Novel Janus based on the <i>α</i> phase of silver monochalcogenides: a first-principles study of <i>α</i>-Ag₂ <i>XY</i> ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>X</mml:mi> <mml:mrow> <mml:mo>/</mml:mo>

Abstract Motivated by the rapid progress in two-dimensional (2D) Janus materials and the intriguing physical properties exhibited by group IB chalcogenide compounds, we propose a new class of Janus monolayers with the formula α -Ag 2 XY ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>X</mml:mi> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>Y</mml:mi> <mml:mo>=</mml:mo> </mml:mrow> </mml:math> S, Se, Te). Using first-principles calculations based on density functional theory, we systematically investigate their structural stability, electronic band structures, and transport properties. The inherent lack of mirror symmetry in these Janus structures gives rise to unique characteristics not found in their symmetric counterparts. Our results reveal that Janus α -Ag 2 XY monolayers possess strongly anisotropic mechanical properties, stemming from their inherently directional lattice arrangements. Notably, they exhibit low in-plane Young’s moduli, reflecting their mechanical softness and flexibility, which are advantageous for flexible nanoelectronic and wearable technologies. Electronic structure analysis shows that all proposed monolayers are indirect band gap semiconductors with moderate band gaps, making them suitable for applications that require efficient carrier transport and tunable optical absorption. The combination of anisotropic mechanical flexibility and favorable electronic properties highlights Janus α -Ag 2 XY monolayers as promising candidates for next-generation 2D material-based electronic and optoelectronic applications.