5MeV Si Ion Modification on Thermoelectric SiO2/SiO2+Cu Multilayer Films
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5MeV Si Ion Modification on Thermoelectric SiO2/SiO2+Cu Multilayer Films C. Smith1 S. Budak1, T. Jordan2, J.Chacha2, B. Chhay3, K. Heidary2, R. B. Johnson 3, C. Muntele1, D.ILA4 2
1 Center for Irradiation of Materials, Alabama A&M University, Normal, AL USA Department of Electrical Engineering, Alabama A&M University, Normal, AL USA 3 Department of Physics, Alabama A&M University, Normal, AL USA 4 Department of Physics, Fayetteville St. University, Fayetteville, NC USA
Abstract We prepared samples by electron beam physical vapor deposition EB-PVD followed by ion bombardment. The samples were than characterized by photoluminescence (PL), x-ray photoelectron spectroscopy (XPS). PL was used to characterize the available energy states. XPS was used to determine the binding energies. The ML’s are comprised of 100 alternating layers of SiO2/SiO2+Cu. *Corresponding author: C. Smith; Tel.: 256-372-5866; Fax: 256-372-5855; Email: [email protected]
1. INTRODUCTION In previous studies we have demonstrated the improved thermoelectric properties of SiO2 MLs embedded with various nanoparticles, such as Au, Ag and Cu [9-12]. ML structures are fabricated to reduce the phonon conduction through the sample, thus increasing the figure of merit. The efficiency of the thermoelectric devices and materials is determined by the figure of merit ZT [9]. The figure of merit is defined by ZT = S 2σT / κ , where S is the Seebeck coefficient, ı is the electrical conductivity, T is the absolute temperature, and ț is the thermal conductivity [10, 11]. Increasing S can increase ZT, by increasing ı, or by decreasing ț. In this study we have reported on the growth of SiO2/SiO2+Cu multi-layer We define ML as polycrystalline layers on the order of 10 nanometers that exhibit non bulk properties. Koeler described a superlattice structure as a pair of layers of materials that has single crystalline structure of 10nm thickness and less. Typically, the ML structures are fabricated between 5 to 10 nanometers in order to take advantage of the quantum confinement properties. Quantum dots (QDs) have been used to increase the performance of devices for numerous applications. Reed first coin the term quantum dot to describe semiconductor particle that had a Ion implantation is used to modify the ML region without damage. The stopping powers of the ion traveling through the layers can be tailored to maximum the electronic stopping power within the layer while minimizing the nuclear stopping power.
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Figure 1. Multilayer thin films
2. EXPERIMENTAL We have deposited the 100 alternating layers of SiO2/SiO2+Cu nana-layers films on silicon substrates at the total thickness of 382 nm. Figure 1. shows the fabricated ML films that were fabricated by using two Telemark electron beam 4-pocket guns. After EB-PVD we bombarded the samples with 5 MeV Si ions. The ion bombardment was performed with the 5SDH National Electrostatic Corp. Pelletron ion beam accelerator at the Howard J. Foster Center for Irradiation of Materials at Alabama A&M University. The fluenc
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