Electrical Properties of Magnesium Carbon Co-Sputtered Thin Films Applied Post Hydroxylation Treatment
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Electrical Properties of Magnesium Carbon Co-Sputtered Thin Films Applied Post Hydroxylation Treatment Masafumi Chiba1, Daisuke Endo1, Mikihiko Maizono2, Mikiteru Higashi1, and Hideo Kiyota3 1 Department of Materials Chemistry, Tokai University, 317 Nishino, Numazu, Shizuoka 4100395, Japan 2 Course of Materials Science and Technology, Graduate School of Tokai University, 317 Nishino, Numazu, Shizuoka 410-0395, Japan 3 Department of Mechanical Systems Engineering, Tokai University, 9-1-1 Toroku, Kumamoto, Kumamoto 862-8652, Japan ABSTRACT Indium oxide doped with tin oxide, or ITO, has been widely used as an electrode material for flat panel displays. However, the rare metal in ITO is a limited natural resource. We succeeded in developing a material composed solely of elements with abundant reserves. We present the results of analyzing the electronic structure of an Mg-based compound based on its electrical conductivity. Mg-C thin films were prepared by sputtering method. A new transparent and electrically conductive material, Mg(OH)2-C, was formed after reacting the Mg-C film with moisture in air. On average, its transmittance of visible light was 90%. The mechanism for the effect of carbon on the electrical conductivity of Mg(OH)2 was examined on the basis of XPS spectra and DV-Xa molecular orbital calculations. The value of the band gap shows that Mg(OH)2 is an insulator. It was revealed that a new orbital appears when the number of substituting carbon atoms increases in the Mg(OH)2 lattice. It was possible to measure the new orbital that consisted of C-2s and C-2p. In addition, a comparison between the calculated electronic state around the valence band and the result measured by XPS of the obtained film reveals that they are in extremely close agreement. INTRODUCTION Indium oxide doped with tin oxide, otherwise known as ITO, has been widely used as a key material for liquid crystal display technologies because of its high transparency and electrical conductivity [1]. The rare metal in ITO is a limited natural resource. Baba reported very interesting general remarks about the importance of the rare metal in the current issue of the journal [2]. Since the scarcity of the rare metal indium has been repeatedly emphasized, alternative transparent and electrical conductive materials have been actively studied over the last decade [3-5]. As mentioned above, transparent conductive materials are based on metal oxides. It is well known that metal oxides are somewhat like semiconductors in that the balance between the band gap and conductivity is very important for obtaining high electric conductivity and optical transparency [6, 7]. Recently, Kondoh’s group reported intriguing results on the transparency of Mg-C compounds [8]. Although they obtained colored glassy films, the electrical conductivity of the film samples was not confirmed. According to the calculated binary Mg-C phase diagram [9], this element pair is expected to be immiscible, suggesting that the mixing enthalpy for alloying Mg and C is positive. In a series
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