The structure and electronic properties of the ( √ 13 × √ 13)R13.9 • and (2 √ 3 × 2 √ 3)R30 • ordered phases of C 60 on the Pt(111) surface are investigated using combined dynamic low-energy electron diffraction and density functional theory (DFT) calculations. The two phases have the same local adsorption structure, while they are predicted by DFT calculations to exhibit very different electronic structures due to their different inter-C 60 orientations and distances. This result demonstrates the structural tuning of electronic properties for molecular films or junctions composed of the same materials.

Quantum well (QW) resonances are identified in Ag films on an Fe(100) surface and are used in low energy electron microscopy to monitor film morphology during annealing and growth. We find that Ag films thermally decompose to thicknesses that are stabilized by QW states at the ÿ point. Novel growth morphologies are also observed that highlight the competition between kinetic limitations and the QW state energetics that promote electronic growth. These combined observations help to explain the unusual bifurcation mode of thermal decomposition that was reported previously for this system. DOI: 10.1103/PhysRevLett.93.236104 PACS numbers: 68.55.Jk, 68.37.Nq, 68.55.Ac, 73.21.Fg The properties of ultrathin metal films exhibit remarkable quantum size effects (QSE) due to the discrete quantum well (QW) states that are caused by electron confinement [1]. Considerable early interest in metallic QW states was focused on their role in oscillatory magnetic interlayer coupling [2]. It has also been established recently that QW states can have a dramatic influence on film morphology [3][4][5][6][7][8][9][10][11][12][13] in the same nanoscale thickness regime that magnetic coupling and QSE in other properties, such as work function [14], thermal desorption [15], and interlayer relaxations [8], are observed. In particular, it was found that film morphology can be dominated during growth or annealing by film thicknesses that support strongly bound QW states at the ÿ point, which induce total energy local minima compared to other thicknesses. This ideally occurs with the same periodicity in film thickness that QW states cross the Fermi level. However, a beating of the QW period and the discrete layer spacing is sometimes evident in film morphology [3,11]. The consideration of QW state energetics has therefore accounted for a variety of multiple layer height features in the film morphologies of several systems. This phenomenon, which is often referred to as electronic growth, is envisioned to be a mechanism for self-organization in fabrication.A particularly interesting example of electronic growth was seen in the thermal stability of atomically flat Ag films on the Fe(100) surface [12]. With the exception of N 2 and N 5 monolayer (ML) thick Ag films, which were stable during annealing up to high temperature, an initially uniform N ML thick film was found to transform, or bifurcate, to a combination of N ÿ 1 and N 1 ML thick regions upon slight annealing above room temperature. This unusual behavior was attributed to the shape of the local energy versus thickness landscape defined by QW states in N ÿ 1, N, and N 1 film thicknesses. While the stability of 5 ML thick Ag films was clearly related to the existence of a QW state far below the Fermi level, the energy landscape has negative curvature between QW-induced energy minima [12,13].Thus, for these energetically unfavorable film thicknesses, the system may lower its total energy through bifurcation. The surprising aspect of this result was that an initially uniform N ML thick ...

The temporal evolution of nonequilibrium coverage profiles in the Pb wetting layer on the Si(111) surface is studied using low energy electron microscopy. The initial coverage step profile propagates rapidly at a constant velocity with an unperturbed shape. A model is proposed that attributes this nonclassical equilibration behavior to the diffusion of thermally generated adatoms on top of the wetting layer. This model can account for the observed convectionlike mass transport, as well as its dramatic dependence on Pb coverage. Such anomalous mass transport is believed to facilitate the remarkably efficient self-organization of uniform Pb quantum island height on the Si(111) surface that was observed previously.