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Nanostructured surfaces exhibit remarkable chemical, physical and microbiological properties and have therefore various technical and industrial applications. The ultrashort laser pulse irradiation (wavelength λ = 355 nm, pulse duration Δtp = 12 ps, repetition rate f = 100 kHz) of copper samples with appropriate laser parameters results in the formation of a micro- and nanostructured surfaces. The influence of these hierarchically textured surfaces on the secondary electron yield (SEY) was studied especially with regard to their morphological and geometrical properties. Specific SEY changes are caused by both, the shape and the depth of the microstructures, as well as the morphology of the formed nanostructures; that can be either compact flower head-like nanostructures, non-compact filament-shaped nanostructures, molten and resolidified spherical structures, or minor modified surfaces. The measured SEY as a function of the primary electron energy is correlated with the surface topography that forms upon laser irradiation. The SEY decreases with increasing accumulated laser fluence and ablated volume, respectively. Especially flower-head-like nanostructures can be produced at high laser power (P ≥ 400 mW) and low scanning velocity (v ≤ 10 mm/s) and represent a surface with strongly reduced SEY maximum as low as 0.7.

The precise machining of silicon carbide composite (SiC–SiC) as a high-tech material with extraordinary characteristics is required for different applications in aerospace, light weight construction and car industry. Laser machining enable new approaches for fabrication processes but the regularly applied ablation processes can cause damage to the SiC–SiC material. Here we propose and demonstrate a new approach for gentle SiC–SiC machining making use of a laser-induced plasma for reactive species generation enabling chemical material removal processes. A fs-laser (775 nm, 150 fs, 1 kHz) was focussed to a CF4/O2 gas mixture igniting a laser-induced plasma (LIP) approximately 100 μm in front of a SiC–SiC sample. This LIP initiate material removal processes of the textured, multiphase SiC–SiC sample without a mechanical damage of the SiC–SiC composite structure. Different surface features such as etching of the cover SiC layer, etching of the SiC matrix and exposure, thinning and sharpen of the SiC fibres, underetching of the fibres has been observed. Across the whole etched area, no mechanical damage such as cracks, delamination's, broken fibres were observed so that a gentle machining process can be expected.

High-quality, ultra-precise processing of surfaces is of high importance for high-tech industry and requires a good depth control of processing, a low roughness of the machined surface and as little as possible surface and subsurface damage but cannot be realized by laser ablation processes. Contrary, electron/ion beam, plasma processes and dry etching are utilized in microelectronics, optics and photonics. Here, we have demonstrated a laser-induced plasma (LIP) etching of single crystalline germanium by an optically pumped reactive plasma, resulting in high quality etching. A Ti:Sapphire laser (λ = 775 nm, EPulse/max. = 1 mJ, t = 150 fs, frep. = 1 kHz) has been used, after focusing with a 60 mm lens, for igniting a temporary plasma in a CF4/O2 gas at near atmospheric pressure. Typical etching rate of approximately ~ 100 nm / min and a surface roughness of less than 11 nm rms were found. The etching results were studied in dependence on laser pulse energy, etching time, and plasma – surface distance. The mechanism of the etching process is expected to be of chemical nature by the formation of volatile products from the chemical reaction of laser plasma activated species with the germanium surface. This proposed laser etching process can provide new processing capabilities of materials for ultra—high precision laser machining of semiconducting materials as can applied for infrared optics machining.

Ultrahigh-precision machining of glass is indispensable for optical component fabrication and therefore for applications. In this regard, plasma jet assisted chemical etching technologies enable new fabrication processes for enhanced optical functionalities due to their deterministic localized machining capabilities. This technique has been successfully applied to fused silica and silicon. However, applications require specific glass properties are related to complex material compositions of the glass. Hence, reactive plasma etching of these optical glasses is a challenging task. For instance, etching of metal oxide containing glass like N-BK7 by a fluorine-based reactive atmospheric plasma jet (RAPJ) exhibits currently limitations due to the formation of non-volatile reaction products that remain on the glass surface as a layer. Therefore, a procedure consisting of RAPJ etching and laser ablation is proposed for the machining of N-BK7. The capability of laser-based removal of residual layers is compared to water-based solving of the residual layer. After RAPJ etching of N-BK7 using a CF4–O2 gas mixture with an average microwave power of 16 W, the samples are cleaned either by a water-based solvent or by the ablation with a nanosecond-pulsed ultraviolet laser. The laser irradiation with fluences of 2.8 J/cm2 results in a localized removal of the residual layer. It is demonstrated that the roughness of the laser-cleaned N-BK7 surface is similarly low as solvent-based cleaned samples but the pulsed laser enhanced cleaning allows a dry processing at atmospheric pressure as well as a localized processing with a high lateral resolution.

