MeV Si Ions Bombardment Effects on the Thermoelectric Properties of Si/Si+Ge Multi-Layer Superlttice Nanolayered Films
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1267-DD05-14
MeV Si Ions Bombardment Effects on the Thermoelectric Properties of Si/Si+Ge Multi-Layer Superlattice Nanolayered Films M. Pugh1, S. Budak1, C. Smith2, J. Chacha1, K. Ogbara3, K. Heidary1, R. B. Johnson 3, C. Muntele2, D. ILA2 1
Department of Electrical Engineering, Alabama A&M University, Normal, AL USA 2 Center for Irradiation of Materials, Alabama A&M University, Normal, AL USA 3 Department of Physics, Alabama A&M University, Normal, AL USA Abstract
Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and K is the thermal conductivity. ZT can be increased by increasing S, increasing σ or decreasing K. MeV ion bombardment caused defects and disorder in the film and the grain boundaries of these nano-scale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. We have prepared 100 alternating layers of Si/Si+Ge nanolayered superlattice films using the ion beam assisted deposition (IBAD). The 5 MeV Si ions bombardments have been performed using the AAMU Pelletron ion beam accelerator to make quantum clusters in the nanolayered superlattice films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. We have characterized the thermoelectric thin films before and after Si ion bombardments as we measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity for different fluences. *Corresponding author: S. Budak; Tel.: 256-372-5894; Fax: 256-372-5855; Email: [email protected] 1. Introduction Thermoelectric devices utilizing the Seebeck effect and the Peltier effect have been widely investigated for applications to thermoelectric power generation and thermoelectric cooling [1, 2]. A large-scale industrial application of thermoelectric (TE) devices depends on the research and development of efficient TE materials [3]. A growth in the commercial applications of thermoelectric devices depends primarily on increasing the figure of merit ZT of the materials used in the devices. The dimensionless figure of merit ZT is given as ZT=S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature in Kelvin (K), and K is the thermal conductivity [4-6]. ZT values could be tailored by increasing the Seebeck coefficient S and the electrical conductivity σ, and reducing the thermal conductivity K by bombarding the structure with MeV Si ions. Ion beam bombardment induces the formation of quantum dots of Si and Ge in the multilayer film systems. In addition to, the quantum
well confinement of phonon transmission due to Bragg reflection at lattice interfaces [7,8] the defects and disorder in the lattice caus
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