Effects of MeV Si ion bombardments on the Properties of Nano-layers of SiO2/SiO2+Zn4Sb3
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1020-GG07-22
Effects of MeV Si ion bombardments on the Properties of Nano-layers of SiO2/SiO2+Zn4Sb3 S. Budak1, S. Guner1, C. Muntele1, C. C. Smith2, R. L. Zimmerman1, and D. ILA1 1 Center for Irradiation of Materials, Alabama A&M University, 4900 Meridian Street, PO Box 1447, Normal, AL, 35762 2 MSFC, NASA, MSFC, Huntsville, AL, 35812 Abstract We prepared 8 periodic nano-layers of SiO2/SiO2+Zn4Sb3. The deposited multilayer films have a periodic structure consisting of alternating layers where each layer is between 1-10 nm thick. The purpose of this research is to generate nanolayers of nanostructures of Zn4Sb3 with SiO2 as host and as buffer layer using a combination of codeposition and MeV ion bombardment taking advantage of the electronics energy deposited in the MeV ion track due to ionization in order to nucleate nanostructures. The electrical and thermal properties of the layered structures were studied before and after bombardment by 5 MeV Si ions at various fluences to form nanostructures in layers of SiO2 containing Zn4Sb3. Rutherford Backscattering Spectrometry (RBS) was used to monitor the stoichiometry before and after MeV bombardments. Keywords: Ion bombardment, Thermoelectric properties, Rutherford backscattering, Van der Pauw method, 3ω method, Seebeck coefficient, Figure of merit *Corresponding author: D. ILA; Tel.: 256-372-5866; Fax: 256-372-5868; [email protected]
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1. INTRODUCTION The single phase β-Zn4Sb3 is one of the high performance thermoelectric materials and still attracts great interest due to its convenience primarily on increasing the figure of merit, ZT. The performance of any thermoelectric substance is evaluated by the dimensionless figure of merit expression ZT = S 2σ T / κ , where S, σ, κ and T are the Seebeck coefficient (V/K), electrical conductivity (Ω-1m-1), thermal conductivity (W/m-K) and absolute temperature (K), respectively [1]. In the bulk form β-Zn4Sb3, has a high figures of merit (ZT) between 450 and 670 K and a maximum of about 1.3 at a temperature of 670 K while its room temperature ZT is equal to 0.2 [2]. In comparison to bulk form of substances, mono or multilayer thin film fabrication provides a potential to increase the thermoelectric properties of materials. Advantages of reduced size include enhancement of the density of states which increases the Seebeck coefficient [3] and lowers the thermal conductivity [4], both effects increase the ZT. In a study performed by Zhang et al on Zn4Sb3 thin films prepared by magnetron sputtering technique, a ZT of 1.2 at 460 K has been obtained for a 349 nm thick Zn4Sb3 film specimen [5]. It is also
reported that the low electrical resistivity and high Seebeck coefficient can be achieved simultaneously in a film specimen with properly controlled thickness and microstructure. A study on the thermoelectric properties of Ni45Cu55 alloy is consistent with this report and proves that the dispersed microstructures of SiO2 increase the Seebeck coefficient of the material [6]. There are also multilayer thin film investigations p
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