Properties of Nano-layers of Nanoclusters of Ag in SiO2 Host produced by MeV Si ion bombardment *
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1020-GG07-21
Properties of Nano-layers of Nanoclusters of Ag in SiO2 Host produced by MeV Si ion bombardment * C. C. Smith1, S. Budak2, S. Guner2, C. Muntele2, R. A. Minamisawa2, R. L. Zimmerman2, and D. ILA2 1 MSFC, NASA, MSFC, Huntsville, AL, 35812 2 Center for Irradiation of Materials, Alabama A&M University, 4900 Meridian Street, PO Box 1447, Normal, AL, 35762 Abstract We prepared 50 periodic nano-layers of SiO2/AgxSiO2(1-x). The deposited multi-layer 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 nanocrystals of Ag with SiO2 as host and as buffer layer using a combination of co-deposition and MeV ion bombardment taking advantage of the electronics energy deposited in the MeV ion track due to ionization in order to nucleate nanoclusters. Our previous work showed that these nanoclusters have crystallinity similar to the bulk material. Nanocrystals of Ag in silica produce an optical absorption band at about 420 nm. Due to the interaction of nanocrystals between sequential nanolayers there is widening of the absorption band. The electrical and thermal properties of the layered structures were studied before and after 5 MeV Si ions bombardment at various fluences to form nanocrystals in layers of SiO2 containing few percent of Ag. Rutherford Backscattering Spectrometry (RBS) was used to monitor the stoichiometry before and after MeV bombardments. Keywords: Ion bombardment, thermoelectric properties, multi-nanolayers, SiO2/Ag+SiO2, Rutherford backscattering spectrometry, Van der Pauw method, 3ω method, Seebeck coefficient, Figure of merit. *Corresponding author: D. ILA; Tel.: 256-372-5866; Fax: 256-372-5868; Email: [email protected]
1. INTRODUCTION Metal and semiconductor nanoclusters embedded in transparent matrices exhibit linear and nonlinear optical properties that are of interest to the field of opto-electronics. By using the same technique it is feasible to produce these clusters for converting heat into electrical power [1]. The efficiency of the thermoelectric devices is determined by the figure of merit ZT [2]. The figure of merit is 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 [3-4]. Z T can be increased by increasing S, by increasing σ, or by decreasing κ. Efficient thermoelelctric devices have a high electrical conductivity and a low thermal conductivity [5].
2. EXPERIMENTAL We have grown SiO2/AgxSiO2(1-x) nano-layers films on silica substrates with the Ion Beam Assisted Deposition (IBAD) system. The multilayer films were sequentially deposited to have a periodic structure consisting of alternating SiO2 and AgxSiO2(1-x) layers. The two electron-gun evaporators for evaporating the two solids were turned on and off alternately to make multilayers. The base pressure obtained in IBAD chamber was 6x10-6 torr. The growth rate was monitored by an Inficon Quartz Crystal Monitor. The film
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