Ion Bombardment Improvement on Thermoelectric Properties of Multilayered Bi2Te3/Sb2Te3 Deposited by Magnetron Sputtering
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1020-GG07-02
Ion Bombardment Improvement on Thermoelectric Properties of Multilayered Bi2Te3/Sb2Te3 Deposited by Magnetron Sputtering Bangke Zheng, S. Budak, B. Chhay, R. L. Zimmerman, and D. ILA Department of Physics, Center for Irradiation of Materials (CIM), Alabama A&M University, P.O.Box 1447, Normal, AL, 35762 Abstract We have grown the multi layer of Bi2Te3 and Sb2Te3 super-lattice film systems using the magnetron sputtering system. The purpose of using magnetron sputtering system is to o keep the stoichiometry of Bi2Te3 and Sb2Te3 so as to keep the electrical and thermal conductivity advantage of the layered structure of bulk Bi2Te3 and Sb2Te3. Magnetron sputtering is operated at relatively low temperature. The prepared super-lattice thin film systems were then bombarded by 5 MeV Si ions to form nano-clusters in the layers to increase the electrical conductivity and to decrease the thermal conductivity. We measured the cross plane electrical and thermal conductivities before and after MeV Si ions bombardment. 1. Introduction As shown in Fig. 1, these thin films form a periodic quantum well structure consisting of tens to hundreds of alternating layers with different band gap. The thickness of each layer is 10 nm. The performance of super-lattice thin film thermoelectric device is quantified by the dimensionless figure of merit ZT = S2 σT/ k [1]. 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 super-lattice structure with MeV Si ions. The bombardment will form nanoscale cluster (quantum dot) structures. In addition to the quantum well confinement of the phonon transmission due to Bragg scattering and reflection at lattice interface [1, 2, 3], the defect and disorder in the lattice caused by bombardment and the grain boundaries of these nano-scale cluster formed by bombardment increase the scattering of phonon and increase the chance of the inelastic interaction of phonon and the annihilation of phonon, inhabiting heat transport in the direction perpendicular to the lattice [4, 5, 6, 7]. Phonon is chiefly absorbed and dissipated along the lattice, thus cross plane thermal conductivity will decrease. These quantum dot clusters also increase the Seebeck coefficient and electrical conductivity due to the increase of the electronic density of states in nano-scale cluster miniband.
Heats up
Metal Cu
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10nm BixTe1-x/ SbyTe1-y 70 layers n type SL
Cool down
Metal Cu
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SiO2 Si substrate
Figure 1. Schematic of BixTe1-x/ SbyTe1-y superlattice TE device 2. Experiment The magnetron sputtering deposition system with two target holders (guns) was used to deposit Bi2Te3/ Sb2Te3 multilayer thin films. The chamber was pumped down by a turbo pump to a background pressure of 2 ×10-5 Torr. The two guns in our magnetron sputtering device are oriented at a certain angle to get off-axis plasma plume, which will form the lattice with preferential orientation for electric conductivity in each layer. The mu
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