Temperature-dependent structure, elasticity, and entropic stability of Bi phases on Cu(111)

We have used low energy electron microscopy (LEEM) to characterize the structure and stability of Bi phases on Cu{111}. As a function of temperature we find that the Cu{111}(3√×3√)R30∘-Bi surface alloy phase gradually dealloys and is fully depleted from Bi at a temperature of 803 K. The dealloying leads to a defect induced change of its elastic properties. The Bi surface alloy phase coexists with a Bi overlayer phase that exhibits a sharp decrease in density in a narrow temperature interval just below the temperature where the surface alloy phase has fully dealloyed. LEEM is used to directly evaluate the structure as well as the entropic contributions that determine the stability of each of the phases