|Phone: (607) 255-3555|
|Fax: (607) 255-6428|
|Address: Department of Physics, Clark Hall, Cornell University, Ithaca, NY 14853-2501|
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Condensed Matter Physics and Chemistry
We would like to understand the phenomena and processes occurring at surfaces of physical, chemical, and biological systems. Since surfaces are ubiquitous, the fundamental understanding obtained in this area of research has important implications and relevance in natural and technological environment, such as in catalysis, electronic materials, atmospheric chemistry, corrosion, biomaterials. The particular approach we take involves carrying out experiments which probe the properties and response of the systems in the extremes of time and space. We use a solid surface to trap atoms and molecules and to study them with angstrom spatial and femtosecond temporal resolutions, and to build up three-dimensional materials. We are interested in understanding the interrelationship between the physical and chemical properties of matter from one atom or molecule and up. By following the time evolution of physical and chemical processes, we are able to reveal the forces and interactions which govern the dynamical transformation.
Our research currently lies in three main areas: time resolved phenomena with femtosecond lasers; atomically resolved and single molecule imaging, spectroscopy, dynamics, and chemistry with low temperature scanning tunneling microscopes (LT-STM); nonequilibrium materials synthesis and device fabrication. We like to develop new instruments and experimental capabilities which allow us to make measurements in the femtosecond time scales and with atomic resolution. We use nonlinear optics with femtosecond lasers to probe the fundamental vibrational dynamics of molecules, energy transfer, charge transfer, and the dissociation and formation of chemical bonds. LT-STMs are used to image and manipulate molecules on the surface, to perform inelastic electron tunneling spectroscopy and microscopy on single molecules, to stimulate light emission from single molecules, and to induce atomic motions and molecular transformations (bond dissociation and association) with sub-angstrom precision by the tunneling electrons. We are combining the time resolution, tunable energy, and coherence of femtosecond lasers with the spatial resolution of LT-STMs to investigate the structural, energetics, and dynamics of individual atoms and molecules. In the materials area, we use the STM to bring two smaller species together and form a larger entity, i.e. to carry out molecular synthesis. In addition, we use supersonic molecular beams for nonequilibrium growth of thins films for electronic and optoelectronic applications. Currently, we are focusing on the growth of wide band gap semiconductors (SiC, GaN, AlN) for the fabrication of blue light emitters. A major challenge is to grow high quality thin films on a substrate with a large lattice mismatch, such as wide band gap semiconductors on silicon.