Quantitative Multilayer Cu(410) Structure and Relaxation Determined by QLEED

Rezwan Ahmed,Seigi Mizuno,Michio Okada,Jessiel Siaron Gueriba,Wilson Agerico Diño,Takamasa Makino

doi:10.1038/s41598-019-52986-w

Abstract

Industrially relevant catalytically active surfaces exhibit defects. These defects serve as active sites; expose incoming adsorbates to both high and low coordinated surface atoms; determine morphology, reactivity, energetics, and surface relaxation. These, in turn, affect crystal growth, oxidation, catalysis, and corrosion. Systematic experimental analyses of such surface defects pose challenges, esp., when they do not exhibit order. High Miller index surfaces can provide access to these features and information, albeit indirectly. Here, we show that with quantitative low-energy electron diffraction (QLEED) intensity analyses and density functional theory (DFT) calculations, we can visualize the local atomic configuration, the corresponding electron distribution, and local reactivity. The QLEED-determined Cu(410) structure (Pendry reliability factor RP ≃ 0.0797) exhibits alternating sequences of expansion (+) and contraction (−) (of the first 16 atomic interlayers) relative to the bulk-truncated interlayer spacing of ca. 0.437 Å. The corresponding electron distribution shows smoothening relative to the bulk-determined structure. These results should aid us to further gain an atomic-scale understanding of the nature of defects in materials.

Highlights

We found that Cu(410) exhibits an alternating sequence of expansion (+) and contraction (−), viz., (+; −; +; −; +; −; −), as compared to the bulk-truncated interlayer spacing
To define the first interlayer spacing, we took the difference in the average positions of the first group of four atoms, viz., (1, 2, 3, 4) = A layer, and that of the second group of four atoms, viz., (5, 6, 7, 8) = B layer
The corresponding electron distribution shows smoothening relative to the bulk-determined structure

Summary

Introduction

A thorough understanding of the nature of reactions, e.g., catalysis and corrosion, entails an understanding of the elementary dynamical processes involved, in which mass, charge, and energy transport play important roles Needless to say, this requires knowledge of the (local) atomic configurations. [Cu plays an important role in catalysis, and finds wide utility in applications, e.g., thin film growth, fabrication, and electronics.] This can be attributed to the ubiquitous morphologically rough features, viz., defects in the form of steps and vacancies, esp., if they do not exhibit order. These defects serve as active sites, exposing the incoming adsorbates to both high and low coordinated surface atoms. For the case of Ag(410), previous quantitative LEED (QLEED) analyses found no surface relaxation (neither expansion: +nor contraction: −, with respect to the bulk-truncated values) of the first interlayer spacing, and a (−; +) sequence for second and third interlayer spacings, respectively

Methods

Results

Conclusion