Hydrogen annealing effects on local structures and oxidation states of atomic layer deposited SnOx

Divalent tin is of great interest, but comes with a drawback—its metastable nature. In pursuing divalent tin, the authors systematically examine the change in oxidation states of Sn using a set of ALD SnOx films annealed in different atmospheres at temperatures ranging from 350 to 650 °C. Although the majority of Sn in the film was tetravalent after deposition, x-ray photoelectron spectroscopy and x-ray absorption near-edge structure verified the presence of divalent Sn after annealing in H2, and the divalent Sn content increased as the annealing temperature was raised. The local structures of Sn processed under these conditions were probed using extended x-ray absorption fine structure. Data from samples annealed in H2 at 350, 450, and 550 °C were fitted well using a rutile SnO2 model; the sample annealed in H2 at 650 °C could only be fitted using a hybrid of SnO2 and SnO models. Annealing in N2 and O2 resulted in tetravalent Sn. X-ray reflectivity showed that the density of the as-deposited film was as ...