MeV Ion Beam Bombardments Effects on the Thermoelectric Properties of Zn4Sb3 / CeFe(4-x)CoxSb12 Nano-Layered Superlattic
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MeV Ion Beam Bombardments Effects on the Thermoelectric Properties of Zn4Sb3 / CeFe(4-x)CoxSb12 Nano-Layered Superlattices S. Budak1, C. C. Smith2, B. Zheng1, C. I. Muntele1, R. L. Zimmerman1, and D. ILA1 1 Center for Irradiation of Materials, Alabama A&M University, 4900 Meridian Street, P.O. Box 1447, Huntsville, AL, 35762 2 MSFC, NASA, Huntsville, AL, 35805 Abstract We prepared multilayers of semiconducting half-heusler β-Zn4Sb3 and skutterudites CeFe(4x)CoxSb12 compound thin films by ion beam assisted deposition (IBAD) system for the application of thermoelectric (TE) materials. Rutherford backscattering spectrometry (RBS) was used to analyze the composition of thin films. The thin films were then bombarded by 5 MeV Si ions for generation of nanodots in the films. We measured the cross-plane thermal conductivity by a house developed 3ω-method system, cross-plane Seebeck coefficient by a (MMR) Seebeck system, and cross plane electrical conductivity of these nanolayered systems by a (MMR) Hall system before and after bombardment. Both β-Zn4Sb3 and CeFe(4-x)CoxSb12 systems have been identified as promising thermoelectric materials for the application of thermal-to-electrical energy conversion. The nanodots produced by MeV ion beam can cause significant change in both electrical and thermal conductivity of thin films, thus improving the efficiency. The MeV ion-beam bombardment resulted in decrease in the thermal conductivity of thin films and increase in the efficiency of thermal-to-electrical energy conversion. 1. INTRODUCTION Thermoelectric materials are important due to the interest in their applications in thermoelectric power generation and microelectronic cooling [1]. Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity [2]. The performance of the thermoelectric materials and devices is shown by a dimensionless Figure of Merit, ZT = S 2σT / κ , where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity [3]. ZT can be increased by increasing S, increasing σ, or decreasing κ. Since the bulk form of the half-heusler β-Zn4Sb3 and skutterudites CeFe(4-x)CoxSb12 compound have higher figure of merits at higher temperatures [4] ,we worked on the thin films of these materials. In this study, we report on the growth of Zn4Sb3/CeFe2Co2Sb12 nano-layered superlattices on the silica substrates using an ion-beam assisted deposition (IBAD) system, and high energy Si ion bombardments of the films for reducing thermal conductivity and increasing electrical conductivity. 2. EXPERIMENTAL We have grown Zn4Sb3/CeFe2Co2Sb12 nano-layered superlattices on the silica substrates using IBAD system. The multilayer films were sequentially deposited to have a periodic structure consisting of alternating Zn4Sb3 and CeFe2Co2Sb12 layers. The deposited multi-layer films have
an alternating layers of 1-10 nm thick. The two electron-gun evaporators for evaporating Zn4Sb3 and CeFe2Co2Sb12 were turned on and o
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