Zengbo Wang

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.

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.

Peculiarities of light scattering by nanoparticles and nanowires near plasmon resonance frequencies

Results related to the peculiarities of light scattering by nanoparticles and nanowires near plasmon resonance frequencies are reported. It is shown that the scattering problem for weakly dissipative media cannot be analyzed in the dipole approximation, in contrast to the classical Rayleigh scattering. A structure of the Poynting vector in the near field area is obtained. It is shown that small variations of the size parameter or/and the incident light frequency may lead to drastic transformations of the near field distribution.

OPTICAL RESONANCE AND NEAR-FIELD EFFECTS IN DRY LASER CLEANING

Optical problems, related to the particle on the surface, i.e. optical resonance and near-field effects in laser cleaning are discussed. It is shown that the small transparent particle with size by the order of the wavelength may work as a lens in the near-field region. This permits to focus laser radiation into the area with the sizes, smaller than the radiation wavelength. It leads to 3D effects in surface heating and thermal deformation, which influences the mechanisms of the particle removal.

Laser generation of nano-bumps below 2 nm height on silicon for debris-free marking/patterning

By rapidly scanning a 532nm diode pumped Nd:YVO4 laser beam at nano-second pulses below the ablation threshold, a uniform array of nano-bumps of less than 2nm in height (diameter of around 20 µm) was generated on a p-type � 100� Si wafer. This height is two orders of magnitude lower than previously reported values. The array was produced at 30000 bumps per second. The effect of laser fluence (energy density) and scanning speed on the characteristics of the nano-bumps was investigated and the wettability of the laser nano-textured surfaces was examined. The mechanisms of nano-bump formation are discussed. Also presented are the application of the technique for debris free, invisible marking/texturing of silicon and the recognition of such marks/patterns. (Some figures in this article are in colour only in the electronic version)

Numerical Simulation of Excimer Laser Cleaning of Film and Particle Contaminants

Laser cleaning is a promising surface preparation technique for applications in high value manufacturing industries. However, understanding the effects of laser processing parameters on various types of contaminants and substrates, is vital to achieve the required cleaning efficacy and quality. In this paper, a two-dimensional transient numerical simulation was carried out to study the material ablation characteristics and substrate thermal effects in laser cleaning of aerospace alloys. Element birth and death method was employed to track the contaminant removal on the surface of the material. The result shows that contaminant ablation increases with laser power and number of pulses. The finite element method (FEM) model is capable enough to predict the optimum number of pulses and laser power required to remove various contaminants. Based on the simulation results, the mechanism of the excimer laser cleaning is proposed. Thus, the use of numerical simulation can be faster and cheaper method of establishing the optimum laser cleaning window and reducing the number of experimental tests.

Ultrafast phase transitions in Ge1Sb2Te4 films induced by femtosecond laser beam

Ultrafast phase transitions triggered by single femtosecond laser pulse in Ge1Sb2Te4 films were investigated. By proper control of the film thickness, ultrafast crystalline and amorphous phase transformations have been achieved in Ge1Sb2Te4 films. These utlrafast phase transitions were confirmed by reflectivity change and x-ray diffraction measurement.

Laser-assisted nanofabrication

Laser assisted nanofabrication for surface nanopatterning is investigated. To overcome the limitation of light wavelength, pulsed lasers were applied to combine with atomic force microscope (AFM) and nanoparticle self-assembled mask to achieve sub-30 nm patterning on the metallic surfaces. The mechanisms of the formation of nanostructure patterns are discussed. Progress on numerical simulation and physical modeling of laser assisted nanofabrication has been demonstrated. The method of AFM tip or particle enhanced laser irradiation allows the study of field enhancement effects as well as its potential applications for nanolithography.