Dresden 2006 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

TT: Tiefe Temperaturen

TT 6: Solids At Low Temperature: Amorphous and Tunnel Systems, Glasses, ...

TT 6.8: Vortrag

Montag, 27. März 2006, 12:30–12:45, HSZ 105

Thermal conductivity of suspended silicon nanowire at low temperature — •Olivier Bourgeois, Thierry Fournier, and Jacques Chaussy — CRTBT-CNRS, laboratoire associé à l’UJF et à l’INPG, 25 avenue des Martyrs, BP 166, 38042 Grenoble, Cedex 9, France

We report sensitive thermal conductivity measurement (down to few femtoW/K) at low temperature by means of the 3ω method of silicon suspended nanowires. The silicon nanowires have a square shape cross sections and are made by e-beam lithography. They are suspended between two electrically isolated pads, and hence thermally isolated from the heat bath. A thin film of niobium nitride, a highly resistive thermometric element, is deposited on top of the wire in order to measure the thermal conductivity using the 3ω method. The geometry of the nanowire section is designed to match the order of magnitude of the dominant phonon wave length in silicon at low temperature which is expected to be of the order of 100 nm at 1K. The width of the nanowires varies between 100 nm and 200 nm for a thickness 130 nm and a length ranging from 5µm to 10 µm. The mean free path of the phonons is much larger than the length of the wire, hence these nanowires can be considered as ballistic quasi 1D thermal conductors at sufficientlt low temperature. Under these conditions, the thermal conductivity of the Si nanowire is expected to be strongly influenced by the reduced dimensions. Below 0.9K a clear deviation from the classical cubic law is observed in the 200nm wide wires which is associated to the universal behavior of the thermal conductance.