Experimental and Numerical Study of Optical Trap Assisted Nanopatterning

Abstract

Optical trap assisted nanopatterning (OTAN) is a laser direct-write nanopatterning

tool. In this process, a particle is trapped by a Bessel or Gaussian beam and positioned near a substrate. Another processing laser is illuminated on the particle to create a near-eld focusing effect below the sphere, modifying the substrate. This

thesis presents an in-depth study of an OTAN process and its applications using both experimental and numerical approach.

OTAN was initially shown to produce user-dened nanoscale patterns on a

at polyimide surface, but it is not limited to such a case. Here, we discussed four aspects of the OTAN system: (i) substrate materials from polymers to semiconductors, (ii) self-positioning nature (Bessel beam-based), (iii) probe geometry, and (iv) nonlinear process for 3D patterning. The mutual goal of these projects is not only a study of fundamental physics but also exploring the capabilities and potential applications of OTAN.

To begin with, we explored a different substrate system, where a silicon surface

was used. In addition, the use of the Bessel beam trapping enables the bead to follow the topography of the surface since the confinement is in the transverse direction. We showed continuous nanoscale features produced across the step with high uniformity. Additionally, we used beam splitter systems to split one trapping beam to two beams, which trapped a pair of spheres and produced parallel features simultaneously. We used these features to extract lateral positional accuracies due to Brownian motion.

The thesis also presents a study of non-spherical probe shapes. Dicolloidal particles were used to control the near-eld focal intensity and location. We used these particles to produce features and compared them with the surface morphologies predicted by simulations. Finally, we explored the 3-D nanoscale additive structuring aspect of the OTAN system, where OTAN was combined with multiphoton interaction for the creation of feature sizes down to one tenth of the illumination light using a femtosecond laser.

These results provide a complete view of the versatile applications and fundamental physics underlying the OTAN technique, suggesting that OTAN is a viable

approach for direct-write nanoscale patterns on various substrate materials, probe

geometries, and substrate topographies.