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 13 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 35 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. These same four investigators also share laboratory space at Yale's Energy Sciences Institute.

lithograph
Figure 3: Example of lithographically defined spiral arrays.

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.

Related efforts revolve around developing THz spectroscopic polarimetry wherein the full polarization state of every spectral component in a broadband THz pulse is experimentally determined.  The THz optical activity of chiral samples will be quite small, so therefore, initial efforts have employed metamaterials consisting of lithographically defined Archimedean spiral arrays. These metamaterials produce dramatic effects on the transmitted THz polarization rotation angle, ellipticity angle, and handedness.

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
Fellow, American Academy for the Advancement of Science, 2015

Recent Publications
Christopher Koenigsmann, Teresa S. Ripolles, Bradley J. Brennan, Christian F.A. Negre, Matthieu Koepf, Alec C. Durrell, Rebecca L. Milot, Jose A. Torre, J. Bisquert, V. S. Batista, G. W. Brudvig, R. H. Crabtree, and C. A. Schmuttenmaer, “Substitution of a Hydroxamic Acid Anchor into the MK-2 Dye for Enhanced Photovoltaic Performance and Water Stability in a DSSC.” Phys. Chem. Chem. Phys., 16, 16629–16641 (2014). DOI: 10.1039/c4cp02405b

Jason B. Baxter, Christiaan Richter, and Charles A. Schmuttenmaer, “Ultrafast Carrier Dynamics in Nanostructures for Solar Fuels.” Ann. Rev. Phys. Chem., 65, 423 (2014). DOI:  10.1146/annurev-physchem-040513-103742

Rebecca L. Milot, Gary F. Moore, Robert H. Crabtree, Gary W. Brudvig, and Charles A. Schmuttenmaer, “Electron Injection Dynamics from Photoexcited Porphyrin Dyes into SnO2 and TiO2 Nanoparticles.” J. Phys. Chem. C, 117, 21662–21670 (2013). DOI: 10.1021/jp406734t

Michael R. C. Williams, Daniel J. Aschaffenburg, Benjamin Ofori-Okai, and Charles A. Schmuttenmaer, “Intermolecular Vibrations in Hydrophobic Amino Acid Crystals: Experiments and Calculations.” J. Phys. Chem. B, 117, 10444–10461 (2013). DOI: 10.1021/jp406730a

Stafford W. Sheehan, Heeso Noh, Gary W. Brudvig, Hui Cao, and Charles A. Schmuttenmaer, “Plasmonic Enhancement of Dye-Sensitized Solar Cells using Core-Shell-Shell Nanostructures.” J. Phys. Chem. C, 117, 927–934 (2013). DOI: 10.1021/jp311881k

Daniel J. Aschaffenburg, Michael R. C. Williams, Diyar Talbayev, Daniel F. Santavicca, Daniel E. Prober, and Charles A. Schmuttenmaer, “Efficient Measurement of Broadband Terahertz Optical Activity.” J. Appl. Phys., 100, 241114 (2012). DOI: 10.1063/1.4729148

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

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

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