Thermal and electrical conduction in ultrathin metallic films: 7 nm down to sub-nanometer thickness

Abstract

For ultrathin metallic films (e.g., less than 5 nm), no knowledge is yet available on how electron scattering at surface and grain boundaries reduces the electrical and thermal transport. The thermal and electrical conduction of metallic films is characterized down to 0.6 nm average thickness. The electrical and thermal conductivities of 0.6 nm Ir film are reduced by 82% and 50% from the respective bulk values. The Lorenz number is measured as 7.08 × 10-8 W Ω K-2, almost a twofold increase of the bulk value. The Mayadas-Shatzkes model is used to interpret the experimental results and reveals very strong electron reflection (>90%) at grain boundaries. This work reports the first-time measurement of thermal and electrical conduction of ultra-thin metallic films down to 0.6 nm thickness. Significant reductions of more than 80% for electrical and 50% for thermal conductivities are observed. The ultra-thin film's Lorenz number deviates from the bulk value significantly, with an almost 200% increase. Very strong electron reflection (>90%) at grain boundaries is obtained. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.