The surface treatment of carbon fiber/epoxy composites with a pulsed infrared (1064 nm wavelength) nanosecond (7 ns pulse duration) laser has been investigated. It is found that single 1064 nm lase...

Ultrashort-pulse laser processing of copper is performed in air to reduce the secondary electron yield (SEY). By UV (355 nm), green (532 nm), and IR (1064 nm) laser-light induced surface modification, this study investigates the influence of the most relevant experimental parameters, such as laser power, scanning speed, and scanning line distance (represented as accumulated fluence) on the ablation depth, surface oxidation, topography, and ultimately on the SEY. Increasing the accumulated laser fluence results in a gradual change from a Cu[Formula: see text]O to a CuO-dominated surface with deeper micrometer trenches, higher density of redeposited surface particles from the plasma phase, and a reduced SEY. While the surface modifications are less pronounced for IR radiation at low accumulated fluence ([Formula: see text] J/cm[Formula: see text]), analogous results are obtained for all wavelengths when reaching the nonlinear absorption regime, for which the SEY maximum converges to 0.7. Furthermore, independent of the extent of the structural transformations, an electron-induced surface conditioning at 250 eV allows a reduction of the SEY maximum below unity at doses of 5×10-4 C/mm[Formula: see text]. Consequently, optimization of processing parameters for application in particle accelerators can be obtained for a sufficiently low SEY at controlled ablation depth and surface particle density, which are factors that limit the surface impedance and the applicability of the material processing for ultrahigh vacuum systems. The relations between processing parameters and surface features will provide guidance in treating the surface of vacuum components, especially beam screens of selected magnets of the Large Hadron Collider or of future colliders.

High-quality, low-defect laser machining of dielectric materials remains challenging due to the high energy densities required for inducing the physical processes of laser ablation. Therefore, experiments were performed to demonstrate the laser-induced frontside etching (LIFE) of silicon by nanosecond laser pulses at a wavelength of 1550 nm, utilizing a thin chromium layer as the absorber. Etching was found at a fluence range from 200 to 700 mJ/cm², where the etched surfaces were smooth in the center (5 to 80 nm rms). The etching process was accompanied by incubation as well as saturation effects. At a fluence of 280 mJ/cm², an averaged etching rate of about 0.05 nm/pulse was determined for a high number of laser pulses (N > 1000). At the edges where the fluence was below the etching threshold of about 200 mJ/cm², chromium film melting and the formation of different kinds of laser-induced periodic surface structures (LIPSS) were observed. The LIFE was accompanied by different surface modifications. The optical absorption of silicon likely increased due to the incorporation of chromium into the silicon and the formed defects near the surface. Further, LIPSS were observed at fluences near the threshold of laser etching. In particular, the formation of regular linear ripples with a period of approximately 1.52 µm was observed. The morphological characteristics of the ripples suggest that the mechanism was related to surface scattering at surface features or small ripples and the hydrodynamic instabilities of the molten silicon. In addition, outside the etching track, periodic but nonlinear LIPSS were observed in the chromium film. These hexagonal arranged dot-like patterns had a period of around 440 nm. It is suggested that the hexagonal dot-like patterns resulted from the multi-pulse irradiation and the sequential stress relaxation in the chromium film below the melting point of chromium during spot movement.

High-quality submicron pattern formation in dielectrics by lasers is challenging, in particular with regard to large areas. Self-assembly and self-organization mechanisms, which arise from the interaction of the laser photons with the material of the sample, can provide conditions for efficient micron patterning of large surface areas. This study demonstrates the formation of submicron ripples in fused silica (SiO2) by nanosecond laser irradiation, which extends the category of lasers capable of the controllable manufacturing of laser-induced surface structures (LIPSS). A newly designed layer system was deposited on the surface of samples, comprising, on top of the dielectric substrate, an interlayer, an absorber, and a confinement layer. The samples were irradiated though the dielectric substrate with single nanosecond (λ = 1064) nm laser pulses. It was found that the period of the LIPSS can be tuned by changing the nanosecond laser energy, the confinement strength, and the laser pulse length from 5 ns to 25 ns. LIPSS with periods in the range of 400–600 nm, with a depth of up to 140 nm and with an orientation perpendicular to the polarization direction of the laser light, were found experimentally. The design of the sample finally enables an intra-pulse modification of the dielectric surface that provides temporal conditions near the dielectric substrate surface for surface plasmon polaritron (SPP) generation. The proposed mechanism of LIPSS formation thus comprises the ablation of the absorber layer and a plasma formation confined between the substrate surface and the confinement layer. This process causes a modification of the substrate surface. In consequence, temporary SPP generation occurs at the modified SiO2 surface, resulting in a lateral intensity modulation of the nanosecond laser beam within the pulse duration. This lateral intensity modulation of the laser pulse causes localized variation of the ablation, which finally results in the LIPSS found. The experimentally observed dependencies of the LIPSS period on the pulse energy, the confinement layer thickness, and the pulse length can be explained with the proposed model. The findings of this work provide a method of enabling local adjustment of the LIPSS period, which can be used in applications such as writing hierarchical structures of variable sizes.

