Atomic Undercoordination in Ag Islands on Ru(0001) Grown via Size-Selected Cluster Deposition: An Experimental and Theoretical High-Resolution Core-Level Photoemission Study.

Luca Sbuelz,Ueli Heiz,Eugenio Nicolini,Federico Loi,Monica Pozzo,Alessandro Baraldi,Dario Alfé,Silvano Lizzit,Ezequiel Tosi,Paolo Lacovig,Luca Bignardi,Aras Kartouzian

doi:10.1021/acs.jpcc.1c02327

Abstract

The possibility of depositing precisely mass-selected Ag clusters (Ag1, Ag3, and Ag7) on Ru(0001) was instrumental in determining the importance of the in-plane coordination number (CN) and allowed us to establish a linear dependence of the Ag 3d5/2 core-level shift on CN. The fast cluster surface diffusion at room temperature, caused by the low interaction between silver and ruthenium, leads to the formation of islands with a low degree of ordering, as evidenced by the high density of low-coordinated atomic configurations, in particular CN = 4 and 5. On the contrary, islands formed upon Ag7 deposition show a higher density of atoms with CN = 6, thus indicating the formation of islands with a close-packed atomic arrangement. This combined experimental and theoretical approach, when applied to clusters of different elements, offers the perspective to reveal nonequivalent local configurations in two-dimensional (2D) materials grown using different building blocks, with potential implications in understanding electronic and reactivity properties at the atomic level.

Highlights

The atomic coordination number (CN) plays a crucial role in determining physical and chemical properties in condensed matter
The unusual asymmetric spectral lineshape toward lower binding energy (BE), which cannot be justified by electron−hole pair excitation or energy losses, as it would result in the build-up of a tail at higher BEs, clearly reveals the presence of a multicomponent structure The spectrum can be properly fitted with two components at 368.20 and 368.05 eV, corresponding to bulk (Agbulk) and first-layer (Agsurface) components
This peak assignment is based on the fact that the 3d5/2 spectrum measured at high photon energy (650 eV) shows a reduced spectral weight at lower binding energies. This can be interpreted based on the increased mean free path of photoelectrons at higher kinetic energies. This assignment is confirmed by density functional theory (DFT) calculations of the SCLS, which was estimated to be of −146 ± 20 meV with respect to the bulk component, in very good agreement with our experimental outcomes

Summary

Introduction

The atomic coordination number (CN) plays a crucial role in determining physical and chemical properties in condensed matter The importance of this quantity is well recognized in the field of heterogeneous catalysis.[1] It is well-established that the chemical properties for several systems are determined by the presence of a large population of atoms sitting at defect sites, edges, corners, and nanofacets in catalytic active nanoparticles.[2,3] The importance of these local configurations was revealed both in noble[4,5] and transition metal[6,7] nanoparticles, for which it has been demonstrated that a high concentration of low-coordination atomic sites results in increased chemical reactivity. The same quantities are used in conjunction with diffusion properties, to determine growth, nucleation, and aggregation processes,[13] which in turn define the presence of undercoordinated atomic species in the adlayer structure

Methods

Results

Conclusion