Abstract
The present work discusses a technology for deposition and characterization of thin molybdenum oxide (MoOx, MoO3) films studied for gas sensor applications. The samples were produced by reactive radio-frequency (RF) and direct current (DC) magnetron sputtering. The composition and microstructure of the films were studied by XPS, XRD and Raman spectroscopy, the morphology, using high resolution SEM. The research was focused on the sensing properties of the sputtered thin MoO3 films. Highly sensitive gas sensors were implemented by depositing films of various thicknesses on quartz resonators. Making use of the quartz crystal microbalance (QCM) method, these sensors were capable of detecting changes in the molecular range. Prototype QCM structures with thin MoO3 films were tested for sensitivity to NH3 and NO2. Even in as-deposited state and without heating the substrates, these films showed good sensitivity. Moreover, no additional thermal treatment is necessary, which makes the production of such QCM gas sensors simple and cost-effective, as it is fully compatible with the technology for producing the initial resonator. The films are sensitive at room temperature and can register concentrations as low as 50 ppm. The sorption is fully reversible, the films are stable and capable of long-term measurements.
Highlights
MoO3 is one of the most promising inorganic materials with a wide potential for technological applications as large-area electrochromic devices, optical switching coatings and high-density memory devices [1]
The X-ray photoelectron spectroscopy (XPS) profile analyses showed that the structure changes between the surface and the bulk
The films consist of stoichiometric MoO3 with nano-size structure on the surface and amorphous nearly stoichiometric MoO2 in the bulk
Summary
MoO3 is one of the most promising inorganic materials with a wide potential for technological applications as large-area electrochromic devices (displays and smart windows), optical switching coatings and high-density memory devices [1]. Thin MoOx films can be used for many other applications, such as catalysts [2], lubricants [3], solid-state microbatteries [4]. The aim of the present work was to the study the gas sensing properties of films prepared by RF and DC-magnetron sputtering. To this end, thin MoOx and MoO3 films were deposited on different substrates.
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