First-principles study of structures, elastic and optical properties of single-layer metal iodides under strain

Abstract

The structure, elastic, electronic and optical properties of two-dimensional (2D) MI2 (M = Pb, Ge, Cd) under strain are systematically studied by the first-principles method. It is proved that the monolayer structure of 2D-MI2 is stable by phonon spectra. Moreover, the large ideal strain strength (40%), the large range of strain and the elastic constants of far smaller than other 2D materials indicate that the single-layer PbI2 and GeI2 possess excellent ductility and flexibility. By applying appropriate strain to the structure of 2D-MI2, the band gaps of single-layer MI2 can be effectively controlled (PbI2: 1.04 ∼ 3.03 eV, GeI2: 0.43 ∼ 2.99 eV and CdI2: 0.54 ∼ 3.36 eV). It is found that the wavelength range of light absorbed by these three metal iodides is 82–621 nm, so 2D-MI2 has great absorption intensity for ultraviolet light in a large wavelength range, and the strain of structure can effectively regulate the optical parameters.

Surface and dynamical properties of GeI2

“…This, in turn, is consistent with its low cleavage energy [14] and proneness to facile intercalation [13]. It is worth mentioning that even though numerous theoretical efforts on GeI 2 predict a range of band gaps (1.72-3.05 eV [14][15][16][17][18][19][20]), density functional theory (DFT) is generally notorious for underestimating the ground state band gap of materials [48][49][50][51]. On the other hand, while DFT will tend to underestimate the band gap, DFT will frequently agree with the optical gap, which can often be much smaller than the ground state band gap because of Coulombic interactions.…”

“…Monolayer GeI 2 is predicted to be a semiconductor with a modestly large band gap (E g ∼ 1.72-3.05 eV) [14][15][16][17][18][19][20] that is thought to be thermally stable at high temperatures (∼600 K) [14,17] with electron mobility values similar to that of single-layer MoS 2 [14]. GeI 2 also offers the possibility of diminished edge scattering and can exist without dangling bonds [14,21,22] as iodine passivates the germanium bonds [21,22].…”

Layered GeI2: A wide-bandgap semiconductor for thermoelectric applications–A perspective

“…Pristine layered germanium (II) iodide (GeI 2 ) is a two-dimensional (2D) van der Waals (vdW) material, which is predicted to be thermally stable at temperatures as high as ~600 K (Liu et al, 2018;Hu et al, 2020). Adding to its versatility, for potential nanodevice applications, are its: (i) low cleavage energy (~0.16 J/m 2 ) (Liu et al, 2018), which is even lower than that of graphite (Zacharia et al, 2004); (ii) calculated appreciable charge carrier mobilities (Liu et al, 2018); (iii) a wide-bandgap (Liu et al, 2018;Hoat et al, 2019;De Andrade Deus and De Oliveira, 2020;Hu et al, 2020;Naseri et al, 2020;Ran et al, 2020;Opoku et al, 2022), which is now experimentally verified (Dhingra et al, 2022b); and (iv) the fact that it can exist without the undesirable edge disorders (Avilov and Imamov, 1968;Urgiles et al, 1996;Liu et al, 2018) that have plagued some well-researched 2D materials (Wimmer et al, 2008;Banhart et al, 2010;Mucciolo and Lewenkopf, 2010;Wurm et al, 2011;Komsa et al, 2012;Dugaev and Katsnelson, 2013;Lo et al, 2014;Shi et al, 2014;Addou et al, 2015;Dong et al, 2015;Lin et al, 2016;Mlinar, 2017;Rosenberger et al, 2018;Blades et al, 2020;Debbarma et al, 2021). Besides being a great candidate for standalone nanodevice applications, its heterostructures have also shown some promise for applications in development of low-power spintronic devices (Shao et al, 2021) as well as for enhancing photocatalytic hydrogen generation performance (Opoku et al, 2022).…”