We report the fabrication of libraries of nanostructured TiO2 films with a gradient in nanoparticle crystalline phase and dimensions. By supersonic cluster beam deposition it is possible to produce rutile nanoparticles with a diameter smaller than 10nm and to spread them into a co-deposited amorphous titania matrix. Upon thermal annealing rutile nanocrystals act as growth seeds of a film with a spatially controlled rutile/anatase ratio. Films with controlled crystalline phase variation have been deposited on micropatterned substrate to produce arrays of chemoresistive sensors of volatile organic compounds. Devices with different nanocrystalline structures and performances are obtained by a simple one-step thermal treatment after deposition.

We have produced nanostructured titanium dioxide thin films by supersonic cluster beam deposition. The as-deposited films have a nanocrystalline or amorphous structure depending on the mass distribution of the precursor clusters. This can be controlled by aerodynamic separation effects typical of supersonic expansions. On thermal annealing at temperatures from 400 to 800 • C in ambient atmosphere, amorphous-to-anatase and anatase-to-rutile phase transitions have been observed. The nanostructure and microstructure evolution of the film upon annealing has been characterized by atomic force microscopy and transmission electron microscopy. The influence of the precursor clusters in the evolution of the film nanostructure at high temperatures has been demonstrated. This observation opens up new perspectives for batch fabrication of devices based on cluster-assembled materials.

We report a spectroscopic ellipsometry investigation of the electronic and morphological properties of\ud cluster-assembled nanoporous metallic gold films deposited from a low-energy supersonic cluster beam. We\ud modeled the optical response of the medium by explicitly introducing a variable degree of porosity in the film\ud and finite-size effects due to the cluster nanometeric size. We deduced the characteristic size of the individual\ud clusters within the nanoporous structure and their depth-resolved arrangement. Comparison with independent\ud data available in the literature yielded extremely good quantitative agreement with the results extracted from\ud our model, in terms of the degree of porosity of the films and of their surface roughness. The cluster-size\ud distribution in the films obtained by the optical model matched extremely well the one obtained by atomicforce\ud microscopy on isolated clusters. This demonstrates that, though the clusters are in contact with one\ud another in the porous film, they retain their crystallographic individuality when assembled in three-dimensional\ud structures

Abstract. We report an experimental and theoretical investigation of the growth and structure of large carbon clusters produced in a supersonic expansion by a pulsed microplasma source. The absence of a significant thermal annealing during the cluster growth causes the formation of disordered structures, where sp 2 and sp hybridizations coexist for particles larger than ∼90 atoms. Among the various structures, we recognize sp 2 closed networks encaging sp chains. This 'nutshell' configuration can prevent the fragmentation of sp species upon deposition of the clusters, thus allowing the formation of nanostructured films containing carbynoid species, as shown by Raman spectroscopy. Atomistic simulations confirm that the observed Raman spectra are the signature of the sp/sp 2 hybridization typical of isolated clusters and surviving in the film and they provide information about the structure of the sp chains. Endohedral sp chains in sp 2 cages represent a novel way in which carbon nanostructures may be organized with potentially interesting functional properties.

Ultrafine cobalt and ruthenium clusters are deposited on carbon paper substrates by cluster beam deposition using a matrix assembly cluster source and a pulsed microplasma cluster source, respectively. When used to catalyze the oxygen evolution reaction (OER), the cobalt and ruthenium clusters show electrocatalytic performance superior to the state-of-the-art Ru/C and RuO 2 nanoparticle catalysts on both a mass and a specific-surface-area basis. Typically, the cobalt clusters can deliver 10 mA cm −2 at a low overpotential of 320 mV and show a small Tafel slope of 50 mV dec −1 and a mass-based turnover frequency of 0.01 s −1 at an overpotential of 300 mV, outperforming many cobalt-based OER catalysts.