Philippe Guyot-Sionnest Professor
Born Nancy, France, 1961.
Ingenieur de l'Ecole Polytechnique, Paliseau, France, 1983.
Diplome d'Etude Approfondie, Orsay, France, 1984.
University of California, Berkeley, Ph.D., 1987.
Research Scientist, Universitè Paris-Sud, Orsay, France, 1988-91.
The University of Chicago, Professor, 1991-
Joint Appointment in the Department of Physics.
2002 Fellow, American Physical Society
1992 David and Lucile Packard Fellow.
1990 Prix National des Lasers, Sociètè Française de Physique.
OFFICE: 929 E. 57th St., GCIS E 111, Chicago, IL 60637
Chemistry and physics share tremendous potential at the nm scale. This is where chemistry excels and where physics predicts that many properties can be tuned. For example, quantum states, charging, spin, phonons and plasmons show large effects at the nm scale. Colloidal synthesis has become the enabling science of making nanostructures by chemical precipitation. The research in the group is driven by physical concepts and enabled by synthesis.
Quantum Confined Semiconductors
Nanocrystals of semiconductor materials show very strong effect of quantum confinement and controlling the size leads to exquisite tuning of energy levels. The group is working on the effect of small amounts of additional charges, i.e. quantum dot ions, on the optical, magnetic and electronic properties. We synthesize semiconductor nanocrystals, and control their sizes and their surfaces. Microscopy and nonlinear spectroscopy are used to study basic aspects of electron dynamics and interaction in such strongly confined structures. We currently focus on the doping of nanocrystals, the unusual infrared response, the electrochromic effects, as well as the potentially novel electrical transport properties in films made of these artificial atoms.
As the potential is more reducing (-), electrons are added to the CdSe quantum dots. The conductance of a film of dots (red line) first increases linearly with the occupation of the 1Se orbital (dashed blue line), up to ½ filling, at which point it decreases. The conductance then increases again as the 1Pe shell (dashed green line) occupation increases. Shell occupation is controlled by the electrochemical potential and measured by the optical absorption of the sample. Science 300, 1277 (2003)
Plasmonic Metal Nanoparticles
Metal objects of dimensions small compared to the optical wavelength exhibit very strong optical response because of a collective excitation of all the valence electrons in the particle, called a “Plasmon”. The resonance frequency is tightly determined by the shape of the object and the width is determined by losses due to scattering of the electrons. This leads to gold and silver being the best materials with high chemical stability. Since the resonance is a shape effect rather than size, optimizing colloidal synthesis to yield a specific shape is one goal. Needle shape nanostructures are particularly advantageous as they allow to focus the external electric field to very high values. Our research aims to observe the maximum effect of the very large local fields on the photoresponse of individual nanoparticles and assemblies.
Solutions of gold and gold/silver core/shell colloids exhibit very different colors, effectively covering the visible spectrum. This is not a quantum effect, but rather a collective electronic resonance determined the shape of the metal particles. JPCB 108, 5882 (2004)
Atomic Layer Deposition of ZnO in Quantum Dot Thin Films, Adv. Mat. 21, 232 (2009)
Slow Electron Cooling in Colloidal Quantum Dots, Science 322, 929 (2008)
Mn2+ as a radial pressure gauge in colloidal core/shell nanocrystals Phys. Rev. Lett. 99, 265501 (2007)
Spin blockade in the conduction of colloidal CdSe nanocrystal films, J. Chem. Phys. 127, 014702 (2007)
Mechanism of silver(I)-assisted growth of gold nanorods and bipyramids, J. Phys. Chem. B 109, 2219 (2005)
Variable range hopping conduction in semiconductor nanocrystal solids, Phys. Rev. Lett. 92, 216802 (2004)
Conducting n-type CdSe Nanocrystal solids, Science 300, 1277 (2003)
Electrochromic nanocrystal quantum dots, Science, 201, 2390 (2001)
N-type colloidal semiconductor nanocrystals, Nature, 407, 981 (2000).
Synthesis and characterization of strongly luminescing ZnS-Capped CdSe nanocrystals, J. Phys. Chem. 100, 468 (1996).
Photoluminescence of Single Semiconductor Nanocrystallites by Two-Photon Excitation Microscopy. Chem. Phys. Lett. 229, 317 (1994).