Dynamics of surface thermal expansion and diffusivity using two-color reflection transient gratings
- California Univ., Berkeley, CA (United States). Dept. of Chemistry
We report ultrafast measurements of the dynamic thermal expansion of a surface and the temperature dependent surface thermal diffusivity using a two-color reflection transient grating technique. Studies were performed on p-type, n-type, and undoped GaAs(100) samples at several temperatures. Using a 75 fs ultraviolet probe with visible excitation beams, the electronic effects that dominate single color experiments become negligible; thus surface expansion due to heating and the subsequent contraction caused by cooling provide the dominant influence on the diffracted probe. The diffracted signal was composed of two components, thermal expansion of the surface and heat flow away from the surface, allowing the determination of the rate of expansion as well as the surface thermal diffusivity. At room temperature a signal rise due to thermal expansion was observed, corresponding to a maximum average displacement of {approx} 1 {angstrom} at 32 ps. Large fringe spacings were used, thus the dominant contributions to the signal were expansion and diffusion perpendicular to the surface. Values for the surface thermal diffusivity of GaAs were measured and found to be in reasonable agreement with bulk values above 50{degrees}K. Below 50{degrees}K, the diffusivity at the surface was more than an order of magnitude slower than in the bulk due to increased phonon boundary scattering. Comparison of the results with a straightforward thermal model yields good agreement over a range of temperatures (12--300{degrees}K). The applicability and advantages of the transient grating technique for studying photothermal and photoacoustic phenomena are discussed.
- Research Organization:
- Lawrence Livermore National Lab., CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States); Department of Defense, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-48; AC03-76SF00098
- OSTI ID:
- 10185635
- Report Number(s):
- UCRL-JC-111288; CONF-930159-57; ON: DE93040547
- Resource Relation:
- Conference: OE/LASE `93: International Society for Optical Engineering (SPIE) conference,Los Angeles, CA (United States),13-23 Jan 1993; Other Information: PBD: Feb 1993
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
GALLIUM ARSENIDES
THERMAL EXPANSION
SURFACE PROPERTIES
DIFFRACTION GRATINGS
DIFFRACTION
P-TYPE CONDUCTORS
N-TYPE CONDUCTORS
DOPED MATERIALS
OPTICS
400102
665000
CHEMICAL AND SPECTRAL PROCEDURES
PHYSICS OF CONDENSED MATTER