Anisotropic properties of two-dimensional (2D) tin dihalide (SnX2, X= Cl, Br, I) monolayer binary materials.

This paper investigated the electronic properties and photoresponse of 2D SnX2 (X = Cl, Br, I) monolayer binary materials using computation techniques. The calculated band structure and density of states (DOS) indicate that these are large band gap semiconducting materials with an indirect band gap. The studied chemical bonding mechanism shows the existence of the hybrid bonding of ionic and covalent bonds in these dihalide materials. The valence and conduction band edge positions are also estimated, using the concept of electronegativity and band gap, to investigate the photocatalytic activity of SnX2. Next, we investigated the polarization and energy-dependent dielectric and optical functions along the crystallographic axes of these materials in the linear response approach of the perturbing incident oscillating light field. These materials exhibit an anisotropic behavior of these functions, especially in the high-energy visible and low-energy UV regions. The absorption of incident light photons is very fast in SnI2 than in SnBr2 and SnCl2 in the low-energy UV region. It demonstrates the higher absorption coefficient in SnI2 and optical conductivity. The obtained average static refractive index of SnCl2 is comparable to that of glass (1.5), showing its application as transparent material. The low reflection coefficient, less than 20%, makes them superior for antireflection coating materials in the IR and visible regions. The prominent energy loss peaks show the existence of plasmon resonances in these materials. The most loss occurs in the UV region. The investigated electronic and photoresponse properties indicate that these Sn-based dihalide materials are excellent for electronic devices and optoelectronic applications. Also, the calculated VB and CB edge positions with respect to the normal hydrogen electrode (NHE) show the favorable water-splitting capability of these materials.