The surface nanostructurations by means of near field enhancement with nanospheres

Laser-matter interaction is a unique and simple approach to structure materials or locally modify their properties at the micro and nanoscale level. Playing with the pulse duration and the laser wavelength, a broad range of materials and applications can be addressed. Direct irradiation of surfaces with laser beam through a standard optical beam setup allows an easy and fast structuring of these surfaces in the range of few micrometers. However, the irradiation of materials through an array of dielectric nanospheres provides a unique opportunity to break the diffraction limit and to realize structures in the range of hundred of nanometers. This simple, fast and low-cost near-field nanolithography technique is presented and discussed, as well as its great potential. The theoretical aspects of the near-field enhancement effects underneath the particles have been studied with a simple model based on the Mie theory. A commercial FDTD software has also been used to study the influence of the substrate and the surrounding media, on the energy profile of the photonic jet generated under the sphere. A specific study has been dedicated to the influence of the dispersion of the sphere diameter on the morphology of the ablation craters. This technique has been used for patterning bi-layer substrates. The process leads to the formation of a nanoporous membrane which has been used to realize an array of gold nanodots on silicon. We have also associated the Laser-Induced Forward Transfer (LIFT) process with the near-field nanolithography to print, in a single laser shot, an array of metallic nanobumps.