Bistability of bilayer islands under anisotropic misfit stress

The equilibrium shapes of bilayer islands under anisotropic misfit stress have been theoretically characterized from a thermodynamics point of view. Based on an energy variation calculation, it is found that when the ratio σ between the components of the misfit stress is such that σ = ? 1, both square and rectangular shaped bilayer islands may coexist depending on the island volume and stress level. When σ ≠ ? 1 and σ < 0, the possibility of formation rectangular islands along both perpendicular directions is also discussed.