Zeitschriftenaufsätze und Buchbeiträge

Fast energy release, which is a fundamental property of reactive multilayer systems, can be used in a wide field of applications. For most applications, a self-propagating reaction and adhesion between the multilayers and substrate are necessary. In this work, a distinct approach for achieving self-propagating reactions and adhesion between deposited Ni/Al reactive multilayers and silicon substrate is demonstrated. The silicon surface consists of random structures, referred to as silicon grass, which were created by deep reactive ion etching. Using the etching process, structure units of heights between 8 and 13 µm and density between 0.5 and 3.5 structures per µm^2 were formed. Ni and Al layers were alternatingly deposited in the stoichiometric ratio of 1:1 using sputtering, to achieve a total thickness of 5 µm. The analysis of the reaction and phase transformation was done with high-speed camera, high-speed pyrometer, and X-ray diffractometer. Cross-sectional analysis showed that the multilayers grew only on top of the silicon grass in the form of inversed cones, which enabled adhesion between the silicon grass and the reacted multilayers. A self-propagating reaction on silicon grass was achieved, due to the thermally isolating air pockets present around these multilayer cones. The velocity and temperature of the reaction varied according to the structure morphology. The reaction parameters decreased with increasing height and decreasing density of the structures. To analyze the exact influence of the morphology, further investigations are needed.

We report the first observation of the coupling of strong optical near fields to wavepackets of free, 100 eV electrons with <50 fs temporal resolution in an ultrafast point-projection microscope. Optical near fields are created by excitation of a thin, nanometer-sized Yagi-Uda antenna, with 20 fs near-infrared laser pulses. Phase matching between electrons and near fields is achieved due to strong spatial confinement of the antenna near field. Energy-resolved projection images of the antenna are recorded in an optical pump-electron probe scheme. We show that the phase modulation of the electron by transverse-field components results in a transient electron deflection while longitudinal near-field components broaden the kinetic energy distribution. This low-energy electron near-field coupling is used here to characterize the chirp of the ultrafast electron wavepackets, acquired upon propagation from the electron emitter to the sample. Our results bring direct mapping of different vectorial components of highly localized optical near fields into reach.

This article reports a new approach toward fabrication and directed assembly of nanoparticulate reactive system (Nanofoils) on patterned substrates. Different from current state-of-the-art, gas phase electrodeposition uses nanoparticles instead of atoms to form densely packed multilayered thin films at room temperature-pressure. On ignition, the multilayer system undergoes an exothermic self-propagating reaction. The numerous contact points between two metallic nanoparticulate layers aid in high heat release. Sub-10-nm Platinum (Pt) and Aluminum (Al) particles are synthesized through cathode erosion of metal electrodes in a flow of pure nitrogen gas (spark ablation). Pt/Al bilayer stacks with total thickness of 3-8 µm undergo self-propagating reaction with a 10.3 mm s^−1 wavefront velocity on local ignition. The reaction wavefront is captured using high speed videography. Calorimetry studies reveal two exothermic peaks suggesting Pt/Al alloy formation. The peak at 135 &ring;C has a higher calorific value of 150 mW g^−1 while the peak at 400 &ring;C has a 12 mW g^−1 exothermic peak. X-ray diffraction study shows reaction-products are cubic Al2Pt with small quantities of orthorhombic Al6Pt and orthorhombic AlPt2. Electron microscopy studies help draw a correlation between film morphology, bimetallic interface, nanoparticle oxidation, and self-propagating reaction kinetics that is significant in broadening our understanding towards nanoparticulate reactive systems.

Solid-state dewetting (SSD) of the immiscible Ag/Ni bi-layers was studied. After annealing at 400 &ring;C for 1 min, the Ag film was dewetted on the Ni film, and this is the first observation about the SSD of one metal film on another metal film. The easier dewetting of Ag than Ni was attributed to its lower melting point, faster grain boundary self-diffusion and poor wettability between them. At 500 &ring;C, the void formation in the bottom Ni layer was highlighted and compared to Ni single layer: many voids in the former while no visible voids in the latter, indicating that the presence of Ag accelerated the SSD of Ni. It was attributed to the vertical stress gradient in the bottom Ni film of Ag/Ni bi-layers, which accelerated the Ni diffusion and formation of the voids in the underlying Ni film around and below the Ag particles. Besides, voids were more easily formed below the Ag particles than between them due to the large lattice mismatch at the Ag/Ni interface and the possible formation of Ag-Ni alloys. The destabilization of the Ag on the Ni film contributes to the understanding of dewetting kinetics, which is beneficial to realize the controllable nanofabrication.

In this paper, the combination of an advanced nanopositioning technique and a tip-based system, which can be used as an atomic force microscope (AFM) and especially for field emission scanning probe lithography (FESPL) is presented. This is possible through the use of active microcantilevers that allow easy switching between measurement and write modes. The combination of nanopositioning and nanomeasuring machines and tip-based systems overcomes the usual limitations of AFM technology and makes it possible to perform high-precision surface scanning and nanofabrication on wafer sizes up to 4 in. We specifically discuss the potential of nanofabrication via FESPL in combination with the nanofabrication machine (NFM-100). Results are presented, where nanofabrication is demonstrated in form of a spiral path over a total length of 1 mm and the potential of this technique in terms of accuracy is discussed. Furthermore, ten lines were written with a pitch of 100 nm and a linewidth below 40 nm was achieved, which is in principle possible over the entire range of motion.