Synthesis, Characterization and Gas Sensing Study of ZnO-SnO2 Nanocomposite Thin Films

Abstract

Thin nanocomposite films composed of ZnO and SnO2 at 0.5–5 mol.% concentrations were synthesized by a new solid-phase low-temperature pyrolysis under the developed protocols. This hetero-oxide material was thoroughly studied by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques to be compared with electrical and gas-sensing properties. We have found that the films have a poly-nanocrystal structure of ZnO and SnO2 crystals with characteristic grain sizes at 10–15 nm range. When comparing the chemiresistive response of the films with varied tin dioxide content, the sample of Sn:Zn optimum ratio taken as 1:99 yields 1.5-fold improvement upon to 5–50 ppm NO2 exposure at 200 °C. We argue that these remarkable changes have matured from both a reducing the intergrain potential barrier down to 0.58 eV and increasing the concentration of anionic vacancies at this rational composite. The results demonstrate that solid-phase low-temperature pyrolysis is a powerful technique for adjusting the functional gas-sensing properties of hetero-oxide film via modifying the ratio of the oxide components.

High Gas Sensitivity to Nitrogen Dioxide of Nanocomposite ZnO-SnO2 Films Activated by a Surface Electric Field

“…A comparative analysis of the gas sensitivity to NO 2 of nanocomposite ZnO-SnO 2 structures presented in Table 1 and in this paper shows that the size of nanostructures (nanocrystallites) is essential for high gas sensitivity to low concentrations of NO 2 in the air. In all works, the nanostructures of the gas-sensitive material are formed by different technologies, and have sizes from 5 to 17 nm [15,29,30,[40][41][42]. In addition, when the operating temperature of the gas sensor decreases, the response and recovery times increases [30,81].…”

“…Each layer was dried in air and in a drying cabinet at a temperature of 100 • C. Heat treatment was carried out at 500 • C for two hours (Figure 1). The synthesis technique is described in more detail in previous studies [15,36]. To make gas sensors based on ZnO-SnO2 thin films, precursor was applied over a Pt counter-pin structure multi-sensor platform, MSP 632, and dried at 100 °C.…”

“…Excellent results are shown by thin films based on tin dioxide, with the addition of other oxides in small concentrations [9,[15][16][17][18] or heterostructures [19,20]. In this case, the nature, the oxidation degree, the crystallites size, and the modifying agents' concentration are the controlling factors of the density of surface defects and the surface area of oxide nanomaterials [21], as well as the concentration of surface oxygen [15,22]. In such materials, ZnO-ZnO, SnO 2 -SnO 2 homostructures, and ZnO-SnO 2 heterojunctions, as well as Schottky barriers, are formed [23].…”

“…On the other hand, thin films of nanocomposite materials are used to determine low concentrations of gases (fractions and ppm units). Excellent results are shown by thin films based on tin dioxide, with the addition of other oxides in small concentrations [9,[15][16][17][18] or heterostructures [19,20]. In this case, the nature, the oxidation degree, the crystallites size, and the modifying agents' concentration are the controlling factors of the density of surface defects and the surface area of oxide nanomaterials [21], as well as the concentration of surface oxygen [15,22].…”

“…If crystallite size is higher, the sensitivity is usually lower [43][44][45]. On the other hand, the best gas-sensitive properties are shown for materials with the one component concentration equal to 10% or lower [15,29,46]. The first case can be explained by the existence of a depletion-enrichment zone comparable to the size of nanoparticles.…”