Scientific Papers

Comprehensive study of formaldehyde gas sensing performance of a GTO thin film incorporated with gold nanoparticles


It is basically known that being exposure to high amount of formaldehyde (HCHO) gas could end up leading to cause cancer in humans [1]. When practically experimenting in rats, those which inhaled formaldehyde had high risks of leukemia and cancers inside nose [1]. People who are frequently exposed to formaldehyde in their workplace are at a substantial risk of developing nasopharyngeal cancer [1], [2]. So, formaldehyde is being considered as a potential cause of disease. Nevertheless, HCHO still can easily be found from the daily essential products. For example, formaldehyde is usually used for anti-corrosion coating to prevent and avoid wooden furniture from getting rot. By immersing HCHO to seeds, farmer could also avoid invading from bugs. Actually, there is a safety level of 0.08 ppm within 30 min recommend by the World Health Organization (WHO) [2]. The concentrations of 100 ppm is immediately dangerous to life and health (IDLH) and national institute for occupational safety and health (NIOSH) which even suggests a lower content as 20 ppm [3]. Thus, the research of formaldehyde detector is necessary for people to sustain the innoxious environment and human safety.

Nowadays, numerous formaldehyde sensing devices based on semiconducting metal oxides (SMOs) have been reported [4], [5], [6], [7], [8]. Lots of SMO materials like NiO [4], ZnO [5], AZO [6], SnO2 [7], and ITO [8] have been reported to manufacture chemiresistive-type gas sensors. For example, SnO2 has been widely utilized in many applications, including as a glaze opacifier, pigment, electronic ceramic, capacitor, conductive coating and lens polishing agent [9]. As a popular n-type material, SnO2 possesses the capacity to adsorb oxygen molecules, an advantageous energy band gap of 3.6 eV and excellent conductivity (∼102 Ω−1·cm−1) [10].

In this study, a novel SMO material, i.e., gallium tin oxide (GTO), is synthesized by incorporating a small proportion of gallium oxide (Ga2O3) into SnO2. The inclusion of Ga2O3 in the composite material yields a wider bandgap about 4.8 eV and improves thermal stability under higher temperature conditions [11].

A highly sensitive formaldehyde sensor is manufactured by incorporating a GTO thin film with gold nanoparticles (Au NPs). The GTO thin film is deposited by radio frequency (RF) sputtering and Au NPs are formed by vacuum thermal evaporation (VTE).

A formaldehyde sensor using GTO microflowers by hydrothermal method was reported by Du et al. in 2018. [12]. The composition ratio between Ga2O3 and SnO2 was 3:97 wt%. This sensor demonstrated the sensing response of 95.8 (3.0) under 50 ppm (1 ppm) to HCHO gas at 230 ℃ [12]. In this work, based on the decoration of Au NPs on the surface of GTO thin film, the studied sensor exhibits a high sensing response of 275 accompanied with a response (recovery) time of 16 s (11 s) when exposed to 20 ppm HCHO/air ambiance at 300 ℃. Meanwhile, a sensing response of 21 is found in a lower formaldehyde content of 50 ppb HCHO/air at the same temperature. The studied sensor also reveals good selectivity, repetitivity, and stability for long-term (120 days) test.

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