DFT study of NH3 adsorption on pristine, Ni- and Si-doped graphynes

The electronic sensitivity of pristine, Ni- and Si-doped graphynes to ammonia (NH3) molecule was investigated using density functional theory, including dispersion correction. It was found that NH3 is weakly adsorbed on the sheet, releasing energy of 2.9-4.4 kcal/mol, and the electronic properties of the sheet are not significantly changed. Although both Ni-doping and Si-doping make the sheet more reactive and sensitive to NH3, Si-doping seems to be a better strategy to manufacture NH3 chemical sensors because of higher sensitivity. Our calculations show that the HOMO/LUMO gap of the Si-doped sheet is significantly decreased from 2.13 to 1.46 eV after the adsorption of NH3, which may increase the electrical conductance of the sheet. Therefore, the doped sheet might convert the presence of NH3 molecules to electrical signals. Moreover, the shorter recovery time of the Si-doped sheet is because of the middle adsorption energy of 39.3 kcal/mol in comparison with 55.1 kcal/mol for the Ni-doped sheet.