Molybdenum-based nanostructured mixed oxides for sensing applications: Effect of the Mo oxide composition on the structure of sol-gel thin films

In this work, we report on the structural investigation by transmission electron microscopy of molybdenum-based mixed oxides for use as gas sensitive films. In particular, sol-gel thin films of molybdenum-titanium and molybdenum-tungsten oxides, deposited by spin coating on silicon substrates, have been analyzed by selected area electron diffraction, conventional, and high-resolution transmission electron microscopy. Our results show that the relative percentage of the molybdenum precursors used during the sol-gel deposition controls the morphology of the films, by modifying the size and the arrangements of the polycrystalline grains on the substrate

Pt/MoO3 nano-flower/SiC Schottky diode based hydrogen gas sensor

In this paper, we report the development of a\ud novel Pt/MoO3 nano-flower/SiC Schottky diode based device\ud for hydrogen gas sensing applications. The MoO3\ud nanostructured thin films were deposited on SiC substrates\ud via thermal evaporation. Morphological characterization of\ud the nanostructured MoO3 by scanning electron microscopy\ud revealed randomly orientated thin nanoplatelets in a densely\ud packed formation of nano-flowers with dimensions ranging\ud from 250 nm to 1 μm. Current-voltage characteristics of the\ud sensor were measured at temperatures from 25°C to 250°C.\ud The sensor showed greater sensitivity in a reverse bias\ud condition than in forward bias. Dynamic response of the\ud sensor was investigated towards different concentrations of\ud hydrogen gas in a synthetic air mixture at 250°C and a large\ud voltage shift of 5.7 V was recorded upon exposure to\ud 1% hydrogen

Comparison of single and binary oxide MoO3, TiO2 and WO3 sol-gel gas sensors

A systematic comparison of sol-gel prepared titanium dioxide (TiO2), WO3, and MoO3 single metal oxide based gas sensors was conducted. Process variables such as solution concentration, deposition parameters, gelling time, annealing time and temperature, remained constant. Sensors based on binary compound MoO3-TiO2 and MoO3-WO3 were also investigated to determine if the performance is superior to their single oxide constituents. The sensors were systematically exposed to O2, O3, CO and NO2 gases and ethanol vapor at concentration levels of particular interest. MoO3 binary compound based sensors showed promising O3, CO and NO2 gas response. Their use as a sensing film for gas is limited due to the materials low evaporating temperature, limiting its operating temperature below 350 °C. However, the binary oxide of MoO3-WO3 showed a high response to ethanol vapor and a highly selective response to NO2

p-and n-type Fe-doped SnO2 gas sensors fabricated by the mechanochemical processing technique

Fe-doped SnO2 sensors were fabricated using micromechanical synthesis technique. The Fe-doped sensor was compared to pure SnO2. Fe-doped SnO2 responded as a p-type semiconductor to oxygen concentrations of up to 10% at 300 °C. As the temperature increased to 400°C, the material responded as an n-type semiconductor. Furthermore, a higher surface area and smaller grains size diameters were achieved when doping SnO2 with Fe. This translated into improved dynamic gas sensing properties and also improved responses to gases such as ethanol

Highly sensitive layered ZnO/LiNbO3 SAW device with InOx selective layer for NO2 and H2 gas sensing

Layered surface acoustic wave (SAW) devices for the monitoring of NO2 and H-2 in synthetic air have been fabricated on XZ LiNbO3 with a 1.2 mu m ZnO guiding layer. To increase selectivity and sensitivity, InOx layers of thickness 40 and 200nm were employed. The sensor's performance was analyzed in terms of frequency shift as a function of different gas concentrations. The sensors were tested over a range of operating temperatures between 100 and 273 degrees C. A large response magnitude with fast response and recovery time was observed. Positive frequency shifts of 91 kHz for 2.125 ppm of NO, and negative frequency shifts of 319 kHz for 1% of H-2 in synthetic air are presented; demonstrating the high sensitivity of the layered SAW structure with the DC sputtered InOx thin film. The surface of the layered SAW structure was studied by atomic force microscopy (AFM) before and after the deposition of the InOx selective layer. The AFM analysis demonstrates that the NO films deposited on ZnO, the guiding layer, resulted in an increase in surface area due to the highly uniform nanostructured surface morphology of InOx

Physical and gas sensing properties of MoO3-WO3 nanostructured oxides

9nonenoneA. Taurino; M. Catalano; R. Rella; P. Siciliano; K. Galatsis; Y.X. Li; W. Wlodarski; E. Comini; G. SberveglieriA., Taurino; M., Catalano; R., Rella; P., Siciliano; K., Galatsis; Y. X., Li; W., Wlodarski; Comini, Elisabetta; Sberveglieri, Giorgi