Role of substrate thermal conductivity and vapor pressure in dropwise condensation
Not provided.
Energy & Fuels↗
Engineering topics
Kaviany, Massoud
Publications and source records attributed to Kaviany, Massoud.
From thermoelectricity to phonoelectricity
Here in this study, we review the history and progress of solid-state heat harvesting. Efficiency models, material metrics, and current research are discussed for thermoelectrics, thermionics, laser-coolers, and modern technologies. Then, we discuss nonequilibrium optical phonon harvest in the phonovoltaic cell. We make an effort to distinguish between the harvest of equilibrium heat, or thermal-electricity, and the targetted harvest of a particular nonequilibrium phonon mode, or phonoelectricity. We survey the state of phonovoltaic research, focusing on phonovoltaic materials, the electron-phonon coupling, and entropy production in a phonovoltaic cell. Throughout this review, discussions are connected to the electron and phonon structures, interactions, and transport. The modern thermal-electric harvesters are shown to reshape broad-spectrum, high-entropy heat into a narrow-spectrum of low-entropy emissions in order to efficiently generate thermal-electricity. Phonoelectricity, in contrast, intervenes before a low-entropy population of nonequilibrium optical phonons becomes high-entropy heat. In particular, the phonovoltaic cell generates phonoelectricity by utilizing the nonequilibrium, low-entropy, and high temperature optical phonon population produced by, e.g., the relaxation of electrons excited by an electric field. A phonovoltaic material has an ultranarrow electronic bandgap, such that the hot optical phonon population can relax by producing electron-hole pairs (and power) instead of multiple acoustic phonons (and entropy). The phonovoltaic device has an electric diode, e.g., a p-n junction, such that the internal electric field of the diode splits the electrons and holes in order to produce an electric current, and thus, power. The low entropy and high-temperature of the nonequilibrium optical phonon population enable efficient, in-situ heat harvesting. Bilayer graphene, for example, can theoretically convert the nonequilibrium population of optical phonons generated in a field-effect transistor into electricity with an efficiency exceeding 70% of the Carnot limit. The thermal-electric devices, in contrast, are either inefficient or restricted to ex-situ power generation. Lastly, as the phonoelectric Carnot limit is defined by the local nonequilibrium between electron and optical phonon populations, rather than the spatial nonequilibrium across the device, the Carnot limit can be very large without inducing melting.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Role of compression metallization in UO 2 fission-product energy cascade track: Multiscale electron-phonon analyses
While the electronic stoppage of charged fission fragments is relatively well understood, the subsequent energy cascade is not. Recent efforts to investigate this cascade and predict the resulting damage have used a two-temperature model (TTM) of the electronic and phononic systems coupled with a classical molecular dynamics (MD) simulation of the crystal lattice. In order to accurately predict the track radius produced by a fission fragment in UO 2 , this model (TTM + MD) requires that UO 2 , an insulator, have metallic properties, e.g., a substantial electron thermal conductivity and heat capacity. However, it has been predicted that UO 2 becomes metallic under large pressures, and we perform ab initio (DFT-HSE) simulations to support this prediction. We show that the average U-U bond length decreases within and near the ion track during TTM + MD simulations, supporting the use of volume contraction to model the pressurized UO 2 cell. Additionally, we evaluate the electron, phonon, and electron-phonon coupling properties of UO 2 for variations in the pressure. In particular, we calculate the electronic heat capacity and thermal conductivity, and the electron-phonon energy coupling for use in subsequent TTM + MD simulations. The ab initio parameterized TTM + MD simulations provide a set of the track radii predictions which bracket and include the experimentally observed radii. The accuracy of the ab initio parameterized TTM + MD simulations depends on the pressure and degree of electron-phonon non-equilibrium assumed during the ab initio calculations. We suggest improvements to the current TTM + MD methodology in light of these results. Here we show that the pressure-induced transition of UO 2 from insulator to metal and subsequent energy transfer from the electronic to phononic systems can accurately explain radiation damage during swift, heavy ion stoppage in UO 2 . We make some additional observations regarding the accumulation and recombination of damage along the ion track and make comparison to the common SRIM model of ion stoppage and damage accumulation.
36 MATERIALS SCIENCE↗
Thermal actuation in $\mathrm{TRPV1}$: Role of embedded lipids and intracellular domains
The transient response potential cation channel TRPV1 responds to high temperature, but many of the mechanisms driving its thermal actuation remain unclear. Its recently resolved structure has enabled a number of molecular dynamics (MD) studies focused on illuminating these mechanisms. Here we add to these efforts by performing the first all-atom MD simulations of its most recently resolved structure at different temperatures. While the complete, thermally induced transition of TRPV1 from its closed to open configuration remains elusive, our analysis of the hydrogen bonding networks, thermodynamics, hydration, and principal components of motion provide a wealth of information on the mechanisms which initiate or influence the thermal opening in TRPV1. In particular, we (i) support the previously proposed mechanism driving thermal actuation in the extracellular pore of TRPV1, (ii) present new hypotheses regarding the thermal actuation in the C-terminal and adjacent linker domains, and (iii) support and build upon the existing hypothesis regarding the role of the vanilloid binding pocket and lipids embedded therein.
