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The shapes of ͑111͒ oriented two-dimensional ͑2D͒ islands and facets, the latter being part of threedimensional ͑3D͒ crystallites of Pb, were equilibrated at 104 -520 K. Island sizes were in the range of 15-90 nm radius, facets typically at 100-270 nm radius. They were imaged by scanning tunneling microscopy to provide the exact outline of the bounding step. Increased step roughening with increasing temperature decreases the radius anisotropy of islands and facets in a consistent manner. Products of island/facet radius times local step curvature versus temperature were obtained experimentally, serving as the basis of absolute step and kink energies at 0 K. They are f 1A (0)ϭ128.3Ϯ0.3 meV, f 1B (0)ϭ115.7Ϯ5.8 meV, and kA ϭ42.5 Ϯ1.0 meV, kB ϭ60.6Ϯ1.6 meV, respectively. The combination of studying small 2D islands ͑unstable at high temperature͒ and large 2D facets allows measurements over a very large range of temperatures.

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A 1µm 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 ∼ 32 meV/ Å2 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 ∼ 0.34.

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