Phosphine-stabilised Au9 clusters interacting with titania and silica surfaces: The first evidence for the density of states signature of the support-immobilised cluster

Abstract

Chemically made, atomically precise phosphine-stabilized clusters Au9(PPh3)8(NO3)3 were deposited on titania and silica from solutions at various concentrations and the samples heated under vacuum to remove the ligands. Metastable induced electron spectroscopy was used to determine the density of states at the surface, and X-ray photoelectron spectroscopy for analysing the composition of the surface. It was found for the Au9 cluster deposited on titania that the ligands react with the titania substrate. Based on analysis using the singular value decomposition algorithm, the series of MIE spectra can be described as a linear combination of 3 base spectra that are assigned to the spectra of the substrate, the phosphine ligands on the substrate, and the Au clusters anchored to titania after removal of the ligands. On silica, the Au clusters show significant agglomeration after heat treatment and no interaction of the ligands with the substrate can be identified.

Toward Control of Gold Cluster Aggregation on TiO2 via Surface Treatments

“…The intensity of the P peaks are not shown because the intensity depends on the residence time of the samples in vacuum. 10 Triphenylphosphine ligands bound to the Au cluster core display a P 2p XPS peak with binding 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 14 energy of 131 -132 eV. 6 Table 1).…”

Sub-monolayer Au9cluster formationviapulsed nozzle cluster deposition

“…The total amount of solvent attaching to the surface through the deposition method thus is signicantly less than when depositing clusters by dipping the substrate into solution. 13,16 The circular feature identied on some heavily deposited surfaces in AFM (Fig. S4 †) may be accounted for by vacuum degradation over lengthy depositions affecting the solvent evaporation rate.…”

“…The interactions between atomically precise nanoclusters and substrates have been shown to be crucial to stabilising and retaining nanocluster properties and can also enhance catalysis. [11][12][13] Metal nanoclusters can also be generated in gas phase cluster sources and deposited on substrates; however, they must be used immediately and cannot be stored for any period of time. While vacuum generated nanoclusters can be deposited directly onto treated substrates for further analysis, 14,15 chemically synthesised nanoclusters have required any deposition to take place outside of vacuum, thus introducing contamination through the exposure to of the surface to atmosphere and solvents from solution based deposition methods and potentially affecting any surface treatments made in vacuum.…”

Effect of Charge and Phosphine Ligands on the Electronic Structure of the Au8 Cluster

“…In addition to tuning their size by binding with ligands, gold clusters also find new stable geometries when they interact with ligand molecules, which are explained by charge transfers resulting from ligand–gold interactions that weaken Au–Au bonds. 17 Ligands are often removed to generate bare metal clusters with exposed sites for enhanced catalytic activity through certain techniques such as calcination in a controlled atmosphere, 10 heating under vacuum, 18 and low-temperature chemical reactions with peroxides. 11 The catalytic activity of these nanoparticles is related to the cluster size and geometry and their electronic structure, which is influenced by the absence, concentration, and configuration of attached ligands.…”