59 BASIC BIOLOGICAL SCIENCES↗
Bilayer graphene phonovoltaic-FET: In situ phonon recycling
A new heat harvester, the phonovoltaic (pV) cell, was recently proposed. The device converts optical phonons into power before they become heat. Due to the low entropy of a typical hot optical phonon population, the phonovoltaic can operate at high fractions of the Carnot limit and harvest heat more efficiently than conventional heat harvesting technologies such as the thermoelectric generator. Previously, the optical phonon source was presumed to produce optical phonons with a single polarization and momentum. In this work, we examine a realistic optical phonon source in a potential pV application and the effects this has on pV operation. Supplementing this work is our investigation of bilayer graphene as a new pV material. Our ab initio calculations show that bilayer graphene has a figure of merit exceeding 0.9, well above previously investigated materials. This allows a room-temperature pV to recycle 65% of a highly nonequilibrium, minimum entropy population of phonons. However, full-band Monte Carlo simulations of the electron and phonon dynamics in a bilayer graphene field-effect transistor (FET) show that the optical phonons emitted by field-accelerated electrons can only be recycled in situ with an efficiency of 50%, and this efficiency falls as the field strength grows. Still, an appropriately designed FET-pV can recycle the phonons produced therein in situ with a much higher efficiency than a thermoelectric generator can harvest heat produced by a FET ex situ.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Phonovoltaic. III. Electron-phonon coupling and figure of merit of graphene:BN
The phonovoltaic cell harvests optical phonons like a photovoltaic harvests photons, that is, a nonequilibrium (hot) population of optical phonons (at temperature $T$ p,O ) more energetic than the band gap produces electron-hole pairs in a $p$-$n$ junction, which separates these pairs to produce power. A phonovoltaic material requires an optical phonon mode more energetic than its band gap and much more energetic than the thermal energy ($E$ p,O $ΔE$ e,g ≫ $k$ B $T$ ) , which relaxes by generating electrons and power (at rate $\dot{γ}$ e-p ) rather than acoustic phonons and heat (at rate $\dot{γ}$ p-p ). Graphene (h-C) is the most promising material candidate: when its band gap is tuned to its optical phonon energy without greatly reducing the electron-phonon (e-p) coupling, it reaches a substantial figure of merit [ $Z$ pV = $ΔE$ e,g $\dot{γ}$ e-p / $E$ p,O ($\dot{γ}$ e-p + $\dot{γ}$ p-p ) ≈ 0.8 ] . A simple tight-binding (TB) model presented here predicts that lifting the sublattice symmetry of graphene in order to open a band gap proscribes the e-p interaction at the band edge, such that $\dot{γ}$ e-p → 0 as $ΔE$ e,g → $E$ p,O . However, ab initio (DFT-LDA) simulations of layered h-C/BN and substitutional h-C:BN reveal that the e-p coupling remains substantial in these asymmetric crystals. Indeed, h-C:BN achieves a high figure of merit ( $Z$ pV ≈ 0.6 ) . At 300 K and for a Carnot limit of 0.5 ( $T$ p,O = 600 K ) , a h-C:BN phonovoltaic can reach an efficiency of η pV ≈ 0.2 , double the thermoelectric efficiency ( $ZT$ ≈ 1) under similar conditions.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Thermal conductivity switch: Optimal semiconductor/metal melting transition
Not Available
Kim, Kwangnam↗
Phonocatalysis. An ab initio simulation experiment
Using simulations, we postulate and show that heterocatalysis on large-bandgap semiconductors can be controlled by substrate phonons, i.e., phonocatalysis. With ab initio calculations, including molecular dynamic simulations, the chemisorbed dissociation of XeF{sub 6} on h-BN surface leads to formation of XeF{sub 4} and two surface F/h-BN bonds. The reaction pathway and energies are evaluated, and the sorption and reaction emitted/absorbed phonons are identified through spectral analysis of the surface atomic motion. Due to large bandgap, the atomic vibration (phonon) energy transfer channels dominate and among them is the match between the F/h-BN covalent bond stretching and the optical phonons. We show that the chemisorbed dissociation (the pathway activation ascent) requires absorption of large-energy optical phonons. Then using progressively heavier isotopes of B and N atoms, we show that limiting these high-energy optical phonons inhibits the chemisorbed dissociation, i.e., controllable phonocatalysis.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Phonovoltaic. I. Harvesting hot optical phonons in a nanoscale p − n junction
Not Available
Melnick, Corey↗
Optical phonon production by upconversion: Heterojunction-transmitted versus native phonons
Not Available
Shin, Seungha↗
Toward reversing Joule heating with a phonon-absorbing heterobarrier
Using a graded heterobarrier placed along an electron channel, phonons emitted in Joule heating are recycled in situ by increasing the entropy of phonon-absorbing electrons. The asymmetric electric potential distribution created by alloy grading separates the phonon absorption and emission regions, and emission in the larger effective-mass region causes momentum relaxation with smaller electron kinetic energy loss. These lead to smaller overall phonon emission and simultaneous potential-gain and self-cooling effects. Larger potential is gained with lower current and higher optical-phonon temperature. The self-consistent Monte Carlo simulations complying with the lateral momentum conservation combined with the entropy analysis are applied to a GaAs:Al electron channel with a graded heterobarrier, and under ideal lateral thermal isolation from surroundings, the phonon recycling efficiency reaches 25% of the reversible limit at 350 K, and it increases with temperature. In conclusion, the lateral momentum contributes to the transmission across the barrier, so partially nonconserving lateral momentum electron scattering (rough interface) can improve efficiency.
