Deposition of Composite Nanoparticle-Based Thin Films for Gas Sensing

Abstract

Working principle of conductometric gas sensors is based on modulation in electrical conductivity of the sensing material due to adsorption-desorption reactions between the target gas and the sensor surface. Nano-structuring the sensing material increases the effective surface area for interaction between the target gas and the sensing material thereby enhancing the sensorial response. Metal oxide semiconductors (MOS) have shown remarkable sensing performance to oxidizing and reducing gases. The combination of different MOS has often demonstrated to synergistically improve the gas sensing performance via the formation of highly sensitive heterojunctions at their interface.In this work, we deposited thin films composed of nanoparticles (NPs) of p-type CuOx and n-type WOx to enhance the effective surface area of the material and to realize the maximum number of nano p-n heterojunctions in the material. The films were prepared using the Nanogen-Trio NP source equipped with three 1′′ magnetrons, mounted on a custom-built deposition chamber and sputtered by a DC power supply. Depositions were executed in Ar+O2 gas mixture. The O2 admixture may significantly enhance the mass flux of NPs. Furthermore, the O2 admixture allows one to tune the desired stoichiometry of the respective metal oxides. On the other hand, the pronounced hysteresis complicates the deposition of WOx NPs. The deposition process was controlled using an in-house developed software to prepare thin films composing a mixture of NPs with a defined volumetric ratio of the individual materials.This work demonstrates the versatility of our custom-built gas aggregation source that facilitates the preparation of multi-composite NP-based thin film giving the best sensorial response.