A comprehensive understanding of the dynamics and solidification of biomolecular condensates is closely tied to analysis of their mechanical characteristics. Despite recent technical advances in rheological studies of condensates, these still vastly rely on methods restricted to small forces, rendering measurements of droplets with higher elasticities and after transition to solids challenging. In this work, we develop assays for in-depth mechanical characterization of biomolecular condensates by scanning probe microscopy. We demonstrate this technique by measuring the rheological behavior of heterotypic poly-L-lysine heparin condensates, showcasing their multi-route transition from liquid-like to gel as well as their rejuvenation by chemical alterations of the medium. Due to the widespread application of scanning probe microscopy in biological fields, its capability for rapid, high-throughput, high-force range studies, and integration with nanoscale morphological measurements, our probe-based method is a significant step toward advancing the understanding of condensate behavior, leading to accelerated development of therapies.

A silver microelectrode with a diameter of 30 μm in an aqueous K 2 SO 4 electrolyte was irradiated with 55 fs and 213 fs laser pulses.This caused the emission of electrons which transiently charged the electrochemical double layer.The two applied pulse durations were significantly shorter than the electron-phonon relaxation time.The laser pulse durations had negligible impact on the emitted charge, which is incompatible with multiphoton emission.On the other hand, the observed dependence of emitted charge on laser fluence and electrode potential supports the thermionic emission mechanism.

Ultrashort pulse laser induced processes in the nanotechnology at interfaces are presented. A special focus is placed on femtosecond far field investigations of defect generation in solids [1-4] and on electrochemical in-situ techniques in graphene nanosheet synthesis [5]. Further, deterministic nanostructuring of solids and hot electron electrochemistry is discussed [6]. Apertureless scanning near-field nanolithography with a femtosecond Yb-doped fiber laser oscillator allows non-thermal electromagnetic energy transfer [7]. [1] W. Kautek and O. Armbruster, Springer Series in Materials Science 191 (2014) 43-66. [2] O. Armbruster, A. Naghilou, M. Kitzler, W. Kautek, J. Phys. Chem. C 119 (2015) 22992−22998. [3] O. Armbruster, A. Naghilou, M. Kitzler, W. Kautek, Appl. Surf. Sci. 396 (2017) 1736–1740. [4] A. Naghilou, O. Armbruster, W. Kautek, Appl. Surf. Sci. 418 (2017) 487-490. [5] M. Pfaffeneder-Kmen, I. Falcon Casas, A. Naghilou, G. Trettenhahn, W. Kautek, Electrochim. Acta 255 (2017) 160-167. [6] O. Armbruster, H. Pöhl, W. Kautek, (2018), in publication. [7] I. Falcón Casas, W. Kautek, Nanomaterials 8 (2018) 536

Laser nano- and micromachining exhibits multiple technological applications particularly in cyber physical production systems, where the integrity of production processes has to be maintained (e.g. in the implementation of Industry 4.0). Key characteristics of laser processing, such as the ablation threshold was commonly related to the fundamental parameters (fluence, pulse number, and irradiated area) by empirical adaptation and optimization. The description of the pulse number dependence (incubation, laser-induced defects) and the irradiation area dependence (intrinsic defects) of the threshold fluence still resorts to phenomenological models. This deficit can be resolved by a combined description of pulse number and beam radius based on a model involving high density and low density defects in the solid material. This extended defect model can describe single and multiple nanosecond and femtosecond pulse ablation experiments on various technological materials such as polystyrene, monocrystalline silicon, and stainless steel. While this model allows a quantification of the laser-induced threshold fluence in dependence of pulse number (incubation) and irradiated area (beam radius), the physical mechanisms involved in the interaction between light and defects, be it intrinsic or laser-generated, are still marginally understood. Further experimental and theoretical effort in this direction is aiming at the provision of the deterministic understanding required in any field applying intense laser light with multiple pulses and various spot sizes, which is essential in e.g. laser cutting, drilling, marking, engraving, hardening, and welding.

In this work, we present structured capillaries that were inspired by the microstructures of the external scent efferent system as found in different European true bug species (Pentatomidae and Cydnidae). These make use of small, orientated structures in order to facilitate fluid movement towards desired areas where defensive substances are evaporated. Gland channels and microstructures were investigated by means of scanning electron microscopy and abstracted into three-dimensional models. We used these models to create scent channel replicas from different technical substrates (steel and polymers) by means of laser ablation, laser structuring and casting. Video analysis of conducted fluid-flow experiments showed that bug-inspired, artificial scent fluid channels can indeed transport different fluids (water solutions and oils/lubricants) passively in one direction (velocities of up to 1 mm s−1), while halting the fluid movement in the opposite direction. At the end of this contribution, we present a physical theory that explains the observed fluid transport and sets the rules for performance optimization in future work.

