Influence of MgPc modification on NO2 sensing characteristics of RGTO grown SnO2 thin films

In the present study, we report a 100% enhancement in NO2 sensing response of tin oxide (SnO2) thin films through surface modification utilizing magnesium phthalocyanine (MgPc). For this purpose, SnO2 thin films were grown by Rheotaxial Growth and Thermal Oxidization (RGTO) method and were later modified by MgPc. Deposition of MgPc over SnO2 film was carried out by vacuum sublimation method. During deposition of MgPc, the substrates were heated to 200 °C. The MgPc modified SnO2 films (SnO2: MgPc) exhibit higher sensor response (18.5 for 5 ppm NO2), faster response/recovery time (6 s/169 s) and lower operating temperature (175 °C) as compared to pristine SnO2 films which exhibit maximum response at an operating temperature of 300 °C. Work function measurements and X-ray photoelectron spectroscopy (XPS) studies indicate formation of p-n hetero junctions in modified films due to electron transfer from SnO2 (n-type) to MgPc (p-type). In addition, MgPc modification results into intensification of oxygen adsorption sites (from 6.5% to 32.5%) on the sensor surface. Formation of p-n junctions at the interface and enhancement of adsorbed oxygen on the surface establish the basis for superior response i.e higher sensor response and faster response and recovery time of SnO2: MgPc films.