Regular Arrays of Pt Clusters on Alumina: A New Superstructure on Al$_2$O$_3$/Ni$_3$Al (111)

TL;DR

This study reveals a new hexagonal superstructure of tiny Pt clusters on alumina, with potential applications in single atom catalysis, and explores how different deposition conditions influence cluster organization.

Contribution

The paper reports the discovery of a novel hexagonal array of Pt clusters at room temperature and analyzes how temperature and pre-formed seeds affect cluster organization on alumina.

Findings

New hexagonal Pt cluster structure with 1.38 nm spacing at RT

High-density assembly of 1-6 atom Pt clusters

Different cluster organizations depend on deposition temperature and surface sites

Abstract

Alumina ultrathin films obtained by high temperature oxidation of a Ni$_3$Al (111) surface are a good template to grow regular arrays of metal clusters. Up to now two hexagonal organizations called 'dot' and 'network' structures have been observed with distances between clusters of 4.1 and 2.4 nm, respectively. In the present article we report on an investigation by in situ Grazing Incidence Small Angle X-ray Scattering (GISAXS), showing that Pt deposited at room temperature (RT) and for a low coverage forms a new hexagonal structure with a distance between clusters of 1.38 nm. For the first time, an assembly of tiny Pt clusters (1-6 atoms) with a very high density (5.85x10 13 cm$^{-2}$) and presenting a good organization on an alumina surface, is obtained. This system could be used to investigate by surface science techniques the new emerging field of Single Atom Catalysis (SAC). By deposition at 573 K small Pt clusters are organized on the network structure. By deposition of Pt at 573 K on pre-formed Pd seeds, large Pt (Pd) clusters containing a hundred of atoms are organized on the dot structure and they remain organized up to 733 K. We show that the three structures are interrelated. The different organizations of the Pt clusters on the alumina surface are explained by the presence of 3 types of sites corresponding to different adsorption energy for Pt atoms.