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Limited stability of metal nanoparticles hinders their long-term uses and applications. For metal nanoclusters, this is even more critical, as physicochemical properties rely on the structure of only a few hundred atoms. Here, we study the irreversible change that Au25(SR)18suffers upon interaction with 2D metal surfaces. Experimental and density functional theory results allow us to identify the triggering factors of the decomposition process. Our thermodynamic-based approach can be extended to other metal nanocluster/substrates, turning it into a useful tool for predicting the nanoscale stability of these systems.

Thermal desorption in an ultrahigh vacuum of n-hexanethiol (C6T) self-assembled monolayers (SAMs) prepared from ethanolic solutions on Au(111) and Au(001) unreconstructed surfaces was investigated by X-ray photoelectron spectroscopy. The SAMs desorption was performed from room temperature (RT) to 380 K. We report that the hexanethiolate surface saturation coverage is bigger (∼0.4 ML) for the SAM on Au(001) than on Au(111) (∼0.33 ML). We identified a greater stability for C6T SAMs on Au(001). Large amounts of physisorbed species were found on preferred oriented (111) polycrystalline Au at the low coverage regime at RT, while the SAM on the Au(001) single crystal at this conditions desorbs at a steady pace. At 340 K, both SAMs remain stable at the coverage expected for the lying-down phases that maximizes the van der Waals interactions. We observe that at higher temperatures the carbon alpha–sulfur bond breaks, producing free S on both gold surfaces.

The determination of the amount of gold adatoms and vacancies present at the thiol–gold interface of the (√3 × √3)-R30° lattice on Au(111), usually observed for long-chain alkanethiols, is crucial to complete our knowledge on the species resulting from the thiol–substrate interaction. While this issue has been addressed for short and intermediate alkanethiols where Au adatom-complexes of the type RS–Auad–SR, known as staples, are formed, this issue is still under discussion for long-chain alkanethiols where different and contradictory models have been proposed. In this report we present X-ray diffraction data of the (√3 × √3)-R30° structure for hexadecanethiol, allowing us to establish such basic structural features as the existence of Au adatoms and vacancies, the thiol adsorption-induced reconstruction of the surface, and the structure of the interface. These results allow us to reject the notion that vacancies and adatoms coexist within the same unit cell, and allow us to note that over the whole thiol–Au(111) interface the two exist in equal proportions. Vacancies appear on the gold surface as vacancy islands, and gold-adatoms appear flanked by two sulfur atoms, as observed on thiol-protected gold clusters and short thiols on Au(111). The coexistence of radicals and staples in the same (√3 × √3)-R30° cell is consistent with experiment and theory.

We discuss some characteristic phenomena that take place when high-aspect-ratio metallic nanopatterns decay by surface diffusion. We compare results obtained by means of a continuous 2D model, a kinetic 3D Monte Carlo model, and also experimental results in which nanostructured Au surfaces decay during an annealing. In all of these cases, we found structures that are very stable against surface diffusion currents in which the surface area is much higher than the one associated with a compact material. According to our models, such structures usually are complex surfaces exhibing voids, tunnels, channels, etc., and they are very different from the compact shapes expected after the annealing of low-aspect-ratio metallic nanopatterns.

The surface structure of self-assembled monolayers of hexanethiolate (HT) on the Au(100)-(1 × 1) surface has been studied by density functional theory (DFT) calculations and their results compared to scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) data. We have found two novel surface structure models consisting of adsorbed thiolates on the Au(100)-(1 × 1) surface that fairly account for experimental STM and XPS observations. Surprisingly, these models exhibit better thermodynamic stability than those consisting of thiolate–Auad–thiolate moieties on a reconstructed Au(100)-(1 × 1) surface. Also these proposed models are more stable than the thiolate–Auad–thiolate containing c(4 × 2) lattice on the reconstructed Au(111) suggesting a surface dependent chemistry for thiolates on Au. However, the possible existence of other models with similar or better stability than those proposed in this work and also the possible coexistence of different surface structures and chemistry on the substrate surface cannot be excluded.

Properties of small metal nanoclusters rely on the exact arrangement of a few atoms. Minor structural changes can rapidly destabilize them, leading to disintegration. Here, we evaluate the energetic factors accounting for the stabilization and integrity of thiolate-capped gold nanoclusters (AuNCs). We found that the core-cohesive and shell-binding energies regulate the disintegration process on a solid substrate by investigating the different energetic contributions, as shown here in a combined experimental and theoretical study. As the AuNC size increases, the core-cohesive energy and shell stability (imposed by S-Au and hydrocarbon chain interactions) counterbalance the AuNC–substrate interaction and slow down the AuNC disintegration. Thus, the decomposition can not only be understood in terms of desorption and transfer of the capping molecules to the support substrate but conversely, as a whole where ligand and core interactions play a role. Taken together, our experimental and theoretical results serve as guidelines for enhancing the stability of AuNCs on solid-state devices, a key point for reliable nanotechnological applications such as heterogeneous catalysis and sensing.