The fabrication of sub-micron and nanopatterns at large surface areas by lasers is still a challenge, but the use of laser-induced, self-organized processes provides a promising approach. Here, the guided formation of nanodroplets ordered in two directions during irradiation of 15 nm thick molybdenum (Mo) film on Al2O3 (1–102) substrate with a fibre laser having a wavelength of 1064 nm and selectable pulse duration from 5 to 600 ns is demonstrated. The two-step process comprises laser-induced ripple formation and remelting of the ripples for nanodroplet generation. The ripples with period of ∼1.1 µm are oriented perpendicularly to the laser polarization. The ripples are fabricated by irradiation with 46 laser pulses with a duration between 25 to 100 ns and fluences of 0.3 to 1.3 J/cm², respectively. After a subsequent laser irradiation with 10 pulses at fluences above 1 J/cm² and a pulse duration of 100 ns, two kinds of Mo droplets are observed: (i) large, periodically ordered droplets with a diameter of ∼360 nm and a distance along and orthogonal to the laser-generated ripples of about 1 µm and 1.1 µm, respectively, in addition to (ii) small, less-ordered droplets with a size of about 120 nm localized in the former ripple valleys.

Experimental evidence for near-surface micro- and nanoscopic processes at ultrashort pulsed laser irradiation (wavelength 775 nm, pulse duration 150 fs) of soda-lime glass near the laser ablation threshold is acquired by transmission electron and secondary electron microscopy (SEM, TEM) as well as by energy disperse x-ray spectroscopy (EDX) investigations of laser-induced subsurface bubbles. Well separated laser irradiations result in individual micrometre bubbles while submicron bubble groups or asymmetrically damaged bubbles appear for overlapping pulses. The overlapping laser irradiations result in a direction dependent damage for the successive bubbles when the inter-pulse distance is small. TEM/SEM studies of cross sectioned bubble prove that precipitations and jets are formed in the centre of the micron bubbles’ bottom. This nano-jets inside the bubble can be related to the self-focusing of the femtosecond laser. A modified layer with a composition deviation from the bulk glass can be a key factor for the formation of the bubble with a thin shell about 100 nm. Moreover, next to the central main bubble, nanometre sized bubbles appear below the surface. Thermal processes inside the bubble cause a smooth inner surface as well as redeposited material mainly opposite to the jet formed at the bottom. The different glass composition near the surface strongly suggests that the altered glass surface composition contributes to the forming mechanism of these near-surface features. Implications of these sub-surface bubbles and jet formation for laser ablation related applications comprise incubation as well as roughness development that limits the achievable precision.

Atmospheric pressure plasma jet machining technology not only provides a flexible and efficient way to generate and correct optical freeform surfaces made of fused silica, it can also be applied as a surface smoothing or polishing technique. Thermal plasma jet treatment leads to softening and redistribution of the material. An accurate temperature regime during the process is inevitable to achieve a uniformly smoothed surface. The possibilities for inȭprocess temperature control are demonstrated. Surface roughness values can be significantly reduced by a factor of 1000 depending on the initial roughness of the ground surface.

Recently, plasma produced by focusing femtosecond laser in gases has been introduced as an etching tool in materials processing. Proper control of the plasma in this application necessitates the apt understanding of the different morphological features of the plasma. In this contribution we show that, the plasma produced in air goes through several stages of morphological development–from ellipsoidal to spherical to toroidal plasma, whereas in argon, axial compression of an ellipsoidal plasma is observed. To explain this dissimilarity, we have quantified the temperature by emission spectroscopy (Planck analysis with Wien’s approximation). The evolution of temperature shows a triple exponential dependence in time which can be correlated with different stages of morphological changes of the plasma. Open Source Field Operation and Manipulation simulations using experimentally determined temperature values show that—(i) the reverse pressure gradient propagates radially inwards and compresses the plasma in both air and argon and forms a localized high pressure zone at the center that generates a secondary pressure wave in air, but not in argon, and (ii) the baroclinic torque that is generated because of the Richtmyer–Meshkov instability, dominates the rate of vorticity in air, whereas effects of flow compressibility and velocity gradients dominate the vortices in argon. Knowledge of the initial state and the dynamics of the subsequent stages of the plasma formation can be utilized for control and optimization of laser-induced plasma applications.

