Study Of Fe Self-assembly On Cu(111) And Ru(0001)

Self-organized growth of low dimensional nano-scale material has attracted lots of theoretical and experimental interest due to its new physics and its potential application. Long range interaction mediated by surface state electron and surface stress are two kinds of driving force for self-organized growth at single crystal surfaces. During the past two decades, a great achievement of experiment and theory has been made in the self-assembly of low dimensional system. The in-depth understanding of self-assembly is not only for the interest of fundamental research, but also is the groundwork of the challenging area in nanotechnology. In this thesis, I will introduce three works as a Ph. D student.(1) Atomic superlattice formation mechanism revealed by scanning tunneling microscopy and kinetic Monte Carlo simulations,(2) Anomalous temperature dependence of antistripe width in the annealing of submonolayer Fe on Ru(0001),(3) Gd atomic superlattice and string on Ag(111).We study the interaction of single Fe atoms on Cu(111) and Ag(111) substrates with LT STM and KMC. In Fe/Cu(111), a self-assembled hexagonal quasi-superlattice with perturbation of around20%dimers/clusters is obtained. In Fe/Ag(111), however, a disorder-like 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 to diffusion barrier and the square of the repulsive ring radius versus the superstructure lattice constant, play important roles for superstructure formation.Utilizing STM, we investigate the coverage and temperature dependent morphology evolution of sub-monolayer Fe on Ru(0001) near the surface alloy temperature. Sub-monolayer Fe deposited on Ru(0001) at room temperature grows in the three dimensional island format. The morphology is investigated after annealing at various temperatures. Annealing around900K, large compact islands are divided into small pieces by triangular vacancy islands and labyrinth anti-stripes. The width of the anti-stripes increases with increasing temperature, in sharp contrast with other systems where the opposite behavior was commonly found. The observed anomaly can be attributed to the simultaneous surface alloying and amorphization during the annealing process.Inspired by our first work, we manage to grow ordered Gd atomic string and superstructure on Ag(111). We investigate the spatial dependent spectra of atomic superlattice and atomic string. The spectra at the center of atoms in the atomic superlattice fist reveal the existence of the occupied electron band of surface state below Fermi level. In combination with KMC simulation of the island diffusion of atomic superlattice, we show that the atomic diffusion process determines the scaling exponential of the island diffusion constant to the number of atoms.