Nanomaterials by Ultrafast Laser Processing of Surfaces

This paper reviews our work on the application of ultrafast pulsed laser processing of surfaces for nanomaterials production. Two distinct approaches are reviewed including laser surface modification in controlled gas and liquid media respectively. In particular, it is shown that the artificial surfaces obtained by femtosecond (fs) laser texturing of Si in reactive gas atmosphere exhibit roughness at both micro-and nano-scales that mimics the hierarchical morphology of natural surfaces. Depending on the functional coating deposited on the laser patterned three dimensional structures we can achieve artificial surfaces that are: (a) of extremely low surface energy, thus water repellent and self-cleaned; (b) responsive, i.e., show the ability to change their surface energy in response to different external stimuli such as light, electric field and pH. Moreover, the behaviour of different kinds of cells cultured on laser engineered substrates of various morphologies was investigated. Furthermore it is shown that laser ablation of materials in liquid media leads to surface nanostructures (NS) formation while the ablated material is dispersed in the liquid in the form of nanoparticles (NP). It is shown that the formation of NS alters the optical properties of the solid due to plasmon resonance of free electrons in NS. Results on the formation of NS and NP using ultrafast laser pulse durations from fs to few picoseconds (ps) are presented. Potential biological and optoelectronic applications of the NS and NP produced through this technique are additionally presented.