Laser-induced structural transformations in MoO 3 investigated by Raman spectroscopy
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Laser-induced structural transformations in MoO3 investigated by Raman spectroscopy E. Haro-Poniatowskia) and C. Julienb) Laboratoire des Milieux D´esordonn´es et H´et´erog`enes, Universit´e Pierre et Marie Curie, Tour 22, case 86, 4 place Jussieu, 75252 Paris cedex 05, France
B. Pecquenard and J. Livage Chimie de la Mati`ere Condens´ee, Universit´e Pierre et Marie Curie, 4 place Jussieu, 75252 Paris cedex 05, France
M. A. Camacho-L´opez Departamento de F´ısica, Universidad Aut´onoma Metropolitana Iztapalapa, Apdo. Postal 55-534, M´exico, D. F. 09340 (Received 10 February 1997; accepted 6 August 1997)
The glass-crystalline transformation induced by laser irradiation is studied in MoO3 . Before crystallization we have found that the system evolves from a low temperature glass phase to a high temperature glass phase. The crystallization kinetics depend strongly on the initial irradiation power. The power densities needed to induce the phase transformations, of the order of 15 Wymm2 , are relatively low and suggest the possibility of using this material as a data storage medium.
I. INTRODUCTION
MoO3 is a material belonging to the transition metal oxides and has considerable industrial importance. Molybdenum oxides are attractive as cathode materials, exhibiting high electronic conductivity and high ionic mobility together with a low energy barrier for lithium insertion and extraction.1 MoO3 is also an active selective catalyst for the oxidation of hydrocarbons and alcohols.2 In thin film form, the molybdenum trioxide photochromism and electrochromism properties have been investigated because of its potential applications in display devices.3,4 MoO3 can exist in different crystalline polymorphs, the thermodynamically stable orthorhombic a –MoO3 ,5 the metastable monoclinic b –MoO3 ,6 and another metastable phase reported in Ref. 7 and denoted as MoO3 0 . a –MoO3 has a layered structure consisting of double layers of MoO6 octahedra held together by covalent forces. Several phases with a stoichiometric Mo : O ratio between 2.75 and 2.91 exist.1 The well-defined phases are reported in the literature: Mo4 O11 , Mo17 O47 , Mo5 O14 , Mo18 O52 ,8 Mo8 O23 ,9 Mo19 O55 , Mo20 O58 , Mo21 O61 , and Mo22 O64 .10 The electrical properties of amorphous MoO3 thin films have been widely studied.11 The structural properties of the material in bulk and thin film form have been reviewed recently.1,3,12
Laser-induced crystallization processes have been analyzed in a variety of situations. Some years ago laser annealing of ion-implanted semiconductors was extensively investigated.13 More recently local laser crystallization or amorphization of materials was considered for optical memory purposes.14 For these applications materials easily obtained in thin film form and with a low intensity threshold for crystallization under laser irradiation are necessary. Raman spectroscopy is a very suitable in situ technique for studying laser-induced processes. The structural effects can be studied as a
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