Miniaturized pacemakers with a surface consisting of a Ti alloy may have to be removed after several years from their implantation site in the heart and shall, therefore, not be completely overgrown by cells or tissue. A method to avoid this may be to create at the surface by laser-ablation self-organized sharp conical spikes, which provide too little surface for cells (i.e., fibroblasts) to grow on. For this purpose, Ti-alloy substrates were irradiated in the air by 790 nm Ti:sapphire femtosecond laser pulses at fluences above the ablation threshold. The laser irradiation resulted in pronounced microstructure formation with hierarchical surface morphologies. Murine fibroblasts were seeded onto the laser-patterned surface and the coverage by cells was evaluated after 3–21 days of cultivation by means of scanning electron microscopy. Compared to flat surfaces, the cell density on the microstructures was significantly lower, the coverage was incomplete, and the cells had a clearly different morphology. The best results regarding suppression of cell growth were obtained on spike structures which were additionally electrochemically oxidized under acidic conditions. Cell cultivation with additional shear stress could reduce further the number of adherent cells.

Laser spot size and pulse number are two major parameters influencing the ablation of solids. The extended defect model describes the dependence of the threshold fluence on the basis of high and low density defects. This model was successfully applied to silicon and stainless steel. It is demonstrated that heat accumulation cannot describe the.experimental results. (C) 2016 Published by Elsevier B.V.

The neotropical flatbug species Dysodius lunatus and Dysodius magnus show a fascinating camouflage principle. Its appearance renders the animal hardly visible on the bark of trees. However, when getting wet due to rain, bark changes its colour and gets darker. In order to keep the camouflage effect, it seems as if some Dysodius species benefit from their ability to hold a water film on their cuticle and therefore change their optical properties when wetted by water too. This camouflage behaviour requires the insect to have a hydrophilic surface and passive surface structures, which facilitate the liquid spreading. Here we show morphological and chemical characterisations of the surface, especially the cuticular waxes of Dysodius magnus. Scanning electron microscopy revealed that the animal is covered with pillar-like microstructures which in combination with a surprising chemical hydrophilicity of the cuticle waxes, render the bug almost superhydrophilic: Water spreads immediately across the surface. We could theoretically model this behaviour assuming the effect of hemi-wicking (a state in which a droplet sits on a rough surface, partwise imbibing the structure around). Additionally the principle was abstracted and a laser patterned polymer surface, mimicking the structure and contact angle of Dysodius-wax, shows exactly the behaviour of the natural role model – immediate spreading of water and the formation of a thin continuous water film changing optical properties of the surface.

Ultrashort pulse laser interaction with nitrogen-doped type I-b diamond was investigated with near-infrared femtosecond laser pulses at repetition rates of 5kHz and 11MHz. High spatial frequency laser-induced periodic surface structures with periodicities of 50 and 200nm were generated perpendicular to the polarization of the electric field. The novel 50nm features are found to be due to a phase transition from crystalline diamond to a graphitic phase in contrast to the 200nm laser-induced periodic surface structures consisting still of crystalline material.

Pulse laser ablation experiments at semiconductor-grade silicon (111) and SAE 304 stainless steel were performed with femto- and nanosecond pulse durations. Threshold fluences in dependence of beam radius (1.6-100 mu m) and density of low -density defects (LDDs) have been determined for both materials and pulse durations. The experimental findings are supported by a recent quantitative model describing the strong dependence of the modification/ablation/damage threshold fluence on beam radius and pulse number. The importance of LDDs in the ablation mechanism has been confirmed. (C) 2016 Elsevier B.V. All rights reserved.

A non-destructive, in-line, and low-cost focusing device based on an image sensor has been developed and demonstrated. It allows an in situ focus determination for a broad variety of laser types (e.g. cw and pulsed lasers). It provides stringent focusing conditions with high numerical apertures. This approach does not require sub-picosecond and/or auxiliary lasers, or high fluences above damage thresholds. Applications of this system include, but are not limited to the laser-illumination of micro-electrodes, pump-probe microscopy on thin films, and laser ablation of small samples without sufficient surface area for focus determination by ablation. An uncertainty of the focus position by an order of magnitude less than the respective Rayleigh length could be demonstrated.

