NIST: Laser Studies of Molecular Dynamics at Surfaces

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Laser Studies of Molecular Dynamics at Surfaces

Measurement of chemical and physical events which occur at the atomic-molecular layer at interfaces or surfaces is essential for developing new technology which exploits nanometer-scale dimensions. Examples of systems where molecular physics at an interface can determine performance include subnanometer films in semiconductor electronics, integrated molecular-optoelectronic systems, and processes in biological membranes.

Recent advances in laser technology and new laser-based spectroscopic techniques have made it possible to observe directly events which occur at the molecular level at surfaces and interfaces. In our laboratory we are using femtosecond lasers to measure rates and mechanisms for interface processes such as the coupling and relaxation of excited carriers, phonons, and surface electronic and vibrational states (particularly molecular states) at metal, semiconductor, and dielectric surfaces. In these measurements, the initial states are excited using an ultrashort laser pulse, and the subsequent evolution is measured with time-delayed laser pulses tuned to probe specific states of the system. In a new class of experiments we are using infrared pulses and sum frequency generation to measure the structure and dynamics of surface-immobilized membrane proteins, important for drug design, biomaterials and biosensors (see Nonlinear Optical Measurements at Interfaces).

Resources:

Femtosecond laser sources for generating ultrafast pulses from the far IR through the UV; instrumentation for temporal, spectral, directional, and polarization analyses of surface-generated optical signals; apparatus for preparation and study of surface systems in air, and in liquids.

References: - Obtaining publications

"Imaging and Autocorrelation of Ultrafast Infrared Laser Pulses in the 3-11 Micrometer Range Using Silicon CCD Cameras and Photodiodes,": Briggman, K.A., Richter, L.J., and Stephenson, J.C.,; Opt. Lett. 26, 238 (2001). (Preprint 70 kB PDF)
"Vibrationally resolved sum-frequency generation with broad-bandwidth infrared pulses,": Richter, L.J., Petralli-Mallow, T.P., and Stephenson, J.C.,; Opt. Lett. 23, 1594 (1998). (Preprint 294 kB PDF)
"Depletion-electric-field-induced Second-harmonic Generation near Oxidized GaAs(001) Surfaces,": Germer, T.A., Kolasinski, K.W., Stephenson, J.C., and Richter, L.J.,; Phys. Rev. B 55, 10694 (1997).
"Femtosecond Laser-induced Desorption of CO from Cu(100): Comparison of Theory and Experiment,": Struck, L.M., Richter, L.J., Buntin, S.A., Cavanagh, R.R., and Stephenson, J.C.,; Phys. Rev. Lett. 77, 4576 (1996).
"Picosecond Time-resolved Adsorbate Response to Substrate Heating: Spectroscopy and Dynamics of CO/Cu(100),": Germer, T.A., Stephenson, J.C., Heilweil, E.J., and Cavanagh, R.R.,; J. Chem. Phys. 101, 1704 (1994).
"Hot Carrier Excitation of Adlayers: Time-resolved Measurement of Adsorbate-Lattice Coupling,": Germer, T.A., Stephenson, J.C., Heilweil, E.J., and Cavanagh, R.R.,; Phys. Rev. Lett. 71, 3327 (1993).
"Subpicosecond Transient IR Spectroscopy of Adsorbates: Vibrational Dynamics of CO/Pt(111),": Beckerle, J.D., Cavanagh, R.R., Casassa, M.P., Heilweil, E.J., and Stephenson, J.C.,; J. Chem. Phys. 95, 5403 (1991).

For technical information or questions, call:

John Stephenson Phone: (301) 975-2372 Fax: (301) 869-5700 Email: john.stephenson@nist.gov		Kimberly Briggman Phone: (301) 975-2358 Fax: (301) 869-5700 Email: kbriggma@nist.gov

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Online: September 1997 - Last updated: November 2005