Two-Dimensional Antimony Oxide

Two-dimensional (2D) antimony, so-called antimonene, can form antimonene oxide when exposed to air. We present different types of single- and few-layer antimony oxide structures, based on density functional theory (DFT) calculations. Depending on stoichiometry and bonding type, these novel 2D layers have different structural stability and electronic properties, ranging from topological insulators to semiconductors with direct and indirect band gaps between 2.0 and 4.9 eV. We discuss their vibrational properties and Raman spectra for experimental identification of the predicted structures.

Figure 1

Type (I) antimonene oxide structures with one layer in side view (a) and top view (b), and two layers in (c) and (d). Type (II) antimonene oxide heterostructures with different stoichiometry of the oxidized layers: (e) and (f) ${\mathrm{Sb}}_2\mathrm{O}$; (g) and (h) ${\mathrm{Sb}}_2{\mathrm{O}}_2$; and (i) and (j) ${\mathrm{Sb}}_2{\mathrm{O}}_3$. Type (II) structures in top view show the oxidized layer only. Oxygen (antimony) atoms are shown in red (gray). Labels a and b on the figures indicate the in-plane lattice vectors. For details about the structural parameters, see Tables S1 and S2 in the Supplemental Material [33].

Figure 2

Exemplary display of phonon modes of the monolayer antimonene oxide structures investigated here. The type (II) ${\mathrm{Sb}}_2\mathrm{O}$ and ${\mathrm{Sb}}_2{\mathrm{O}}_2$ on the left-hand side are shown from the top. All other structures are shown from the side. Green arrows indicate the displacements of the atoms and are to logarithmic scale.

Figure 3

Calculated frequencies of Raman-active vibrational modes in (a) antimonene, (b) type (I), (c)–(e) type (II) antimonene oxide structures, as indicated in the insets and shown in Fig. 1. Except for (b), the height of the bars indicates the calculated Raman activity (log. scale).

Figure 4

Electronic band structures and density of states calculated using the hybrid functional HSE12 [39] and inclusion of spin-orbit interactions (SOI) for (a) type (I) ${\mathrm{Sb}}_2{\mathrm{O}}_2$, (b) type (II) ${\mathrm{Sb}}_2{\mathrm{O}}_2$, and (c) type (II) ${\mathrm{Sb}}_2{\mathrm{O}}_3$ monolayers. Gray dashed lines are the results without SOI and are almost congruent with the bands with SOI for (b) and (c). The zero of energy is set to the Fermi energy.