The laser structuring of CIGS (copper indium gallium (di)selenide) solar cell material without influence and damaging the functionality of the active layer is a challenge for laser methods The shock-wave-induced thin-film delamination (SWIFD) process allows structuring without thermal modifications due to a spatial separation of the laser absorption from the functional layer removal process. In the present study, SWIFD structuring of CIGS solar cell stacks was investigated. The rear side of the polyimide was irradiated with a KrF-Excimer laser. The laser-induced ablation process generates a traverse shock wave, and the interaction of the shock wave with the layer-substrate interface results in a delamination process. The effect of a water confinement on the SWIFD process was studied where the rear side of the substrate was covered with a ∼2 mm thick water layer. The resultant surface morphology was analysed and discussed. At a sufficient number of laser pulses N and laser fluences Φ, the CIGS layer can be selectively removed from the Mo back contact. The water confinement, as well as the increasing laser beam size A0 and N, results in the reduction of the necessary minimal laser fluence Φth. Further, the delaminated CIGS area increased with increasing Φ, N, and A0.

The machining of optical glass materials with beam technologies enables novel fabrication processes for innovative optical elements with freeform surfaces. However, the complex material composition of optical glass such as N-BK7® is challenging for non-abrasive, pure chemical machining. N-BK7 can be machined utilizing reactive atmospheric plasma jet (RAPJ) etching. However, the etching mechanism results in process-inherent surface composition changes that limit potential applications of RAPJ-machining. A residues layer is formed which causes a temporally changing etching behavior and an increased roughness. Therefore, a process sequence of utilizing RAPJ etching and laser cleaning is proposed and demonstrated that enables to overcome the stated limitations. In this cyclic sequence, N-BK7 optical glass is etched first with a fluorine-containing reactive atmospheric plasma jet resulting in an etched but also residues-modified surface. Thereafter, the residues are removed by pulsed UV laser irradiation without ablation of the glass. This combined laser-enhanced reactive plasma jet etching allows etching of optical glass with a higher average etching rate and smoother machined surfaces.

The well-reproducible, fast and cost-effective nanostructuring is a big challenge for laser methods. The laser nanostructuring of fused silica assisted by chromium nanotriangles was studied using a KrF excimer laser (λ = 248 nm, Δtp = 25 ns, top hat beam profile). Therefore, a fused silica substrate was covered with periodically ordered polystyrene (PS) spheres with a diameter of 1.59 μm. Subsequently, this system was covered with 30 nm chromium by electron beam evaporation. Afterwards the PS spheres were removed and the bare and resultant periodic Cr triangles were irradiated. The laser irradiation with high laser fluences resulted in a removal of the chromium and in localized modifications of the fused silica like a localized ablation of the fused silica. The resultant structures were studied by scanning electron (SEM) and atomic force microscopy (AFM) as well as the surface composition was analysed by energy-dispersive X-ray spectroscopy (EDX). The laser process allows the production of well-defined periodic hole structures into the fused silica surface where the resultant surface structure depends on the laser parameters. The multi-pulse irradiation of the Cr/SiO2 sample with moderate laser fluences (Φ ∼ 650 mJ/cm2) allows the fabrication of periodic pyramidal-like structures (depth Δz = 130 nm).

The unique properties of halide perovskites are suitable for low-cost high-efficiency photovoltaic applications. For commercialization of this technology, it is pivotal to upscale towards solar modules. Monolithic interconnection of solar cells is a necessary step for realization of thin-film solar modules and the laser scribing of the constituent layers with well-defined profiles of high accuracy is a promising approach for high speed processing. Here the laser ablation and scribing of methylammonium lead iodide perovskite (CH3NH3PbI3: MAPbI3) layers are investigated. Nanosecond (ns) and picosecond (ps) laser pulses were used to ablate and scribe MAPbI3 films on FTO/glass by irradiation from the film- and the glass-side. Depending on the irradiation configuration laser ablation or lift-off delamination was determined to be the dominating mechanism of thin-film removal. Various surface modifications such as film smoothening and decomposition of the MAPbI3 have been observed, especially when nanosecond laser pulses are used. The complete removal of the MAPbI3, film without damaging the FTO/substrate, has been achieved for all studied laser sources.

