SANFORD A. SAFRON Professor of Chemistry Ph.D., Harvard, 1969

Physical Division Department of Chemistry Florida State University E-mail: safron@chem.fsu.edu Phone: (850) 644-5239 DLC 314

Research - Selected Publications - Other Information

     Helium Atom Scattering Homepage

Interfaces and surfaces are among the most fundamentally interesting and technologically fertile of chemical environments. They also are among the most difficult to investigate, particularly for insulating materials. High-resolution helium atom scattering (HAS) is a singular technique in that it can be applied equally well to metals, semiconductors and insulators. It employs low-energy, non-penetrating, chemically inert atoms as surface probes, which are sensitive only to the electronic structure of the topmost surface layer regardless of the nature of the material. This technique is unique, also, in providing both structural and dynamical information about the interface from the same experimental configuration. Moreover, it is capable of doing this in situ and in real-time during the growth of ultrathin films.

Helium atom scattering experiments in this group started out to determine the periodicity and corrugation of the surface electron density and the surface lattice dynamics (that is, the collective vibrational modes of the surface -- surface phonons) of cleaved single crystal alkali halides, the prototypical ionic insulators, and binary metal oxides (such as NiO). More recently, we have focused on the structure, lattice dynamics and phase transitions of monolayer films of alkali halides, KCN and organics (e.g., alkyl halides and p-polyphenylenes) grown layer-by-layer onto alkali halide substrates through the use of simple sublimation sources. Investigations into more complex interfaces, such as the mixed KO-TaO2 surface of cleaved KTaO3 (001) and the (110) surface of rutile TiO2, have led us to explore, in addition, the more general use of HAS for studies of surface phase transitions, diffusion, reactions and other kinetic processes.

Further experiments in this laboratory are planned to use the HAS technique to study the surface structure, lattice dynamics and phase transitions of mixed ionic insulators (such as KCN/KBr and KTaO3/KNbO3) and organic compounds, of materials grown by chemical reactions (such as NH4Cl from NH3 and HCl), of cut and polished titania, and of ultra cold films of H2, D2 and HD on various crystalline substrates.

Finally, we have begun a collaboration with several theoretical groups, both in the United States and in Europe, to develop microscopic models for comparison with the results of the scattering experiments. This effort until recently has been concerned with the dynamics and epitaxial growth of the alkali halides. However, we are interested in developing and applying similar model calculations to the structure, dynamics and growth of metal oxide interfaces.
 

"High Resolution Helium Atom Scattering as a Probe of Surface Vibrations", S. A. Safron, in Advances in Chemical Physics, Volume XCV, I. Prigogine and S. A. Rice, eds. (John Wiley and Sons, New York, 1996) pp. 129-212.

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Sanford Safron was a visiting professor at the Max Planck Institute fur Stromungsforschung, Gottingen, Germany, Associate Chair for Facilities, and is the Chairman of the Program in Chemical Physics at FSU.
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