Transition metal-decorated germanene for NO, N2 and O2 sensing: A DFT study

Detecting hazardous and toxic gasses is important to avoid harmful effects on human health and two-dimensional nanostructures have emerged as candidate materials for sensing or scavenging gasses. The chemical interactions between NO, O2, and N2 gas molecules and Cu-, Ag-, and Au-decorated germanene were investigated by using density functional theory simulations, and the potential applications as gas sensors or scavengers were addressed. Except for O2, the studied molecules were physisorbed on pristine germanene, where the most favorable adsorption site is located at the middle of the lattice hexagon, with adsorption energy values ranging from 0.09 eV for the N2 to 0.49 eV for NO adsorbed through the N atom. The results also show that the studied molecules have larger adsorption energies in Cu-, Ag-, and Au-decorated germanene, with energy values of 0.4 eV for the N2 molecule and 1.04 eV for the NO molecule. Therefore, molecule-metal-germanene complexes are more energetically favorable than the molecule-germanene ones and are thus predicted to have an enhanced sensing capability. The larger NO adsorption energies on Ag- (0.8 eV) and Au- (0.87 eV) decorated germanene, in comparison with those of N2 (around 0.1 eV) and O2 (around 0.37 eV), indicate their good selectivity towards NO. To estimate their potential application as NO sensors in gas-insulated switchgear, we calculated the work function and desorption time of the studied molecules adsorbed on Cu-, Ag-, and Au-decorated germanene, obtaining considerable changes in the work function (around 0.5 eV) between the different molecules adsorbed on Cu-decorated germanene, and recovery times of the order of seconds at a temperature of 400 K. The results suggest that metal-germanene complexes are stable in ambient conditions and they are good candidates for sensing and scavenging nitrogen monoxide.