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.
Results
Showing 1 to 20 of 22 for “"phonon dynamics"”.
-
Computational Methods for Studying Phonon Dynamics
… of the structure’s normal modes, often termed phonons, which are collective motions of atoms vibrating at certain frequencies. These vibrational modes play important roles in a variety of material properties and physical phenomena such as chemical reactions, phase transitions, mass/ion …
-
MONITORING PHONON DYNAMICS IN QUANTUM MATERIALS BY TIME-RESOLVED SPONTANEOUS RAMAN SCATTERING
… activity has been devoted to the study of phonon dynamics in photoexcited quantum materials, employing time-resolved spontaneous Raman spectroscopy (TRRS) as the primary experimental approach. Among ultrafast spectroscopies, TRRS provides unique access to phonons and other low-energy …
-
Nanoscale Coherent-Acoustic-Phonon Dynamics in Molybdenum Disulfide Using Ultrafast Electron Microscopy
… defect-mediated anisotropic acoustic-phonon dynamics in molybdenum disulfide (MoS2) have been directly imaged on the nanometer-picosecond spatiotemporal scales in real space. MoS2 is a prototypical material system of transition metal dichalcogenides extensively studied due to the …
-
Dynamics of Phonons in Crystals as Studied by Picosecond Coherent Anti-Stokes Raman Spectroscopy
The dynamics of the motions of ions and molecules in crystals are of fundamental interest, but due to the short correlation times of the motions (generally in the picosecond or subpicosecond range) the study of the dynamics is a difficult experimental problem. At the same time, theoretical progress …
-
Theoretical studies of electron dynamics and relaxation in photoexcited quantum well structures
… on the quantum mechanical aspects of electron dynamics and relaxation (or capture) in QW structures with particular attention paid to understanding and interpreting the results from the various optical experiments performed on QW structures. First, the transfer matrix technique used to …
-
Photoinduced dynamics studied by ultrafast single-shot pump-probe spectroscopy
… applications to study irreversible photoinduced dynamics. First, the ultrafast laser sources and the related control and characterization techniques are discussed. In particular, we have invented a two-stage dual-beam noncollinear optical parametric amplifier to provide tunable sources for …
-
Real-Time Dynamics of Electrons and Phonons from First Principles
… equation (TDBE) to investigate coupled electron–phonon dynamics in crystalline solids from femtosecond to picosecond timescales. The approach explicitly resolves the dynamics of momentum- and mode-dependent electron and phonon populations, where electron–phonon and phonon–phonon scatterings are …
-
Phonon hydrodynamic transport at elevated temperature
For over half a century, phonon hydrodynamic transport was deemed exotic and mattered only at extremely low temperatures. In this work, by combining the theoretical and experimental approach, we successfully predict and confirm the existence of phonon hydrodynamic transport in graphite above 200 K. …
-
Phonon hydrodynamic transport at elevated temperature
For over half a century, phonon hydrodynamic transport was deemed exotic and mattered only at extremely low temperatures. In this work, by combining the theoretical and experimental approach, we successfully predict and confirm the existence of phonon hydrodynamic transport in graphite above 200 K. …
-
Spectroscopic perspectives on ultrafast coupling phenomena in perovskite oxides
In this thesis, I study ultrafast dynamics in perovskite oxides using time resolved broadband spectroscopy. I focus on the observation of coherent phonon propagation by time resolved Brillouin scattering: following the excition of metal transducer films with a femtosecond infrared pump pulse, …
-
PRECISION MEASUREMENT TO STUDY STRONGLY CORRELATED SYSTEMS-FROM A SINGLE ION TO PHONONS IN AN ION CHAIN
… the main part is devoted to studying the phonon dynamics in trapped ion system where the dynamics are governed by strongly correlated Bose-Hubbard Hamiltonian. Trapped ion system allows us to tune the onsite phonon-phonon interaction from positive to negative which leads to several …
-
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 …
-
Electronic excitation and atomic forces in optically excited group V semimetals
… atomic motion, referred to as coherent phonon motion. The recent development of ultrafast optical spectroscopy has greatly advanced our understanding of these phenomena. However, many aspects of ultrafast phenomena are still poorly understood. For instance, experiments on a variety of …
-
Single and multi-exciton dynamics in nanoscale semiconductors
… to unambiguously elucidate the single-exciton dynamics of J-aggregate nanotubes in solution. Inversion of spectroscopic signals from eight transient grating experiments completely characterizes the time evolution of the single-exciton density matrix by determining the process matrix. We confirm …
-
Influence of Electronic Structure and Lattice Dynamics on Oxygen Ion Transport in Solid-State Ionic Conductors
… migration barrier. Next, migration entropy and phonon density of states (DOS) are highlighted as the main factors regulating the pre-exponential factor of oxygen ion conductivity across different materials. The phonons of oxygen ions near the hopping ion significantly contribute to migration …
-
Machine Learning for Phonon Thermal Transport
… change. As one of the major energy carriers, phonons play an indispensable role in various energy-related processes. The past decades witnessed continuous development in phonon measurements and computation techniques. However, at least two significant challenges impede our further exploration …
-
Heat dissipation from carbon nano-electronics
… method, which we use to directly compute the phonon lifetimes and thermal transport coefficients. After we set the conceptual foundations, the TBC of the CNT-SiO2 interface is computed using non- equilibrium molecular dynamics (MD) simulations and the new Green-Kubo method that we have …
-
The multi Davydov-Ansatz
… several aspects of open quantum system dynamics and quantum many-body theory. By two artifices alongside the time-dependent variational principle we extract from this Ansatz, commonly considered ill-behaved and not converging, a highly stable and converging method. Its extremely …
-
Nano-engineering of Atomically Thin Novel 2D Materials and Their Heterostructures
… two TMD monolayers can profoundly modulate the phonon dynamics by creating Moire supperlattices and periodic patterns. As an example, I studied WSe2/WS2 heterobilayers and showed that the heterostrain can lead to large displacement of phonon modes, modulated by the interlayer twist angle. …
-
Nano-engineering of Atomically Thin Novel 2D Materials and Their Heterostructures
… two TMD monolayers can profoundly modulate the phonon dynamics by creating Moire supperlattices and periodic patterns. As an example, I studied WSe2/WS2 heterobilayers and showed that the heterostrain can lead to large displacement of phonon modes, modulated by the interlayer twist angle. …
Page 1 of 2