Effects of Ambient Air on Functional Stability of Single-Molecule Spin Logic Gate

Single-molecule spin logic gates provide fundamental functions and are of importance in the field of molecular spintronics. Here, by using the first-principles method, the effects of ambient gas molecules (CO₂, O₂, N₂, or H₂O) on the functional stability of the investigated single-molecule spin logic gate consisting of two serially connected cobalt dibenzotetraaza14annulene (CoDBTAA) molecules between single-walled carbon nanotubes (SWCNTs) electrodes, have been theoretically investigated. The calculated results suggest that the investigated spin logic gate can realize AND, NOR, or XNOR logic functions depending on the definition of the input and output signals. It is found that these logic functions are not affected by CO₂ adsorption. On the contrary, these logic functions are no longer retained upon O₂, N₂, or H₂O adsorption. Further analysis reveals that the interaction between the CoDBTAA molecule and the CO₂ adsorbate is very weak while it is strong for O₂, N₂, or H₂O molecules. Therefore, the electronic states of the logic gate around Fermi energy (E_F) are almost unchanged for CO₂ adsorption. While the adsorption of O₂, N₂, or H₂O obviously modifies the electronic states around E_F. The strong interaction between CoDBTAA and these three gas adsorbates drives the conductive electronic states to move far away from E_F, resulting in the blocking of both spin-up and spin-down currents and further voiding the logic functions. This work suggests that ambient air has an important effect on the functional stability of single-molecule devices and should be carefully evaluated in the future design of functional single-molecule devices.