Nanostructure formation on bulk metals (silver, gold, copper and titanium) by femtosecond Ti-sapphire laser irradiation (775 nm, 150 fs) is studied aiming the production of low-reflectivity surfaces and the better understanding of the development process. The experiments were performed in nitrogen, air, oxygen and helium environments at atmospheric pressure. The samples were irradiated with fluences in the 0.1–2 J/cm2 range and an average pulse number of 100 falling over a given area. The reflectivity of the treated surfaces was determined by a microspectrometer in the 450–800 nm range and their morphology was studied by scanning electron microscopy. The gas ambience influenced the results via two effects: formation processes and the chemically-induced modifications of the nanostructures. In case of He the nanoparticle aggregates–otherwise generally present–are predominantly missing, which leads to a lower darkening efficiency. The presence of oxygen enhances the darkening effect for copper mostly at lower fluences, while causes a slow increase in reflectivity in the case of titanium (in case of pure oxygen) in the high fluence range. The surface morphology in case of nitrogen and air were quite similar probably due to their close molecular mass values.

Nearly nothing is known about the consequences of ultra-long-distance running on knee cartilage. In this mobile MRI field study, we analysed the biochemical effects of a 4,486 km transcontinental multistage ultra-marathon on femorotibial joint (FTJ) cartilage. Serial MRI data were acquired from 22 subjects (20 male, 18 finisher) using a 1.5 T MR scanner mounted on a 38-ton trailer, travelling with the participants of the TransEurope FootRace (TEFR) day by day over 64 stages. The statistical analyses focused on intrachondral T2* behaviour during the course of the TEFR as the main outcome variable of interest. T2* mapping (sagittal FLASH T2* weighted gradient echo) is a validated and highly accurate method for quantitative compositional cartilage analysis of specific weightbearing areas of the FTJ. T2* mapping is sensitive to changes in the equilibrium of free intrachondral water, which depends on the content and orientation of collagen and the proteoglycan content in the extracellular cartilage matrix. Within the first 1,100 km, a significant running load-induced T2* increase occurred in all joint regions: 44.0% femoral-lateral, 42.9% tibial-lateral, 34.9% femoral-medial, and 25.1% tibial-medial. Osteochondral lesions showed no relevant changes or new occurrence during the TEFR. The reasons for stopping the race were not associated with knee problems. As no further T2* elevation was found in the second half of the TEFR but a decreasing T2* trend (recovery) was observed after the 3,500 km run, we assume that no further softening of the cartilage occurs with ongoing running burden over ultra-long distances extending 4,500 km. Instead, we assume the ability of the FTJ cartilage matrix to reorganize and adapt to the load.

Central to the use of Ge-Sb-Te based phase-change materials for data storage applications is their crystallization capability since it determines memory writing time. Although being intensively studied to identify intrinsic limits and develop strategies to enhance memory performance, the crystallization process in these materials is still not fully explored. Therefore, this study focuses on the determination of crystal growth dynamics in an epitaxial phase-change material thin film model system offering the advantage of high crystalline quality and application-relevant sizing. By introducing a method that combines time-resolved reflectivity measurements with high-resolution scanning transmission electron microscopy, crystal growth velocities upon fast cooling after single ns-laser pulse irradiation of the prototypical phase-change material Ge2Sb2Te5 are determined. As a result, an increase in crystal growth velocity from 0.4 to 1.7 m/s with increasing laser fluence is observed with a maximum rate of 1.7 m/s as the upper detectable limit of the studied material.

Metal surfaces can be nanostructured by laser irradiation making use of different effects ranging from thin film generation to nanostructures formation. Here, the colorization of pure nickel surfaces by nanosecond laser irradiation in air is demonstrated and studied in detail. Correlations between chromaticity coordinates and laser-processing parameter show that the accumulated fluence is the dominating factor in creation of a specific colored surface. The color of the laser-irradiated surfaces shows both angle-dependent and angle-independent in reliance on the processing conditions. The examination of the laser-colored surface demonstrates that lateral and vertical organized, laser-induced structures with nano-, micro-, and mesoscopic scales can be found simultaneously which contribute to the colorization in a particular manner. A comprehensive analysis of the processes involved in the color formation at nickel was performed by examining the surfaces by SEM, reflectometry, XPS, and XRD to verify the multi-process mechanisms of color formation. The most saturated colors result from interference effects within the redeposited layers. It was found that controlling the hatching distance applying optimized laser fluence enables a wider color range and allows a very precise setting of the color. Based on the extracted laser-processing parameters, the surface coloration of arbitrary pattern with desired optical properties becomes practicable, and nanosecond laser color marking can, therefore, be expanded to potentially new applications.

