J. Phys. NFrance 11 (2001) O EDP Sciences, Les Ulis Cobalt oxide thin films prepared by metalorganic chemical vapor deposition from cobalt acetylacetonate A.U. Mane, K. Shalini and S.A. Shivashankar Materials Research Centre, Indian Institute of Science, Bangalore 560012, India Abstract. Thin films of cobalt oxide have been deposited on various substrates, such as glass, Si(100). SrTi03(100), and L&03(100), by low pressure metalorganic chemical vapor deposition (MOCVD) using c o b a l t o acetylacetonate as the precursor. Films obtained in the temperature range 400-600°C were uniform and highly crystalline having C q 0 4 phase as revealed by x-ray diffraction. Under similar conditions of growth, highly oriented thin films of cobalt oxide grow on SrTi03(100) and LaA1&(100). The microstructure and the surface morphology of cobalt oxide films on glass, Si(100) and single crystalline substrates, Sffi03(100) and LaA103(100) were studied by scanning electron microscopy. Optical properties of the films were studied by uv-visible-near IR spectrophotometry. 1. INTRODUCTION Because of their many interesting and useful properties, (binary) transition metal oxides have a variety of potential and actual applications in their thin film form. Cobalt forms two stable oxides: COO (rocksalt structure, a = 0.426 nm) and Co304 (normal spinel structure, a = 0.808 nm). Thin films and coatings of cobalt oxides have been studied for possible uses such as oxygen sensors, solar-selective absorbers, and protective layers [1,2]. It has been suggested recently that, because of structural and chemical compatibility, thin films of Co304 may be useful as buffer layers for strongly oriented or epitaxial films of functional oxides such as perovskite-type ferroelectrics and cuprate superconductors [3]. Thin films of cobalt oxides have been prepared on various substrates by methods such as sputtering [4], pulsed laser deposition [5], sol-gel process [6], nebulized spray pyrolysis [2], and metalorganic chemical vapor deposition (MOCVD) [3,7,8]. Additionally, electrolytic methods have been used to produce coatings of "black cobalt" on substrates such as stainless steel for application as solar-selective absorbers [9]. In this same vein, the optical properties of polycrystalline films of C0304 deposited on glass by sputtering and CVD have been studied [4]. It has been shown that, depending on deposition conditions, Co304 films on glass may have a (100) or (111) preferred orientation [3]. However, the growth rate, microstructure, and morphology of Co304 films and their dependence on growth conditions and on the substrate material do not appear to have been reported in detail. As part of our effort to study the growth and microstructure of various oxides, we have examined the CVD of Co3O4 and COO using the metalorganic precursor cobalt(Q acetylacetonate, Co(acac)?. In addition to the deposition of polycrystalline films on substrates such as glass and Si(100), we have studied the epitaxial growth of Co3O4, which occurs at surprisingly low temperatures [lo]. The lattice parameter of Co304, a = 0.808 nm, so that a12 is matched closely to cubic SrTiOl (a = 0.395 nm), but less closely to pseudo-cubic LaA103 (a = 0.379 Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:2001381