arXiv subjects

Haoxue Han

Publications and source records attributed to Haoxue Han.

4 recordsLinked to original sources

arXiv2017

Phonon-interference resonance effects in nanoparticles embedded in a matrix

We report an unambiguous phonon resonance effect originating from germanium nanoparticles embedded in silicon matrix. Our approach features the combination of phonon wave-packet method with atomistic dynamics and finite element method rooted in continuum theory. We find that multimodal phonon resonance, caused by destructive interference of coherent lattice waves propagating through and around the nanoparticle, gives rise to sharp and significant transmittance dips, blocking the lower-end frequency range of phonon transport that is hardly diminished by other nanostructures. The resonance is sensitive to the phonon coherent length, where the finiteness of the wave packet width weakens the transmittance dip even when coherent length is longer than the particle diameter. Further strengthening of transmittance dips are possible by arraying multiple nanoparticles that gives rise to the collective vibrational mode. Finally, it is demonstrated that these resonance effects can significantly reduce thermal conductance in the lower-end frequency range.

physics.comp-ph↗

arXiv2015

Functionalization mediates heat transport in graphene nanoflakes

Self-heating is a severe problem for high-power microelectronic devices. Graphene and few-layer graphene have attracted tremendous attention for heat removal thanks to their extraordinarily high in-plane thermal conductivity. However, this high thermal conductivity undergoes severe degradations caused by the contact with the substrate and the functionalization-induced point defects. Here we show that thermal management of a micro heater can be substantially improved via introduction of alternative heat-escaping channels implemented with graphene-based film covalently bonded to functionalized graphene oxide through silane molecules. Theoretical and experimental results demonstrate a counter-intuitive enhancement of the thermal conductivity of such a graphene-based film. This increase in the in-plane thermal conductivity of supported graphene is accompanied by an improvement on the graphene-substrates thermal contact. Using infrared thermal imaging, we demonstrate that the temperature of the hotspots can be lowered by 12 $^o$C in transistors operating at 130 W mm$^{-2}$ , which corresponds to half of an order-of-magnitude increase in the device lifetime. Ab initio and molecular dynamics simulations reveal that the functionalization constrains the cross-plane scattering of low frequency phonons, which in turn enhances in-plane heat conduction of the bonded graphene film by recovering the long flexural phonon lifetime.

cond-mat.mes-hall↗

arXiv2014

Phonon nanocapacitor for storage and lasing of terahertz lattice waves

We introduce a novel ultra-compact nanocapacitor of coherent phonons formed by high-finesse interference mirrors based on atomic-scale semiconductor metamaterials. Our molecular dynamics simulations show that the nanocapacitor stores THz monochromatic lattice waves, which can be used for phonon lasing - the emission of coherent phonons. Either one- or two-color phonon lasing can be realized depending on the geometry of the nanodevice. The two color regimes of the capacitor originates from the distinct transmittance dependance on the phonon wave packet incident angle for the two phonon polarizations at their respective resonances. Phonon nanocapacitor can be charged by cooling the sample equilibrated at room temperature or by the pump-probe technique. The nanocapacitor can be discharged by applying tunable reversible strain, resulting in the emission of coherent THz acoustic beams.

cond-mat.mes-hall↗

arXiv2014

Phonon Interference and Thermal Conductance Reduction in Atomic-Scale Metamaterials

We introduce and model a three-dimensional (3D) atomic-scale phononic metamaterial producing two-path phonon interference antiresonances to control the heat flux spectrum. We show that a crystal plane partially embedded with defect-atom arrays can completely reflect phonons at the frequency prescribed by masses and interaction forces. We emphasize the predominant role of the second phonon path and destructive interference in the origin of the total phonon reflection and thermal conductance reduction in comparison with the Fano-resonance concept. The random defect distribution in the plane and the anharmonicity of atom bonds do not deteriorate the antiresonance. The width of the antiresonance dip can provide a measure of the coherence length of the phonon wave packet. All our conclusions are confirmed both by analytical studies of the equivalent quasi-1D lattice models and by numerical molecular dynamics simulations of realistic 3D lattices.

cond-mat.mes-hall↗