A. Lasagni

Laser Interference Metallurgy - using interference as a tool for micro/nano structuring

Abstract Interfering laser beams of a high-power pulsed laser provide the opportunity of applying a direct lateral interaction with the surface microstructure of metals in micro/nano-scale based on photo-thermal nature mechanisms. This “Laser interference metallurgy” allows the creation of periodic patterns of features with a well defined long-range order on metallic surfaces at the scale of typical microstructures (from the sub micrometer level up to micrometers). This technique is an approach to initiate metallurgical processes such as melting, recrystallization, recovery, and defect and phase formation in the lateral scale of the microstructure itself and with an additional long range order given by the interference periodicity. In this work, the laser interference theory is described and used to calculate multi-beam interference patterns. A method to calculate the numbers of laser beams as well as the geometrical arrangement of the beams to obtain a desired periodical pattern prior to experiments is presented. The formation of long-range-ordered intermetallic compounds as well as macroscopic and microscopic variations of mechanical properties on structured metallic thin films are presented as examples.

3D Nano-characterisation of materials by FIB-SEI/EDS tomography

Focus ion beam-tomography is able to characterize materials from > 10 nm. The 3D-volumes are generated from serial FIB cross-sections, which can be imaged by the different modes of a scanning electron microscope (SEM) like secondary electrons (SE), energy-dispersive X-ray spectroscopy analysis (EDS), etc. This article reports on different examples of FIB-tomography in Al-alloys and porous Ni sample, as well as on the different methods for an adequate sectioning and imaging of the serial cross sections.

Direct fabrication of surface architectures on polymers and copolymers using laser interference patterning

Surface pattering engineering techniques are essential to fabricate advanced topographies that can be use to modulate cell and tissue response in bio-materials. Particularly, direct laser interference patterning permits fabrication of repetitive arrays and microstructures by irradiation of the sample surface with coherent beams of light. In this study, we explore the possibilities of this technique to produce advanced architectures on several polymeric substrates. The previously calculated interference patterns using the well known interference theory could be directly reproduced on the polymeric surfaces. Moreover, the cross-section of the structured polymers changes depending on the intensity of the laser beams and number of laser pulses, and photomachinability of polymers is highly influenced by laser wavelength. High absorbance of the polymeric materials at specific wavelengths allows the reduction of the laser intensity required to achieve a determined structure depth. In addition, copolymers of methylmetacrylate-styrene were also studied showing that different types of periodic structures could be obtained depending on laser intensity. The obtained results were compared with thermal simulations by finite element methods as well as classical models.

Microstructure – Mechanical Properties Relationship of Laser Interference Irradiated Ni/Al Multi-Film

Due to the corresponding intermetallic compounds, Ni/Al multi-layered thin film systems are important to protect against the mechanical and chemical impacts on the bulk component. The mechanical properties of these intermetallic compounds, NiAl, can be further improved by combining with other stiff phases. The mechanical properties would be optimized if the lateral surface composite can be made in such a way that the different phases are arranged periodically with a preferred orientation, micro-scaled period and reticulated phase interfaces. Such optimized surface composites have been achieved by laser interference irradiation in a nano-grained structure. In this study, the thin film systems are produced by physical vapor deposition and subsequently irradiated by the interference pattern of two or more coherent laser beams. The corresponding periodical heat treatment has been analyzed by thermal simulation, and thermal simulation results are compared with the experimental results. Further, the phase transitions during laser interference irradiation are calculated. The structural investigations of irradiated films - grain sizes and deformation by TEM, stress and texture by XRD - are compared with the mechanical properties - hardness and Youngs modulus by NI-AFM.

Design and calculation of advanced microstructural patterns by laser interference metallurgy

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.