Atomic superlattice formation mechanism revealed by scanning tunneling microscopy and kinetic Monte Carlo simulations

Abstract

We study the interaction of single Fe atoms on Cu͑111͒ and Ag͑111͒ substrates with low-temperature scanning tunneling microscopy and kinetic Monte Carlo simulations. In Fe/Cu͑111͒, a self-assembled hexagonal quasisuperlattice with perturbation of around 20% dimers/clusters is obtained. In Fe/Ag͑111͒, however, a disorderlike structure is found even though long-range interactions among atoms are observed. In combination with kinetic Monte Carlo simulations, possible mechanisms of the superstructure formation are discussed. We find that two parameters, i.e., the ratio of adatom interaction energy ͑the depth of the first energy minimum͒ to diffusion barrier and the square of the repulsive ring radius versus the superstructure lattice constant, play important roles for superstructure formation.

Formation of Fe Cluster Superlattice in a Metal-Organic Quantum-Box Network

“…3(c) has been obtained from analyzing 1600 adatom pairs. The deduced mean distance d nn ¼1:1AE0:1nm is in agreement with the values of 1.2 nm [29] and 1.1 nm [30] reported for Fe on bare Cu(111). The distance distribution is significantly more narrow than the ones reported for adatom superlattices on homogeneous surfaces.…”

“…The period of the interaction energy E int is given by half the Fermi wavelength of the surface state, the adatom nearest neighbor distance d nn is the position of the first 086102-2 minimum of E int given by the adatom scattering phase [6,7] and the overlap with the short range repulsion inhibiting cluster formation [8,27]. The formation of these patches at T dep % 12 K is consistent with the reported values of diffusion [28][29][30] and short range repulsive [29] barriers for Fe adatoms on Cu(111). The d nn histogram shown in Fig.…”

“…Since Co, Cu, and also Fe adatoms present comparable (1.1 to 1.3 nm) nearestneighbor distances [7,8,29,30], their interaction potentials and scattering properties are similar and we attribute the steering of Fe adatoms towards the cavity center to the LDOS at E F having a maximum there. For cavities hosting more than one adatom, the superposition of two attractive potentials has to be considered, one arising from the confinement due to the molecules, the other created by the adatoms themselves [11,13].…”

Multiplet features and magnetic properties of Fe on Cu(111): From single atoms to small clusters

“…The diffusion of Fe on Cu(111) was studied in the past. The diffusion barriers reported from DFT calculations are E m = 25 [37], 22 [38], and 28 meV [39], and the barriers and attempt frequencies measured from temperature-dependent adatom diffusion rates are E m = 22 ± 7 meV, ν 0 = 1 × 10 10±2 Hz [39], and E m = 23.8 ± 1.5 meV, ν 0 = 4 × 10 8±1 Hz [40]. In our simulations, we take E m = 25 meV and a universal preexponential factor of ν 0 = 10 12 Hz.…”

Direct capture and electrostatic repulsion in the self-assembly of rare-earth atom superlattices on graphene

“…A viable route is self-assembly at surfaces [13]. Former examples of self-assembled superlattices of 3d transition metals [14][15][16][17][18] or rare earths [19][20][21][22] used long-range adsorbate-adsorbate interactions mediated by surface-state Friedel oscillations on close-packed metal surfaces. However, for the single-atom-magnet systems mentioned above, direct adsorption onto metal substrates is unsuited since long-lived magnetic quantum states require protection against electron and phonon scattering [12,22,23], explaining why thin MgO or graphene separation layers are needed.…”