First-principles investigation of two-dimensional trichalcogenide and sesquichalcogenide monolayers

We have used density functional theory to investigate the dynamical stability and the electronic structure of several new semiconducting two-dimensional single layers, with chemical compositions such as ${\mathrm{AB}X}_3$ and ${\mathrm{A}}_2{X}_3$. The calculated interlayer binding energies and the absence of imaginary states in the phonon spectra indicate the possibility to isolate them in the form of a single layer. Also, the calculated band edges reveal that some of these two-dimensional materials are promising candidates for water-splitting applications.

Figure 1

Bulk crystal structure of (a) ${\mathrm{AlSiTe}}_3$ (similar for ${\mathrm{InSiTe}}_3)$, (b) ${\mathrm{As}}_2{\mathrm{S}}_3$ (similar for ${\mathrm{As}}_2{\mathrm{Se}}_3)$, (c) $\beta \text{−}{\mathrm{As}}_2{\mathrm{Te}}_3$, (d) $\beta \text{−}{\mathrm{Al}}_2{\mathrm{Te}}_3$, and (e) ${\mathrm{B}}_2{\mathrm{S}}_3$. The chalcogen atoms (S, Se, or Te), Si, Al (In), As, and B are represented by yellow, red, blue, gray, and purple spheres, respectively.

Figure 2

Top and side view of a crystal structure of a monolayer of ${\mathrm{AlSiTe}}_3$ (similar for ${\mathrm{InSiTe}}_3)$. The black lines indicate the primitive cell of the system. The chalcogen (Te), Si, and Al are represented by yellow, red, and blue spheres, respectively.

Figure 3

Crystal structure of (a) orpiment ${\mathrm{As}}_2{\mathrm{S}}_3$ (similar for ${\mathrm{As}}_2{\mathrm{Se}}_3)$, (b) $\beta \text{−}{\mathrm{As}}_2{\mathrm{Te}}_3$, (c) $\beta \text{−}{\mathrm{Al}}_2{\mathrm{Te}}_3$, and (d) ${\mathrm{B}}_2{\mathrm{S}}_3$ monolayers: top and side views. The chalcogen atoms (S, Se, or Te) are shown in yellow color, and As, Al, and B are shown in gray, blue, and purple color, respectively. Black lines indicate the primitive cell of the crystals.

Figure 4

Phonon-dispersion curves of ${\mathrm{AlSiTe}}_3$ (left side) and ${\mathrm{InSiTe}}_3$ (right side).

Figure 5

Phonon-dispersion curves from the top to the left side of ${\mathrm{As}}_2{\mathrm{S}}_3,{\mathrm{As}}_2{\mathrm{Se}}_3,\beta \text{−}{\mathrm{As}}_2{\mathrm{Te}}_3,\beta \text{−}{\mathrm{Al}}_2{\mathrm{Te}}_3$, and ${\mathrm{B}}_2{\mathrm{S}}_3$ single layers.

Figure 6

Calculated electronic band structure of ${\mathrm{AlSiTe}}_3$ (left) and ${\mathrm{InSiTe}}_3$ (right) monolayers using the HSE06 functional. States with negative energies correspond to valence states, while states with a positive energy correspond to conduction states.

Figure 7

Total and partial density of states of ${\mathrm{AlSiTe}}_3$ (top) and ${\mathrm{InSiTe}}_3$ (bottom) monolayers. The Fermi level is set at zero level.

Figure 8

Calculated electronic band structure of $A_2{X}_3$ monolayers using the HSE06 functional: from the top to the left, ${\mathrm{As}}_2{\mathrm{S}}_3,{\mathrm{As}}_2{\mathrm{Se}}_3,\beta \text{−}{\mathrm{As}}_2{\mathrm{Te}}_3,\beta \text{−}{\mathrm{Al}}_2{\mathrm{Te}}_3$, and ${\mathrm{B}}_2{\mathrm{S}}_3$. States with negative energies correspond to valence states, while states with a positive energy correspond to conduction states.

Figure 9

Total and partial density of states (PDOS) of $A_2{X}_3$ monolayers: from the top to the left, ${\mathrm{As}}_2{\mathrm{S}}_3,{\mathrm{As}}_2{\mathrm{Se}}_3,\beta \text{−}{\mathrm{As}}_2{\mathrm{Te}}_3,\beta \text{−}{\mathrm{Al}}_2{\mathrm{Te}}_3$, and ${\mathrm{B}}_2{\mathrm{S}}_3$. The Fermi level is set at zero level.

Figure 10

Band edges of the semiconducting trichalcogenide single layers obtained with HSE06, with reference to the water redox potential. Valence- and conduction-band edges are shown with green and red color, respectively, and the dotted lines indicate the water reduction $({\mathrm{H}}^{+}/{\mathrm{H}}_2)$ and oxidation $\left({\mathrm{H}}_2\mathrm{O}/{\mathrm{O}}_2\right)$ potentials at pH = 0.