Tuning electronic and optical properties of free-standing Sn2Bi monolayer stabilized by hydrogenation

Abstract

In this study, we systematically investigated the structural, mechanical, electronic and optical properties of Sn2Bi monolayer, a sheet experimentally synthesized recently [PRL, 121, 126801 (2018)] which has been hydrogenated (Sn2BiH2) to stabilize free-standing form using density functional theory (DFT). For tuning the band structure and electronic properties, the mechanical strain and electric field are used. Our investigations show that in this free-standing sample, there are electron flat bands and free hole bands like the recently synthesized sample on silicon wafer, which provide the possibility of having strongly localized electrons and free holes with high mobility. Also, the band gap of Sn2BiH2 monolayer has experienced a growth of 80% compared with the experimental sample. The relevant results to strain suggest that the band gap can be properly manipulated by biaxial strain (-13% to +21%) within a range from 0.2 to 1.6 eV. It should be mentioned that the stability and flexibility of the corresponding monolayer under tensile and compressive strain are due to the strong σ bonds between atoms. We also realized the strain can cause indirect-direct transition in the band gap. Furthermore, our optical findings indicate that the Sn2BiH2 monolayer has almost metallic properties in a specific range of UV spectrum and it is transparent in the IR and visible spectrum of electromagnetic radiation. All these tunable properties and nontrivial features portend that Sn2BiH2 monolayer has great potentials in applications as nearinfrared detectors, thermoelectric devices, field-effect transistors, sensors, photocatalysis, energy harvesting, and optoelectronics.

Prediction of hydrogenated group IV–V hexagonal binary monolayers

“…S1 ). The same instability has also been reported for freestanding monolayer while it can be greatly stabilized by hydrogenation 34 , 35 .…”

“…In fact, the structures represent more stability when the atoms are lighter. By comparison, one can easily realize that all the predicted monolayers are more stable than the hydrogenated Sn 2 Bi ( Sn 2 BiH 2 ), which was discussed in our previous study to have a cohesive energy of − 2.95 eV/atom 35 . Also, the Si 2 SbH 2 , Si 2 BiH 2 , Ge 2 SbH 2 , and Ge 2 BiH 2 monolayers are more stable than SiSb (− 3.50 eV/atom), SiBi (− 3.31 eV/atom), GeSb (− 3.12 eV/atom), and GeBi (− 2.98 eV/atom) binary compounds, respectively.…”

A DFT study on the mechanical properties of hydrogenated and fluorinated germanene sheets

“…Adsorption, especially by hydrogen and halogens is another well-known method for stabilizing and tuning the physical properties of nano-materials [25]. For instance, Mohebpour et al have suggested that hydrogenation stabilizes the freestanding structure of the newly onsubstrate synthesized Sn2Bi compound [26,27]. Moreover Saffari et al suggest that chlorination of CH3NH3PbI3 perovskite solar cells leads to an increased band gap and optical parameters, such as refractive index and extinction coefficient, which eventually enhances the efficiency of the solar cells [28].…”

Penta-SiCN: A Highly Auxetic Monolayer

“…Further, the complex refractive index ( N ) is expressed as , where η­(ω) and K (ω) are the refractive index and extinction coefficient, respectively. These parameters are expressed as Furthermore, the reflectivity R (ω) and absorption coefficient α­(ω) are expressed as Additionally, the electron energy loss function L (ω) is given by the relation , and can also be expressed in terms of ε 1 (ω) and ε 2 (ω) as All these optical parameters are calculated in the interval between 0 and 20 eV for parallel ( E ∥ x ) and perpendicular ( E ∥ z ) polarization of electric field.…”