Facet-Dependent Gas Adsorption Selectivity on ZnO: A DFT Study

Semiconductor-based gas sensors are of great interest in both industrial and research settings, but poor selectivity has hindered their further development. Current efforts including doping, surface modifications and facet controlling have been proved effective. However, the methods-selectivity correlation is ambiguous because of uncontrollable defects and surface states during the experiments. Here, as a case study, using a DFT method, we studied the adsorption features of commonly tested gases-CH2O, H-2, C2H5OH, CH3COCH3, and NH(3-)on facets of ZnO(0001 over bar ), ZnO(101 over bar 0) and ZnO(101 over bar 1). The adsorption energies and charge transfers were calculated, and adsorption selectivity was analyzed. The results show ZnO(0001 over bar ) has obvious CH2O adsorption selectivity; ZnO(101 over bar 0) has a slight selectivity to C2H5OH and NH3; and ZnO(101 over bar 1) has a slight selectivity to H-2, which agrees with the experimental results. The mechanism of the selective adsorption features was studied in terms of polarity, geometric matching and electronic structure matching. The results show the adsorption selectivity is attributed to a joint effort of electronic structure matching and geometric matching: the former allows for specific gas/slab interactions, the latter decides the strength of the interactions. As the sensing mechanism is probably dominated by gas-lattice interactions, this work is envisioned to be helpful in designing new sensing material with high selectivity.

Automated summary

Semiconductor-based gas sensors have potential applications in various industries and research fields, but their poor selectivity has been a major obstacle. This study investigated the adsorption characteristics of commonly tested gases on different facets of ZnO using a DFT method. The results showed that each facet exhibited different levels of selectivity towards different gases, and the selective adsorption was attributed to a combination of electronic structure matching and geometric matching.