Laser Induced Oxidation Effects in Bismuth Thin Films
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Laser Induced Oxidation Effects in Bismuth Thin Films Marco A. Zepeda1,2, Michel Picquart2, and Emmanuel Haro-Poniatowski2 1
Departamento de Atención a la Salud, Universidad Autónoma Metropolitana Unidad Xochimilco, México DF 2
Departamento de Física, Universidad Autónoma Metropolitana Unidad Iztapalapa, México DF Corresponding author: [email protected] Keywords: Bi, laser-induced reaction, Raman spectroscopy ABSTRACT The Laser induced oxidation process of bismuth was investigated using Raman spectroscopy. Upon laser irradiation (λ = 532 nm) pure Bismuth was transformed gradually into Bi2O3. Raman spectra of the samples showed the characteristics peaks for pure Bi located at 71 cm-1 and 96 cm-1. The oxidation process was monitored by Raman spectra with four additional bands located at about 127 cm-1, 241 cm-1, 313 cm-1 and 455 cm-1. Maintaining constant the exposure time of irradiation, the intensity of these bands depended on laser irradiation power. The presence of Bi2O3 in the sample was confirmed through by energy dispersion spectroscopy (EDS). INTRODUCTION The electronic and vibrational properties of bismuth, which is a semimetal, are determined by its rhombohedral crystal structure and by the mixture of covalent and metallic bonding [1]. Bi thin-films have been intensively studied because of its special thermoelectric properties; also superconductivity and quantum-size phenomena have also been reported. On a Bi single crystal, two main peaks are observed by Raman spectroscopy, corresponding to the Eg mode at 70 cm-1 and A1g mode at 97 cm-1. Additionally, a continuum of broad bands centered around 22 cm-1 and 67 cm-1 extending over more than 100 cm-1 are also observed. Various combinations of phonons could be responsible for this continuum [2]. Bismuth oxide can be obtained from bismuth through an oxidation process in air or oxygen. It is also known as one of the initial components used in the synthesis of hightemperature superconductors. Five polymorphs of bismuth oxides are known and have been widely investigated for their conductivity properties. Three of them are stable (-Bi2 O3, monoclinic; -Bi2O3, cubic and -Bi2O3, triclinic) and two are metastable (-Bi2O3, tetragonal and -Bi2O3, body centered cubic) [3-4]. Differential thermal analysis of a Bi2O3 powder has also been reported [5]. The first observed transition is from to phase occurring at 727 °C, further heating leads to sample melting at 822 °C. Upon cooling the sample exhibits a phase transformation from -Bi2O3 to -Bi2O3 at 639 °C and finally from -Bi2O3 to -Bi2O3. Huang et al. [6] reported the study of the oxidation process in electrodeposited bismuth films. Salazar-
Perez et al. [3] studied the thermal oxidation of nano-sized bismuth particles prepared by chemical reduction and the dependence of the different phases obtained on annealing temperature. Kumari et al. [7] studied the laser oxidation of thin films prepared by thermal evaporation, showing the strong dependence of the morphology and crystalline orientation of the Bi thin f
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