MeV Si ions bombardment effects on the thermoelectric properties of nano-layers of nanoclusters of Ag in SiO 2 host S. Budak a , S. Guner b,c , R.A. Minamisawa d , D. ILA b, ⁎ a Department of Electrical Engineering, Alabama A&M University, Normal, AL 35762, USA b Center for Irradiation of Materials, Department of Physics, Alabama A&M University, Normal, AL 35762 USA c Department of Physics, Fatih University, B. Cekmece, Istanbul 34500, Turkey d IBN 1-IT, Forschungszentrum Julich, D-52425, Julich, Germany abstract article info Available online 1 March 2009 PACS: 81.07.- b Keywords: Ion bombardment Thermoelectric properties Multi-nanolayers Rutherford backscattering Figure of merit We prepared 50 periodic nano-layers of SiO 2 /Ag x SiO 2(1 -x) with Au layer deposited on both sides as metal contacts. The deposited multi-layer films have a periodic structure consisting of alternating layers where each layer is 10 nm thick. The purpose of this research is to generate nano-layers of nanocrystals of Ag with SiO 2 as host and as buffer layer using a combination of co-deposition and MeV ion bombardment taking advantage of energy deposited in the MeV ion track 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 SiO 2 containing few percent of Ag. Rutherford Backscattering Spectrometry (RBS) was used to monitor the stoichiometry before and after MeV bombardments. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Semiconductor and metal nanoclusters embedded in transparent matrices exhibit linear and nonlinear optical properties which are of interest to the field of opto-electronics. It is feasible to produce these clusters for converting heat into electrical power by using the same technique [1]. The efficiency of the thermoelectric devices and films are determined by the figure of merit ZT [2]. The figure of merit is ZT =S 2 σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity [3–5]. ZT can be increased by increasing S, by increasing σ, or by decreasing κ. Efficient thermoelectric devices have a high electrical conductivity and a low thermal conductivity as well as high thermopower coefficient [5]. The purpose of this research is to generate nano-layers of nanocrystals of Ag with SiO 2 as host and as buffer layer using a combination of co-deposition and MeV ion bombardment taking advantage of energy deposited in the MeV ion track to nucleate nanoclusters. 2. Experimental We have grown SiO 2 /Ag x SiO 2(1 -x) nano-layers films on silica substrates using the Ion Beam Assisted Deposition (IBAD) system. The multilayer films were sequentially deposited to have a periodic structure consisting of alternating SiO 2 and Ag x SiO 2(1 -x) layers. The two electron-gun evaporators for evaporating the two solids were turned on and off alternately to grow the multilayers. The base pressure obtained in IBAD chamber was 6 × 10 -6 Torr. The growth rate was monitored by an Inficon Quartz Crystal Monitor. The film geome- try used for the deposition of SiO 2 /Ag x SiO 2(1 - x) nano-layers films is shown in Fig. 1 . The geometry in Fig. 1 shows Au contacts on the top and bottom of the multilayers. These two Au contacts were used in the Seebeck coefficient measurements. The electrical conductivity was measured by the Van der Pauw system and the thermal conductivity was measured by a homemade 3ω thermal conductivity measurement system. The electrical conductivity, thermal conductivity and Seebeck coefficient measurements have been performed at a temperature of 22 °C. Detailed information about the 3ω technique may be found in Refs. [6–9]. In order to nucleate nanocrystals in the layers, 5 MeV Si ion bombardments were performed with the Pelletron ion beam accel- erator from the Center for Irradiation of Materials at Alabama A&M University (CIM-AAMU). The 5 MeV energy of the bombarded Si ions was selected using a SRIM08 simulation software. The Si ions range was optimized to reach the substrate at 3.5 μm depth below the nanolayers film/substrate interface. Therefore, the nucleation of the Ag nanocrystals was induced primarily by the Si ions energy loss, without influence of the implanted specie in the film composition or possible formation of Si nanocrystals in the studied film. Fig. 2 shows the simulation of the Si ions energy loss in the nano-layered films Surface & Coatings Technology 203 (2009) 2479–2481 ⁎ Corresponding author. Tel.: +1 256 372 5866; fax: +1 256 372 5868. E-mail address: ila@cim.aamu.edu (D. ILA). 0257-8972/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2009.02.041 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat