Quantum Spin Sensor for Open-shell Molecules

Zig-zag graphene nanoribbons (ZGNRs) exhibit symmetric spin distributions on their edges, making them susceptible to perturbations due to molecular adsorption. This study investigates the impact of adsorption of closed-shell (e.g. N2, CO, CO2) and open-shell paramagnetic (e.g. O2, NO, NO2) molecules on the spin-polarized quantum transport properties of zig-zag graphene nanoribbons using density functional theory and nonequilibrium Green’s function (NEGF-DFT) methods. We found that closed-shell molecules physisorbed on graphene nanoribbons, while open-shell molecules chemisorbed strongly at the edges. This chemisorption disrupts the symmetric spin distribution, leading to spin-polarized transmission. The underlying mechanism for spin-polarized transmission in open-shell molecule adsorbed cases is quantum interference between the localized states of the molecule and the delocalized states of the graphene nanoribbons. The bond current, the current between a pair of two atoms, analysis shows that physisorbed closed-shell molecules act as a scattering center, which reduces the current through graphene nanoribbons. We showed that the interaction of open-shell molecules with the graphene nanoribbons depends on the electronic properties of adsorbed molecules. Thus a variation in destructive quantum interference pattern is observed for different open-shell molecules resulting in different spin current. This phenomenon can be used for molecular recognition of open-shell paramagnetic species, providing avenue for quantum spin sensors technology.