Thin-film synthesis of the orthorhombic phase ofSnO2

We demonstrate the formation of an ${\mathrm{SnO}}_2$ thin film in an orthorhombic phase which has previously been found in high-pressure experiments. Our starting point was the pulsed-laser deposition of an amorphous film of SnO on Si [001] substrates. During a series of subsequent heat treatments in air, the film crystallized in a sequence of three phases. First, after heating to $300°\mathrm{C},$ the litharge phase of SnO was formed. Next, while heating to $700°\mathrm{C},$ the film absorbed oxygen and formed the high-pressure orthorhombic phase of ${\mathrm{SnO}}_2.$ Eventually, after heating to $1150°\mathrm{C},$ the film was fully converted to the stable cassiterite phase of ${\mathrm{SnO}}_2.$ The experiments performed to date are not conclusive, but indirect evidence indicates that the litharge structure is important as an intermediary in the formation of the orthorhombic phase, in contrast to the transformation route at high pressure.