Order From The Disorder: Hyperbranched Nanostructures Self-assembled From The Gas Phase. Applications To Photovoltaic, Water Splitting and Smart Surfaces

The assembly of nanoscale building blocks in engineered mesostructures is one of the fundamental goals of nanotechnology. Among the various processes developed to date, self-assembly emerges as one of the most promising since it relays solely on basic physico-chemical forces. Our research is focused on a new type of self-assembly strategy from the gas-phase: Scattered Ballistic Deposition (SBD). SBD arises from the interaction of a supersonic molecular beam with a static gas and enables the growth of quasi-1D hierarchical mesostructures. Overall, they resemble a forest composed of individual, high aspect-ratio, tree-like structures, assembled from amorphous or crystalline nanoparticles, depending on the material. Moreover, when starting from an amorphous ensemble of nanometric clusters, it is possible to obtain hyperbranched hierarchical objects with single crystalline subdomains extending for hundreds of nanometers.

SBD is a general occurring phenomenon and can be obtained with different vapour or cluster sources. SBD by Pulsed Laser Deposition is a convenient physical vapor technique that allows the generation of supersonic plasma jets from any inorganic material irrespective of melting temperature, preserving even the most complex stoichiometries. One of the advantages of PLD over other vapour deposition techniques is extremely wide operational pressure range, from UHV to ambient pressure. These characteristics allowed us to develop quasi-1D hierarchical nanostructures from different transition metal oxides, semiconductors and metals. In some cases it was possible to achieve highly hyperbranched nanostructures with peculiar optical and electrical properties. Finally, a novel remote plasma source developed to mimic the SBD-PLD physics on large area will be presented.

Potential applications range from innovative solar cells and water splitting architectures to gas sensors, thermal barriers, etc. In this communication we will discuss the application of these materials to solar energy harvesting and storage, stimuli responsive photonic crystals and smart surfaces with digital control of their wettability behaviour.