Short pulse laser irradiation has the ability to bring a material into a state of strong electronic, thermal, phase, and mechanical nonequilibrium and trigger a sequence of structural transformations leading to the generation of complex multiscale surface morphologies, unusual metastable phases, and microstructures that cannot be produced by any other means. In this article, we provide an overview of recent advancements and existing challenges in the understanding of the fundamental mechanisms of short pulse laser interaction with materials, including the material response to strong electronic excitation, ultrafast redistribution and partitioning of the deposited laser energy, the peculiarities of phase transformations occurring under conditions of strong superheating/undercooling, as well as laser-induced generation of crystal defects and modification of surface microstructure.

The spot size dependence of pulse laser-induced ablation thresholds of solid materials cannot be satisfactory described by the two existing quantitative models based on defect densities and on heat accumulation. In the present study, the heat accumulation model was amended but still yielded results in contradiction to experimental observations. The existing defect model was extended to account for incubation where optically active high-density defects with a separation below the radiation wavelength are generated. The reduction of the threshold for large beam radii could be ascribed to the laser spot covering a finite number of optically active low-density defects (LDD) embedded in the matrix material. This new generic model combining the spot size and pulse number dependence of femtosecond pulse laser-induced ablation thresholds was demonstrated with high-impact polystyrene. The average distance of the optically active LDD obtained from the generic model could be confirmed by scanning electron microscopy.

The absorption of sub-picosecond pulse laser radiation by the electronic system of dielectrics and metals leads to non-thermal processes such as ballistic transport, electron–electron collision, and electron emission across interfaces. Multi-photon excitation and impact ionization with subsequent avalanche ionization occur in dielectrics and single photon absorption in metals. Finally, electron–phonon-scattering sets in, electrons and lattice equilibrate, and thermal phenomena take over. The state of the current understanding of non-thermal phenomena is reviewed.

The mechanisms of graphite particle and polystyrene-co-divinyl benzene microsphere removal from flat polycarbonate substrates by nanosecond pulse laser interaction at 532 nm were studied both experimentally and theoretically. These model contaminants exhibited an extremely contrasting behavior in respect to phase separation and collateral damage to the polycarbonate substrate. Opaque graphite particles within the irradiated spot area either desorbed due to their thermal expansion or undertook vaporization/ablation. The transparent polystyrene microspheres caused local ablation of the substrate in their optical near-field. This process led to the removal of the particles, but eradicated the available cleaning fluence window. The opaque graphite particles, on the other hand, showed efficient clearance, particularly in a practicable cleaning window above 0.5 J/cm(2) and low pulse numbers of about two. Besides the mechanisms occurring within the irradiated spot, a separation process in the proximity beyond the laser spot (more than double the Gaussian radius) could be related to the action of high-amplitude surface acoustic waves (SAW). A minimum surface acceleration of 10(9) cm/s(2) was calculated to be sufficient to overcome the adhesion forces in this particle separation model.

The separation mechanism of opaque and transparent model micro-particles, graphite and polystyrene copolymer spheres, respectively, from polymethyl methacrylate (PMMA) substrates were investigated employing a ns-pulse laser radiating at 532 nm. The particles transparent in the visible wavelength range could be removed from PMMA efficiently in a very narrow fluence range between 1 and 2 J/cm(2) according to a simple 1D thermal expansion model. Above this fluence region, with single pulses, the transparent microspheres caused local ablation of the PMMA substrate in the optical microlens nearfield. This process led to removal of the particles themselves due to the expansion of the ablation plasma. The irregularly shaped graphite particles shaded the underlying substrate from the incoming radiation so that no optical nearfield damage mechanism could be observed. Therefore, a substantial cleaning window between 0.5 and more than 16 J/cm(2) was provided. The graphite data suggest an ablation mechanism of the particulates themselves due to a high optical absorption coefficient.

We investigate the dielectric response of solar cell devices based on oxygen-doped poly(3-hexylthiophene):[6,6]-phenyl-C-61-butyric acid methyl ester (P3HT:PCBM) blends as a function of temperature between 133 K and 303 K. The spectra are analyzed using a recently introduced model [O. Armbruster, C. Lungenschmied, and S. Bauer, Phys. Rev. B 84, 085208 (2011)] which is based on a trapping and reemission mechanism of charge carriers. A dominating trap depth of 130 meV is determined and the broadening of this trap level identified as purely thermal. In addition we estimate the density of charge carriers after doping as well as their mobility. We show that the concentration of mobile holes approximately doubles by heating the device from the lowest to the highest measured temperature. This is indicative of a second, shallow trap level of approximately 14 meV. Dielectric spectroscopy hence proves to be a valuable tool to assess device parameters such as dopant concentration, charge carrier transport characteristics, and mobility which are of crucial interest for understanding degradation in organic semiconductor devices.