Theoretical Study Of Structural And Electronic Properties Of Sc-based Mxenes

MXenes,M_n+1X_n T_x（T_x denotes surface termination）,a family of 2D transition metal carbides and nitrides,have been produced by extracting A atoms from layered ternary M_n+1AX_n.Here,M represents transition metals,A represents elements mainly from IIIA and IV groups in the periodic table,and X is C or/and N.Due to their versatile patential application such as in lithium-and sodium-ion batteries,supercapacitors,water purification,gas-and bio-sensors,and hydrogen production,MXenes are regarded at the cutting edge of material research.Herein,we systematically explored the electronic properties of Sc-based MXenes via first-principles calculations,with the aim to extend their applicability.All functional groups are more likely to occupy the three-fold sites above the second Sc layer on both sides.Most systems are metallic and the density of states at Fermi level increases as n increases.OH-Functionalized carbides and OH/SH-terminated nitrides manifest ultralow work functions,potential in field-effect transistors.Furthermore,we identified three novel semiconductors（Sc₂CCl₂,Sc₂C（SH）₂,and Sc₂NO₂）besides Sc₂CO₂,Sc₂CF₂,and Sc₂C（OH）₂ in literature.Specifically,Sc₂NO₂ is a ferromagnetism spin gapless semiconductor,and the first functionalized MXene intrinsically exhibiting such property,promising for spintronics.Type-II heterojunctions are readily available between Sc-based semiconducting MXenes,facilitating charge separation for optoelectronics and solar energy conversion.Further photocatalytic analysis indicates that Sc₂CCl₂ is capable of oxidizing H₂O into O₂.In addition,we studied the strain effect on the electronic properties of the spin-gapless semiconductor Sc₂NO₂ and found that the system would undergo interesting phase transition from compressive to tensile strain:ferromagnetism half metal→ferromagnetism spin gapless semiconductor→antiferromagnetism semiconductor.Our results provide new insights into the possible applications of MXenes and encourages further studies in this field.