2. Articole

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Author: search.filters.author.Nika, DenisSubject: search.filters.subject.phonons

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    Phonons and thermal transport in Si/SiO2 multishell nanotubes: Atomistic study [Articol]
    (MDPI, 2021) Isacova, Calina; Cocemasov, Alexandr; Nika, Denis; Fomin, Vladimir
    Thermal transport in the Si/SiO2 multishell nanotubes is investigated theoretically. The phonon energy spectra are obtained using the atomistic lattice dynamics approach. Thermal conduc- tivity is calculated using the Boltzmann transport equation within the relaxation time approximation. Redistribution of the vibrational spectra in multishell nanotubes leads to a decrease of the phonon group velocity and the thermal conductivity as compared to homogeneous Si nanowires. Phonon scattering on the Si/SiO2 interfaces is another key factor of strong reduction of the thermal conduc- tivity in these structures (down to 0.2 Wm−1K−1 at room temperature). We demonstrate that phonon thermal transport in Si/SiO2 nanotubes can be efficiently suppressed by a proper choice of nanotube geometrical parameters: lateral cross section, thickness and number of shells. We argue that such nanotubes have prospective applications in modern electronics, in cases when low heat conduction is required.
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    Resonant terahertz light absorption by virtue of tunable hybrid interface phonon–plasmon modes in semiconductor nanoshellsn [Articol]
    (MDPI, 2019) Nika, Denis; Fomin, Vladimir; Devreese, Josef; Pokatilov, Evghenii; Tempere, Jacques
    Metallic nanoshells have proven to be particularly versatile, with applications in biomedical imaging and surface-enhanced Raman spectroscopy. Here, we theoretically demonstrate that hybrid phonon-plasmon modes in semiconductor nanoshells offer similar advantages in the terahertz regime. We show that, depending on tm,n,nhe doping of the semiconductor shells, terahertz light absorption in these nanostructures can be resonantly enhanced due to the strong coupling between interface plasmons and phonons. A threefold to fourfold increase in the absorption peak intensity was achieved at specific values of electron concentration. Doping, as well as adapting the nanoshell radius, allowed for fine-tuning of the absorption peak frequencies.
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    Thermal transport in semiconductor nanostructures, graphene, and related two-dimensional materials [Articol]
    (IOP Publishing Ltd, 2018) Cocemasov, Alexander.; Isacova, Calina; Nika, Denis
    We review experimental and theoretical results on thermal transport in semiconductor nanostructures (multilayer thin films, core/shell and segmented nanowires), single- and few-layer graphene, hexagonal boron nitride, molybdenum disulfide, and black phosphorus. Different possibilities of phonon engineering for optimization of electrical and heat conductions are discussed. The role of the phonon energy spectra modification on the thermal conductivity in semiconductor nanostructures is revealed. The dependence of thermal conductivity in graphene and related two-dimensional (2D) materials on temperature, flake size, defect concentration, edge roughness, and strain is analyzed.
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    Engineering of Thermal Fluxes in Phonon Mismatched Heterostructures [Articol]
    (American Scientific Publishers, 2009) Nika, Denis; Zincenco, N.D.; Pokatilov, E.P.
    The authors investigated theoretically the lattice thermal fluxes in planar three-layered heterostructures with inner silicon or germanium layer using the face-centered cubic cell dynamic lattice model. It has been established that the acoustically mismatched claddings significantly influence on the phonon spectra and thermal flux of heterostructures. The claddings with small sound velocity reduce average phonon velocity and decrease thermal flux in the nanostructure. The claddings with high sound velocity have an opposite effect. The predicted effects can be used for the engineering of the thermal properties of acoustically mismatched heterostructures and for the improving of the thermal management and thermoelectric properties of nanodevices.