Universal exponents and step-step interactions on vicinal Pb(111) surfaces

A 1 mum diameter Pb crystallite, supported on Ru(001), was equilibrated and imaged by scanning tunneling microscopy at 298 K. The vicinal shapes close to the (111) facet at the top of the crystal were analyzed in detail to determine the critical shape exponent and the step-step interaction energy as well as the interaction constant of the potential. An average shape exponent of 1.47 and a step interaction energy of similar to32 meV/Angstrom(2) were obtained. The exponent is very close to the theoretically predicted universal value of 3/2 and as such provides clear evidence for a dominant 1/x(2) step interaction potential. The ratio of step free energy to step interaction energy for Pb at 298 K is similar to0.34.