Structural transformations in MoOx thin films grown by pulsed laser deposition

In this work, laser-induced crystallization in MoOx thin films (1.8 less than or equal to x less than or equal to 2.1) is reported. This transformation involves a MoOx oxidation and subsequently a crystallization process from amorphous MoO3 to crystalline alpha-MoO3. For comparison purposes crystallization is induced thermally, in an oven, as well. The crystallization kinetics is monitored by Raman spectroscopy; a threshold in the energy density necessary to induce the phase transformation is determined in the case of photo-crystallization. This threshold depends on the type of substrate on which the film is deposited. For the thin films deposited on glass substrates, the structural transformation is from amorphous MoOx to the thermodynamically stable alpha-MoO3 crystalline phase. For the thin films deposited on Si(100) the structural transformation is from amorphous MoOx to a mixture of alpha-MoO3 and the thermodynamically unstable beta-MoO3 crystalline phases. The structural transformations are also characterized by scanning electron microscopy and light-transmission experiments.