Background Pre-race determinants influencing performance and finishing of one of the largest transcontinental multistage ultramarathons were investigated. Methods Forty-four participants of the TransEurope FootRace 2009 (TEFR), running 4486 km in 64 stages (average 70.1 km daily) were analyzed regarding training and running history. This included years of regular endurance running (PRY), number of finished marathons, ultramarathons (UM) and multistage ultramarathons (MSUM), pre-race records (PRR) for marathon and specific UM races and the extent of pre-race training (PRT) in the last year before TEFR: volume (km/week), duration (h/week) and intensity (km/h). Results Mean total running speed during TEFR was 8.25 km/h.Seventy-one percent of subjects finished the race. The mean PRT-volume extends 5500 km. Finishers and non-finishers of the TEFR did not show significant difference in any tested pre-race determinants. There was no association between PRY, number of finished marathons, UM, and MSUM and TEFR performance. There was very strong positive correlation between PRT-intensity and TEFR performance. PRT volume correlated with a medium effect size to TEFR performance. PRR in specific ultra-races (6-hour, 50-km, 100-km races) showed a high correlation to TEFR performance. Performance in ultramarathon correlates inversely with age. Conclusions Like in other endurance disciplines with shorter distances, in ultra-long multistage endurance running the athletes also need a stage-specific pre-race experience, training and adaptation if he wants to end up with a good performance. But dropping out of a MSUM seems not to be consistent with regard to specific pre-race experience. Further research results of TEFR project may reveal potential risk factors for non-finishing a transcontinental footrace.

In this paper, LIPSS (laser-induced periodic surface structures) are generated on the K9 glass surface by using an ultrashort pulsed laser with pulse width of 8 ps, wavelength of 532 nm and repetition frequency of 1 KHz. Two kinds of LIPSS are generated on the surface of K9 glass, in the laser fluence range from 1.52 J/cm2 to 9.38 J/cm2 and pulse number from 1 to 50, namely low space frequency LIPSS (LSFL) and supra-wavelength periodic surface structures (SWPSS). When the laser fluence is increased, LSFL (F = 1.9 J/cm2 ~ 9.38 J/cm2) can be generated on the surface of K9 glass. LSFL with a period in the range of 480 nm to 510 nm are found with 1 to 20 pulses when the laser fluences higher than 1.9 J/cm2. For low pulse numbers, the depth of the LSFL structures grows with increasing pulse number. It is noticed that when the laser fluence reaches the threshold of the LIPSS (LSFL), the formation of the LIPSS happened together with the removal of the material surface. In other words, the ablation craters are formed gradually at higher pulse numbers with the laser fluence above the LIPSS formation threshold. Furthermore, the depth of the ablation crater is increased with higher pulse numbers, and SWPSS appear at the bottom of the crater. The period of SWPSS is 1.2 μm to 1.5 μm. The LSFL found in this paper can be used to reduce the reflection coefficient of the K9 material from 4% to less than 2.2 % at wavelengths above 1.2 μm.

In this work, the local structure of metastable Ge2Sb2Te5 (GST) phase change thin films crystallised by laser irradiation of amorphous GST films is studied by state-of-the-art aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM). By analysing simulated and experimental atomic-resolution Cs-corrected STEM images, a structure model for metastable GST is proposed. The GST lattice is described by a distorted rock-salt like structure with an ordered Te sublattice at the 4(a) site and a disordered sublattice of Ge, Sb and vacancies at the 4(b) site, where only a distorted octahedral atomic arrangement of Ge and Sb atoms exists without layered ordering of intrinsic vacancies. Additionally, no evidence for the presence of either tetrahedral Ge atoms in the GST lattice or an amorphous component at the grain boundaries is found. Moreover, a formation of vacancy layers in metastable GST in direction under the influence of focused electron beam irradiation is observed. These vacancy layers vanish during repeated scanning of the electron beam over these defects. The gained outcomes of this study shed new insight into understanding the atomic arrangement and phase change mechanism in GST thin films as well as the control of disorder in phase change materials.

The results of laser scribing experiments of CIGS thin films deposited on Mo-coated stainless steel sheets, using laser pulses with a wavelength of 1550 nm and a pulse duration of 6 ns, are presented in this study. It is shown that a removal of the CIGS from the Mo film is possible without edge melting of the CIGS or damaging of the Mo. The critical parameter for inducing the delamination lift-off process of the CIGS from the Mo was identified to be the scribing speed of the laser. In dependence on the laser parameters two different material removal processes were found. For a low pulse overlap the laser pulse penetrates the CIGS film and is absorbed in the interface between the CIGS and the Mo causing a lift-off process of the CIGS from the Mo back contact. For a high pulse overlap an ablation process starting from the top side of the CIGS film was found. The composition and morphology of the sample material after the laser patterning were analysed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and micro-Raman spectroscopy.

