A5009282407- Advanced Thermoelectric Materials and Devices
- Thermal properties of materials
- Phase-change materials and chalcogenides
- Topological Materials and Phenomena
- Advanced Semiconductor Detectors and Materials
- Spectroscopy and Laser Applications
- Semiconductor Quantum Structures and Devices
- Solid-state spectroscopy and crystallography
- Machine Learning in Materials Science
- Advanced Thermodynamics and Statistical Mechanics
- Graphene research and applications
- Cold Atom Physics and Bose-Einstein Condensates
- Chalcogenide Semiconductor Thin Films
- Semiconductor Lasers and Optical Devices
- Electronic and Structural Properties of Oxides
- Thermography and Photoacoustic Techniques
- Thermal Radiation and Cooling Technologies
- Laser Design and Applications
- Quantum and electron transport phenomena
- Advanced Chemical Physics Studies
- Advancements in Semiconductor Devices and Circuit Design
- Boron and Carbon Nanomaterials Research
- Surface and Thin Film Phenomena
- High-pressure geophysics and materials
- Force Microscopy Techniques and Applications
King's College London
2025
National University of Ireland
2022-2023
University College Cork
2020
University of California, Davis
2012-2013
Max Planck Institute for Polymer Research
2013
CEA Grenoble
2008-2010
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
2008-2010
CEA LITEN
2008-2010
University of Leeds
2004-2008
University of Belgrade
1976-2004
This paper presents a theoretical investigation of the microscopic mechanisms responsible for heat transport in bulk Si, Ge and SiGe alloys, with goal providing insight into design rules efficient Si-based nanostructured thermoelectric semiconductors. We carried out detailed atomistic study thermal conductivity, using molecular dynamics Boltzmann equation. investigated detail effects physical approximations underlying each approach, as well effect numerical involved implementation two...
Abstract The proximity to structural phase transitions in IV-VI thermoelectric materials is one of the main reasons for their large phonon anharmonicity and intrinsically low lattice thermal conductivity κ . However, GeTe increases at ferroelectric transition near 700 K. Using first-principles calculations with temperature dependent effective potential method, we show that this rise consequence negative expansion rhombohedral increase lifetimes high-symmetry phase. Strong induces...
We present an ab initio study which identifies dominant effects leading to thermal conductivity reductions in carbon and boron-nitride nanotubes with isotope disorder. Our analysis reveals that, contrary previous speculations, localization cannot be observed the measurements. Observable reduction of is mostly due diffusive scattering. Multiple scattering induced interference were found prominent for concentrations > or approximately 10%; otherwise, conduction mainly determined by independent...
Isotopic composition can dramatically affect thermal transport in nanoscale heat conduits such as nanotubes and nanowires. A 50% increase conductivity for isotopically pure boron (11B) nitride was recently measured, but the reason this enhancement remains unclear. To address issue, we examine through using an atomistic Green's function formalism coupled with phonon properties calculated from density functional theory. We develop independent scatterer model 10B defects to account isotope...
Abstract The interactions between electrons and lattice vibrations are fundamental to materials behaviour. In the case of group IV–VI, V related materials, these strong, exist near electronic structural phase transitions. prototypical example is PbTe whose incipient ferroelectric behaviour has been recently associated with large phonon anharmonicity thermoelectricity. Here we show that it primarily electron-phonon coupling involving electron states band edges leads instability in PbTe. Using...
We present an ab initio study that identifies the main electron-phonon scattering channels in $n$-type PbTe. develop electronic transport model based on Boltzmann equation within relaxation time approximation, fully parametrized from first-principles calculations accurately describe dispersion of bands near band gap. Our computed mobility as a function temperature and carrier concentration is good agreement with experiments. show longitudinal optical phonon dominates PbTe, while acoustic...
We present a first principles based model of electron-phonon scattering mechanisms and thermoelectric transport at the L $\Sigma$ valleys in <200b>$p$-type PbTe, accounting for their thermally induced shifts. Our calculated values all parameters room temperature are very good agreement with experiments wide range doping concentrations. Scattering due to longitudinal optical phonons is main mechanism $p$-type while transverse modes weakest. The contribute most 300 K sizeable energy difference...
We show how tuning the proximity to soft optical mode phase transition via chemical composition affects lattice thermal conductivity $\ensuremath{\kappa}$ of ${\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}\mathrm{Te}$ alloys. Using first-principles virtual-crystal simulations, we find that anharmonic contribution is minimized at due maximized acoustic-optical interaction. Mass disorder significantly lowers and flattens dip in over a wide range, thus shifting minimum away from transition....
We investigated how dimensionality affects heat transport in Si-Ge superlattices (SLs) by computing the thermal conductivity of planar and arrays Ge nanowires (NWs) nanodots embedded Si. studied with ∼10 nm periods using a fully atomistic Monte Carlo solution Boltzmann equation relaxation time approximation. found that for larger than 4 nm, room temperature cross-plane equally thick Si layers is their nanowire dot counterparts similar sizes (up to 100%), while trend reversed below nm.
The major obstacle in the design of materials with low lattice thermal conductivity is difficulty efficiently scattering phonons across entire frequency spectrum. Using first principles calculations, we show that driving PbTe to brink ferroelectric phase transition could be a powerful strategy solve this problem. We illustrate concept by applying tensile [001] strain and its alloys another rock-salt IV-VI material, PbSe; alloying rhombohedral GeTe. This induces extremely soft optical modes...
