Morphology of crystalline alpha-MoO3 thin films spin-coated on Si (100)

Thin films of crystalline alpha -MoO3 with thicknesses between 35 and 150 n m were prepared on Si (100) wafers by spin-coating of peroxo-polymolybdic s olutions. Variations of the morphology of the films with spin-coating condi tions and thermal treatments applied afterwards were investigated by means of confocal laser Raman spectroscopy, X-ray diffraction and scanning electr on microscopy. Thickness and uniformity of the films, and size, anisotropy and orientation of alpha -MoO3 crystals with respect to the Si substrate ca n be tuned by adequately adjusting the concentration of the precursor solut ion, the solvent, and the spin-rate during spin-coating. Size, anisotropy a nd orientation of crystals are nevertheless interconnected and cannot be tu ned independently. The three variables are themselves dictated by the thick ness of the films. However, the choice of the solvent used for the precurso r solution seems to provide some additional flexibility in the tuning of th e morphology of alpha -MoO3 crystals, while the minimum thickness required to obtain stable crystalline alpha -MoO3 films under the conditions we used for calcination is estimated to be 35 nm. (C) 2000 Elsevier Science S.A. A ll rights reserved.