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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 59 for “"phonon modes"”.
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Effects of isotope doping on the phonon modes in graphene
… is studying the effect of isotope doping on the phonon properties of graphene. The advantage of the isotope enrichment technique is that only phonon frequencies or thermal properties can be modified without changing the electrical or chemical properties. We calculated the values of the phonon …
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Raman Scattering From the Superconductor Niobium-Diselenide
… (CDW) state. The Raman spectrum shows amplitude modes of A and E symmetry near 40 cm('-1) induced by the CDW. At 7 K this material becomes superconducting, and at 2 K we observe additional Raman peaks near 20 cm('-1), one each of A and E symmetry. These are close in energy to the energy gap …
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Photophysics of carbon nanotubes
… exhibit dramatic changes in their electron and phonon dispersion relations due to the curvature of the nanotube sidewall and the enhanced electron correlation effects associated with one dimensionality. The optical transition energies in small-diameter carbon nanotubes show a strong dependence …
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Interlayer Defect Effects on the Phonon Properties of Bilayer Graphene and its Nanoribbon
Phonon properties of AB (Bernal) stacked bilayer graphene (BLG) with various types of defects have been investigated theoretically. Forced Vibrational (FV) method has been employed to compute the phonon modes of disordered BLG. A downward linear shift of E2g mode frequencies has been observed with …
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Hard, Soft, and Sticky Spheres for Dynamical Studies of Disordered Colloidal Packings
… packings. The first set of experiments studied phonon modes in two-dimensional colloidal crystals composed of soft microgel particles with hard polystyrene particle dopants distributed randomly on the triangular lattice. By mixing hard and soft spheres we obtain close-packed lattices of spheres …
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Thermal transport in low dimensional semiconductor nanostructures
… DFT, the interatomic force constants and the phonon dispersion relations were calculated using DFPT as implemented in Quantum Espresso. In order to fundamentally understand the effect of atomic arrangements, we calculated the phonon conductance in a ballistic approach using a Green's function …
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Computational Modeling of Geometry Dependent Phonon Transport in Silicon Nanostructures
… depend on nanostructure boundary geometry. Phonons are quantized mechanical vibrations that are the dominant carrier of heat in semiconductor materials and their aggregate behavior determine a nanostructure's thermal performance. Phonon-geometry scattering processes as well as waveguiding …
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Raman spectroscopy of metallic carbon nanotubes
… that the frequency and linewidth of certain phonon modes of metallic carbon nanotubes depend strongly the Fermi energy, because they couple strongly to low lying electron hole pairs. Next, we report the first experimental observation of electronic Raman scattering in carbon nanotubes. This …
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X-ray Studies of Lattice Dynamics
… has recently shown great promise as a tool for phonon studies, complementing more traditional neutron scattering techniques. Quasi-elastic x-ray scattering from thermally populated phonon modes has been used to study lattice dynamics and phonon phase transitions in several systems. Several …
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Raman spectroscopy: from ferroelastic domain identification to strain tuning
… which are intimately related to specific phonon modes, as in the case of BiCrO3 or LaVO3, respectively. A method based on the Raman tensor formalism, which allows an assignment of the BiFeO3 Raman modes of pure as well as mixed character/symmetries is proposed. Relying on this assignment …
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Raman Scattering in GaN and ZnO
… the analysis of positions of the E2H and A1(LO) phonon modes, biaxial stress and plasmon coupling of the Al(LO) mode are observed and compared to a bulk GaN sample. The stress-related shift rate for the AI(LO) mode in hexagonal GaN is established to be 2.7 ± 0.4 cm-1/GPa through series of GaN …
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Effects of Substrate and Molecular Adsorption on Raman Scattering From Individual Single -Walled Carbon Nanotubes
… (KAs) leading to broad and softened ALO1 phonon modes, as well as O2 induced enhancement of double resonance processes. Effects of adsorption of NH3 on Raman scattering measurements are also explored and correlated to charge transfer (Fermi level shift) in carbon nanotubes.
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Theoretical studies of electron dynamics and relaxation in photoexcited quantum well structures
… Next, a general discussion of the electron-phonon interactions important for QW structures is made, stressing the role of confined polar optical phonons including the electron-phonon coupling for confined slab and interface phonons. In addition, optical deformation potential phonon-electron …
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Control of Excitons and Quantum Emitters in Two-Dimensional Materials
… show the coupling efficiency of different phonon modes to the quantum emitters in hBN, and a correlation between the local strain and localized exciton energy in TMDs. In addition, a strain gradient applied by a nanoscale tip modulates the local band structure of a suspended monolayer TMDs …
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A Study on the Use of Inverse Opals Composed of Zinc Oxide Aggregate Popcorn Particles to Improve the Efficiency of Dye- Sensitized Solar Cells
… in ZnO morphology do not have an effect on phonon modes when using the same excitation wave length. To assess the effect of inverse opal structure on DSSC efficiency, further optimization of the EPD technique with regard to popcorn particle inverse opals is anticipated. Future studies will …
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Study of phonon-dislocation interaction in LiF and KCl crystals
… provides a useful tool for the study of phonon-dislocation interaction. In this thesis, thermal conductivity measurements on plastically deformed LiF and KCl crystals are discussed. LiF crystals were deformed in such a way that four slip systems were activated, in a hope to better …
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Characterization of nanostructured hexagonal boron nitride patterned via high-resolution ion beam lithography
… and observe complimentary information about the phonon modes and the absorption and scattering of light from such nanostructures. Specifically, we observe geometry and layer dependent photo-thermal expansion of h-BN nanostructures that are mediated by phonons. This work demonstrates a thorough …
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Simulation of Thermal Effects in Semiconductor Materials and Devices
… to describe the behavior of both electrons and phonons and their interaction with each other, as well as their interaction with external potentials by coupling the transport equations with the Poisson equation. Several methods of solving the transport equations and simulating charge and thermal …
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Theory of phase transitions in liquid crystals and plastic crystals
… surface, and (iii) temperature dependent surface phonon modes. Orientational fluctuations in the disordered methane I phase are briefly discussed.
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Study of Thermoelectric and Lattice Dynamics Properties of 2D Layered MX (M = Sn, Pb; X = S, Se, Te) and ZrS2 Compounds using First-principles Approach
… addition, lowering the dimensionality increases phonon scattering near interfaces and surfaces in 2D materials, which leads to a reduction of the lattice thermal conductivity (?!) and consequently to a higher efficiency. Particularly, for the materials used in the present investigation, the …
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