Prof. Dr. Evgeny L. Gurevich

Laser Applications Technology
Ruhr-Universität Bochum

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  • The effect of laser nitriding on surface characteristics and wear resistance of niti alloy with low power fiber laser
    Wang, H. and Nett, R. and Gurevich, E.L. and Ostendorf, A.
    Applied Sciences (Switzerland) 11 (2021)
    The laser nitriding was performed in nitrogen gas at room temperature (20◦ C) and low temperature (−190◦ C) by a low power fiber laser to modify the wear and abrasion resistance of NiTi alloy. The surface roughness and element composition were analyzed by roughness device and energy-dispersive X-ray spectroscopy respectively. The results of roughness show that laser treatment can change the surface roughness due to the laser remelting. The effect of laser nitriding on the microhardness, friction coefficient, and worn scars of NiTi alloy was also studied, which shows that the microhardness of the NiTi alloy increases after laser nitriding. The optical microscope and scanning electron microscope were used to characterize the surface of NiTi alloy after wear testing to observe the microstructure of worn scars. The results show that the laser nitriding with different parameters can induce a nitride layer with different thicknesses and the higher energy deposition is the key factor for the formation of the nitride layer, which can decrease the friction coefficient and reduce wear loss during the application of NiTi alloy. The improvement of wear resistance can be attributed to the hard nitriding layer. © 2021 by the authors. Li-censee MDPI, Basel, Switzerland.
    view abstract10.3390/app11020515
  • Corrosion behavior of NiTi alloy subjected to femtosecond laser shock peening without protective coating in air environment
    Wang, H. and Jürgensen, J. and Decker, P. and Hu, Z. and Yan, K. and Gurevich, E.L. and Ostendorf, A.
    Applied Surface Science 501 (2020)
    Laser shock peening with femtosecond laser was used to improve the corrosion resistance of biomedical NiTi alloy without protective coating in the air environment. The energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) based analysis showed that the laser ablation could produce titanium oxide layer and femtosecond laser shock peening (FsLSP) can generate residual stress in the surface layer of NiTi alloy. The FsLSP improved the corrosion resistance of NiTi in 3.5% NaCl solution and Hank's solution and also prevented the formation of corrosion cracks and pits during corrosion testing. The reasons for the improvement of corrosion behavior may be the generation of residual stress and titanium oxide film during the laser surface treatment. © 2019 Elsevier B.V.
    view abstract10.1016/j.apsusc.2019.144338
  • Femtosecond laser shock peening on the surface of NiTi shape memory alloy
    Wang, H. and Gurevich, E.L. and Ostendorf, A.
    Procedia CIRP 94 (2020)
    Laser shock peening with a femtosecond laser system was presented in this research work. The NiTi shape memory alloy was processed by the femtosecond laser shock peening (FsLSP) treatment without a protective layer in the air. Femtosecond laser shock peening is a new surface technology, which can induce an intense shock wave with low single laser pulse energy under atmospheric conditions. The surface topography, roughness, microhardness, and wear resistance were measured on the surface of NiTi alloy before and after femtosecond laser peening treatment. The results showed that the surface roughness and microhardness could be increased after femtosecond laser shock peening, which may be due to the laser ablation and micro-plastic deformation induced by the shock wave. The wear property of NiTi alloy was improved, which may be attributed to the FsLSPed surface texturing and enhancement of surface microhardness. © 2020 The Authors. Published by Elsevier B.V.
    view abstract10.1016/j.procir.2020.09.071
  • Influence of defects on structural colours generated by laser-induced ripples
    Maragkaki, S. and Skaradzinski, C.A. and Nett, R. and Gurevich, E.L.
    Scientific Reports 10 (2020)
    The colourisation of metallic surface which appears due to periodic surface patterns induced by ultrashort laser pulses is studied. Ripples due to the sub-micrometer size of their period act as a diffraction grating, generating structural colours. Carefully chosen strategy of the laser spot scanning allows us to mimic the nanostructures responsible for structural colours of some flowers on the metal substrate. We investigate the correlation between the colourising effects and the artificially-induced defects in the ripples structure and show that these defects can make the colours observable in a larger range of viewing angles. Further we address the influence of the processing parameters on the spectral profile of the reflected light. © 2020, The Author(s).
    view abstract10.1038/s41598-019-56638-x
  • Laser printing of plasmonic nanosponges
    Syubaev, S. and Gurbatov, S. and Modin, E. and Linklater, D.P. and Juodkazis, S. and Gurevich, E.L. and Kuchmizhak, A.
