are being developed to test these
Glass Dynamics. Near the glass transition, there is strong circumstantial evidence that the liquid
breaks up into microscopic regions of differing viscosity. Multidimensional analysis
of single-molecule experiments measure these effects directly and quantitatively near
the transition. Polarization-resolved MUPPETS measurements can trace this heterogeneity
to its origins at higher temperatures and shorter relaxation times.
Our research draws on chemistry, laser physics, statistical mechanics, spectroscopy,
and biology to answer broad questions in chemistry, physics, and materials science.
Growth into unfamiliar areas is expected and is facilitated by interactions with students
and postdocs from a variety of fields.
Verma, S. D.; Corcelli, S. A.; Berg, M. A. Rate and Amplitude Heterogeneity in the
Solvation Response of an Ionic Liquid. J. Phys. Chem. Lett. 2016, 7, 504–508.
Wu, H.; Berg, M. A. Two-Dimensional Anisotropy Measurements Show Local Heterogeneity
in a Polymer Melt. J. Phys. Chem. Lett. 2014, 5, 2608 – 2612.
Sahu, K.; Wu, H.; Berg, M. A. Rate Dispersion in the Biexciton Decay of CdSe/ZnS Nanoparticles
from Multiple Population-Period Transient Spectroscopy. J. Am. Chem. Soc. 2013, 135, 1002 – 1005. DOI: 10.1021/ja3112109.
Berg, M. A. Multidimensional Incoherent Time-Resolved Spectroscopy and Complex Kinetics.
Adv. Chem. Phys. 2012, 150, 1 - 102.
Kern, S. J.; Sahu, K.; Berg, M. A. Heterogeneity of the Electron-Trapping Kinetics in
CdSe Nanoparticles. Nano Lett. 2011, 11, 3493 - 3498. DOI: 10.1021/nl202086b.