Metal Oxide Nanowire Preparation and Their Integration into Chemical Sensing Devices at the SENSOR Lab in Brescia

Abstract

Metal oxide 1D nanowires are probably the most promising structures to develop cheap stable and selective chemical sensors. The purpose of this contribution is to review almost two-decades of research activity at the Sensor Lab Brescia on their preparation during by vapor solid (n-type In2O3, ZnO), vapor liquid solid (n-type SnO2 and p-type NiO) and thermal evaporation and oxidation (n-type ZnO, WO3 and p-type CuO) methods. For each material we’ve assessed the chemical sensing performance in relation to the preparation conditions and established a rank in the detection of environmental and industrial pollutants: SnO2 nanowires were effective in DMMP detection, ZnO nanowires in NO2, acetone and ethanol detection, WO3 for ammonia and CuO for ozone.

The Use of Copper Oxide Thin Films in Gas-Sensing Applications

“…The starting solution, an aqueous solution containing copper chloride CuCl 2 , was used, being a source of copper, heated to a specific temperature to increase the solubility of various constituents, and then deposited on glass substrates using spray pyrolysis. Various methods allow obtaining copper oxides with different morphologies, including nanowires [44,46], nanoparticles [33,47], nanoflowers [26,48], nanofibers [38,49], nanorods [50,51], nanostructures [35,36,42], nanobelts [24], hollow spheres [8,23], and nanosheets [52]. Table 1 lists various deposition techniques and nanoscale forms of CuO-based gas sensors.…”

IoT-Enabled Gas Sensors: Technologies, Applications, and Opportunities

“…Amperometric Sensors: these have the variation of the electrical current as a sensing parameter, where the reduction of the cathode to hydroxyl ions generate a current, proportional to the concentration of the target gas. The cathode and anode must be linked with a resistor, in where the variation of the current on the load resistor can be measured as a tension value [32,93,118,119].…”

“…Over the past 10 years, the use of nanostructures as metal oxide semiconductors to sense gases has become a topic of interest of some research groups, with reports of ameliorated sensing characteristics [22,65,66,118,119]. Response time and energy consumption are also topics of research, where the most part of commercial solutions have response times of seconds, sometimes reaching a few minutes; the energy consumption of these devices can reach the order of 500 milliwatts (mW) or even higher, due to the necessity of the heater.…”

“…These sensors perform the detection by measuring the variation on the internal resistance, which occurs when combustible gases are present in the ambient atmosphere. The process of detecting gas on this type of sensor consists on the chemical reaction between the catalytic element and the combustible gases on the environment, generating an elevation on the temperature These sensors can be easily miniaturized, including the use of nanomaterials to develop the sensing elements, which have demonstrated an increased performance on these transducers; the use of an external stimulus, as ultraviolet (UV) light, have shown better efficiency on measurements at room temperature [118,119]. The most common materials used on these transducers are tin oxide (SnO 2 ), zinc oxide (ZnO), tungsten trioxide (WO 3 ) and titanium dioxide (TiO 2 ).…”

“…The heating process must be adequate to the target gas, as the sensor will respond to different gases if the temperature is not suitable for the gas of interest. A physical gas filter, to eliminate interference from other gases, can be added to the sensing element, upgrading the performance of the measurements [28,38,119,120].…”