Discrete model for laser driven etching and microstructuring of metallic surfaces

We present a unidimensional discrete solid-on-solid model evolving in time using a kinetic Monte Carlo method to simulate micro-structuring of kerfs on metallic surfaces by means of laser-induced jet-chemical etching. The precise control of the passivation layer achieved by this technique is responsible for the high resolution of the structures. However, within a certain range of experimental parameters, the microstructuring of kerfs on stainless steel surfaces with a solution of $\mathrm{H}_3\mathrm{PO}_4$ shows periodic ripples, which are considered to originate from an intrinsic dynamics. The model mimics a few of the various physical and chemical processes involved and within certain parameter ranges reproduces some morphological aspects of the structures, in particular ripple regimes. We analyze the range of values of laser beam power for the appearance of ripples in both experimental and simulated kerfs. The discrete model is an extension of one that has been used previously in the context of ion sputtering and is related to a noisy version of the Kuramoto-Sivashinsky equation used extensively in the field of pattern formation.Comment: Revised version. Etching probability distribution and new simulations adde

MEXEM – Mars Exposed Extremophile Mixture – a space experiment to investigate the capability of anaerobic organisms to survive on Mars

Assessing the habitability of Mars and detecting life, if it ever existed there, depends on knowledge of whether the combined environmental stresses experienced on Mars are compatible with life as we know it and whether a record of that life could ever be detected. So far, only few investigations were performed to understand the combined effect of different environmental stresses on survival and growth of anaerobic and extremophilic organisms. In the space experiment MEXEM (formerly known as MASE-in-SPACE) the hypothesis will be tested that selected terrestrial organisms, enrichment cultures and original samples from extreme Mars-analogue environments on Earth are able to withstand the Martian environ- mental stress factors due to their highly effective cellular and molecular adaptation and repair mechanisms. In addition, artificially fossilized and aged isolates from Mars-analogue environments on Earth will be examined and assessed with respect to their suitability for biosigna- ture identification. MEXEM samples will be (i) oxygen-depleted natural sediment samples, (ii) natural sediments spiked with selected, defined strains representative for the respective analogue site, (iii) individual (facultative) anaerobic / micro-aerophilic species including ciliates and viruses, (iv) defined mixtures of these biological entities, (v) isolated strains from samples collected inside the ISS and (vi) artificially fossilized isolates from the natural environments. Most of these samples and isolates were obtained from Mars-analogue envi- ronments on Earth in the frame of the EC funded project MASE (Grant Agreement 607297) and from the space experiment EXTREMOPHILES (PI C. Moissl-Eichinger). MEXEM will be flown outside on the ISS in the new exobiology facility ESA is building now. It offers the possibility to simulate of the martian environment, in particular the martian UV cl e, which cannot be done in the lab, but also martian atmosphere and pressure in LEO

Pattern formation during microstructuring of metals in acidic etchants with laser-jet-technique

Laser-jet-etching is a technique to cut and microstructure stainless steel in sulphuric and phosphoric acid where a laser induces a thermochemical wet etching reaction. Several dynamical regimes and bifurcations are observed by measurement of the electrochemical potential and the reflected laser light during the process. In dependency on the control parameters feed velocity, laser power, jet velocity and applied potential the reaction exhibits either a fix point or an oscillating behaviour. In the oscillating regime the kerfs show a periodic ripple structure. The electrochemical potential (active, passive) and the topology of the interface in the micrometer and nanometer scale are important order parameters. The formation of the ripples is caused by an interface instability and changes of the roughness in the nanometer range. Both give rise to a feedback of the reaction on the absorption of the laser and results in synchronous oscillations of the potential and the reflected laser

Strukturbildung beim Mikrostrukturieren von Metallen in sauren Ätzmitteln mit dem Laser-Jet-Verfahren

Laser-jet-etching is a technique to cut and microstructure stainless steel in sulphuric and phosphoric acid where a laser induces a thermochemical wet etching reaction. Several dynamical regimes and bifurcations are observed by measurement of the electrochemical potential and the reflected laser light during the process. In dependency on the control parameters feed velocity, laser power, jet velocity and applied potential the reaction exhibits either a fix point or an oscillating behaviour. In the oscillating regime the kerfs show a periodic ripple structure. The electrochemical potential (active, passive) and the topology of the interface in the micrometer and nanometer scale are important order parameters. The formation of the ripples is caused by an interface instability and changes of the roughness in the nanometer range. Both give rise to a feedback of the reaction on the absorption of the laser and results in synchronous oscillations of the potential and the reflected laser

A Flexible Micro-Electrode Array with an Embedded Flexible CMOS-Chip for Medical Applications

Micro-electrodes and micro-electrode arrays are essential in a variety of medical applications like deep brain stimulators, cochlear implants or retinal implants. To have a close interface to the human tissue for stimulating neurons or recording action potentials, these micro-electrode arrays must be flexible and should have a large area and a large number of electrodes. In order to electrically connect such large electrode numbers in implantable devices with integrated electronics, simple wiring is no longer possible. In fact to reduce the number of conductor paths, electrodes have to be connected via a bus system. Therefore it is necessary to bring CMOS circuitry in close proximity to the stimulation electrodes, by this forming an "intelligent electrode". To keep the system flexible th e silicon chips have to be thinned. In this paper the design and fabrication steps of such a flexible intelligent implantable MEAsystem and results on mechanical and electrical properties are presented. Furthermore, alternatively coating of the electrodes with carbon nanotubes by electrophoresis has been investigated and will be presented

MARSBOx: Fungal and Bacterial Endurance From a Balloon-Flown Analog Mission in the Stratosphere

Whether terrestrial life can withstand the martian environment is of paramount interest for planetary protection measures and space exploration. To understand microbial survival potential in Mars-like conditions, several fungal and bacterial samples were launched in September 2019 on a large NASA scientific balloon flight to the middle stratosphere (∼38 km altitude) where radiation levels resembled values at the equatorial Mars surface. Fungal spores of Aspergillus niger and bacterial cells of Salinisphaera shabanensis, Staphylococcus capitis subsp. capitis, and Buttiauxella sp. MASE-IM-9 were launched inside the MARSBOx (Microbes in Atmosphere for Radiation, Survival, and Biological Outcomes Experiment) payload filled with an artificial martian atmosphere and pressure throughout the mission profile. The dried microorganisms were either exposed to full UV-VIS radiation (UV dose = 1148 kJ m⁻² ) or were shielded from radiation. After the 5-h stratospheric exposure, samples were assayed for survival and metabolic changes. Spores from the fungus A. niger and cells from the Gram-(–) bacterium S. shabanensis were the most resistant with a 2- and 4-log reduction, respectively. Exposed Buttiauxella sp. MASE-IM-9 was completely inactivated (both with and without UV exposure) and S. capitis subsp. capitis only survived the UV shielded experimental condition (3-log reduction). Our results underscore a wide variation in survival phenotypes of spacecraft associated microorganisms and support the hypothesis that pigmented fungi may be resistant to the martian surface if inadvertently delivered by spacecraft missions