A Detailed Study of the Synthesis of Bismuth Thin Films by PVD-Methods and their Structural Characterization
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A Detailed Study of the Synthesis of Bismuth Thin Films by PVD-Methods and their Structural Characterization Enrique Camps1, Sandra E. Rodil2, J. Antonio Salas3, Horacio V. Estrada3 1 Instituto Nacional de Investigaciones Nucleares, Ocoyoacac, MEX, 2 Instituto de Investigaciones en Materiales – UNAM, México, DF 3 Centro Nacional de Metrología, Querétaro, QRO 76246, MEXICO Keywords: evaporation, sputtering, laser ablation. ABSTRACT A comprehensive and rather complete study for the synthesis of Bismuth thin-films using physical vapor deposition (PVD) techniques aimed at identifying key features of their crystallographic structure and morphology/topography, as a function of the synthesis method is presented. These films were deposited on oxidized and non-oxidized polished silicon substrates, glass-plates and polyimide flexible films, by thermal evaporation (resistive boat and e-beam) DC- and RF-magnetron assisted sputtering, and pulsed laser (ablation) deposition (PLD). The synthesis was performed controlling the main deposition parameters of these methods. XRD-spectra conclusively indicate that the films can be preferentially oriented along the [003] or [012] Bi-structure’s directions, depending on the source-to- substrate (STS)-distance, sputtering power, substrate’s temperature and PLD ion’s kinetic energy. It is also concluded that a relatively short STS-distance results in a rather polycrystalline structure, near independent to the used sputtering power. INTRODUCTION Bismuth is a very interesting material in many aspects. It differs from many other materials because of its energy band structure [1-2] which identifies it as a semimetal, for which Bi is, electrically, considerable different from metals, and somewhat from semiconductors. In most cases, the electrical current is based on the motion of either positive or negative charges [3]; its resistivity decreases with temperature, similar to pure semiconductors but opposite to metals; its charge carrier concentration is lower than metals and similar to heavily doped semiconductors. These characteristic features put bismuth into a special place when considering thermoelectric applications [4] identified as one of the materials with a highest figure of merit, or highest thermoelectric sensitivity; in fact, bismuth was one of the elements that led to the discovery of the Seebeck effect. Magnetically, it may exhibit a considerably large magnetoresistance, especially at low temperatures [2]. Bismuth is also an interesting material for its high resistancestrain sensitivity [5]. Many other applications and properties have been in the past reported in the literature for bismuth films [6].
However, for the adequate manifestation of these interesting features and properties, it is necessary to have films with a highly ordered (near monocrystalline) crystal structure, as in the case of bismuth’s magnetoresistance [1,4]; for this case, such a “monocrystalline” structure has been achieved through a molecular beam epitaxy (MBE) and electrodeposition methods (ED) methods [4].
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