Charles A. Schmuttenmaer

Professor of Chemistry
Member of Yale faculty since 1994

E-mail: charles.schmuttenmaer@yale.edu
Web site: http://thz.yale.edu/

TRTS
Figure 1: Optical pulse (red) photoexcites the sample at time tpp prior to the THz pulse arrival. The FIR refractive index and absorption coefficient can be determined at this instant in time by analyzing the changes of the THz pulse upon transmission through the photoexcited sample.

Research A little over 10 years ago, the Schmuttenmaer group opened up the far-infrared (FIR) region of the spectrum to direct time-resolved studies. The importance of time-resolved studies in a general sense has been demonstrated over the last 30 years by researchers utilizing visible, UV, and IR lasers. New frontiers in chemistry, physics, biology, optics, electronics, and communications have been uncovered. 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, and it is often referred to as terahertz (THz) spectroscopy.

DSSC
Figure 2: Dye molecules inject electrons into the phototoanode of a DSSC upon absorbing photons which can be monitored on a sub-picosecond time scale using THz spectroscopy.

We have exploited the unique features of this experimental method to characterize the efficiency of electron injection in photoanodes for dye-sensitized solar cells (DSSCs), which are a promising alternative to silicon photovoltaic solar cells.  We have also probed transient photoconductivity in bulk semiconductors such as GaAs and ZnO, quantum dots such as CdSe and InP, and nanoparticles such as SnO2, ZnO, and TiO2 (including nanotubes). Time-resolved THz spectroscopy reveals the mobility of the photoinjected electrons immediately after excitation 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. Prof. Schmuttenmaer is a founding member of the Yale Green Energy Consortium (http://www.chem.yale.edu/~green), along with Profs. Batista, Brudvig, and Crabtree.

OMC
Figure 3: THz absorption spectrum of tyrosine at room temperature (black) and 78 K (red) along with calculated stick spectrum.

A second major research area involves steady state THz spectroscopy. For example, it is possible to probe and understand the low-frequency collective vibrational modes in organic molecular crystals by comparing the results of high level ab initio quantum chemical calculations with their experimentally measured THz spectra. The vibrational frequencies and intensities are influenced by the strength of the covalent bonds, electrostatic interactions, hydrogen bonding interactions, charge-induced dipole interactions, and even van der Waals interactions.  The energy scale of these interactions spans roughly 4 orders of magnitude, which makes these calculations particularly difficult.

Education
B.S. University of Illinois, Urbana-Champaign, 1985
Ph.D. University of California, Berkeley, 1991
Postdoctoral Fellow, University of Rochester, 1991-94

Honors
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

Recent Publications
Michael R.C. Williams, Alan B. True, Timothy A. French, Konstanze Schroeck, Artur F. Izmaylov, & Charles A. Schmuttenmaer, “Terahertz Spectroscopy of Enantiopure and Racemic Polycrystalline Valine.” Phys. Chem. Chem. Phys., 13, 11719 – 11730 (2011). DOI: 10.1039/c1cp20594c

Christiaan Richter & Charles A. Schmuttenmaer, “Exciton-like Trap States Limit Electron Mobility in TiO2 Nanotubes” Nat. Nanotechnol. 5, 769 (2010). DOI:10.1038/nnano.2010.196

Jason B. Baxter & Charles A. Schmuttenmaer, “Electron Dynamics in Bulk ZnO Measured by Terahertz Spectroscopy II: Transient Photoconductivity.” Phys. Rev. B, 80, 235206 (2009). DOI: 10.1103/PhysRevB.80.235206

Gonghu Li, Christiaan P. Richter, Rebecca L. Milot, Lawrence Cai, Charles A. Schmuttenmaer, Robert H. Crabtree, Gary W. Brudvig, & Victor S. Batista, “Synergistic Effect between Anatase and Rutile TiO2 Nanoparticles in Dye-Sensitized Solar Cells.” Dalton Transactions, 10078 – 10085 (2009). DOI: 10.1039/b908686b

William R. McNamara, Robert C. Snoeberger III, Gonghu Li, Christiaan Richter, Laura J. Allen, Rebecca L. Milot, Charles A. Schmuttenmaer, Robert H. Crabtree, Gary W. Brudvig, & Victor S. Batista, “Hydroxamate Anchors for Water-Stable Attachment to TiO2 Nanoparticles.”  Energy Environ. Sci., 2, 1173 – 1175 (2009). DOI: 10.1039/b910241h

C.A. Schmuttenmaer, “Exploring Dynamics in the Far-Infrared with Terahertz Spectroscopy.” Chem. Rev., 104, 1759 – 1779 (2004).

M.C. Beard, G.M. Turner, & C.A. Schmuttenmaer, “Transient Photoconductivity in GaAs as Measured by Time-Resolved THz Spectroscopy.” Phys. Rev. B. 62, 15764-15777 (2000).

Charles A. Schmuttenmaer

Research Interests