Manipulating electronic properties of two-dimensional MXenes Cr2TiC2FCl by phonon vibration

Although the manipulation of physical properties is common in applications of two-dimension (2D) materials, it is rare to tailor electronic properties by phonon vibration. In this article, we tailor the electronic band structure of Cr₂TiC₂FCl monolayer from indirect semiconducting state to metallic state by phonon modes ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:msubsup><mml:mi>A</mml:mi> <mml:mn>1</mml:mn> <mml:mn>2</mml:mn></mml:msubsup> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:msubsup><mml:mi>A</mml:mi> <mml:mn>1</mml:mn> <mml:mn>5</mml:mn></mml:msubsup> </mml:mrow> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:msubsup><mml:mi>A</mml:mi> <mml:mn>1</mml:mn> <mml:mn>6</mml:mn></mml:msubsup> </mml:mrow> </mml:math> mode) with the Raman and infrared active. The <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:msubsup><mml:mi>A</mml:mi> <mml:mn>1</mml:mn> <mml:mn>4</mml:mn></mml:msubsup> </mml:mrow> </mml:math> mode makes Cr₂TiC₂FCl monolayer become direct semiconductor with a little gap, which can elevate the optical absorption efficiency of Cr₂TiC₂FCl monolayer, especially in the visible region. Meanwhile, both the conduction band minimum (CBM) and valence band maximum (VBM) are contributed by the spin-down channel; so, the electron hopping between VBM and CBM also does not need the participation of spin flipping and chiral phonon in Cr₂TiC₂FCl monolayer under the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:msubsup><mml:mi>A</mml:mi> <mml:mn>1</mml:mn> <mml:mn>4</mml:mn></mml:msubsup> </mml:mrow> </mml:math> mode. These results are significant for the application of 2D materials in the semiconductor laser, solar cell, and photodetector.