Irradiation with a single nanosecond laser pulse in the melting regime can result in a characteristic change in the surface morphology of crystalline silicon. This has been verified experimentally in a variety of situations, where dimple-shaped surface topographies are produced. In this work, the dimple height, depth, and width are modeled following and extending in a more rigorous manner the approach of Wood and Giles [Phys. Rev. B 23, 2923–2942 (1981)] and that of Schwarz-Selinger and coworkers [Phys. Rev. B 64, 155323 (2001)], upon varying the laser irradiation parameters such as peak energy density, pulse duration, and wavelength. This is achieved with numerical simulations of one-dimensional heat flow as input to the analytical fluid-flow equations.

Quasi-percolated nanostructured silver thin films are used as the starting morphology for inducing simultaneously changes in shape and ordering effects by laser irradiation. The complex fingered nanostructures are transformed into nanospheres which in turn are arranged in micro-circular patterns when irradiated through a pinhole. These transformations are characterized by transmission electron microscopy and atomic force microscopy. The observed effects are explained using Fresnel diffraction theory. Good agreement with the experimental results is obtained. These results suggest that precise patterning engineering can be achieved through control of the spatial parameters such as the pinhole diameter and the distance from the mask to the sample.

2009) UV-laser-induced modifications through a single slit on quasi-percolated silver nanostructured films, Radiation Effects andIn this work, we report the synthesis of quasi-percolated Ag thin films by pulsed laser deposition. These Ag nanostructures are the starting material for obtaining spatially ordered silver nanoparticles by ultraviolet laser irradiation. The laser transformations are investigated by transmission electron microscopy. We have previously demonstrated that the arrangement of these silver nanoparticle assemblies can be controlled by irradiating the samples through suitable masks, such as razor edge or a phase grating among others, taking advantage of their respective diffractive properties. In this work, the effect of the irradiation through a single slit is discussed. A simple optical model based on Fresnel diffraction is presented in order to explain the obtained results.

The formation of gratings on the surface of a silicon wafer by nanosecond laser irradiation through a phase mask using an ArF laser emitting at 193 nm is studied. The phase mask along with some focusing optics is capable to generate via interference a periodic intensity distribution, which can be used for surface patterning. The surface patterning strongly depends on the laser energy density and on the number of pulses, as revealed by Atomic Force Microscopy (AFM). The results show that irradiation even with a single laser pulse produces periodic depth modulations on the surface. The spatial surface modulation is in the micrometer (1.7 μm) range while the depth modulation is in the nanometer regime (1-20 nm). With increasing number of pulses (1-100) the depth modulation amplitude increases smoothly. Increasing the number of pulses further results in the progressive destruction of the grating, vanishing completely after ~5000 pulses. This evolution is also monitored in-situ by measuring the intensity of the first order-diffracted probe beam and the behavior is in accordance with what is observed by AFM. Finally, we qualitatively explain the results invoking thermally induced effects in the melted Si: these physical processes involved are probably thermocapillary and/or Marangoni effects inducing material displacement as the surface melts.

Single-pulse (532 nm, 8 ns) micropatterning of silicon with nanometric surface modulation is demonstrated by irradiating through a diffracting pinhole. The irradiation results obtained at fluences above the melting threshold are characterized by scanning electron and scanning force microscopy and reveal a good agreement with Fresnel diffraction theory. The physical mechanism is identified and discussed on basis of both thermocapillary and chemicapillary induced material transport during the molten state of the surface.