Stability of 2D Alkaline-Earth Metal Silicides, Germanides and Stannides

Abstract

By means of ab initio calculations, we have estimated stability of 2D Me[Formula: see text] ([Formula: see text], Ca, Sr, Ba and [Formula: see text], Ge, Sn) in the T and Td phases, which are similar to the ones of 2D transition metal chalcogenides, in addition to their phonon spectra. The T phase is found to be more stable for 2D Ca[Formula: see text], Sr[Formula: see text] and Ba[Formula: see text], whereas the Td phase is predicted to be the ground state for 2D Mg[Formula: see text]. We have also discussed that imaginary frequencies in the calculated phonon spectra of 2D Me[Formula: see text], which appeared in the vicinity of the [Formula: see text] point, were not necessarily associated with the dynamic instability.

Interplay between structural changes, surface states and quantum confinement effects in semiconducting Mg2Si and Ca2Si thin films

“…1 and 2). Even though 2D Mg 2 Si in the T phase (or the cubic phase) is dynamically unstable, 4 we found that the cubic Mg 2 Si thin film consisting of two ( d = 0.5 nm) and more Mg 2 Si layers were the most energetically preferable structures. In particular, the total energy difference of 163 meV (hereinafter, the total energy is expressed per one Me 2 Si formula unit) was found between the cubic and orthorhombic Mg 2 Si thin films consisting of two Mg 2 Si layers.…”

“…The thickness of slabs under investigation was varied within B0.2-17 nm where the slabs of B0.2 nm corresponded to the 2D structure. 4,5 The following slab orientations have been considered: orthorhombic Ca 2 Si(100), Ca 2 Si(010), and Ca 2 Si(001), as well as cubic Me 2 Si(111) and Me 2 Si(110). For the sake of convenience hexagonal symmetry was used for all cubic Me 2 Si(111) slabs.…”

“…For all 2D Me 2 X the ionic nature of chemical bonds prevails and alkali-earth metal atoms serve as pseudopassivating species for X atoms. 4–6 In addition, we have recently explored a possibility to form nanotubes based on 2D Me 2 Si. 7…”

“…3 By analyzing phonon spectra the dynamical stability of twodimensional (2D) alkali-earth metal silicides, germanides, and stannides (Me 2 X, where Me = Mg, Ca, Sr, Ba and X = Si, Ge, Sn) has already been reported along with their band structures indicating semiconducting properties. 4,5 Even though bulk Ca 2 X, Sr 2 X, and Ba 2 X crystallize in the orthorhombic structure, 2D Ca 2 X, Sr 2 X, and Ba 2 X have been found to be dynamically stable in the T phase with the hexagonal symmetry, being a building block of a metastable cubic structure also existing in the bulk of these compounds. However, 2D Mg 2 X displays orthorhombic distortion that leads to the phase known as the T d phase instead of the T phase, while the cubic phase is stable in the bulk form of Mg 2 X.…”

“…For all 2D Me 2 X the ionic nature of chemical bonds prevails and alkali-earth metal atoms serve as pseudopassivating species for X atoms. [4][5][6] In addition, we have recently explored a possibility to form nanotubes based on 2D Me 2 Si. 7 The fabrication of Mg 2 Si(111) thin films with the cubic structure on a Si(111) substrate can be carried out by molecular beam epitaxy 8 or reactive deposition epitaxy.…”