Yu-Cheng Tsai

Nanopatterning on rough surfaces using optically trapped microspheres

While nanofabricated structures find an increasingly large number of applications, few techniques are able to pattern rough or uneven surfaces, or surfaces with pre-existing structure. In this letter we show that optical trap assisted nanopatterning (OTAN), a near-field laser based technique, is able to produce nanoscale features on surfaces with large roughness but without the need for focus adjustment. Patterning on model surfaces of polyimide with vertical steps greater than 0.5 μm shows a high degree of uniformity, demonstrating that OTAN is a suitable technique to pattern nontraditional surfaces for emerging technologies.

Non-spherical particles for optical trap assisted nanopatterning

Optical trap assisted nanopatterning is a laser direct-write technique that uses an optically trapped microsphere as a near-field objective. The type of feature that one can create with this technique depends on several factors, one of which is the shape of the microbead. In this paper, we examine how the geometry of the bead affects the focus of the light through a combination of experiments and simulations. We realize nanopatterning using non-spherical dielectric particles to shape the light-material interaction. We model the resulting nanoscale features with a finite difference time domain simulation and obtain very good agreement with the experiments. This work opens the way to systematic engineering of the microparticle geometry in order to tailor the near-field focus to specific nanopatterning applications.

Generating Sub-Micron Features On Rough Surfaces Using Optical Trap Assisted Nanopatterning

Near‐field intensity enhancement enables laser modification of materials with feature sizes below the classical diffraction limit. However, the need to maintain close distances between the objective element and the substrate typically limit demonstrations of this technology to flat surfaces, even though there are many cases where the ability to produce sub‐micron features on rough or structured surfaces are needed. Here, we show the use of a new technique, optical trap assisted nanopatterning (OTAN), for the production of nanoscale features on rippled substrates. The ability to position a microbead near‐field objective close to the surface without the need for active feedback and control allows one to continuously move the bead across a rough surface without sticking. Sub‐micron patterning of polyimide is demonstrated on surfaces with 1.1 μm steps showing good uniformity. Finally, the enabling technology allows for straightforward parallelization where multiple patterns can be created simultaneously over ...

Multiphoton polymerization using optical trap assisted nanopatterning

In this letter, we show the combination of multiphoton polymerization and optical trap assisted nanopatterning (OTAN) for the additive manufacturing of structures with nanometer resolution. User-defined patterns of polymer nanostructures are deposited on a glass substrate by a 3.5 μm polystyrene sphere focusing IR femtosecond laser pulses, showing minimum feature sizes of λ/10. Feature size depends on the applied laser fluence and the bead surface spacing. A finite element model describes the intensity enhancement in the microbead focus. The results presented suggest that OTAN in combination with multiphoton processing is a viable technique for additive nanomanufacturing with sub-diffraction-limited resolution.

Generation of nanoscale anticounterfeiting patterns on silicon by optical trap assisted nanopatterning

Among the different strategies aimed at protecting products from counterfeiting, hidden security patterns are used by manufacturers to mark their products in a unique way. However, most anticounterfeiting patterns bear the risk of being reproduced by an unauthorized party who has gained knowledge of the exact technique and process parameters. In this paper, we use optical trap assisted nanopatterning to create unique security markings by taking advantage of statistical fluctuations when generating nanoscale features within the pattern. We image the patterns by optical microscopy, scanning electron microscopy, and atomic force microscopy and propose a three-level examination process that allows for an efficient yet highly secure authentication.

Elucidating the mechanism of nanocone and nanohole formation on Si by optical trap assisted nanopatterning

Using optical trap-assisted nanopatterning (OTAN), we are able to control the formation of nanocones and nanoholes in Silicon. The effects are described by integrating FDTD and heat transfer modeling to account for the nanoscale features.

Laser direct-write nanopatterning by near-field multiphoton polymerization using optically trapped microspheres

We use Gaussian beam to position a microsphere in a polymer precursor environment near a substrate. Pulsed laser is focused by a microsphere to induce multiphoton polymerization in the near-field, enabling additive direct-write nanoscale processing.

Measuring the sphere-surface interaction in optical trap assisted nanopatterning

Near-field methods rely on a precise positioning of the optical element above the surface. In this work, we measure the interaction potential of a trapped microsphere near a sample surface by high-speed microscopy.

Speed investigations toward an industrial application of optical trap assisted nanopatterning

Optical trap assisted nanopatterning is a viable method of producing parallel nanoscale features over rough surfaces and large areas. The maximum writing speed on various surfaces is elucidated to evaluate the performance of the method.

Optical trap assisted nanopatterning for structured surfaces

We investigate the use of optical trap assisted nanopatterning for creating nanoscale features on surfaces with pre-existing topography. Uniform patterns over silicon and polyimide surfaces with several micrometer deep grooves are demonstrated.