Electronic structure tuning via surface modification in semimetallic nanowires

Electronic structure properties of nanowires (NW) with diameters of 1.5 nm and 3 nm based on semimetallic $\alpha$-Sn are investigated by employing density functional theory and perturbative $GW$ methods. We explore the dependence of electron affinity, band structure and band gap values with crystallographic orientation, NW cross-sectional size and surface passivants of varying electronegativity. We consider four chemical terminations in our study: methyl ($\rm{CH_3}$), hydrogen ($\rm{H}$), hydroxyl ($\rm{OH}$), and fluorine ($\rm{F}$). Results suggest a high degree of elasticity of Sn-Sn bonds within the SnNWs' cores with no significant structural variations for nanowires with different surface passivants. Direct band gaps at Brillouin zone centers are found for most studied structures with quasi-particle corrected band gap magnitudes ranging from 0.25 eV to 3.54 eV in 1.5 nm diameter structures indicating an exceptional range of properties for semimetal NWs below the semimetal-to-semiconductor transition. Band gap variations induced by changes in surface passivants indicate the possibility of realizing semimetal-semiconductor interfaces in NWs with constant cross-section and crystallographic orientation allowing the design of novel dopant-free NW-based electronic devices.