Researchers Uncover Physical Properties Of Novel Orthorhombic Sb2X3 Monolayers (Material Science)

Mehrdad Faraji and colleagues in their recent paper, explored the atomic lattice, dynamical stability, electronic and optical properties of Sb2X3 (X= S, Se and Te) monolayers crystallize in the orthorhombic structures using the density functional theory (DFT) simulations. Their study recently appeared in the Journal Scientific Reports.

Sb2S3 and Sb2Se3 are well-known layered bulk structures with weak Van der Waals interactions. Many experimental studies have demonstrated that Sb2X3(X= S, Se, Te) can be efficiently used as potential material for various applications. Over the past years, there have been many researches which revealed excellent properties of the hexagonal Sb2X3 (X = S, Se, Te) monolayers, but the physical properties of novel orthorhombic Sb2X3 (X = S, Se, Te) monolayers still undiscovered. Thus, this inspired M. Faraji and colleagues to investigate the properties of novel Sb2X3 monolayers using DFT simulations.

“We performed density-functional theory (DFT) calculations using the plane-wave basis projector augmented wave (PAW) method along with generalized gradient approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) functional.”, told M. Faraji, researcher at TOBB University of Economics and Technology.

On the basis of HSE06 and PBE/GGA functionals, they first showed that all the considered novel monolayers are semiconductors. Later, they found the electronic bandgap of Sb2S3, Sb2Se3 and Sb2Te3 monolayers by using the HSE06 functional, which are predicted to be 2.15, 1.35 and 1.37 eV, respectively, appealing for applications in nanoelectronics. In addition, the cohesive energy of Sb2S3, Sb2Se3 and Sb2Te3 are found to be -7.94 and -7.36 eV/atom and -6.81 eV/ atom respectively. These findings indicated, the formation of Sb2S3 is more favorable than the others. Moreover, it has been shown by analysing the AIMD trajectories that the structure could stay intact at 500 K with very stable energy and temperature profiles, proving the thermal stability of the Sb2X3 monolayer.

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Figure 1. Phonon dispersions of (a) Sb2S3, (b) Sb2Se3 and (c) Sb2Te3 monolayers. Optimized atomic structure indicated as inset. (d) Electrostatic potential for the Sb2X3 monolayers. © M. Faraji et al.

“We found, phonon branches are free from any imaginary frequencies indicating the dynamical stability of the structures and the more negative values for cohesive energies suggest that the energetically more stable monolayer, and the structures represent more stability when the atoms get lighter.”, told M. Faraji.

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Figure 2. (a) Imaginary and real parts of the dielectric function as a function of photon energy of the Sb2S3, Sb2Se3 and Sb2Te3 monolayers for the in-plane polarizations (E ∥ x and E ∥ y), predicted using the RPA + HSE06 approach. Absorption coefcient as a function of (b) wavelength and (c) energy for the Sb2X3 monolayers for the in-plane polarizations (E ∥ x and E ∥ y) in the UV–vis range of light, predicted using the RPA + HSE06 approach. © M. Faraji et al.

They also discussed the optical responses of the monolayers using the RPA+HSE06. Their calculations indicated that the first absorption peaks of these novel monolayers along in-plane polarization, are located in IR and visible range of light, suggesting its prospect for applications in optoelectronics. Moreover, the in-plane optical anisotropy of these novel 2D materials is highly desirable for the design of polarization-sensitive photodetectors.
Finally, they showed that Sb2X3 monolayers can be used for thermoelectric application because of their larger power factors, the power factor for the hole-doped Sb2Te3 can reach 5.45 (10¹¹ Wm¯1K−21).

“Our results confirm the stability and highlights the outstanding prospect for the application of Sb2X3 nanosheets in novel electronic, optical and energy conversion systems.”, concluded authors of the study.

Featured image: (a) Electronic band structure © M. Faraji et al.

Reference: Bafekry, A., Mortazavi, B., Faraji, M. et al. Ab initio prediction of semiconductivity in a novel two-dimensional Sb2X3 (X= S, Se, Te) monolayers with orthorhombic structure. Sci Rep 11, 10366 (2021).

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