    Nanomaterials 10 (2020)
    Three-dimensional porous nanostructures made of noble metals represent novel class of nanomaterials promising for nonlinear nanooptics and sensors. Such nanostructures are typically fabricated using either reproducible yet time-consuming and costly multi-step lithography protocols or less reproducible chemical synthesis that involve liquid processing with toxic compounds. Here, we combined scalable nanosecond-laser ablation with advanced engineering of the chemical composition of thin substrate-supported Au films to produce nanobumps containing multiple nanopores inside. Most of the nanopores hidden beneath the nanobump surface can be further uncapped using gentle etching of the nanobumps by an Ar-ion beam to form functional 3D plasmonic nanosponges. The nanopores 10–150 nm in diameter were found to appear via laser-induced explosive evaporation/boiling and coalescence of the randomly arranged nucleation sites formed by nitrogen-rich areas of the Au films. Density of the nanopores can be controlled by the amount of the nitrogen in the Au films regulated in the process of their magnetron sputtering assisted with nitrogen-containing discharge gas. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/nano10122427
  • Laser shock peening on high-strength steel
    Wang, H. and Keller, S. and Bai, Y. and Kashaev, N. and Gurevich, E.L. and Ostendorf, A.
    Proceedings of SPIE - The International Society for Optical Engineering 11546 (2020)
    High strength steel has been used in the aviation industry and automotive body structural applications to reduce its mass through a reduction in thickness. Therefore, it is very important to enhance its mechanical property, such as microhardness. In the present research, the high strength steel samples were treated by laser shock peening (LSP) with different laser pulse energy and laser pulse width. The microhardness and residual stress were measured to compare the difference between laser energy of 3 J with 10 ns and 5 J with 20 ns. The results in the study show that the surface LSP treatment can increase the microhardness and the compressive residual stress can be found when the samples were tested by hole drilling testing. © 2020 SPIE.
    view abstract10.1117/12.2574988
  • Laser-induced surface relief nanocrowns as a manifestation of nanoscale Rayleigh-Plateau hydrodynamic instability
    Pavlov, D.V. and Gurbatov, S.O. and Kudryashov, S.I. and Gurevich, E.L. and Kuchmizhak, A.A.
    Applied Surface Science 511 (2020)
    Nanoscale hydrodynamic instability of ring-like molten rims around ablative microholes produced in nanometer-thick silver and gold films by tightly focused nanosecond (ns) laser pulses was experimentally explored in terms of laser pulse energy and film thickness. These parametric dependencies of basic instability characteristics - order and period of the resulting nanocrowns - were analyzed, revealing its apparently Rayleigh-Plateau character, as compared to much less consistent possible van der Waals and impact origins. Along with fundamental importance, these findings will put forward ns pulsed laser ablation as an alternative facile inexpensive table-top approach to study such hydrodynamic instabilities developing at ns temporal and nanometer spatial scales as well as to produce unique plasmon-active hierarchical surface morphologies applicable for chemo- and biosensing. © 2020 Elsevier B.V.
    view abstract10.1016/j.apsusc.2020.145463
  • Microhardness and microabrasion behaviour of NiTi shape memory alloy after femtosecond laser shock peening without coating in air
    Wang, H. and Gurevich, E.L. and Ostendorf, A.
    Proceedings of SPIE - The International Society for Optical Engineering 11273 (2020)
    The experiment study presents the influence of femtosecond laser shock peening (FsLSP) without a protective layer in the air on the surface hardness and surface mechanical property of NiTi shape memory alloy. Femtosecond laser shock peening is a new possibility of direct laser ablation without any protective layer under atmospheric conditions, which can produce intense shock waves with low pulse energy in the air. The average surface roughness values of the NiTi alloy samples were measured, because the surface roughness may affect its friction resistance. The results showed that the surface roughness of NiTi increased after femtosecond laser shock peening treatment. In comparison with the initial state, the coefficient of friction decreased and surface microhardness increased after femtosecond laser shock peening treatment with different FsLSP parameters. This improvement of wear properties may be attributed to the enhancement of surface microhardness and surface titanium oxide layer induced by the shock wave and laser ablation during FsLSP treatment. © 2020 SPIE.
    view abstract10.1117/12.2543550
  • Mode-locked diode laser-based two-photon polymerisation
    Surkamp, N. and Zyla, G. and Gurevich, E.L. and Klehr, A. and Knigge, A. and Ostendorf, A. and Hofmann, M.R.
