Tunable near-field heat transfer with piezoelectric materials.

Abstract

Realizing a thermal counterpart for electronic devices has been recently proposed; a thermal analogue requires processing information by heat currents rather than by electric currents. Phononic heat currents are fundamentally limited by the speed of acoustic phonons smaller than the speed of electrons by orders of magnitude alongside the reduction of heat flow by local Kapitza resistances arising from the mismatch of vibrational modes at interfaces. Overlooked due to the relatively weak heat flux limited by the Stefan-Boltzmann law in the far-field limit, energy transfer mediated by thermal photons with contactless devices in the near-field limit (NFRHT) has been recently considered as an alternative. Several approaches for heat transfer modulation have been applied exploiting the dependence of NFRHT on the geometric asymmetry of the surfaces, the material properties, and the relative motion of the radiating objects. Classes of materials studied include phase-change materials (PCM), ferroelectrics, and chiral materials. In this dissertation, we propose, to the best of our knowledge, for the first time the use of piezoelectrics for near-field radiative transfer modulation. We detect a phase change in the optical properties of oxygen-contaminated AlN attributed to an Oxygen related defect. The piezoelectric properties of AlN enables fast electrical tuning and thus modulation of NFRHT. We show that radiative heat transfer between the two piezoelectric materials can be tuned as much as 40percent by switching between the two phases. In addition, we detect a coherence shift in near field transfer corresponding to the two phases of AlN and demonstrate coherence tuning by a factor of 3.7. We investigate the near-field radiative heat transfer between both the parallel plates and the two sphere geometries. We demonstrate for the first time modulation of NFRHT in the two sphere system via harnessing phase change in the dielectric properties of the emitters material. We adopt the model proposed by Narayanaswamy and Gang for calc