Oxygen- and hydroxyl-edge termination of silicene nanoribbons studied by first-principles calculations

• O- and OH-passivation on silicene edges are energetically favorable over H-passivation.
• Different from the resistence of π-bonds saturation on silicene surface, the oxidation on silicene edges is much easier due to the stronger chemical reactivity of σ-bonds.
• Counting the two new “atom-chains” formed between neighboring OHs on ASiNR-OH edges, the band gaps of O- and OH-functionalized ASiNRs follow the same hierarchy of Δ3p>Δ3p−1>Δ3p−2Δ3p>Δ3p−1>Δ3p−2.

The geometrical structures and electronic properties of the armchair- and zigzag-edge silicene nanoribbons (SiNRs), terminated with oxygen and hydroxyl (ZSiNR-O, ZSiNR-OH, ASiNR-O, ASiNR-OH), have been investigated by using the first-principles method. It is found that the silicene edges are rippled upon the oxygen termination. On one edge of ZSiNR-O, the neighboring Si–O bonds move concordantly right (left) from the silicene plane, while on one edge of ASiNR-O, the neighboring Si–O bonds respectively move right and left to result in larger rippled amplitudes. Comparably, the influence of OH-termination on the silicene edge is small, inducing smaller rippled edges. The electronic structure calculations show that the px electrons of oxygen on the rippled edges of ZSiNR-O sp3 hybridize with the edge Si atoms, forming one more bands. The band gaps of the ASiNR-O and ASiNR-OH also obey the three-family behavior, due to the quantum confinement and the crucial effect of the edges. For ASiNR-OH, by taking account of the new atom chains formed by the hydrogen bonds of the neighboring OHs, the band gaps follow the same hierarchy of Δ3p>Δ3p−1>Δ3p−2Δ3p>Δ3p−1>Δ3p−2 with those of ASiNR-Os.