Electronic and mechanical properties of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>Sc</mml:mtext><mml:mi>X</mml:mi><mml:mi mathvariant="normal">I</mml:mi></mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>(</mml:mo><mml:mi>X</mml:mi><mml:mo>=</mml:mo><mml:mi mathvariant="normal">S</mml:mi><mml:mo>,</mml:mo><mml:mspace width="4pt"/><mml:mtext>Se</mml:mtext><mml:mo>)</mml:mo></mml:mrow></mml:math> monolayers and their heterostructures

Abstract

Inspired by the successful synthesis of bulk ScSI in a recent work [Ferrenti et al., Chem. Mater. 34, 5443 (2022)], we have systematically investigated the mechanical and electronic properties of $\text{Sc}X\mathrm{I}$ $(X=\mathrm{S},\phantom{\rule{4pt}{0ex}}\text{Se})$ monolayers and their heterostructures by using first-principles calculations. Our calculations verify the experimental speculation that the bulk ScSI is readily exfoliatable and the monolayers of $\text{Sc}X\mathrm{I}$ $(X=\mathrm{S},\phantom{\rule{4pt}{0ex}}\text{Se})$ are stable. The Young's moduli with strong anisotropy $(50.2\text{--}91.5\phantom{\rule{0.16em}{0ex}}\mathrm{N}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1})$ of $\text{Sc}X\mathrm{I}$ monolayers are comparable to those of phosphorene $(26\text{--}105\phantom{\rule{0.16em}{0ex}}\mathrm{N}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1})$, but smaller than those of isotropic graphene $(349\phantom{\rule{0.16em}{0ex}}\mathrm{N}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1})$, $\mathrm{Mo}{\mathrm{S}}_{2}$ $(122.3\phantom{\rule{0.16em}{0ex}}\mathrm{N}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1})$, and $h\text{\ensuremath{-}}\mathrm{BN}$ $(276\phantom{\rule{0.16em}{0ex}}\mathrm{N}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1})$, indicating their lower stiffness. In addition, ScSI/ScSeI monolayers show good flexibility with critical strain of 29%/33%. Application of strain can effectively regulate the band gap $({E}_{g})$ and band edge of $\text{Sc}X\mathrm{I}$ $(X=\mathrm{S},\phantom{\rule{4pt}{0ex}}\text{Se})$ monolayers. For instance, the ${E}_{g}$ of the ScSeI monolayer is reduced from 1.83 to 1.59 eV and the band gap type is changed from indirect to direct band gap when a compressive strain of 6% is applied along the $x$ direction, which is attributed to the orbital hybridization between the $d$ orbital of Sc and $p$ orbital of the elements at the $X$ and I sites. More importantly, $\text{Sc}X\mathrm{I}$ $(X=\mathrm{S},\phantom{\rule{4pt}{0ex}}\text{Se})$ monolayers can form type II vertical heterostructure with typical two-dimensional semiconductors due to the deeper energy levels of their valence band maximum and conduction band minimum. In addition, $\text{Sc}X\mathrm{I}$ $(X=\mathrm{S},\phantom{\rule{4pt}{0ex}}\text{Se})$ monolayers can also be used to form type I lateral heterostructure with the ScSeBr monolayer. The excellent ductility, strain-tuned electronic properties, and heterostructure design make $\text{Sc}X\mathrm{I}$ $(X=\mathrm{S},\phantom{\rule{4pt}{0ex}}\text{Se})$ monolayers promising candidates for the application of flexible electronic devices.

Topics & Concepts