Todd D. Krauss

Todd D. Krauss

Professor of Chemistry and Chair, Professor of Optics

Ph.D. 1998, Cornell University

Physical and Biophysical Chemistry: Nanoscale Materials and Devices

Our main research area concerns understanding the fundamental properties of materials with a size in between individual molecules and macroscopic objects. These nanometer scale materials have physical characteristics that are strong functions of their size and shape, with properties that can be easily manipulated to address a given application. Our investigations in this area are currently focused on fundamental photophysical studies of carbon nanotubes and semiconductor nanocrystal quantum dots, and the integration of these materials into novel devices for conversion of solar energy into sustainable fuels. These studies are highly interdisciplinary, and lie at the interface between chemistry, optics, physics, applied physics, and materials science.

Carbon nanotubes consist of a hexagonal network of carbon atoms rolled up into a cylinder. Nanotubes are typically tens to hundreds of microns long, while their diameter is usually only around 1 nanometer. The quantum confinement of electrons around the nanotube results in unexpected properties. For example, carbon nanotubes can be either metallic or semiconducting, depending on the diameter and helicity of the carbon lattice. We are concerned with determining fundamental electronic and optical characteristics of single carbon nanotubes, as well as the design of carbon nanotube membranes for artificial photosynthesis applications (Figure 1). These investigations are carried out using atomic force microscopy, as well as single molecule and ultrafast optical spectroscopy.

Figure 1. Images of a carbon nanotube membrane for water splitting applications. (A) Scanning electron microscope image of vertically aligned nanotubes. The scale bar is 10 µm and the NTs are approximately 150 µm tall. (B) Nanotube arrays following epoxy impregnation to form the freestanding membrane. Scale bar is 10 µm and approximately 20 µm of NT length are exposed above the bulk. (Inset) Photograph of the final, self-supporting membrane approximately 2.5 cm2
Figure 2. Fluorescence from different sized CdSe quantum dots.

Inorganic semiconductor particles containing a few thousand atoms, known as semiconductor quantum dots (Figure 2) also have unique electronic and optical properties. Using state-of-the-art experimental techniques (electrostatic force microscopy and single molecule optical spectroscopy), we are investigating the optical emission characteristics of individual quantum dots and the effect of permanent charges on this emission. We are also studying the fundamental inorganic reaction mechanism that describes the initial formation of quantum dots from molecular precursors.

A significant remaining challenge for materials chemistry is to connect nanometer-sized materials to the macroscopic world. To that end, we are also developing simple synthetic methods to make novel nanocrystals and carbon nanotubes, are exploring chemical modification of their surfaces, and are looking to make integrated nano-systems from these nanoparticle building blocks. Our eventual goal is to build devices that can take solar energy and convert it to clean burning fuels such as hydrogen using nanomaterials as the basis for the device. This latter work is done in collaboration with Professors Bren and Eisenberg from the University of Rochester.

Selected Publications

Smyder, J., Peterson, J.J., Amori, A., Krauss, T. D.  "The Influence of Continuous vs. Pulsed Laser Excitation on Single Quantum Dot Photophysics,"  Phys. Chem. Chem. Phys.  2014,  DOI:
Schäfer, S., Cogan, N.M., Krauss, T. D.  "Spectroscopic investigation of electrochemically charged individual (6,5) single walled carbon nanotubes,"  Nano Lett.  2014143138-3144.
Cogan, N.M.B., Bowerman, C.J., Nogaj, L.J.,Nilsson, B.L., Krauss, T. D.  "Selective Suspension of Single-Walled Carbon Nanotubes using β-Sheet Polypeptides,"  J. Phys. Chem. C  20141185935-5944.
Pilgrim, G.A., Leadbutter, J.W., Qiu, F., Siitonen, A.J., Pilgrim, S.M., Krauss, T. D.  "Electron Conductive and Proton Permeable Vertically Aligned Carbon Nanotube Membranes,"  Nano Lett.  2014141728-1733.
Lee, A.J., Asher, W.B., Stern, H.A., Bren, K.L., Krauss, T. D.  "Single-molecule analysis of cytochrome c folding by monitoring the lifetime of an attached fluorescent probe,"  J. Phys. Chem. Lett  201342727-2733.
Han, Z., Qiu, F., Eisenberg, R., Holland, P.L., Krauss, T. D.  "Robust Photogeneration of H2 in Water Using Semiconductor Nanocrystals and a Nickel Catalyst,"  Science  20123381321-3124.
Lee, A. J., Wang, X., Carlson, L. J., Smyder, J. A., Tu, X., Zheng, M., Krauss, T. D.  "Bright Fluorescence from Individual Single-Walled Carbon Nanotubes,"  Nano Lett.  2011111636-1640.
Evans, C. M., Evans, M., Krauss, T. D.  "Mysteries of TOPSe Revealed: Insights into Quantum Dot Nucleation,"  J. Am. Chem. Soc.  201013210973-10975.
Wang, S., Khafizov, M., Tu, X., Zheng, M., Krauss, T.D.  "Multiple Exciton Generation in Single-Walled Carbon Nanotubes,"  Nano Lett.  2009102381-2386.
Evans, C. M., Guo, L., Peterson, J. J., Maccagnano, S., Krauss, T. D.  "Ultra-bright PbSe Magic Sized Clusters,"  Nano Lett.  200882896-2899.
Huang, L., Krauss, T. D.  "Quantized bimolecular Auger recombination of excitons in single-walled carbon nanotubes,"  Phys. Rev. Lett.  200696057407 .
Peterson, J. J., Krauss, T. D.  "Fluorescence Spectroscopy of Single Lead Sulfide Quantum Dots,"  Nano Lett.  20066510-514.
Hartschuh, A., Pedrosa, H. N., Novotny, L., Krauss, T. D.  "Simultaneous Fluorescence and Raman Scattering from Individual Single-Walled Carbon Nanotubes,"  Science  20033011354-1356.
Du, H., Chen, C.L., Krishnan, R., Krauss, T.D., Harbold, J.M., Wise, F.W., Thomas, M.G., Silcox, J.  "Optical properties of colloidal PbSe nanocrystals,"  Nano. Lett.  200221321-1326.
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Professor Krauss's Contact Information...

Office: Hutchison 465
Phone: (585) 275-5093

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