A layer of lead on clean silicon moves in a surprising way — in waves like a caterpillar. This explains the unexpected ultrafast mass transport observed even at low temperatures for this system. Although solid these single layers of atoms move as fast as molten lead. Computer simulations show that the lead layer forms waves that require almost no energy to keep moving thus explaining the quickness of mass transport. Other metals on surfaces typically move much slower by one atom at a time hopping along the surface. Knowing the critical parameters that give rise to this cooperative liquid-like movement, other systems may be discovered that move the same way and this could have important implications for applications requiring ultrathin films.
Coverage-Dependent Collective Diffusion of Dense Pb Wetting Layer on Si(111)