42 ENGINEERING↗
Ultralow thermal conductivity of β -Cu 2 Se by atomic fluidity and structure distortion
We demonstrate a prototype thermal evolution path for liquid thermal conductivity in solids. Thermal evolution of β -Cu 2 Se shows large interstitial displacement of constituent atoms marked by glass-like transitions and an asymptotic liquid thermal transport. Using ab initio molecular dynamics (AIMD), we identify these transitions, and confirm them with in situ transmission electron microscopy and electron energy loss spectroscopy. The thermal disorder of the Cu+ ions forms homopolar Cu–Cu bonds under a rigid Se framework, and at yet higher temperatures the Se framework undergoes thermal distortion. In conclusion, the non-equilibrium AIMD prediction of lattice thermal conductivity shows significant suppression of the phonon transport, in agreement with experiments and molecular behavior.
36 MATERIALS SCIENCE↗
Lattice thermal conductivity of UO{sub 2} using ab-initio and classical molecular dynamics
We applied the non-equilibrium ab-initio molecular dynamics and predict the lattice thermal conductivity of the pristine uranium dioxide for up to 2000 K. We also use the equilibrium classical molecular dynamics and heat-current autocorrelation decay theory to decompose the lattice thermal conductivity into acoustic and optical components. The predicted optical phonon transport is temperature independent and small, while the acoustic component follows the Slack relation and is in good agreement with the limited single-crystal experimental results. Considering the phonon grain-boundary and pore scatterings, the effective lattice thermal conductivity is reduced, and we show it is in general agreement with the sintered-powder experimental results. The charge and photon thermal conductivities are also addressed, and we find small roles for electron, surface polaron, and photon in the defect-free structures and for temperatures below 1500 K.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Electrical, thermal, and species transport properties of liquid eutectic Ga-In and Ga-In-Sn from first principles
Using ab initio molecular dynamics, the atomic structure and transport properties of eutectic Ga-In and Ga-In-Sn are investigated. The Kubo-Greenwood (K-G) and the Ziman-Faber (Z-F) formulations and the Wiedemann-Franz (W-F) law are used for the electrical and electronic thermal conductivity. The species diffusivity and the viscosity are also predicted using the mean square displacement and the Stokes-Einstein (S-E) relation. Alloying Ga causes more disordered structure, i.e., broadening the atomic distance near the In and Sn atoms, which reduces the transport properties and the melting temperature. The K-G treatment shows excellent agreement with the experimental results while Z-F treatment formula slightly overestimates the electrical conductivity. The predicted thermal conductivity also shows good agreement with the experiments. The species diffusivity and the viscosity are slightly reduced by the alloying of Ga with In and Sn atoms. Good agreements are found with available experimental results and new predicted transport-property results are provided.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Temperature dependent band gap in PbX (X = S, Se, Te)
PbTe is an important thermoelectric material for power generation applications due its high conversion efficiency and reliability. Its extraordinary thermoelectric performance is attributed to band convergence of the light L and heavy Σ bands. However, the temperature at which these bands converge is disputed. In this letter, we provide direct experimental evidence combined with ab initio calculations that confirm an increasing optical gap up to 673 K and predict a band convergence temperature of 700 K, much higher than previous measurements showing saturation and band convergence at 450 K.
36 MATERIALS SCIENCE↗