Formation of light harvesting structures for photovoltaics using laser interference ablation

In this PhD thesis, application of patterning with interfering laser beams for the fabrication of light harvesting structures for the photovoltaic elements was investigated. Interference patterning technique was used to pattern antireflective silicon nitride layer on silicon solar cells, crystalline or multicrystalline silicon substrates and thin metal films. Using the irradiation fluence below the ablation threshold, silicon nitride was locally converted to silicon oxide/oxy-nitride. This resulted in increased absorption of the element in the visible spectral range and improved electric characteristics of the solar cell. Interference patterning technique, combined with anisotropic or isotropic wet chemical etching, was used for the fabrication of the inverted pyramid pattern in crystalline silicon and periodic dimple pattern in monocrystalline silicon. The optimal irradiation conditions were determined. Fabrication of sub-micrometre patterns was investigated. In this case, heat diffusion in the volume between the maximal intensity spots plays a significant role. A three-dimensional model for heat diffusion simulation was introduced. In the last chapter of this thesis, improvements of the interference patterning setup are discussed. Methods to ensure uniform large area fabrication and to increase interference patterning flexibility are discussed

Large-Area Fabrication of LIPSS for Wetting Control Using Multi-Parallel Femtosecond Laser Processing

In this research, the wetting property control of a stainless-steel surface, structured using parallel processing via an array of 64-femtosecond laser beams, is presented. The scanning of an 8 × 8-beam array over the sample was used to uniformly cover the large areas with LIPSS. The static water contact angle and the LIPSS period dependence on processing parameters were investigated. The wettability control of water droplets on laser-patterned stainless steel, ranging from contact angles of ~63°, similar to those of the plain surface, to the superhydrophobic surface with contact angles > 150°, was achieved. The relationship between the static water contact angle and the LIPSS parameters in the Fourier plane was investigated

Effect of Laser Processing on Surface Properties of Additively Manufactured 18-Percent Nickel Maraging Steel Parts

In the present work, the experimental study on laser processing of additively manufactured (AM) maraging steel part surface was conducted. Nanosecond pulsed laser at ablation mode was used for surface modification in oxidizing atmosphere. The morphology, roughness, elemental and phase composition, microhardness and tribological properties of the processed surfaces were investigated. The obtained results revealed that pulsed laser processing under the ablation mode in air allows obtaining modified surface with uniform micro-texture and insignificant residual undulation, providing 3 times lower roughness as compared with the as-manufactured AM part. The intensive oxidation of surface during laser processing results in formation of the significant oxides amount, which can be controlled by scanning speed. Due to the presence of the oxide phase (such as Fe2CoO4 and Ti0.11Co0.89O0.99), the hardness and wear resistance of the surface were significantly improved, up to 40% and 17 times, respectively. The strong correlation between the roughness parameter Ra and mass loss during the tribological test testifies the significant role of the obtained morphology for the wear resistance of the surface.This article belongs to the Section Surface Characterization, Deposition and Modificatio

Laser-induced spatially-selective tailoring of high-index dielectric metasurfaces

Optically resonant high-index dielectric metasurfaces featuring Mie-type electric and magnetic resonances are usually fabricated by means of planar technologies, which limit the degrees of freedom in tunability and scalability of the fabricated systems. Therefore, we propose a complimentary post-processing technique based on ultrashort (≤ 10 ps) laser pulses. The process involves thermal effects: crystallization and reshaping, while the heat is localized by a high-precision positioning of the focused laser beam. Moreover, for the first time, the resonant behavior of dielectric metasurface elements is exploited to engineer a specific absorption profile, which leads to a spatially-selective heating and a customized modification. Such technique has the potential to reduce the complexity in the fabrication of non-uniform metasurface-based optical elements. Two distinct cases, a spatial pixelation of a large-scale metasurface and a height modification of metasurface elements, are explicitly demonstrated