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Showing 1 to 20 of 324 for “"Phonons"”.
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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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The scattering of thermal phonons by mobile dislocations
Submitted by William Weathers (weathrs2@illinois.edu) on 2012-03-21T20:51:27Z No. of bitstreams: 1 1971_malinowski.pdf: 2923570 bytes, checksum: 1135cfc8600631e8b65b51eda59aab8e (MD5)
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Dynamic Properties of Materials: Phonons from Neutron Scattering
A detailed understanding of fundamental material properties can be obtained through the study of atomic vibrations, performed experimentally with neutron scattering techniques and coupled with the two powerful new computational methodologies I have developed. The first approach involves …
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Probing the Superconducting Gap of Lead With Ballistic Phonons
The assumption that quasiparticles are all in thermal equilibrium with the helium-bath leads to erroneous results for temperature dependences of phonon absorption. Instead, we assume that the phonon-imaging experiment creates small regions of raised temperature that contribute non-equilibrium …
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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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Terahertz-field-induced nonlinearity in phonons, electrons and spins
In this thesis, I describe work aimed at understanding nonlinear material responses initiated by strong terahertz (THz) field excitation. I discuss two aspects of nonlinear THz spectroscopy in condensed-matter materials: developments of experimental THz capabilities and spectroscopy methods and …
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Exploring possible coupling between phonons and internal nuclear states
… up with a theory predicting coupling between phonons and internal nuclear states, leading to excitation transfer between nuclei. The aim of this Ph.D. thesis is to experimentally test Hagelstein's theory. In this research, we used Co-57 as the sample to investigate the nuclear excited states. …
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Real-Time Dynamics of Electrons and Phonons from First Principles
Ultrafast laser excitation drives solids far from equilibrium, producing transient electronic and lattice states that cannot be described by equilibrium theories or phenomenological models such as the two-temperature model. This dissertation develops and applies a real-time, ab initio framework …
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Interaction of Excitons and Impurity Atoms With Phonons in Germanium
Made available in DSpace on 2015-05-12T17:11:42Z (GMT). No. of bitstreams: 2 license.txt: 4848 bytes, checksum: 96035ab3f5e1c23cc7138a224ce498bd (MD5) 0004457.PDF: 1897859 bytes, checksum: 03fa2872cd019a618523c174b10f69d8 (MD5) Previous issue date: 1952
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Guiding of plasmons and phonons in complex three dimensional structures
The demand for pathways to fabricate and methodologies to understand 3D structures with advanced functionalities has increased significantly over the last years. Materials exhibiting three-dimensional structure with characteristic length scales ranging from nanometers to micrometers have …
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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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Transport of phonons and electrons in thermoelectric materials and graphene
Understanding transport of phonons and electrons plays a critical role in developing energy conversion and information devices. Thermoelectric materials, which directly convert heat to electricity or vice versa, require both extremely low thermal conductivity and high thermoelectric power factor. …
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Interaction of non-equilibrium phonons with electron-hole plasmas in germanium
… results of experiments on the interaction of phonons and photo-excited electron-hole plasmas in Ge at low temperature. The first two studies involve the low temperature fluid phase known as the electron-hole liquid (EHL). The third study involves a wider range of temperatures and includes the …
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The scattering of thermal phonons by extended defects in dielectric crystals
The scattering of thermal phonons by extended defects in dielectric crystals has been observed through measurements of thermal conductivity and ballistic heat pulse propagation. The thermal conductivities of LiF and NaCt containing 500 low-angle grain boundaries per cm were measured in the range …
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The scattering of high-frequency acoustic phonons in silicon and GaAs
… 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 immersed in …
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Anderson localization of thermal phonons : anomalous heat conduction in disordered superlattices
… devices, thermal energy is carried by phonons, the quantized excitation of atomic vibrations. These phonons scatter with impurities, electrons, grain boundaries, and other phonons. At a sufficiently large scale, phonon dynamics can be approximated as a Brownian random walk, leading to …
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Optically active phonons and electronic transitions in rare-earth tri-fluorides.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 1970
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Raman Scattering Studies of Aluminum-Gallium - Arsenide Based Semiconductor Superlattices (Phonons, Interfaces)
Raman scattering measurements have been made on more than twenty semiconductor superlattices, all grown by molecular beam epitaxy and based on the Al(,x)Ga(,1-x)As system. The samples consist of undoped layers with alternating values of x along the {001} direction, and have periods ranging from …
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The scattering of high-frequency acoustic phonons in silicon and gallium arsenide
… 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 immersed …
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