A Gas Sensor Based on a Single SnO Micro-Disk

Abstract

In this study, individual nanofabricated SnO micro-disks, previously shown to exhibit exceptional sensitivity to NOx, are investigated to further our understanding of gas sensing mechanisms. The SnO disks presenting different areas and thickness were isolated and electrically connected to metallic electrodes aided by a Dual Beam Microscope (SEM/FIB). While single micro-disk devices were found to exhibit short response and recovery times and low power consumption, large interconnected arrays of micro-disks exhibit much higher sensitivity and selectivity. The source of these differences is discussed based on the gas/solid interaction and transport mechanisms, which showed that thickness plays a major role during the gas sensing of single-devices. The calculated Debye length of the SnO disk in presence of NO2 is reported for the first time.

Heating Method Effect on SnO Micro-Disks as NO2 Gas Sensor

“…It is well-known that some amount of energy (heat) is necessary to overcome the activation barrier for the chemisorption ( H Chem ), otherwise, the gas molecules would be in a physisorbed state (Batzill and Diebold, 2005). However, by Equation 1, if the temperature goes too high the coverage decreases and sensor signal drops, in full agreement with previous results involving SnO micro-disks in multi-and singledevice configurations (Suman et al, 2013;Masteghin and Orlandi, 2018). Figure 4B shows the sensor response for the SnO micro-disks at 200 • C reached through two different heating modes, external heating (red spheres), and self-heating (blue triangles).…”

“…Figure 6B clearly shows a lower recovery time when submitted to the external heating method, as a result of both higher pre-exponential factor and more energy available. Besides, we showed that O (ads) − species still remain onto the SnO surface, after stopping the release of the NO 2 (Masteghin and Orlandi, 2018), indicated in Equation (3) (Kaur et al, 2007;Sharma et al, 2013):…”

“…In order to synthesize the SnO disks, SnO 2 powder (Sigma-Aldrich, 99.9% purity), was mechanically mixed with carbon black (Union Carbide, >99% purity) in a molar ratio of 1.5:1 and submitted to the carbothermal reduction route (Suman et al, 2013;Masteghin and Orlandi, 2018). The procedure involved preparing 1 g of the SnO 2 :C mixture that was inserted in the central region of a horizontal tubular furnace, and held at 1,135 • C for 75 min using heating and cooling rates of 10 • C min −1 .…”

“…Among the cited MOSs, SnO 2 has been studied the most, due to its great performance and chemical stability (Batzill and Diebold, 2005). However, more attention has recently been given to other Sn x O y stoichiometries with less stable oxidation states, such as SnO (Suman et al, 2013(Suman et al, , 2015Hien and Heo, 2016;Masteghin and Orlandi, 2018) and Sn 3 O 4 (Suman et al, 2014(Suman et al, , 2015Li et al, 2015;Liu et al, 2016).…”

Special Issue “Advanced Nanomaterials Based Gas Sensors”

“…in the sensing layer. This approach is the one followed in [15,16]. In the first case, the sensing element is a microdisk of SnO.…”