    Electronics Letters 56 (2020)
    In this Letter, the authors present the construction of three-dimensional microstructures by two-photon polymerisation induced by ultrashort pulses of a mode-locked diode laser. The ultrafast light source is based on a diode laser with segmented metallisation to realise a waveguide integrated saturable absorber. It is subsequently amplified and compressed resulting in ultrashort laser pulses of 440 fs length and average output power of 160 mW at a fundamental repetition rate of 383.1 MHz. These pulses are coupled into a customised two-photon polymerisation setup. A series of suspended lines were fabricated between support cuboids for testing the process behaviour. A 3D structure with complex features was polymerised to demonstrate the high potential for mode-locked diode lasers in the field of direct laser writing. © The Institution of Engineering and Technology 2020.
    view abstract10.1049/el.2019.2385
  • Mode-locked diode lasers as sources for two-photon polymerization
    Surkamp, N. and Zyla, G. and Gurevich, E.L. and Esen, C. and Klehr, A. and Knigge, A. and Ostendorf, A. and Hofmann, M.R.
    Proceedings of SPIE - The International Society for Optical Engineering 11349 (2020)
    In this study, we use a hybrid mode-locked external cavity diode laser with subsequent amplification and pulse compression. The system provides laser pulses of 440 fs width (assuming a sech pulse shape) and 160 mW average output power at a repetition rate of 383.1 MHz. The laser oscillator consists of a double quantum well laser diode with a gain segment of 1080 μm length and an absorber element of 80 μm lengths. The chip's back facet is covered with a high reflective coating, the front facet with an anti-reflective coating. The resonator itself is operated in a collimated geometry and folded by two dielectric mirrors. The used output coupler provides a transmission of 20 percent, which is coupled into a tapered amplifier. Two Faraday isolators are used to decouple the laser and the amplifier from any back reflections. Subsequently, the pulses are compressed using a single pass Martinez type pulse compressor. Experiments on Two-Photon Polymerization were conducted on a conventional setup consisting of a 2D galvo-scanner system with an attached microscope objective. The oil immersion objective (NA =1.4) focusses the light pulses through a cover glass into a droplet of the photosensitive material. Process monitoring can be achieved by observing the image on a camera placed behind a semi-transparent mirror in front of the galvo-scanner. Using this experimental setup, test structures that consist of free-hanging lines supported by cuboids were produced. In addition, a procedure for automated linewidth measurements is outlined and used for analyzation of the generated structures. This work shows that mode-locked diode lasers can be used for the fabrication of microstructures by Two-Photon Polymerization. Typically used Ti:Sapphire or fiber lasers can be replaced by mode-locked diode lasers for Two-Photon- Polymerization. This allows for much cheaper Two-Photon-Polymerization systems and therefore, may open this field for more application-based research groups. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
    view abstract10.1117/12.2555890
  • Silicon microprotrusions with tailored chirality enabled by direct femtosecond laser ablation
    Syubaev, S. and Mitsai, E. and Porfirev, A. and Khonina, S. and Kudryashov, S. and Katkus, T. and Juodkazis, S. and Gurevich, E.L. and Kuchmizhak, A.
    Optics Letters 45 (2020)
    Here, we report on formation of nanoprotrusions on the surface of a bulk crystalline silicon wafer under femtosecond-laser ablation with a donut-shaped laser beam. By breaking circular symmetry of the irradiating donut-shaped fs-pulse beam, a switch in geometry of the formed surface nanoprotrusions from regular to chiral was demonstrated. The chirality of the obtained Si nanostructures was promoted with an asymmetry degree of the laser beam. An uneven helical flow of laser-melted Si caused by asymmetry of the initial intensity and temperature pattern on the laser-irradiated Si surface explains this phenomenon. Chirality of the formed protrusions was confirmed by visualizing cross-sectional cuts produced by focused ion beam milling as well as Raman activity of these structures probed by circularly polarized light with opposite handedness. Our results open a pathway towards easy-to-implement inexpensive fabrication of chiral all-dielectric nanostructures for advanced nanophotonic applications and sensing of chiral molecules. © 2020 Optical Society of America
    view abstract10.1364/OL.393979
  • Structural colors with angle-insensitive optical properties generated by Morpho-inspired 2PP structures
    Zyla, G. and Kovalev, A. and Gurevich, E.L. and Esen, C. and Liu, Y. and Lu, Y. and Gorb, S. and Ostendorf, A.
