Charles A. Schmuttenmaer

Professor, Physical Chemistry, Biophysical Chemistry, Biochemistry, Materials Chemistry, Nano Chemistry
E-mail: charles.schmuttenmaer@yale.edu
Web site: http://www.chem.yale.edu/~cas

Biographical Sketch

B.S. University of Illinois, Urbana-Champaign, 1985
Ph.D. University of California, Berkeley, 1991
Postdoctoral Fellow, University of Rochester, 1991-1994
Joined Yale Faculty 1994
Camille and Henry Dreyfus Foundation New Faculty Award, 1994
Yale University Arthur Greer Memorial Prize, 1996
Recipient of the NSF CAREER Award, 1997
Sloan Research Fellowship, 1999 – 2001

Research Description

Efforts in the Schmuttenmaer group over the last 5 years have opened up the far-infrared (FIR) region of the spectrum to direct time-resolved studies. The importance of time-resolved studies in general has been demonstrated over the last 20 years, using visible, UV, and IR lasers. New frontiers in chemistry, physics, biology, optics, electronics, and communications have been unveiled. It is well known that dynamical information can only be obtained when the observation time is short compared to the timescale at which the system is evolving. For example, a photograph of a waterfall with a slow shutter speed reveals only blurred drops. However, a series of high speed photographs will display the individual drops, as well as the manner in which they coalesce and break apart. There now exists the possibility to perform FIR time-resolved spectroscopy on a sub-picosecond timescale.

In broad terms, we have four lines of research, each of which has both experimental and theoretical/computational components. First, we can directly measure rapid intramolecular charge transfer by monitoring the FIR pulse that is emitted during this process. A charge transfer time on the order of 1 ps will generate a pulse in the FIR (as explained by Maxwell's equations). In a similar manner, we can detect the rapid loss of magnetization due to pulsed laser heating of a magnetic thin film. This process is displayed schematically here. Click on the image, which represents the sum of the dipoles of an oriented sample (a molecular monolayer, for example). When the sample is photoexcited, the dipole moment suddenly increases, and that change in polarization radiates a wave in all directions.

Second, solvation in liquids can be better understood by probing low frequency collective dynamics. The very nature of a liquid is characterized by its low frequency intermolecular vibrations and translations, and these motions occur in the FIR region of the spectrum. We directly probe the transient behavior of these intermolecular interactions as the solvent responds to a photoexcited dye molecule nearby.

Third, we determine the transient photoconductivity in bulk GaAs, GaAs thin films, colloidal sintered TiO₂ thin films, and semiconductor nanoclusters on a sub-picosecond timescale. One of the most important attributes of these materials, especially with respect to optoelectronic applications, is their transient photoconductivity. Time-resolved FIR spectroscopy reveals the mobility of the photoexcited electrons immediately after their generation and then follows the subsequent dynamics with sub-picosecond temporal resolution. That is, in addition to determining how much the conductivity changes, we also determine how long the material remains electrically conductive.

Finally, the fourth project is unique in that it does not involve FIR spectroscopy. We have been studying the librational dynamics of water and methanol in binary mixtures, in nanometer-scale confined spaces within reverse micelles and porous glasses, and in highly concentrated salt solutions. The OH librational motion is quite sensitive to hydrogen bonding environment, and displays tremendous variation as the surroundings are changed. We also employ molecular dynamics simulations to infer information that can not be directly measured experimentally.

Selected References

C. A. Schmuttenmaer, “Exploring Dynamics in the Far-Infrared with Terahertz Spectroscopy.” Chem. Rev., 104, 1759 – 1779 (2004).
E. Beaurepaire, G. M. Turner, S. M. Harrel, M. C. Beard, J.-Y. Bigot, and C. A. Schmuttenmaer, “Coherent THz Emission from Ferromagnetic Films Excited by Visible Femtosecond Laser Pulses.” Appl. Phys. Lett., 84, 3465 – 3467 (2004).
M. C. Beard, G. M. Turner, J. E. Murphy, O. I. Micic, M. C. Hanna, A. J. Nozik, and C. A. Schmuttenmaer, “Electronic Coupling in InP Nanoparticle Arrays.” Nano Lett., 3, 1695 – 1699, (2003).
G. M. Turner, M. C. Beard, and C. A. Schmuttenmaer, “Transient Photoconductivity in Dye-Sensitized Nanocrystalline TiO₂ Films as Measured by Time-Resolved THz Spectroscopy.” J. Phys. Chem. B, 106, 11716-11719 (2002). Includes cover art
M. C. Beard, G. M. Turner, and C. A. Schmuttenmaer, “Progress Toward Two-Dimensional Biomedical Imaging with THz Spectroscopy.” Physics in Medicine & Biology, 47, 3841-3846 (2002).
M. C. Beard, G. M. Turner, and C. A. Schmuttenmaer, “THz Spectroscopy.” Invited Feature Article J. Phys. Chem. B, 106, 7146-7159 (2002). Includes cover art.

Last modified: July 10, 2005 (kp)

Charles A. Schmuttenmaer
Professor