Thermoelectric Properties of SiO 2 /SiO 2 +Ag Nanolayered Multilayer Films Effected by MeV Si Ions
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1267-DD05-16
Thermoelectric Properties of SiO2/SiO2+Ag Nanolayered Multilayer Films Effected by MeV Si Ions C. Smith1, S. Budak2, J. Chacha2, M. Pugh2, H. Martin2, T. Langham2, B. Harrell2, K. Heidary2, R. B. Johnson 3, Y. Yang4, C. Muntele1, D.ILA1 1
2
Center for Irradiation of Materials, Alabama A&M University, Normal, AL USA Department of Electrical Engineering, Alabama A&M University, Normal, AL USA 3 Department of Physics, Alabama A&M University, Normal, AL USA 3 Department of Nuclear Engineering, University of Wisconsin, Madison, WI USA Abstract
We have prepared 100 periodic nano-layers of SiO2/AgSiO2 with Au layer deposited on both sides as metal contacts. The deposited multi-layer films have a periodic structure consisting of alternating layers where each layer is 3.3 nm thick. The purpose of this research is to tailor the figure of merit of the thermoelectric materials generated from the nanolayers of nanocrystals of Ag with SiO2 as host and as buffer layer using a combination of co-deposition and MeV ions bombardment taking advantage of energy deposited in the MeV ion track to nucleate nanoclusters. The electrical and thermal properties of the nanolayered structures were studied before and after 5 MeV Si ions bombardment at various fluences to form nanocrystals. In addition to thermoelectric properties, some optical properties of the SiO2/SiO2+Ag multi-layer superlattice films have been studied. Keywords: Ion bombardment, thermoelectric properties, multi-nanolayers, Figure of merit. *Corresponding author: S. Budak; Tel.: 256-372-5894; Fax: 256-372-5855; Email: [email protected] 1. Introduction The performance of a thermoelectric device is quantified by the dimensionless figure of merit ZT=S2σT/K. Our aim is to obtain high ZT values by increasing the Seebeck coefficient S and the electrical conductivity σ, and reducing the thermal conductivity K by bombarding the thin film structure with MeV Si ions. Ion bombardment induces the formation of quantum dots of Ag. In addition, the quantum well confinement of phonon transmission due to Bragg reflection at lattice interfaces [1,2] the defects and disorder in the lattice caused by ion bombardment and the grain boundaries of these nanoscale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. All these effects inhibit heat transport perpendicular to the layer planes [3-5]. Thus, cross plane thermal conductivity will decrease. These quantum dot layers also increase the Seebeck coefficient and electric conductivity owing to the increase of the electronic density of states produced by the one dimensional periodic
potential. We have already studied the improvement of thermoelectric properties for SiO2/SiO2+Ag thin film systems at different thickness and different ion beam bombardment fluences 10–50 nm multilayers [6, 7]. In this study we report on the growth of SiO2-Ag multi-layer super-lattice films using electron beam physical vapor deposition (E-Beam-PVD), and high energy Si ions bombardment of
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