Molybdenum Oxide Thin Films Obtained by the Hot-Filament Metal Oxide Deposition Technique

Abstract

Molybdenum oxide thin films find diverse applications as catalysts, gas sensors, and electrochromic devices. Such films are produced mainly by reactive sputtering and thermal evaporation but other techniques such as chemical vapor deposition and electrochemical deposition have been used. In the present work, the feasibility of an alternative method for the production of molybdenum oxide films using a molybdenum filament heated in a rarefied oxygen atmosphere is demonstrated. The filament heating current, I F , and the oxygen flow rate, F O 2 , are the key deposition parameters and their effect on the deposition rate, R, was investigated. For I F ) 12.5 A, an increase in the R-value from 7.5 to 31 nm/min was observed as F O 2 was increased from 6.0 to 21 sccm. To characterize the chemical bonds, infrared spectroscopy, using both unpolarized and p-polarized infrared beams, and X-ray photoelectron spectroscopy (XPS) were employed. Line shape analysis of the Mo(3d) XPS peak revealed that the Mo atoms were in mixed valence states, Mo 6+ and Mo 5+ , with a high predominance of the former over the latter, thus indicating an oxygen-deficient MoO 3 film. From Rutherford backscattering spectroscopic analysis of the films, an average O/Mo atomic ratio of 2.9 was calculated, consistent with the XPS results. A combination of the XPS and RBS results and the data of other investigators on the oxidation of molybdenum suggests that the film is formed from MoO 2 and MoO 3 species desorbed from the Mo filament. The optical gap, E g , was determined from transmission UV-visible spectra of the films. An average E g value of 3.03 eV was found. The electrochromic properties of the films were investigated for Li + intercalation using an electrochemical cell. A coloration efficiency of 19.5 cm 2 /C at a wavelength of 700 nm was observed.

A Plasmonic Molybdenum Oxide Hybrid with Reversible Tunability for Visible‐Light‐Enhanced Catalytic Reactions

“…[13][14][15][16][17][18][19] As an n-type semiconducting material, molybdenum oxide (MoO 3 ) has found important applications in an array of gas sensors, optoelectronics, and catalysis. [20][21][22] However, the wide bandgap (≈3.05 eV) [ 23 ] renders MoO 3 only responsive to UV light, which accounts for less than 5% of the solar energy. In view of sunlight utilization, photocatalysts working under visible light are more promising in that it contributes a major proportion (around 43%) of the entire solar spectrum.…”

Li diffusion and electrochromism in amorphous and crystalline vanadium oxide thin film electrodes

“…10 Recently we developed a thin film deposition process, the hot filament metal oxide deposition (HFMOD), 11 with which tungsten and molybdenum oxide film electrodes were produced, and their electrochromic properties for Li intercalation were studied. 12,13 In this paper, we investigate the optoelectrochemical properties of vanadium oxide films synthesized onto ITO-coated glass substrates by the HFMOD technique. The investigations were carried out in the amorphous as-deposited films and in those thermally-treated at 200, 300, 400 and 500 o C. The electrochemical characterization was made by cyclic voltammetry and chronopotentiometry.…”

XPS and RBS characterizations of electrosynthesized polypyrrole films doped with a heteropolyanion, SiMo12O404−

“…This spectrum is similar to the one obtained for molybdenum oxide film deposited onto Si substrate. 12 This RBS spectrum was fitted with the atomic composition reported in Table 1 constant at 3, 10, and 0.25 respectively (corresponding to one negative charge borne by the dopant anion) and the C and N were varied between 12 to 16 and 3 to 4 respectively (the ratio between C and N being, obviously, fixed to 4). The doping levels evaluated from these data are also reported in Table 1.…”