Synchrotron XPS was used to investigate a series of chemically-synthesised, atomically-precise gold clusters Au_n(PPh₃)_y (n = 8, 9, 11 and 101, with y depending on cluster size) immobilized on titania nanoparticles. The gold clusters were washed with toluene at 100 °C or calcined at 200 °C to remove the organic ligand. From the position of the Au 4f_7/2 peak it is concluded that cluster size is not altered through the deposition. From the analysis of the phosphorous spectra, it can be concluded that the applied heat treatment removes the organic ligands. Washing and calcination leads to partial oxidation and partial agglomeration of the clusters. Oxidation of the clusters is most likely due to the interaction of the cluster core with the oxygen of the titania surface after removal of ligands. The position of the Au 4f_7/2 peak indicates that the size of the agglomerated clusters is still smaller than that of Au₁₀₁.

Synchrotron XPS was used to investigate a series of chemically synthesised, atomically precise gold clusters Au_n(PPh₃)_y (n = 8, 9 and 101, y depending on the cluster size) immobilized on anatase (titania) nanoparticles. Effects of post-deposition treatments were investigated by comparison of untreated samples with analogues that have been heat treated at 200 °C in O₂, or in O₂ followed by H₂ atmosphere. XPS data shows that the phosphine ligands are oxidised upon heat treatment in O₂. From the position of the Au 4f_7/2 peak it can be concluded that the clusters partially agglomerate immediately upon deposition. Heating in oxygen, and subsequently in hydrogen, leads to further agglomeration of the gold clusters. It is found that the pre-treatment plays a crucial role in the removal of ligands and agglomeration of the clusters.

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.

Triphenylphosphine ligand-protected Au9 clusters deposited onto titania nanosheets show three different atomic configurations as observed by scanning transmission electron microscopy. The configurations observed are a 3-dimensional structure, corresponding to the previously proposed Au9 core of the clusters, and two pseudo-2-dimensional (pseudo-2D) structures, newly found by this work. With the help of density functional theory (DFT) calculations, the observed pseudo-2D structures are attributed to the low energy, de-ligated structures formed through interaction with the substrate. The combination of scanning transmission electron microscopy with DFT calculations thus allows identifying whether or not the deposited Au9 clusters have been de-ligated in the deposition process.

The far infra-red absorption spectra of a series of chemically synthesised, atomically precise phosphine-stabilised gold cluster compounds have been recorded using synchrotron light for the first time. Far-IR spectra of the Au₆(Ph₂P(CH₂)₃PPh₂)₄(NO₃)₂, Au₈(PPh₃)₈(NO₃)₂, Au₉(PPh₃)₈(NO₃)₃, and Pd(PPh₃)Au₆(PPh₃)₆(NO₃)₂ clusters reveal a complex series of peaks between 80 and 475 cm⁻¹, for which all significant peaks can be unambiguously assigned by comparison with Density Functional Theory (DFT) geometry optimisations and frequency calculation. Strong absorptions in all spectra near 420 cm⁻¹ are assigned to the P–Ph₃ stretching vibrations. Distinct peaks within the spectrum of each specific cluster are assigned to the cluster core vibrations: 80.4 and 84.1 cm⁻¹ (Au₆) 165.1 and 166.4 cm⁻¹ (Au₈), 170.1 and 185.2 cm⁻¹ (Au₉), and 158.9, 195.2, and 206.7 cm⁻¹ (Au₆Pd). The positions of these peaks are similar to those observed to occur for the neutral Au₇ cluster in the gas phase (Science, 2008, 321, 674–676). Au–P stretching vibrations only occur for Au₆ near 420 cm⁻¹, although they appear near 180 cm⁻¹ for Au₆Pd and involve gold core vibrations.