Surface Morphology of Laser Superheated Pb(111) and Pb(100)

Superheating of solids is rarely observed due to the presence of a thin disordered surface layer formed below the melting point, Tm, which provides a nucleation site for melting. Premelting is particularly evident in open surfaces. While Pb(110) disorders at a temperature as low as 150 K below Tm = 600.7 K, Pb(111) remains ordered up to Tm - 0.05 K. [1]. Some surfaces that do not premelt can superheat under certain conditions [2-4], Superheating of Pb(111) and Bi(0001), and some superheating of Pb(100) by ~180 ps laser pulses was observed in time-resolved high-energy electron diffraction (RHEED) experiments [2-4], The Pb(111) and Bi(0001) surfaces superheat up to ~120 K and ~90 K above Tm of Pb and Bi, respectively. Evidence of residual order on Pb(100) up to ~15 K above Tm was also observed [3], Molecular dynamics simulations of surface melting of several fee metals showed a good agreement with the experimentally observed superheating of Pb(111) [5], One simulation showed that cooperative movement of the superheated surface atoms results in the filling of vacancies and the surface becomes atomically flat by a superheating surface repair process [5], This annealing mechanism was attributed to the high vibrational amplitudes which atoms are forced into by the ultrafast superheating pulse.