Micro/nano-structuration of silicon using photonic nanojet mechanism

Summary form only given. Developing techniques able to fabricate micro and nanostructures at the surface of a material and on a large scale area is extremely valuable for fostering emerging applications in microelectronics, optics, biology and as a general view in nanoscience and nanoengineering. In this context, techniques combining near field optics and laser ablation are particularly promising. Interestingly, optical field enhancements underneath a nanosphere monolayer can make possible ablation experiments with a periodic assembly of laser fields with lateral sizes that are below the diffraction limit. Besides, the Langmuir-Blodgett (LB) technique has demonstrated its potential for the realization of controlled self-assembly on large surfaces. In this paper, we thus report on the preparation of monolayer of C18 coated silica spheres on large scale (cm²) Silicon substrate using LB deposition technique and we further study the structuration of the LB-prepared samples using a UV nanosecond ArF (193 nm) laser. In particular, we investigate different laser fluence ranges and numbers of laser shots to understand the tradeoff between size, quality of the craters, and the morphology of the surface after irradiation treatment. It is shown that tuning the irradiation fluence yields selectivity of the characteristic lateral dimension of the imprinted craters on the substrate and laser operation in multishot mode allows obtaining high quality and regularity of surface morphology of the resulting millimeter square arrays of holes. Stress of the processed sample surface is also investigated using confocal micro-Raman spectroscopy. While this diagnostic shows the microstructured samples do not exhibit significant stresses, we note a strong enhancement of the Raman mode whatever the excitation wavelength (488, 514.5 and 632.8 nm). This demonstrates the protential of such microstructured samples for silicon photonics applications. Finally, Finite-Difference Time-Doma- n calculations are used to study the origin properties of the microsphere lensing effect and Raman signal enhancement for all tested situations. Structuration tests using different set of spheres (polymer or fused silica beads of different size) will be also presented to extend the capability of this processing technique of micro/nano-patterning.