MeV Si ions bombardment effects on the thermoelectric properties of nano-layers of nanoclusters of Ag in SiO2 host
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 = S2σT/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], [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 SiO2 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.
Section snippets
Experimental
We have grown SiO2/AgxSiO2(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 SiO2 and AgxSiO2(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
Results and discussion
Fig. 3 shows the RBS spectrum and RUMP simulation [12] of 50 periodic nano-layers of SiO2/AgxSiO2(1 − x) films on a Glassy Polymeric Carbon (GPC) substrate when the sample is at the normal angle. Each element which was used in the deposition is revealed in the RBS spectrum and the composition of the multilayer film during the RUMP simulation was shown in Fig. 3. RUMP simulation was used to approximate the layer thickness of about 10 nm. The total thickness is 486 nm with 50 layers. The initial
Conclusion
We have observed the effects of ion fluence on the thermoelectric properties of the SiO2/AgxSiO2(1 − x) alternating layers. The data shows that the thermoelectric properties are positively impacted at the initial fluences. The properties quickly degrade or demonstrate limited response to increasing fluence. This behavior may be due to optimal relation between the Ag nanocrystal size and their limited spatial distribution along the ion track, which gets degraded at higher fluences. Future studies
Acknowledgement
Research sponsored by the Center for Irradiation of Materials, Alabama A&M University and by the AAMURI Center for Advanced Propulsion Materials under the contract number NNM06AA12A from NASA, and by National Science Foundation under Grant No. EPS-0447675.
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