Unraveling the stacking effect and stability in nanocrystalline antimony through DFT

Two-dimensional nanocrystals with semiconducting electronic properties are emerging as promising materials for electronic devices. Here, we present the density functional theory calculations of structural stability, Raman spectra and electronic properties of monolayer, bilayer (AA and AB stacking) and trilayer (AAA and ABC stacking) antimony (Sb). The cohesive energy and phonon band dispersion results revealed that free-standing Sb systems are stable materials. Calculated Raman spectra showed distinct active modes, thus facilitating the characterisation of multilayered structures in different stacking arrangements. It was found that high-frequency in-plane (Eg) and out-of-plane (A1g) modes can shift as much as 16 cm−1 and 28 cm−1 as the layer number increases from monolayer to trilayer. Band structure calculations showed that monolayer and bilayer (AA stacked) Sb are semiconductors with band gap values 1.26 eV and 0.55 eV, respectively, whereas bilayer (AB) and trilayer Sb displayed metallic character. Spin-orbit coupling interaction was also incorporated in band structure calculations and was found to reduce the band gap of monolayer Sb to 1.0 eV while it does not effect on the band gap values of other systems. Moreover, it was seen that nanocrystalline Sb exhibit isotropic mechanical properties. The carrier mobility calculations showed that electron/hole mobility increases by 5/32 times from monolayer to trilayer, respectively.