Pulsed Laser Deposition of Nanostructured Oxides: from Clusters to Functional Films

Nanosecond Pulsed Laser Deposition (PLD) in a background atmosphere is a particularly versatile technique for the production of nanostructured films and surfaces. The ablation plasma plume produced by laser-matter interaction is spatially confined by the presence of a background gas, thus favouring cluster nucleation and reduction of the kinetic energy of the species impinging the substrate. This affects deposition processes and film growth mechanisms leading to the production of nanostructured systems. Here we review our recent work focused on the development of the PLD technique for the controlled synthesis of nanostructured materials, films and surfaces with tailored properties. We show in particular that by playing with the plasma expansion dynamics, through the control of background gas type and pressure and target-to-substrate distance, a fine tuning of morphology, structure and composition can be reached for a number of metal oxides (e.g. tungsten, titanium and silver oxide). Film morphology can be varied from compact to columnar and nanostructured up to highly porous foam-like with corresponding reduction of mass density and increase of surface area. Oxide formation and stoichiometry can be controlled by ablating metal targets in a reactive background gas atmosphere. Film structure can be varied from amorphous to nanocrystalline while different oxide phases can be obtained by post-deposition thermal treatments, also depending on the starting morphology. The first stages of film growth and their relation with the size and the deposition kinetic energy of the building blocks have been investigated by in situ Scanning Tunnelling Microscopy (STM). It is finally shown that nanostructured metals and metal oxides with enhanced performances for specific applications can be designed and synthesized by PLD through a fine tuning of the morphology and structure down to the nanoscale, thus revealing the potential impact of a complete characterization of the PLD bottom-up synthesis process from the single building unit to the assembly of a nanostructured material and finally to application.