Comparative microscopic and spectroscopic analysis of temperature-dependent growth of WO3 and W0.95Ti0.05O3 thin films

• Published in: Journal of materials science Vol. 47; no. 18; pp. 6593 - 6600
• Main Authors: Manciu, Felicia S., Yun, Young, Durrer, William G., Howard, James, Schmidt, Ute, Ramana, Chintalapalle V.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01-09-2012; Springer Nature B.V
• Subjects: Atomic force microscopy; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Crystallites; Crystallography and Scattering Methods; Doping; Materials Science; Morphology; Oxidation; Phase transitions; Photoelectrons; Polymer Sciences; Raman spectroscopy; Solid Mechanics; Spectroscopic analysis; Spectrum analysis; Stoichiometry; Substrates; Surface roughness; Temperature dependence; Thin films; Titanium; Tungsten oxides; X ray photoelectron spectroscopy; Substrate Temperature; Atomic Force Microscopy Topography Image; Metal Oxide Structure; Atomic Force Microscopy; Increase Growth Temperature
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-012-6591-z

We present a comparative microscopic and spectroscopic study of the morphology and composition of WO
3
and W
0.95
Ti
0.05
O
3
thin films, grown by radio-frequency magnetron reactive sputtering at substrate temperatures varied from room temperature to 500 °C, using atomic force microscopy (AFM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). With increasing growth temperature, the AFM results show increase in the average crystallite size and in the surface roughness for both undoped and doped samples. The AFM data, along with the Raman results, clearly indicate that for the given set of experimental conditions, higher growth temperatures are required to obtain crystalline Ti-doped WO
3
films than for WO
3
films. Also, the Raman results suggest a potential phase transformation from a monoclinic WO
3
structure to an orthorhombic, but more probably a tetragonal, configuration in the W
0.95
Ti
0.05
O
3
thin films. This remark is based on the observed shifting, with Ti doping, to lower frequencies of the Raman peaks corresponding to W–O–W stretching modes of WO
3
at 806 and 711 cm
−1
to 793 and 690 cm
−1
, respectively. XPS data indicate that the doped material has a reduced WO
3−
x
stoichiometry at the surface, with the presence of W
6+
and W
5+
oxidation states; this observation could also be related to the existence of a different structural phase of this material, corroborating with the Raman measurements.