Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 45 for “"acoustic phonons"”.
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Spectroscopic surface scattering of confined acoustic phonons in silicon nanostructures
The specularity of phonons at rough crystal surfaces is a fundamental aspect of phonon transport in nanostructures. It directly impacts engineering problems such as heat conduction in nanostructures and dissipation in nanomechanical resonators. At room temperature, the available guidance from …
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The scattering of high-frequency acoustic phonons in silicon and GaAs
The production and propagation of high-frequency acoustic phonons in silicon and GaAs are studied at low temperatures (~ 2K) using the phonon imaging technique. In this technique, a heat source is provided by a focused laser beam which is raster scanned across the surface of the sample which is …
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The scattering of high-frequency acoustic phonons in silicon and gallium arsenide
The production and propagation of high-frequency acoustic phonons in silicon and GaAs are studied at low temperatures ($\le$2K) using the phonon imaging technique. In this technique, a heat source is provided by a focused laser beam which is raster scanned across the surface of the sample which is …
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High-frequency phonon propagation and detection in III-V semiconductors
… propagation and detection of high frequency acoustic phonons in GaAs and InAs is studied. Phonon imaging is used to study scattering of acoustic phonons in GaAs and angular dispersion of acoustic phonons in InAs. Photoluminescence spectroscopy is used to study the effects of nonequilibrium …
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Expanding ultrafast photoacoustics for investigation of mechanical properties and thermal transport
… laser pulses were used to generate and detect acoustic waves. To expand the acoustic phonon frequency bandwidth and range, a thin metal film, a strongly magnetostrictive galfenol film, and strained piezoelectric InGaN/GaN multiple quantum wells were used as transducers. Acoustic wave detection …
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High frequency phonon propagation and detection in III-V semiconductors
… propagation and detection of high frequency acoustic phonons in GaAs and InAs is studied. .Phonon imaging is used to study scattering of acoustic phonons in GaAs and angular dispersion of acoustic phonons in InAs. Photoluminescence spectroscopy is used to study the effects of nonequilibrium …
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Brillouin scattering from single-crystal dysprosium and gadolinium films
… dependence and dispersion of long-wavelength acoustic phonons in single-crystal Dy films and long-wavelength acoustic magnons in single-crystal Gd films. The spectra were analyzed by using elastic and magnetic continuum models for the Dy and Gd systems, respectively.
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Monte Carlo simulation of quasi-one-dimensional semiconductors
… includes multiple subbands, polar optic and acoustic phonons, intervalley scattering, and band structure non-parabolicity.
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Inelastic X-ray scattering studies of broken symmetry in BSCCO
… temperature superconductors the importance of phonons is less well understood and charge ordering properties vary between the families of high-Tc cuperates. While superconductivity in these materials is not believed to originate from phonon excitations, there is evidence for strong …
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Excitons in cuprous oxide: high mobilities and strain confinement
… scattering of excitons with acoustic phonons, iv making none of the usual approximations which are valid at higher temperatures, resulted in good agreement between experiment and theory. The stress dependence is explained by an increased coupling to transverse acoustic phonons …
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Ultrafast dynamics in quantum materials probed by time-and-momentum-resolved techniques
… part of the thesis focuses on the coherent acoustic phonons in quantum materials observed with UED. The crystalline lattice is the building block of any solid-state system and, thus, the most important aspect in condensed matter physics research. The study of coherent acoustic phonons, the …
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Photo-produced phonons in semiconductors
… excitation of a semiconductor generates phonons as a byproduct of electronic excitation. A single carrier sheds this excess by the emission of optical phonons which cascade down in frequency, $\nu,$ by the normal anharmonic processes as they propagate in the crystal. This quasidiffusion …
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Molecular dynamics analysis of spectral characteristics of phonon heat conduction in silicon
… phonon transport. It is found that longitudinal acoustic phonons have the highest contribution to thermal conductivity and that the phonon mean free path varies by orders of magnitude with respect to the phonon spectra. For relaxation times, we observe moderate anisotropy and good agreement with …
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I. Raman scattering and x-ray diffraction study of annealing effects on confined LO and folded LA phonons in GaAs-AlAs superlattices ; II. Picosecond light scattering studies of relaxation and tunneling in GaAs/AlxGa1-xAs mulitple quatum well structures
… broadening on folded LA and confined LO phonons. During the annealing process we followed three folded LA phonon doublets and up to the ninth order of confined LO phonons in the Raman spectrum. The frequencies of folded LA phonons in annealed samples did not shift, but the intensities …
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Transport properties along the channel of a Hemt
… study, the scattering rates for polar optical phonons (POP), acoustic phonons (AP) through deformation potential and impurity scattering are obtained theoretically based on the Fermi's golden rule as a function of position along the channel for an {dollar}Al\sb{0.37}Ga\sb{0.63}As/GaAs{dollar} …
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Mathematical Modelling of Semi Conductor Devices and Processes
… whether non-polar optical, piezoelectric or acoustic phonons, the presence or absence of an electric field and the order of expansion of the collision integral in terms of the phonon energy. Restricted cases of this equation are considered and general solutions given. One particular model, …
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Monte Carlo Calculations of Parallel and Perpendicular Electron Transport in Gallium-Arsenide Heterolayers
… semiconductor structures. Polar optical, acoustic phonon scattering (coupled by the deformation potential or piezoelectrically) and ionized impurity scattering are taken into consideration. The interaction of the electrons among themselves are also accounted for through the effect of …
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Heat transport by phonons in crystalline materials and nanostructures
… experimental studies of heat transport by phonons in crystalline materials and nanostructures, and across solid-solid interfaces. Particularly, this dissertation emphasizes advancing understanding of the mean-free-paths (i.e., the distance phonons propagate without being scattered) of …
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Exploring excitations and vibrations in semiconductor nanocrystals through fluorescence and Raman spectroscopy
… and low-frequency Raman spectroscopy to measure acoustic phonons in nanocrystal solids. These two chapters serve as an introduction to the ideas and methods used throughout the thesis. In Chapter 3, Förster theory is used in conduction with spectrally- and temporally-resolved photoluminescence …
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Hypersonic phononic crystals
Manipulation of the distribution of phonons inM a solid is important for both basic science and applications ranging from heat management to reduction of noise in electronic circuits and creating materials with superior acoustic and acousto-optical properties. This thesis explores hypersonic …
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