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Transport des phonons à l'échelle du nanomètre

Abstract : To understand the mechanisms of the heat transport at small length scales, we are fabricating complex nano-devices and measuring the thermal conductance of suspended silicon nanowires at cryogenic temperatures, principally by the 3 omega method. We demonstrate the dependance of the phonon transport to the dimensions and the geometry of these nanostructures. For nanowires with a length between 8 and 10 µm, and a section of 200x100 nm^2, we observe a deviation of the diffusive regime of Casimir below 5K, which can be explained by taking account the roughness of the surface of the nanowires. When the temperature decreases, the wave length of the phonons increases and ballistic collisions at the surface occur, implying an increase of the mean free path of the phonons, considered before as constant. Important mesoscopic effects on the phonons transport induced by the geometry of the nanowires have been measured for the first time. The presence of zigzag on the length of the wires blocks the current of phonons on a wide range of temperature, with as consequence an important decrease in the order of 40 % of the thermal conductance in comparison with straight nanowires. Experiments in parrallel on silcon NEMS have been performed at low temperatures, and compared with MEMS of same geometries. The mechanical behavior of silcon nanostructures at low scale is also aborded. At the end, first prototypes of zeptoJoules nanocalorimeters (10^-21 J) are presented, which allow thermal characterization of single mesoscopic object.
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Submitted on : Friday, March 5, 2010 - 2:26:24 PM
Last modification on : Thursday, November 19, 2020 - 1:00:56 PM
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Jean-Savin Heron. Transport des phonons à l'échelle du nanomètre. Physique [physics]. Université Joseph-Fourier - Grenoble I, 2009. Français. ⟨tel-00461703⟩

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