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Register a new userHeat transfer between nanoparticles: Thermal conductance for near-field interactions
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Added by
Luciano Lapas Calheiros
Publication date
2008
fields
Physics
and research's language is
English
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We analyze the heat transfer between two nanoparticles separated by a distance lying in the near-field domain in which energy interchange is due to Coulomb interactions. The thermal conductance is computed by assuming that the particles have charge distributions characterized by fluctuating multipole moments in equilibrium with heat baths at two different temperatures. This quantity follows from the fluctuation-dissipation theorem (FDT) for the fluctuations of the multipolar moments. We compare the behavior of the conductance as a function of the distance between the particles with the result obtained by means of molecular dynamics simulations. The formalism proposed enables us to provide a comprehensive explanation of the marked growth of the conductance when decreasing the distance between the nanoparticles.
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The dynamic heat transfer between two half-spaces separated by a vacuum gap due to coupling of their surface modes is modelled using the theory that describes the dynamic energy transfer between two coupled harmonic oscillators each separately connected to a heat bath and with the heat baths maintained at different temperatures. The theory is applied for the case when the two surfaces are made up of a polar crystal which supports surface polaritons that can be excited at room temperature and the predicted heat transfer is compared with the steady state heat transfer value calculated from standard fluctuational electrodynamics theory. It is observed that for small time intervals the value of heat flux can reach as high as 1.5 times that of steady state value.
Extreme near-field heat transfer between metallic surfaces is a subject of debate as the state-of-the-art theory and experiments are in disagreement on the energy carriers driving heat transport. In an effort to elucidate the physics of extreme near-field heat transfer between metallic surfaces, this Letter presents a comprehensive model combining radiation, acoustic phonon and electron transport across sub-10-nm vacuum gaps. The results obtained for gold surfaces show that in the absence of bias voltage, acoustic phonon transport is dominant for vacuum gaps smaller than ~2 nm. The application of a bias voltage significantly affects the dominant energy carriers as it increases the phonon contribution mediated by the long-range Coulomb force and the electron contribution due to a lower potential barrier. For a bias voltage of 0.6 V, acoustic phonon transport becomes dominant at a vacuum gap of 5 nm, whereas electron tunneling dominates at sub-1-nm vacuum gaps. The comparison of the theory against experimental data from the literature suggests that well-controlled measurements between metallic surfaces are needed to quantify the contributions of acoustic phonon and electron as a function of the bias voltage.
We study in this work the near-field radiative heat transfer between two semi-infinite parallel planes of highly n-doped semiconductors. Using a nonlocal model of the dielectric permittivity, usually used for the case of metallic planes, we show that the radiative heat transfer coefficientsaturates as the separation distance is reduced for high doping concentration. These results replace the 1/d${}^2$ infinite divergence obtained in the local model case. Different features of the obtained results are shown to relate physically to the parameters of the materials, mainly the doping concentration and the plasmon frequency.
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