Mechanical stabilities and properties of graphene-like aluminum nitride predicted from first-principles calculations

A graphene-like hexagonal aluminum nitride monolayer (g-AlN) is a promising nanoscale optoelectronic material. We investigate its mechanical stability and properties using first-principles plane-wave calculations based on density-functional theory, and find that it is mechanically stable under various strain directions and loads. g-AlN can sustain larger uniaxial and smaller biaxial strains than g-BN before it ruptures. The third, fourth, and fifth-order elastic constants are essential for accurately modeling the mechanical properties under strains larger than 0.02, 0.06, and 0.12 respectively. The second-order elastic constants, including in-plane stiffness, are predicted to monotonically increase with pressure while the Poisson ratio monotonically decreases with increasing pressure. g-AlN's tunable sound velocities have promising applications in nano waveguides and surface acoustic wave sensors.