Seebeck Coefficient of Nanolayer Growth of Anatase TiO 2-x /Al-foil by Atomic Layer Deposition
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Seebeck Coefficient of Nanolayer Growth of Anatase TiO2-x/Al-foil by Atomic Layer Deposition Matthew Chamberlin1, Renee E. Ahern1, Costel Constantin1 1 Department of Physics and Astronomy, James Madison University, Harrisonburg, VA 22807 ABSTRACT Non-stoichiometric and impurity doped titanium dioxide materials are good candidates for use in high temperature thermoelectric devices. Nanolayers of non-stoichiometric (TiO2-x) thin films were deposited on Al-foil by atomic layer deposition growth method. X-ray diffraction experiments showed anatase phase for these nanolayers. This crystal structure was maintained even after an annealing treatment of 600 °C for 60 minutes under an O2 pressure of ~ 10 psi. This investigation presents for the first time how Al-foil can be functionalized by manipulating the Seebeck coefficient of these TiO2-x nanolayers. INTRODUCTION Due to ever increasing demand for energy consumption and storage for mobile applications, thermoelectric devices that efficiently convert heat into electricity are of major importance. Non-stoichiometric TiO2-x is a good candidate material for thermoelectric applications [1,2]. Titanium dioxide thin films have been widely used in photocatalysts, dyesensitised solar cells, gas sensors, and selfcleaning components because of its low absorption coefficient, and high dielectric constant. TiO2 is an insulator in its intrinsic state; however, the electrical properties of TiO2 can be controlled by oxygen vacancies. In the present study, atomic layer deposition growth method was employed to create potential thermoelectric devices by using non stoichiometric TiO2-x nanolayers that were deposited on Al-foil that we use in our kitchens which is ~ 13,000 cheaper than Silicon.
EXPERIMENTAL DETAILS Thin films of Titanium Dioxide (TiO2-x) were deposited on top of aluminium foil (Alfoil) (i.e. Reynolds heavy-duty purchased from Walmart) by atomic layer deposition (ALD). Our homemade ALD reactor is illustrated in Figure 1(a) and (b). A very nice comprehensive review on the advances of ALD has been recently published by Parsons et al.[3]. The design of our ALD reactor can be found elsewhere [4]. The ALD reactor used titanium isopropoxide [i.e. Ti(OCH(CH3)2)4(l)] as a metal precursor, water as an oxygen precursor, and high purity nitrogen (i.e. 99.99%) gas as a carrier/purging gas. The x-ray diffraction (XRD) experiments were performed with a PANalytical MPD Powder X-ray diffractometer (XRD) that uses a monochromatic x-ray beam with a wavelength of λ = 1.542 Angstroms.
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(a)
(b)
Figure 1. (a) Schematic diagram, and (b) photograph of the ALD reactor. The Seebeck coefficient is defined as the negative ratio between the change in electromotive voltage and the change in temperature (i.e. S = - ΔV/ΔT). The S values were measured using a homemade instrument that is presented in Figure 2. The sample is set onto two blocks of Aluminum and the heating source is provided by a soldering iron through radiation [Figure 2]. The sample constitutes a layer of TiO2-x thin film on top of Al
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