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Laser interference patterning-induced microstructural modifications have been investigated in two noble metal-incorporated oxide thin film systems: Pd0.25Pt0.75Ox and gold-incorporated yttria-stabilized zirconia - Au-YSZ. Transmission electron microscopy was used to investigate the influence of the laser treatment on the microstructure of the samples. In the case of Pd0.25Pt0.75Ox, the formation of a nanocomposite arrangement resulted from the precipitation of metal nanograins in the oxide matrix triggered by laser irradiation. In Au-YSZ, the starting microstructure consisted of gold nanograins embedded in a YSZ matrix. A noticeable growth and coalescence of gold nanograins occurred near the surface in the region of maximum interference. Simultaneously, a foamy morphology, mostly consisting of gold crystals, was formed at the film surface. In contrast to thermal annealing, the laser treatment proposed here is a fast procedure to partially relocate gold at the film surface and provide a local solid lubrication.
Tailoring of micro/nano structures and surface functionalization are key goals in surface processing of materials. A new technology for a unique geometric precise 2D micro/nano design of grain architectures is presented. By means of super lateral grain growth crystalline lattice patterns such as line-, dot- and cross-like patterns were generated. The grain dimensions may be selected between a few nanometers and about 10 micrometers. The phase and grain formation was characterized by Electron Backscatter Diffraction with regard to orientation distribution and texture formation. Furthermore, dynamic aspects of this laser induced recrystallization process are studied, such as the heat transport in the films, comparing the vertical with the lateral solidification velocities by two-dimensional finite element method (FEM) simulations. Finally, the mechanical properties of the tailored thin films have been determined using nanoindentation experiments.
Novel surface engineering techniques of polymeric materials are essential to produce advanced topographies which could for example serve to modulate cell and tissue response in bio-materials. Direct Laser Interference Patterning (DLIP) permits the fabrication of repetitive arrays and microstructures by irradiation of the sample surface with coherent beams of light. Furthermore, the most important advantage of this method is that no additional process steps are required in comparison with other top-down or bottom-up techniques. In this study, we report a novel method for the advanced design of architectures in polymers using a single step process, as well as photo-activation of polymers with low absorption coefficient using a second polymer with relative high absorption coefficient. Previously calculated interference patterns using the well known interference theory could be directly produced on polymeric surface. Moreover, the cross-section of the structured polymers changes depending on the intensity of the laser beams, 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. For (60:40 %) polymethylmetacrylate/polystyrene copolymer substrate, different structures types were observed depending on the laser intensity including swelling and ablation of the material.
Thin films of polyaniline (PANI) deposited onto different substrates were nano-structured using direct laser interference patterning (DLIP) at room temperature and pressure in air atmosphere. Regular line-like arrays with thicknesses up to 600 nm were fabricated by means of this technique in only one single step. The activity of the remained polyaniline was determined by monitoring its doping level using Energy Dispersive X-Ray Analysis (EDX), while its chemical structure was confirmed by Fourier Transform Infrared Spectroscopy using Attenuated Transmission Reflectance (FTIR-ATR). The structuring mechanisms of PANI supported in both polycarbonate (PC) and polyimide (PI) films were demonstrated using cross-sectional analyses performed with a dual-beam workstation (FIB/SEM Tomography). Moreover, by varying the fluence of the laser beam, it is possible to control the width of the PANI arrays, and large areas (mm2 - cm2) could be patterned. Additionally, electrical resistance measurements of the individual PANI strips demonstrated that electrical properties of unmodified regions remain unchanged.
Flash lamp annealing in the millisecond regime of heteroepitaxial silicon carbide on silicon structures involves melting the Si below the SiC layer, but the deep facetted nature of the solid-liquid interface leads to unacceptable surface roughness. This paper describes a method of controlling melting by implanting a high dose of carbon or germanium at a controlled depth below the Si/SiC interface, which significantly alters the melting characteristics of the silicon. Results confirm the effectiveness of these approaches for increasing surface uniformity, making liquid phase processing compatible with standard device fabrication techniques. A thermal model has also been developed to describe this process and results indicate that the theoretical work is consistent with the experimental evidence. The model is a valuable tool for predicting onset of melting, maximum temperatures and process windows for liquid phase epitaxy.
Ni-Ti surface alloy was prepared by ion-implanting Ni into Ti. The surface film was amorphous having a Ni surface content of 10–40 at.%. The material was compared with a Ni-Ti bulk alloy (44.08:55.9) regarding their redox and electrocatalytic behavior in NaOH by cyclic voltammetry. The surface was characterized by x-ray photoelectron spectroscopy, x-ray and electron diffraction, transmission electron microscopy, and atomic force microscopy. The ion-implanted material revealed an enhanced activity toward the redox conversion of Ni(OH)2 ↔ NiOOH and the anodic oxidation of glucose. The effect is discussed considering the enhanced generation of active Ni surface sites from amorphous Ni and the stabilization of higher valence Ni by Ti.
Ni was surface-alloyed with Si by ion implantation. The material was examined for its redox and electrocatalytic behavior in NaOH by cyclic voltammetry. The surface was characterized by x-ray photoelectron spectroscopy, x-ray and electron diffraction, and electron and atomic force microscopy. The ion implantation enhanced activity toward the redox conversion of Ni(OH)2 ↔ NiOOH and the anodic oxidation of glucose reached about 3.5 times and about 2.8 times, respectively. The material is an amorphous mixed oxide of Ni and Si. The effect is discussed considering the true surface area and the generation of active surface sites in relation to the oxygen evolution.
Thin films Ni−Ti (<100 nm) having surface Ni content below 5 at.% were prepared by ion-implanting Ni into Ti surfaces. The Ni-containing phase exposed or buried within the Ti matrix was amorphous. Following an anodic oxidation in NaOH, the material was shown to be redox active and to promote the electrocatalytic oxidation of glucose depending on the surface Ni–Ti composition. Compared to the Ni–Ti bulk alloy (55.9:44.08), the Ni-implanted Ti displayed a more efficient catalytic activity and improved corrosion resistance.
The formation of cavity microstructures in silicon following helium implantation (10 or 40 keV; 1×1015, l×1016 and 5×1016 cm−2) and annealing (800 °C) is investigated by means of Transmission Electron Microscopy (TEM), Rutherford Backscattering Spectrometry and Channeling (RBS/C), and Elastic Recoil Detection (ERD). The processes of cavity nucleation and growth are found to depend critically on the implanted He concentration. For a maximum peak He concentration of about 5×1020 cm−3 the resulting microstructure appears to contain large overpressurized bubbles whose formation cannot be accounted by the conventional gas-release model and bubble-coarsening mechanisms predicting empty cavities. The trapping of Fe and Cu at such cavity regions is studied by Secondary Ion Mass Spectrometry (SIMS).
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