S. Volz

Radiative heat transfer between metallic nanoparticles

In this letter, we study the radiative heat transfer between two nanoparticles in the near and far fields. We find that the heat transfer is dominated by the electric dipole-dipole interaction for identical dielectric particles and by the magnetic dipole-dipole interaction for identical metallic nanoparticles. We introduce polarizability formulas valid for arbitrary values of the skin depth. While the heat transfer mechanism is different for metallic and dielectric nanoparticles, we show that the distance dependence is the same. However, the dependence of the heat flux on the particle radius is different.

Phonon Heat Conduction in Corrugated Silicon Nanowires Below the Casimir Limit

The thermal conductance of straight and corrugated monocrystalline silicon nanowires has been measured between 0.3u2009K and 5u2009K. It is demonstrated that the corrugation strongly reduces the thermal transport by reducing the mean free path of the phonons. The experimental averaged mean free path is remarkably smaller than the smaller diameter of the nanowire, evidencing a phonon thermal transport reduced below the Casimir limit. Monte Carlo simulations highlight that this effect can be attributed to significant multiple scattering of ballistic phonons occurring on the corrugated surfaces. This result suggests an original approach to transforming a monocrystalline material into a phonon glass.

Quantitative Thermoreflectance Imaging: Calibration Method and Validation on a Dedicated Integrated Circuit

We have developed a charge-coupled device-based thermoreflectance microscope which can deliver thermal images of working integrated circuits. However, in any thermoreflectance experiment, the coefficient linking reflectance variations to temperature is different for each material. Calibrations are therefore necessary in order to obtain quantitative temperature imaging on the complex surface of an integrated circuit including several materials such as aluminium and polysilicon. We propose here a system using a Peltier element to control the temperature of the whole package in order to obtain calibration coefficients simultaneously on all the materials visible on the surface of the circuit. Under high magnifications, vertical and lateral movements associated to thermal expansion are corrected using respectively a piezo electric displacement and a software image shifting. The thermoreflectance temperature measurements calibrated with this method are compared to the temperatures measured with separately calibrated thermocouples and diodes, and to a finite elements simulation.

Increase of thermal resistance between a nanostructure and a surface due to phonon multireflections

The thermal resistance between a nanostructure and a half-body is calculated in the framework of particle-phonons physics. The current models approximate the nanostructure as a thermal bath. We prove that the multireflections of heat carriers in the nanostructure significantly increase resistance, in contradiction with former predictions. This increase depends on the shape of the nanostructure and the heat carrier’s mean-free path only. We provide a general and simple expression for the contact resistance and examine the specific cases of nanowires and nanoparticles.

Temperature Study of Sub-Micrometric ICs by Scanning Thermal Microscopy

Surface temperature measurements were performed with a scanning thermal microscope mounted with a thermoresistive wire probe of micrometric size. A CMOS device was designed with arrays of resistive lines 0.35 mum in width. The array periods are 0.8 mum and 10 mum to study the spatial resolution of the SThM. Integrated circuits (ICs) with passivation layers of micrometric and nanometric thicknesses were tested. To enhance signal-to-noise ratio, the resistive lines were heated with an ac current. The passivation layer of nanometric thickness allows us to distinguish the lines when the array period is 10 mum. The results raise the difficulties of the SThM measurement due to the design and the topography of ICs on one hand and the size of the thermal probe on the other hand.