MeV Si ions Bombardment Effects on the Properties of Nano-layers of SiO2/SiO2+Ag
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1074-I03-25
MeV Si ions Bombardment Effects on the Properties of Nano-layers of SiO2/SiO2+Ag Sadik Guner1,2, Satilmis Budak3, Claudiu I Muntele1, Cydale C Smith4, and Daryush Ila1 1 Physics, Alabama A&M University, Center for Irradiation of Materials, 4900 Meridian street, Normal, AL, 35762 2 Department of Physics, Fatih University, Hadimkoy, Buyukcekmece, Istanbul, 34500, Turkey 3 Electrical Engineering, Alabama A&M University, 4900 Meridian Street, Normal, AL, 35762 4 Department of Physics, Alabama A&M University, 4900 Meridian Street, Normal, AL, 35762 Abstract We have grown 50 periodic SiO2 / SiO2+Ag multi-nano-layered systems where the SiO2+Ag layers were 7.26 nm and SiO2 buffer layer were 4 nm, total thickness is 563 nm. Using interferometer as well as in-situ thickness monitoring, we measured the thickness of the layers; using Rutherford Backscattering Spectrometry (RBS) measured the concentration and distribution of Ag in SiO2. The electrical conductivity, thermal conductivity and the Seebeck coefficient of the layered structure were measured at room temperature before and after bombardment by 5 MeV Si ions. The energy of the Si ions were chosen such that the ions are stopped in the silicon substrate and only electronic energy due to ionization is deposited in the layered structure. The electrical conductivity measured using Van der Pauw method. Thermal conductivity of the thin film was measured using an in-house built 3ω thermal conductivity measurement system. Using the measured Seebeck coefficient, thermal conductivity and electrical conductivity, we calculated the dimensionless figure of merit (ZT). We will report our findings of change in the figure of merit as a function of the bombardment fluence. Keywords: Ion bombardment, thermoelectric properties, multi-nanolayers, SiO2/Ag+SiO2, Rutherford backscattering, Van der Pauw method, 3ω method, Seebeck coefficient, Figure of merit. *Corresponding author: S. Guner; Tel.: 256-372-8413; Fax: 256-372-5868; Email: [email protected]
1. INTRODUCTION The best thermoelectric materials were succinctly summarized as “phonon-glass electron-crystal” (or PGEC in short), which means that the materials should have a low lattice thermal conductivity as in a glass, and a high electrical conductivity as in
crystals [1]. Formation of nano-crystals by co-deposition sometimes followed by annealing and/or by MeV Ion Beam Irradiation. At the studies performed by S. Budak et al, this case was proven and positive improvements in thermoelectric properties were recorded [2,3]. The efficiency of the thermoelectric devices is determined by the dimensionless figure of merit ZT [4]. The dimensionless figure of merit is calculated by 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 [5-6]. ZT can be increased by increasing S, by increasing σ, or by decreasing κ. Efficient thermoelectric devices have high Seebeck coefficient, electrical conductivity and a low thermal conductivity [7
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