B. S. Luk’yanchuk

Pulsed laser-assisted surface structuring with optical near-field enhanced effects

The effects of optical resonance and near field in the interaction of transparent particles on a substrate with laser light have been examined experimentally and theoretically. It is found that pits can be created at the contacting point between the particle and the metallic surface by laser irradiation (KrF,λ=248 nm) with a single pulse. The influence of the particle size and the laser fluence on the structuring of the surface has been investigated. The size of the particle ranges from 1.0 μm to 140 nm in diameter. The morphologies of the holes created have been characterized by an atomic force microscope and a scanning electron microscope. For constant laser fluence, the created hole is sensitive to the particle size. For higher-laser fluence, the corresponding hole becomes larger and deeper. With a low fluence of 300 mJ/cm2 and for 140 nm particles, the lateral dimensions of created pits can be down to 30 nm. With a high fluence of 750 mJ/cm2 and 1.0 μm particles, the diameter and the depth of created ...

Near-field laser parallel nanofabrication of arbitrary-shaped patterns

The authors present a simple and efficient technique for laser writing of arbitrary nanopatterns across a large surface area without using projection masks. It is based on the unique near-field focusing effect of a self-assembled particle array on the surface interacting with an angular incident laser beam. The spot resolution can be down to 80nm. More than 6×106 nanolines and c-shaped uniform patterns were fabricated simultaneously over an area of 5×5mm2 by a few laser shots.

Dry laser cleaning of particles from solid substrates: Experiments and theory

The experimental analysis of dry laser cleaning efficiency is done for certified spherical particle (SiO2, 5.0, 2.5, 1.0, and 0.5 μm) from different substrates (Si, Ge, and NiP). The influence of different options (laser wavelength, incident angle, substrate properties, i.e., type of material, surface roughness, etc.) on the cleaning efficiency is presented in addition to commonly analyzed options (cleaning efficiency versus laser fluence and particle size). Found laser cleaning efficiency demonstrates a great sensitivity to some of these options (e.g., laser wavelength, angle of incidence, etc.). Partially these effects can be explained within the frame of the microelectronics engineering (MIE) theory of scattering. Other effects (e.g., influence of roughness) can be explained along the more complex line, related to examination of the problem “particle on the surface” beyond the MIE theory. The theory of dry laser cleaning, based on one-dimensional thermal expansion of the substrate, demonstrates a great...

Laser writing of a subwavelength structure on silicon (100) surfaces with particle-enhanced optical irradiation

Spherical 0.5-μm silica particles were placed on a silicon (100) substrate. After laser illumination with a 248-nm KrF excimer laser, hillocks with size of about 100 nm were obtained at the original position of the particles. The mechanism of the formation of the subwavelength structure pattern was investigated and found to be the near-field optical resonance effect induced by particles on the surface. Theoretically calculated near-field light intensity distribution was presented, which was in agreement with the experimental result. The method of particle-enhanced laser irradiation has potential applications in nanolithography.

Microlens array fabrication by laser interference lithography for super-resolution surface nanopatterning

A technique for large area and fast speed surface nanopatterning of photopolymer surface with laser irradiation through microlens array (MLA) was demonstrated. The laser beam was split into many focused tiny light spots by a 1μm diameter MLA fabricated by laser interference lithography followed by reflow and reactive ion etching. The fabricated MLA exhibits excellent uniformity and surface quality. Up to 6 250 000 nanopatterns can be fabricated over an area of 5×5mm2 under KrF excimer laser single pulse exposure. A spot size down to 78nm was obtained corresponding to super-resolution of λ∕3, λ is the incident laser wavelength.

Direct femtosecond laser nanopatterning of glass substrate by particle-assisted near-field enhancement

Direct femtosecond laser nanopatterning of glass substrate by particle-assisted near-field enhancement was demonstrated in this letter. The nanostructure was characterized by field-emission scanning electron microscopy and atomic force microscopy. No cracks were found on the glass surface. The hole size were measured from 200∼300nm. When laser fluence is close to the damage threshold, a trihole structure was observed. Nonlinear multiphoton absorption and near-field enhancement were the mechanisms of the nanofeature formation. Calculations based on particle-on-surface theory were carried out. The suggested method has potential applications in the nanolithography of a transparent glass substrate for nanostructure device fabrication.

Nanobump arrays fabricated by laser irradiation of polystyrene particle layers on silicon

Two-dimensional (2D) nanobump arrays were fabricated by laser irradiation of a regular lattice of absorptive polystyrene (PS) microspheres on an undoped (100) Si wafer. The experiments were performed with single-pulse 248 nm KrF laser radiation. The structure of the arrays fabricated by this method was characterized by field emission scanning electron microscope and atomic force microscope. The near-field effects under the absorptive particle are studied. The ablation and thermal processes induced by the optical near-field around the particles are investigated. The formation mechanism of nanobumps is discussed.

Fano resonances and topological optics: an interplay of far- and near-field interference phenomena*

Fano resonances and optical vortices originate from two types of interference phenomena. Usually, these effects are considered to be completely independent, and in many cases Fano resonances are observed without any link to vortices, as well as vortices with a singular phase structure that are not accompanied by Fano resonances. However, this situation changes dramatically when we study light scattering at the nanoscale. In this paper, we demonstrate that Fano resonances observed for light scattering by nanoparticles are accompanied by the singular phase effects usually associated with singular optics, and we introduce and describe optical vortices with characteristic core sizes well below the diffraction limit.

Direct and subdiffraction-limit laser nanofabrication in silicon

We propose a method for nanofabrication at a resolution much below the diffraction limit for projection optical lithography using a backside-irradiation method. Feature sizes below λ/260 have been achieved in silicon. An infrared laser (CO2, λ=10.6 μm) was used to illuminate the backside of a Si substrate with Au particles on its polished surface. The morphologies of created features were characterized by atomic force microscope and field emission scanning electron microscope. The formation mechanisms of these nanofeatures have been discussed and associated with localized optical excitations in Au colloid aggregates with a fractal structure. This backside-irradiation laser-assisted nanofabrication method may also be extended to various metals, particle shapes, particle sizes, substrates, and other lasers. It can be used to investigate optical excitations and near fields in these systems.

Peculiarities of light scattering by nanoparticles and nanowires near plasmon resonance frequencies in weakly dissipating materials

Light scattering by a small spherical particle and nanowire with low dissipation rates are discussed according to the Mie theory (and similar solution for the cylinder). It is shown that near plasmon (polariton) resonance frequencies one can see non-Rayleigh anomalous light scattering with quite a complicated near-field energy flux.