GeTe is a well-known ferroelectric and thermoelectric material that undergoes structural phase transition from rhombohedral to the rocksalt structure at $\sim 600-700$ K. We present first principles approach calculate thermal expansion of in up Curie temperature. find minimum Helmholtz free energy with respect each parameter manner similar traditional Gr{\"u}neisen theory, account for temperature dependence elastic constants. obtain variation parameters very good agreement experiments. In...
We investigate coupled electron-lattice dynamics in the topological insulator Bi2Te3 with time-resolved photoemission and x-ray diffraction. It is well established that coherent phonons can be launched by optical excitation, but selection rules generally restrict these modes to zone-center wavevectors Raman-active branches. find surface state couples additional modes, including a continuum of surface-projected bulk from both Raman- infrared-branches, possible contributions surface-localized...
Quantifying electron-phonon interactions for the surface states of topological materials can provide key insights into surface-state transport, superconductivity, and potentially how to manipulate state using a structural degree freedom. We perform time-resolved x-ray diffraction (XRD) angle-resolved photoemission (ARPES) measurements on Bi2Te3 Bi2Se3, following excitation coherent A1g optical phonons. extract compare deformation potentials coupling electronic local A1g-like displacements in...
The nanostructuring of thermoelectric materials is a well-established method suppressing lattice thermal conductivity. However, our understanding the interfaces that form as result nanostructure engineering still limited. In this work, we utilise simple two-body pair potential to calculate boundary resistance basal plane twin boundaries in Bi2Te3 at 300 K using reverse non-equilibrium molecular dynamics simulations. considered interatomic gives an excellent description formation energies and...
A density matrix theory of electron transport and optical gain in quantum cascade lasers an external magnetic field is formulated. Starting from the general kinetic treatment, we describe intra- inter-period dynamics at non-Markovian, Markovian Boltzmann approximation levels. Interactions electrons with longitudinal phonons classical light are included present description. The non-Markovian calculation for a prototype structure reveals significantly different spectra terms linewidth...
Carbon atoms can form structures in one, two and three dimensions due to their unique chemical versatility. In terms of thermal conductivity, carbon polymorphs cover a wide range from very low values with amorphous high diamond, nanotubes graphene. Schwarzites are class three-dimensional fully covalent sp2-bonded polymorphs, the same local environment as graphene nanotubes, but negative Gaussian curvature. We calculate conductivity (10,0) nanotube, schwarzites different curvature, by...
Ferroelectric domain walls are boundaries between regions with different polarization orientations in a ferroelectric material. Using first-principles calculations, we characterize all types of forming on ($11\overline{1}$), (111), and ($1\overline{1}0$) crystallographic planes thermoelectric GeTe. We find large structural distortions the vicinity most these walls, which driven by variations. show that such strong strain-order parameter coupling will considerably reduce lattice thermal...
We report a fully {\it ab-initio} calculation of the temperature dependence electronic band structure PbTe. address two main features relevant for thermoelectric figure merit: variations direct gap and difference in energies topmost valence maxima located at L $\Sigma$. account energy shift states due to thermal expansion, as well electron-phonon interaction computed using non-adiabatic Allen-Heine-Cardona formalism within density functional perturbation theory local approximation. capture...
We calculate the uniaxial and dilatation acoustic deformation potentials, $\Xi^{\text{L}}_{u}$ $\Xi^{\text{L}}_{d}$, of conduction band L valleys PbTe from first principles, using local density approximation (LDA) hybrid functional (HSE03) exchange-correlation functionals. find that choice a does not substantially affect effective masses potentials as long physically correct representation states near gap has been obtained. Fitting electron-phonon matrix elements obtained in perturbation...
We present a first-principles method for the calculation of temperature-dependent relaxation symmetry-breaking atomic driving forces in photoexcited systems. calculate phonon-assisted decay force on low-symmetry E_{g} mode following absorption an ultrafast pulse Bi, Sb, and As. The lifetimes Bi Sb are order 10 fs agreement with recent experiments, demonstrating that electron-phonon scattering is primary mechanism relaxing forces. Calculations range absorbed photon energies suggest larger...
Abstract Increasing the Seebeck coefficient S in thermoelectric materials usually drastically decreases electrical conductivity σ , making significant enhancement of power factor 2 extremelly challenging. Here we predict, using first-principles calculations, that extraordinary properties charged ferroelectric domain walls (DWs) GeTe enable a five-fold increase DW plane compared to bulk. The key reasons for this are confinement free charge carriers at DWs and Van Hove singularities electronic...
A theoretical model describing the electron transport in vertical conductivity quantum dot infrared photodetectors is presented. The carrier wave functions and energy levels were evaluated using strain dependent eight-band k∙p Hamiltonian used to calculate all intra- interperiod transition rates due interaction with phonons electromagnetic radiation. longitudinal acoustic radiation was treated perturbatively within framework of Fermi’s golden rule, while optical considered taking into...
A theoretical model of electron transport in quantum cascade lasers subjected to a magnetic field is developed. The Landau level electronic structure was calculated from the envelope-function Schr\"odinger equation within effective-mass approximation. modeled using self-consistent rate-equation description for full period and its interaction with adjacent periods. scattering processes included are electron--longitudinal-optical-phonon, electron--longitudinal-acoustic-phonon,...