Sebastian Eckhardt

Laser microstructured metal thin films as promising alternative for indium based transparent electrodes

In the search for alternative materials to replace indium-tin-oxide in transparent electrodes we have structured copper and aluminum thin films (between 5 an 40 nm) for tailoring their optical properties. Micrometer scaled holes were produced using the direct laser interference patterning (DLIP) technique. We compared the optical and electrical parameters of nanosecond and picosecond processed thin films. It was found that the optical transmittance of the structured layers was relatively increased between 25 to 125% while the electrical resistance was marginally influenced. In addition, the laser treatment enhanced the diffuse to total transmission ratio (HAZE) by values ranging from 30 to 82% (relative) as a potential advantage of μm structuring. The results also show that both of the studied metals succeed to match the target which is set by typical applications of indium thin oxide (ITO) films. Furthermore, numerical simulations are performed in order to understand the ablation process of thin film material for ps and ns pulses.

Direct laser interference patterning, 20 years of development: from the basics to industrial applications

Starting from a simple concept, transferring the shape of an interference pattern directly to the surface of a material, the method of Direct Laser Interference Patterning (DLIP) has been continuously developed in the last 20 years. From lamp-pumped to high power diode-pumped lasers, DLIP permits today for the achievement of impressive processing speeds even close to 1 m2/min. The objective: to improve the performance of surfaces by the use of periodically ordered micro- and nanostructures. This study describes 20 years of evolution of the DLIP method in Germany. From the structuring of thin metallic films to bulk materials using nano- and picosecond laser systems, going through different optical setups and industrial systems which have been recently developed. Several technological applications are discussed and summarized in this article including: surface micro-metallurgy, tribology, electrical connectors, biological interfaces, thin film organic solar cells and electrodes as well as decorative elements and safety features. In all cases, DLIP has not only shown to provide outstanding surface properties but also outstanding economic advantages compared to traditional methods.

Fabrication of highly efficient transparent metal thin film electrodes using Direct Laser Interference Patterning

The demand of highly efficient transparent electrodes without the use of rare earth materials such as indium requires a new generation of thin metallic films with both high transparency and electrical conductivity. For this purpose, Direct Laser interference Patterning was used to fabricate periodic hole-like surface patterns on thin metallic films in order to improve their optical transparency by selective laser ablation of the material and at the same time keeping the electrical properties at an acceptable level. Metallic films consisting of aluminum and copper with film thicknesses ranging between 5 and 40 nm were deposited on glass substrates and treated with nanosecond and picosecond pulse laser system. In order to analyze the processability of the films, the laser ablation threshold for each material as function of the layer thickness and pulse duration was firstly determined. After analyzing these initial experiments, the samples were structured with a 1.7 μm spatial period hole-like-pattern using three beam direct laser interference patterning. The structural quality of the fabricated structures was analyzed as function laser energy density (laser fluence) using scanning electron microscopy (SEM), atom force microscopy (AFM). Finally, optical and electrical properties of the films were characterized using optical spectroscopy, as well as surface impedance measurements.