In an article recently published in Nanotechnology, we demonstrated a parallel laser processing technique based on colloidal micro/nano-particles, which overcome the drawbacks in tip-based techniques. It utilizes a regular two-dimensional array of self-assembled particles on a flat surface as a lens array, which converts a laser beam into a multiplicity of enhanced optical spots in parallel at focus (see figure). 500 nm-sized SiO2 particles were assembled on a silicon wafer surface over an area of 0.5 cm2, with an estimated amount of hundreds of millions of particles in total.

The samples (particles on silicon) were immersed into the chemical solution (diluted KOH) for laser irradiation. Computer simulation shows that the laser focus spots are in the near fields of the particle-silicon contact points and localized chemical reaction thus takes place within these focus regions. According to our analysis, a very thin oxide layer was formed at each reaction site. Because of the dramatic difference in the silicon/SiO2 etch rate (much higher for silicon), the residual SiO2 layer in fact works as a protection mask for subsequent post-etching processes at higher temperatures in the same chemical enchant, which leads to the conversion of the shapes of the structures from concave holes to convex nano bumps.

Our work shed a new light on parallel laser chemistry processing in the nanoscale. For the first time, it is possible to combine the liquid phase chemical etching with laser nanofabrication in optical near field. The technique is simple and efficient to implement and is very promising for real industrial applications.