Design and calculation of advanced microstructural patterns by laser interference metallurgy
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0890-Y04-02.1
Design and calculation of advanced microstructural patterns by laser interference metallurgy A. Lasagni, C. Holzapfel, F. Mücklich Department for Materials Science, Functional Materials, Saarland University, P.O.Box 15 11 50, D – 66041 Saarbruecken, Germany ABSTRACT Laser Interference Metallurgy is a recently developed method for the laser material surface modification by which various interference patterns can be transformed directly, permanently, and efficiently to the surfaces of different kinds of materials. By using of this technique, different metallurgical effects such as melting, recrystallization, quenching, recovery, defect or phase formation can be exploited. In this work, advanced microstructural patterns are designed by means of the two dimensional Fourier Transformation. After that, the geometrical configuration for the laser interference experiments is calculated. Finally, thin metallic films are irradiated in order to demonstrate the viability of the presented method. The resulted structures were studied by means of Focus Ion Beam and Transmission Electron Microscopy. These surfaces represent a new type of long ordered topographical as well chemical patterns which might be applicable for well defined surface functionalization. INTRODUCTION New methods for micro- and nanofabrication are essential for understanding a variety of scientific problems in many different areas such as biology, physics, chemistry, and materials science. Structuring techniques can be divided into two groups: (1) methods which require mechanical processes to produce the patterning, and (2) methods which employ beams of electromagnetic waves (e.g. visible light, UV) or particles (e.g. electrons, ions). The first group includes techniques based on printing, molding and embossing making use of a master [1]. The second group includes optical lithography, E-Beam lithography, laser writing, holographic patterning and direct laser interference patterning between others. Direct laser interference patterning uses a single preparation step whereas other holographic methods comprise at least two different steps (irradiation, etching, developing, etc). In addition, in the case of laser interference patterning, no masks are required. Relatively large areas can be directly structured (cm²) on the time scale of a few seconds. Direct laser interference patterning has been applied in the case of different materials such as semiconductors, metals, ceramics, and polymers [2-9]. In the case of metals, different metallurgical effects can be exploited, and consequently the term Laser Interference Metallurgy (LIMET) was used in the past [10]. The simplest form of light is a monochromatic, linearly polarized plane wave. This is a sufficient approximation of a real laser beam. The electric field of a wave propagating in a homogeneous and non-absorbing medium can be written as:
E j = E j 0 e i (k r −ω t ) ,
(1)
where Ej0 is the amplitude of the electric field of the j-beam, r is the coordinate along the direction of propagation, ω is t
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