Origins of Nanoscale Heterogeneity in Ultrathin Films

Abstract

A key challenge in thin-film growth is controlling structure and composition at the atomic scale. We have used spatially resolved electron scattering to measure how the three-dimensional composition profile of an alloy film evolves with time at the nanometer length scale. We show that heterogeneity during the growth of Pd on Cu(001) arises naturally from a generic step-overgrowth mechanism relevant in many growth systems.

Nanoscale analysis of the oxidation state and surface termination of praseodymium oxide ultrathin films on ruthenium(0001)

“…In the present case, the spatial resolution during the I(V ) measurement has been determined to 9.0 nm using the established 20%-80% criterion, which is seen to essentially translate into the fingerprinting analysis. Together with the work of Hannon and coworkers, who published a comparable value for an analysis performed of a bimetallic surface alloy [23], this is the highest spatial resolution achieved in I(V )-LEEM fingerprinting to date.…”

Buried Pd slows self-diffusion on Cu(001)

“…We prepare the Cu(001)-c(2 × 2)-Pd buried surface alloy by depositing Pd (5 ML/hour) from an e-beam heated wire source onto the sample held at 210 • C. The structure, and growth, of the c(2 × 2)-Pd alloy are well understood. [10][11][12][13][14][15]20 The buried alloy forms when submonolayer coverages of Pd are deposited on Cu(001) at T> 150 • C. On terraces, Fig. 1 (a), the alloy consists of a c(2 × 2)-ordered Pd-Cu underlayer covered by a relatively pure layer of Cu.…”

“…spatial variations in Pd concentration, or compositional changes at the surface during island ripening measurements. 14,15,22 Fig . 2 shows images of the surface alloy (0.4 ML Pd) with epitaxial Cu adatom islands.…”

“…1. 14,15 In an I-V measurement, specular LEEM images are recorded versus the energy of the incident electrons. The energy-dependent electron reflectivity is sensitive to the surface structure to a depth of several atomic layers.…”

“…9 In the Cu(001)-c(2×2)-Pd buried surface alloy system, the Pd alloy is covered by a nearly pure layer of copper. [10][11][12][13][14][15] It is not evident that the buried Pd will have a significant influence on surface mass transport. In this work, we use Cu-adatom island-ripening measurements to show that Cu(001) surface diffusion is slowed by the presence of buried Pd atoms near the surface.…”