Combination of characterization techniques for atomic layer deposition MoO3 coatings : From the amorphous to the orthorhombic alpha-MoO3 crystalline phase

Thin films of MoO3 deposited on Si(111) and Al2O3(001) substrates by atomic layer deposition have been investigated by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and Raman spectroscopy for detailed characterization of composition and morphology. Comparison of angle resolved x-ray photoelectron spectroscopy (ARXPS) and XPS depth profiles based on Ar+ sputtering is reported. Sputtering induces a reduction of molybdenum in MoO3 from +IV to metallic Mo as the interface toward Si is approached, whereas ARXPS on a 10 nm thin film shows that Mo(VI) remains outside the interface toward Si where lower valent molybdenum compounds are formed. Upon annealing, the as-deposited amorphous thin films of MoO3 crystallize into beta- or alpha-MoO3 as identified by x-ray diffraction. The current study provides a convenient route toward formation of metastable beta-MoO3 and a full crystallization pathway from amorphous to crystalline alpha-MoO3. Combined AFM and Raman analysis have been performed on thin films of alpha-MoO3 deposited on Al2O3(001) and prove that the crystallization proceeds via island growth at 600 degrees C. The Raman intensity ratios between different bands depend strongly on morphology and size of crystalites. (C) 2012 American Vacuum Society. [DOI: 10.1116/1.3643350