Self-organized processes are of special interest for the laser-induced nanostructuring of surfaces. In this study we combined two self-organized processes: the microsphere lithography and the molten phase transformation for the nanostructuring of dielectrics. A fused silica substrate was covered with periodically ordered polystyrene (PS) spheres and the system was subsequently covered with 30 nm chromium. Afterwards the PS spheres were removed and the bare and resultant periodic Cr triangles were irradiated in two steps using a KrF excimer laser. First step: A low laser fluence treatment results in a melting and shape transformation of the triangles. Second step: A high laser fluence treatment of the pre-treated surface results in a nanostructuring of the dielectric surface (and removal of the metal). The surface topography was studied by scanning electron microscopy. Furthermore, the different steps were simulated and compared with the experimental results.

Laser-induced etching techniques feature several unique characteristics that enable ultraprecise machining of transparent materials. However, LIBDE (laser-induced back side dry etching) and LIBWE (laser-induced back side wet etching) are preferentially studied due to experimental feasibilities either using a very thin or a bulk absorber at the rear side of the transparent material. This study aims to fill the gap by examining the thickness dependence of the absorbing material. Multi-pulse-LIBDE (MP-LIBDE) of fused silica using different thick photoresist absorber layers ( d L = 0.2–11.7 μm) was performed with a KrF excimer laser ( λ = 248 nm, t p ≈ 20 ns). The influence of several experimental parameters, such as laser fluence, pulse number, film thickness, on the ablation morphology and the etching rate were investigated. Especially at moderate fluences ( F = 0.7–1.5 J/cm 2 ) MP-LIBDE and LIBWE show several similar process characteristics such as the etching rate dependence on the laser fluence and the pulse number with a typical etching rate of approx. 12 nm at 1 J/cm 2 . However, the specific etching rate values depend on the absorber layer thickness, for instance. The morphology of the etched surface is smooth with a roughness of below 5 nm rms. Further, the modification of the surface has been observed and will be discussed in relation to the multi-pulse laser etching mechanism.

BackgroundThe optimum risk score determining perioperative mortality and morbidity in cardiac surgery remains debated. Advanced glycation end products (AGEs) derived from glycaemic and oxidative stress accumulate to a comparable amount in skin and the cardiovascular system leading to a decline in organ function. We aimed to study the association between AGE accumulation measured as skin autofluorescence (sAF) and the outcome of cardiac surgery patients.MethodsBetween April 2008 and November 2016, data from 758 consecutive patients undergoing coronary artery bypass grafting, aortic valve replacement or a combined procedure were analyzed. Skin autofluorescence was measured using an autofluorescence reader. Beside mortality, for the combined categorical morbidity outcome of each patient failure of the cardiac-, pulmonary-, renal- and cerebral system, as well as reoperation and wound healing disorders were counted. Patients without or with only one of the outcomes were assigned zero points whereas more than one outcome failure resulted in one point. Odds ratios (ORs) were estimated in multivariable logistic regression analysis with other preoperative parameters and the established cardiac surgery risk score systems EuroSCORE II and STS score.ResultsSkin autofluorescence as non-invasive marker of tissue glycation provided the best prognostic value in identifying patients with major morbidity risks after cardiac surgery (OR = 3.13; 95%CI 2.16-4.54). With respect to mortality prediction the STS score (OR = 1.24; 95%CI 1.03-1.5) was superior compared to the EuroSCORE II (OR = 1.17: 95%CI 0.96-1.43), but not superior when compared to sAF (OR = 6.04; 95%CI 2.44-14.95).ConclusionThis finding suggests that skin autofluorescence is a good biomarker candidate to assess the perioperative risk of patients in cardiac surgery. Since the EuroSCORE does not contain a morbidity component, in our view further sAF measurement is an option.

In this paper, laser-induced periodic surface structures (LIPSS) are created by a 532 nm picosecond laser with the pulse duration of 8 ps and the pulse repetition rate of 1 kHz on crystalline silicon. The number of the pulse and the fluence of the laser were changed in the experiment. With the same laser fluence, the uniformity of the ripples is improved by increasing the pulse number. With the same pulse number, the period of the ripples is increased by increasing the laser fluence. Morphologies of LIPSS are measured by AFM. Ripples oriented perpendicular to the polarization of the laser light with two different periods are found in one spot. The period of the LIPSS in the center is 1.38 μm, while it is 528.5 nm at the periphery of the spot. The height from peak to valley of the LIPSS in the center is 59.82 nm, while it is 33.58 nm at the periphery of the spot. It is found that, the laser-induced surface modifications can be classified into three different categories, including LIPSS molten, LIPSS and LIPSS not appear. The threshold of the laser fluence and pulse numbers for the formation of LIPSS is determined. LIPSS created on the crystalline silicon surface can improve material surface properties, e.g. reflectivity or wettability. Those properties have a far-reaching significance for potential application in many fields, such as solar energy utilization, specific wavelength absorption, image security, material lubrication and anti-corrosion.

