Rattling-induced suppression of thermal transport in cubic InOwith Sn-Ga diatomic defect.

We present the first principles study of cubic InOwith a diatomic defect composed of a Sn atom substituting the In atom at the-site and a Ga atom embedded in the nearest-site (structural vacancy) with lattice positions according to the Wyckoff notations. Structural, electronic, phononic and thermal properties were investigated within density functional theory formalism. The lattice anharmonicity effects were taken into account for all possible three-phonon scattering processes.

Thermal Transport Evolution Due to Nanostructural Transformations in Ga-Doped Indium-Tin-Oxide Thin Films.

We report on a comprehensive theoretical and experimental investigation of thermal conductivity in indium-tin-oxide (ITO) thin films with various Ga concentrations (0-30 at. %) deposited by spray pyrolysis technique. X-ray diffraction (XRD) and scanning electron microscopy have shown a structural transformation in the range 15-20 at.

Energetic, structural and electronic features of Sn-, Ga-, O-based defect complexes in cubic InO.

Defect energy formation, lattice distortions and electronic structure of cubic InO with Sn, Ga and O impurities were theoretically investigated using density functional theory. Different types of point defects, consisting of 1-4 atoms of Sn, Ga and O in both substitutional and interstitial (structural vacancy) positions, were examined. It was demonstrated, that formation of substitutional Ga and Sn defects are spontaneous, while formation of interstitial defects requires an activation energy.

In-Plane Thermal Conductivity of Radial and Planar Si/SiO Hybrid Nanomembrane Superlattices.

Silicon, although widely used in modern electronic devices, has not yet been implemented in thermoelectric applications mainly due to its high thermal conductivity, κ, which leads to an extremely low thermoelectric energy conversion efficiency (figure of merit). Here, we present an approach to manage κ of Si thin-film-based nanoarchitectures through the formation of radial and planar Si/SiO hybrid nanomembrane superlattices (HNMSLs). For the radial Si/SiO HNMSLs with various numbers of windings (1, 2, and 5 windings), we observe a continuous reduction in κ with increasing number of windings.

Phonons and thermal transport in graphene and graphene-based materials.

A discovery of the unusual thermal properties of graphene stimulated experimental, theoretical and computational research directed at understanding phonon transport and thermal conduction in two-dimensional material systems. We provide a critical review of recent results in the graphene thermal field focusing on phonon dispersion, specific heat, thermal conductivity, and comparison of different models and computational approaches. The correlation between the phonon spectrum in graphene-based materials and the heat conduction properties is analyzed in details.

Direct observation of confined acoustic phonon polarization branches in free-standing semiconductor nanowires.

Similar to electron waves, the phonon states in semiconductors can undergo changes induced by external boundaries. However, despite strong scientific and practical importance, conclusive experimental evidence of confined acoustic phonon polarization branches in individual free-standing nanostructures is lacking. Here we report results of Brillouin-Mandelstam light scattering spectroscopy, which reveal multiple (up to ten) confined acoustic phonon polarization branches in GaAs nanowires with a diameter as large as 128 nm, at a length scale that exceeds the grey phonon mean-free path in this material by almost an order-of-magnitude.

Breakdown current density in h-BN-capped quasi-1D TaSe3 metallic nanowires: prospects of interconnect applications.

We report on the current-carrying capacity of the nanowires made from the quasi-1D van der Waals metal tantalum triselenide capped with quasi-2D boron nitride. The chemical vapor transport method followed by chemical and mechanical exfoliation were used to fabricate the mm-long TaSe3 wires with the lateral dimensions in the 20 to 70 nm range. Electrical measurements establish that the TaSe3/h-BN nanowire heterostructures have a breakdown current density exceeding 10 MA cm(-2)-an order-of-magnitude higher than that for copper.

Thermal conductivity of graphene with defects induced by electron beam irradiation.

We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ∼7.5 μm size square holes.

Engineering of the thermodynamic properties of bilayer graphene by atomic plane rotations: the role of the out-of-plane phonons.

We investigated theoretically the specific heat of graphene, bilayer graphene and twisted bilayer graphene taking into account the exact phonon dispersion and density of states for each polarization branch. It is shown that contrary to a conventional belief the dispersion of the out-of-plane acoustic phonons - referred to as ZA phonons - deviates strongly from a parabolic law starting from the frequencies as low as ∼100 cm(-1). This leads to the frequency-dependent ZA phonon density of states and the breakdown of the linear dependence of the specific heat on temperature T.

Thermal conductivity of twisted bilayer graphene.

We have investigated experimentally the thermal conductivity of suspended twisted bilayer graphene. The measurements were performed using an optothermal Raman technique. It was found that the thermal conductivity of twisted bilayer graphene is lower than that of monolayer graphene and the reference, Bernal stacked bilayer graphene in the entire temperature range examined (∼300-700 K).

Anomalous size dependence of the thermal conductivity of graphene ribbons.

We investigated the thermal conductivity K of graphene ribbons and graphite slabs as the function of their lateral dimensions. Our theoretical model considered the anharmonic three-phonon processes to the second-order and included the angle-dependent phonon scattering from the ribbon edges. It was found that the long mean free path of the long-wavelength acoustic phonons in graphene can lead to an unusual nonmonotonic dependence of the thermal conductivity on the length L of a ribbon.

Two-dimensional phonon transport in graphene.

Properties of phonons-quanta of the crystal lattice vibrations-in graphene have recently attracted significant attention from the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature, while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.

Dimensional crossover of thermal transport in few-layer graphene.

Graphene, in addition to its unique electronic and optical properties, reveals unusually high thermal conductivity. The fact that the thermal conductivity of large enough graphene sheets should be higher than that of basal planes of bulk graphite was predicted theoretically by Klemens. However, the exact mechanisms behind the drastic alteration of a material's intrinsic ability to conduct heat as its dimensionality changes from two to three dimensions remain elusive.