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

Abstract

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.

Electrochromism in sputter-deposited W–Ti oxide films: Durability enhancement due to Ti

“…The Ti was found to promote stability both for crystallization at elevated temperature and for the electrochromic performance under extended cycling in a Li-conducting electrolyte. Our data are consistent with those in prior work [14][15][16][17][18]26,30] as regards crystallization and support earlier evidence concerning the ability of Ti to prevent permanent incorporation of Li. Furthermore, our data indicate that low sputtering powers are connected with improved stability under electrochemical cycling.…”

“…Other, supporting studies on the electrochromism in W-Ti oxide have been reported for films prepared by sputtering [16][17][18][19], chemical technology involving spraying [20][21][22] dipping [16,23] or spinning [24][25][26], electrodeposition [27,28] and anodization [29]. The enhanced stability has been investigated in depth in recent work on W-Ti oxide films made by sputtering [30,31] and chemical techniques [26]. Data based on electrochemical measurements, transmission electron microscopy, atomic force microscopy and Raman spectroscopy verify [26,30] that the Ti addition makes the crystallization occur at a higher temperature than in a film of pure W oxide.…”

“…The enhanced stability has been investigated in depth in recent work on W-Ti oxide films made by sputtering [30,31] and chemical techniques [26]. Data based on electrochemical measurements, transmission electron microscopy, atomic force microscopy and Raman spectroscopy verify [26,30] that the Ti addition makes the crystallization occur at a higher temperature than in a film of pure W oxide.…”

Electrochromic properties of W1––Ni Ti O3 thin films made by DC magnetron sputtering

“…can be boosted by incorporating some titanium [16][17][18][19][20][21] which prevents crystallization that otherwise may degrade the WO 3 [21][22][23]. Here we combine these beneficial effects and present data from a comprehensive study of W 1-x-y Ni x Ti y O 3 thin films.…”

Hybrid nanocomposites with enhanced visible light photocatalytic ability for next generation of clean energy systems

“…Analyses also showed that the W atoms were in the formal valence band +6, [78] with the observed binding energy peaks at around 35.8 and 37.8 eV being associated with spin-orbit splitting of the W 4f7/2 and W 4f5/2 respectively (Figure 3c). [88] Lastly, in the O core level XPS spectrum (Figure 3d), the 530.8 eV peak corresponding to the O1s [89] showed no changes in all the samples being investigated, thus indicating that Pt coating and r-GO modification, while changing the surface chemical/physical properties of the hybrids did not affect their crystalline structure.…”