TEM-compatible microdevice for the complete thermoelectric characterization of epitaxially integrated Si-based nanowires.

Nanostructured materials present improved thermoelectric properties due to non-trivial effects at the nanoscale. However, the characterization of individual nanostructures, especially from the thermal point of view, is still an unsolved topic. This work presents the complete structural, morphological, and thermoelectrical evaluation of the selfsame individual bottom-up integrated nanowire employing an innovative micro-machined device compatible with transmission electron microscopy whose fabrication is also discussed. Thanks to a design that arranges the nanostructured samples completely suspended, detailed structural analysis using transmission electron microscopy is enabled. In the same device architecture, electrical collectors and isolated heaters are available at both ends of the trenches for thermoelectrical measurements of the nanowire i.e. thermal and electrical properties simultaneously. This allows the direct measurement of the nanowire power factor. Furthermore, micro-Raman thermometry measurements were performed to evaluate the thermal conductivity of the same suspended silicon nanowire. A thermal profile of the self-heating nanowire could be spatially resolved and used to compute the thermal conductivity. In this work, heavily-doped silicon nanowires were grown on this microdevices yielding a thermal conductivity of 30.8 ± 1.7 W Km-1 and a power factor of 2.8 mW mK-2 at an average nanowire temperature of 400 K. Notably, no thermal contact resistance was observed between the nanowire and the bulk, confirming the epitaxial attachment. The device presented here shows remarkable utility in the challenging thermoelectrical characterization of integrated nanostructures and in the development of multiple devices such as thermoelectric generators.

Enhanced Far-Field Thermal Radiation through a Polaritonic Waveguide.

We experimentally demonstrate the enhancement of the far-field thermal radiation between two nonabsorbent Si microplates coated with energy-absorbent silicon dioxide (SiO_{2}) nanolayers supporting the propagation of surface phonon polaritons. By measuring the radiative thermal conductance between two coated Si plates, we find that its values are twice those obtained without the SiO_{2} coating. This twofold increase results from the hybridization of polaritons with guided modes inside Si and is well predicted by fluctuational electrodynamics and an analytical model based on a two-dimensional density of polariton states. These findings could be applied to thermal management in microelectronics, silicon photonics, energy conversion, atmospheric sciences, and astrophysics.

High Surface Phonon-Polariton in-Plane Thermal Conductance along Coupled Films.

Surface phonon-polaritons (SPhPs) are evanescent electromagnetic waves that can propagate distances orders of magnitude longer than the typical mean free paths of phonons and electrons. Therefore, they are expected to be powerful heat carriers capable of significantly enhancing the in-plane thermal conductance of polar nanostructures. In this work, we show that a SiO 2 /Si (10 µ m thick)/SiO 2 layered structure efficiently enhances the SPhP heat transport, such that its in-plane thermal conductance is ten times higher than the corresponding one of a single SiO 2 film, due to the coupling of SPhPs propagating along both of its polar SiO 2 nanolayers. The obtained results thus show that the proposed three-layer structure can outperform the in-plane thermal performance of a single suspended film while improving significantly its mechanical stability.

Current driven magnetic actuation of a MEMS silicon beam in a transmission electron microscope.

Micro-Electro-Mechanical-System (MEMS) devices associated to Transmission Electron Microscopes (TEM) have demonstrated their high potential for atomic resolution imaging of specimen while applying stress for mechanical testing. This paper introduces a novel actuation principle for the MEMS device in TEM relying on the internal magnetic field of the TEM and current flow through the device. The actuation principle is experimentally demonstrated in TEM and entirely modeled in the case of a silicon beam. The model is validated through static and dynamic experimental studies. The thermal side-effect of current flow is taken into account. The major advantages of the proposed magnetic actuation principle are the bidirectional control of the displacement of the device, the intrinsic linear displacement of the device with applied current and the potential milliNewton (mN) range force generation.