BSTRACTA new 2D material

borophene

has been grown successfully recently on single crystal Ag substrates. Three main structures have been proposed (

and striped borophene). However

the stability of three structures is s

till in debate. Using first principles calculations

we examine the dynamical

thermodynamical and mechanical stability of

and striped borophene. Free-standing and borophene is dynamically

thermodynamically and mechanically stable

while striped borophene is dynamically and thermodynamically unstable due to high stiffness along

a

direction. The origin of high stiffness and high instability in striped borophene along

a

direction can both be attributed to strong directional bonding. Our work shows a deep connection between stability and strength

and helps researchers to estimate accurately the mechanical performance of 2D materials.