Selectively arranged single-wire based nanosensor array systems for gas monitoring

Abstract

Gas nanosensors, comprised of arrays of nanoelectrodes with finger-widths of ∼100 nm developed by electron beam lithography and aerosol assisted chemical vapor deposited non-functionalized and Pt-functionalized tungsten oxide nanowires (<100 nm) subsequently integrated across the pairs of electrodes via the dielectrophoresis method, are developed in this work. The functionality of these devices is validated towards various concentrations of NO2 and C2H5OH. The results demonstrate reproducible and consistent responses with better sensitivity and partial selectivity for the non-functionalized systems to NO2, as opposed to the Pt-functionalized systems, which display better sensing properties towards C2H5OH with a loss of response to NO2. These results are explained on the basis of the additional chemical and electronic interactions at the Pt/tungsten oxide interface, which increase the pre-adsorption of oxygen species and make the functionalized surface rather more sensitive to C2H5OH than to NO2, in contrast to the non-functionalized surface.

Tungsten-Based Catalysts for Environmental Applications

“…Results obtained with platinum-doped WO 3 appear possibly contradictory. Chmela et al reported that platinum addition to WO 3 nanowires (<100 nm) caused detrimental effects, with lower sensitivity and selectivity toward NO 2 compared with the unfunction-alized systems, associated with better sensing properties toward C 2 H 5 OH [325]. On the opposite, with nitrided WO 3 (WO x N y nanofibers), platinum addition enhanced the gas sensing characteristics by (i) lowering the operating temperature; (ii) enhancing the sensor reversibility at 50 • C; and (iii) exhibiting an exceptional selectivity toward NO 2 against interfering molecules such as C 2 H 5 OH, C 7 H 8 , CH 4 , CO, NH 3 and NO [326].…”

Comparative Studies of Chemoresistive Gas Sensors Based on Multiple Randomly Connected Wires and Arrays of Single-Wires

“…HRTEM analysis of the tungsten oxide NW employed in this work (Figure 2) revealed that the NWs are highly crystalline with a marked planar spacing of 3.6 Å along the NW, consistent with the unit cell of the monoclinic phase WO3 (ICCD card no. 72-0677) identified in our previous works [2,3]. The typical W4f core level XPS spectrum recorded on the tungsten oxide NWs is also shown in Figure 2 (inset).…”

“…Gas sensors based on M-NW and A-S-NW were fabricated following the same procedure described before. [2,3] Each system was mounted on a TO-8 package and contains a heating element isolated from the electrodes (either IDEs for the M-NW sensors or faced nanoelectrodes for the A-SNW sensors), see Figure 1. The integration of the gas sensitive NWs onto the IDEs was performed directly in vapor-phase via AACVD, whereas the integration of the single NWs previously grown via AACVD was performed using dielectrophoresis technique (i.e., applying an electrical potential between the nanoelectrodes during the re-deposition of NWs via drop coating).…”

“…Both types of sensors (i.e., based on M-NWs and A-S-NWs) were exposed towards various concentration of nitrogen dioxide (NO2) diluted in dry synthetic air using the continuous flow tests system described previously [3]. The total flow was adjusted to 200 sccm, and the sensors were exposed to the measured analyte for 10 min.…”

“…These sensors demonstrated improved gas sensing properties compared to sensors based on polycrystalline films [2]. Also, recently, we have advanced on the fabrication of arrays (A-) of S-NWs sensors with the aim to combine the efficiency of S-NWs and simultaneously enlarge the exposed surface area by integrating several S-NWs connected between faced nanoelectrodes arranged in parallel [3]. Thus, here we compare and evaluate the performance of sensors based on multiple and arrays of single tungsten oxide NWs towards nitrogen dioxide (NO2).…”