In this paper, the authors report a method for continuous trench micromachining on polymethylmethacrylate (PMMA). Visible laser-induced backside wet etching (v-LIBWE) on PMMA using a potassium permanganate (KMnO4)-based absorber liquid was studied. PMMA is widely used in microfluidic devices for chemical and biological applications. Conventional micromachining of channels in the PMMA substrate using CO2 lasers achieves the smallest feature of approximately 85 μm. In this study, a continuous 12 μm-wide trench etching on PMMA was achievable by v-LIBWE using a 532 nm nanosecond pulsed laser. The etching threshold is ∼10 J/cm2, which corresponds to the average power of 58 mW for the repetition rate of 10 kHz. The authors also determined that the lowest scanning speed of 2 mm/s was necessary for the v-LIBWE of PMMA to generate the crack-free surface. Our study provides a new perspective and a convenient approach for the micromachining of the polymer substrate using v-LIBWE.

LIPSS (Laser Induced Periodic Surface Structures) formation at pre-patterned photoresist films was investigated using a partial polarized excimer laser beam (λ = 248 nm, tp = 20 ns). These line and dot pre-patterns were fabricated by the lithography in a photoresist films and have widths of 1–3 µm and 1–5 µm, respectively. LIPSS with a period of 195 nm and a direction along the laser polarization were formed at very low laser fluences (threshold 7 mJ/cm2) and high pulse numbers. With increasing fluence first LIPSS appear at the top surface, extend than to the sidewalls and finally at fluences higher than (F ∼ 17 mJ/cm2) found only at the sidewalls while the top surface is smooth. The height of the LIPSS increases with the pulse number and saturates at approximately 65 nm. The degree of LIPSS order depends on the alignment of the laser polarization to the pattern direction and shape. For parallel alignment of polarization and pattern edges, a high degree of order was found over several hundreds of micrometers along the stripe structure. This order mechanism can accept alignment mismatches up to 10°. This approach may serve as a general guideline for forming well-ordered LIPSS on large areas.

Electrochemical metallization memories have received much attention as candidates for next generation non-volatile memory applications, due to their fast switching speed, simple structure, high scalability and low energy consumption. Chalcogenide compounds like Ge–Sb–Te-based materials are extensively studied solid electrolytes for such devices and considered within the most promising candidates. In this work, the influence of different electrode materials on bipolar resistive switching characteristics of amorphous Ge–Sb–Te thin films with close composition to 2:2:5, prepared by pulsed laser deposition, is studied. Detailed investigations by current-voltage measurements, secondary ion mass spectrometry and cross-sectional transmission electron microscopy in conjunction with energy-dispersive x-ray spectroscopy are presented. Depending on the utilized electrode material, analog switching (Cu, Ag, Ti), digital switching (Co, Cr, Ta, Al) or no switching (Pt, Au and Cr-CrO x ) occurs. This work shows that the switching behavior of Ge–Sb–Te strongly depends on the solubility and reactivity of the electrode material.

The formation of bubbles near the surface of soda-lime glass induced by single pulse irradiation with Ti: Sapphire laser of a wavelength of 775 nm and 150 fs pulse duration below the laser ablation threshold is reported. The bubbles with a diameter of 0.3–3 µm are much smaller than the spot size of ~12 µm and exhibit a semi-spherical surface, an ellipsoidal void and an upper shell thickness of approx. 100 nm. The bubbles are formed in a narrow energy range between bulk glass modification and glass ablation. The bubbles formation is accomplished with some changes of the glass morphology around the bubbles. Damaged bubbles occur near the upper laser energy limit for bubbles formation that show nanoholes or slits in the bubbles shell and opened shells exposing the bottom of the void. It is suggested, that the bubble forming mechanism is related to nonlinear processes of laser photon absorption, laser-induced spallation processes, materials heating after electron relaxation, and thermal driven, viscoplastic-mechanical processes. Mainly the material composition gradient of the soda-lime glass near the surface that affects photon absorption, melting, ablation and material expansion processes enable the formation of these bubbles. The void inside the bubble is formed first by pre-spallation resulting in a detached layer that is lifted further forming the bubbles shell by subsurface laser ablation/evaporation processes of the bulk glass. The upper shell of the bubble is formed by a thermally stable crust of corroded soda-lime glass. The results may have valuable impact to laser ablation processes for high precision fabrication. Further, the fast fabrication of such 3D submicron structures due to the single pulse interaction with the glass enables new technical processes for potential applications in sensing, photonic or microfluidic.