Phase transformations in pulsed laser deposited nanocrystalline tin oxide thin films

Thin SnO_x films have been synthesized with the method of pulsed laser deposition and their microstructure examined using X-ray diffraction (XRD). The films were amorphous as grown and subjected to postdeposition annealing in air to various temperatures. The litharge phase of SnO (α-SnO) was found only in films grown at laser fluences greater than ∼1.9 x 10⁸ W cm^-2 and was stable in the temperature range of ∼300-500 °C. Formation of the orthorhombic SnO₂ phase (o-SnO₂) was correlated with film thickness, being found in thicker films (basically, >500 nm) at ∼500 °C, and was stable up to ∼900 °C. These observations are examined in light of results from time-of-flight mass spectrometric analysis of the ablated plume. The average grain size of these films, as determined from the XRD peak widths, was found to increase with increasing laser fluence and film thickness.