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Wolfe, J.P. Hebboul, Saad Eddine 2011-05-17T17:07:11Z 2011-05-17T17:07:11Z 10000-01-01 1988 "Low-temperature transport properties of high-frequency acoustic phonons are investigated in GaAs, InSb, InP and InAs using the phonon-imaging technique. In this method, a focused laser beam provides a movable heat source on one side of a cooled crystal (~ 2 K). A single small phonon detector on the opposite face records the transmitted heat flux as a function of propagation direction. Ballistic phonons channel along directions in the crystal which are completely determined by the detailed shape of constant-energy surfaces in wavevector space. The resulting focusing patterns are characterized by sharp phonon caustics which are clearly identified from the continuous background due to scattered phonons. In the dispersive regime, where phonon wavelength is comparable to atomic spacing, the angular positions of these caustic lines are very sensitive to phonon frequency, thus providing a novel test for lattice dynamics theories. Experiments are performed with superconducting tunnel junctions and Al bolometers to probe both the high-frequency and low-frequency regimes, respectively. We find that large-k ballistic phonons give rise to distinct focusing patterns in all four types of crystals, with thicknesses varying between 0.4 and 0.8 mm. Due to isotope scattering in the bulk, tunnel-junction experiments yield well-defined caustic patterns with a dominant frequency given by the detector gap 2.6.. In InSb, where zone boundary frequencies are small ( VT A ""' 1.2 THz), the frequency dependence of the dispersive phonon focusing patterns are Ill measured using PbTl (0.43, 0.59 THz) and PbBi (0.69, 0.73, 0.78, 0.82 THz) tunnel junction detectors. The results are interpreted with Monte Carlo calculations based on rigid, dipole, shell, and bond-charge models. Although each model yields satisfactory fits to the previously measured dispersion curves, the predicted patterns show remarkable differences in the caustic structures. This result underscores the utility of phonon imaging in providing new information about the elastic forces between atoms in crystals." Submitted by Carolyn Mead (cmead2@illinois.edu) on 2011-05-17T17:07:11Z No. of bitstreams: 1 1988_hebboul.pdf: 16583917 bytes, checksum: 0aa3a789673a52e9ec3d9e20ff6b2141 (MD5) Made available in DSpace on 2011-05-17T17:07:11Z (GMT). No. of bitstreams: 1 1988_hebboul.pdf: 16583917 bytes, checksum: 0aa3a789673a52e9ec3d9e20ff6b2141 (MD5) Previous issue date: 1988 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Carolyn Mead (cmead2@illinois.edu) on 2011-05-17T17:07:11Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:15:57-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Thesis Thesis U of I Only 1855404 http://hdl.handle.net/2142/23923 en 1988 Saad Eddine Hebboul dispersive phonon imaging III-V Semiconductors low-temperature transport properties high-frequency acoustic phonons GaAs InSb InP InAs Dispersive phonon imaging in III-V semiconductors Dissertation / Thesis text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.