Low-energy electron diffraction (LEED) study of an aperiodic thin film of Cu on 5-fold i-Al-Pd-Mn

Abstract

Thin films of copper grown on five-fold i-AlPdMn at room temperature consist of domains that are rotationally aligned with the five primary symmetry directions of the substrate and which have one-dimensional aperiodic order. This aperiodic order is evident in scanning tunnelling microscopy images as wide and narrow rows that are spaced according to a Fibonacci sequence. A low-energy electron diffraction (LEED) study of this film indicates that the structure within the domains is periodic along the rows, with a repeat distance equal to the nearest-neighbour separation in bulk Cu. To determine the complete structure, a dynamical LEED experiment was performed for a five-layer Cu film at a sample temperature of 85 K. The analysis was performed using two different computational methods, one based on quasicrystalline slabs and the other on periodic approximants. Of the model structures tested, the film is found to be most consistent with a structure based on the Cu{100} surface structure, but having aperiodic displacements, both in-plane and out-of-plane, along a ⟨110⟩ direction.