    Applied Physics A: Materials Science and Processing 126 (2020)
    This paper describes how two-photon polymerization was used to generate biomimetic nanostructures with angle-insensitive coloration inspired by the blue butterflies of Morpho. Less angle dependence was achieved by engineering the structures with a certain degree of disorder, which delimited them from classical photonic crystals. Variations in the processing parameters enabled the color hue to be controlled. In this context, blue, green, yellow, and brown structures were demonstrated. Reflection spectra of the structures were simulated and studied experimentally in a broad range of incident angles. Additionally, a molding technique was performed as a potential scale-up strategy. The application of such biomimetic structures is discussed. © 2020, The Author(s).
    view abstract10.1007/s00339-020-03931-6
  • Studies on ultra-short pulsed laser shock peening of stainless-steel in different confinement media
    Elango, K. and Hoppius, J.S. and Kukreja, L.M. and Ostendorf, A. and Gurevich, E.L.
    Surface and Coatings Technology 397 (2020)
    We investigate the role of liquid confinement media on ultra-short pulsed Laser Shock Peening (LSP). The LSP of stainless-steel 316 and 316 L was studied using Ti: Sapphire laser pulses of about 2 ps duration, maximum energy of about 1 mJ and pulse repetition rate of 5 kHz in different liquid confinement media of Ethanol, Deionized water and separate aqueous solutions of NaCl and Glycerol. It is found that the laser fluence and/or energy attenuating mechanisms like self-focusing, filamentation, plasma breakdown in the confinement media are less significant with ps laser pulses than those with sub-ps or fs pulse durations. It is shown that the resulting surface hardness of the peened steel as a function of laser fluence depends significantly on the confinement media and the relative increase in the hardness increases monotonically with the acoustic impedance of the liquid of the confinement medium used during LSP. © 2020 Elsevier B.V.
    view abstract10.1016/j.surfcoat.2020.125988
  • Surface modification of NiTi alloy by ultrashort pulsed laser shock peening
    Wang, H. and Kalchev, Y. and Wang, H. and Yan, K. and Gurevich, E.L. and Ostendorf, A.
    Surface and Coatings Technology 394 (2020)
    This research paper presents the attempt at ultrashort pulsed laser shock peening with absence of absorptive layer and confining medium which could enhance surface microhardness and the abrasion property of NiTi shape memory alloy. The average roughness values of NiTi specimen were measured on the surface, because the roughness would affect the friction resistance. The microhardness and Young's modulus were investigated at different position of single laser spot by nanoindentation technique. The pin-on-plate sliding abrasion testing were performed with different load-force (0.5 N and 2 N) for different testing time. Results showed that ultrashort pulsed laser shock peening treatment would cause a significant improvement on friction coefficient and abrasion property, which was attributed to the change of surface modification, such as roughness, microhardness, microstructure and titanium oxide layer, but the ultrashort pulsed laser shock peening treatment did not enhance its tensile strength during present research. © 2020 Elsevier B.V.
    view abstract10.1016/j.surfcoat.2020.125899
  • Three-step description of single-pulse formation of laser-induced periodic surface structures on metals
    Gurevich, E.L. and Levy, Y. and Bulgakova, N.M.
    Nanomaterials 10 (2020)
    Two different scenarios are usually invoked in the formation of femtosecond Laser-Induced Periodic Surface Structures (LIPSS), either “self-organization” mechanisms or a purely “plasmonic” approach. In this paper, a three-step model of formation of single-laser-shot LIPSS is summarized. It is based on the periodic perturbation of the electronic temperature followed by an amplification, for given spatial periods, of the modulation in the lattice temperature and a final possible relocation by hydrodynamic instabilities. An analytical theory of the evolution of the temperature inhomogeneities is reported and supported by numerical calculations on the examples of three different metals: Al, Au, and Mo. The criteria of the possibility of hydrodynamic instabilities are also discussed. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/nano10091836
  • Two-photon polymerization with diode lasers emitting ultrashort pulses with high repetition rate
    Zyla, G. and Surkamp, N. and Gurevich, E.L. and Esen, C. and Klehr, A. and Knigge, A. and Hofmann, M.R. and Ostendorf, A.
    Optics Letters 45 (2020)
    In this Letter, we investigate the resolution of two-photon polymerization (2PP) with an amplified mode-locked external cavity diode laser with adjustable pulse length and a high repetition rate. The experimental results are analyzed with a newly developed 2PP model. Even with low pulse peak intensity, the produced structural dimensions are comparable to those generated by traditional 2PP laser sources. Thus, we show that a compact monolithic picosecond laser diode without amplification and with a repetition rate in the GHz regime can also be applied for 2PP. These results show the high application potential of compact mode-locked diode lasers for low-cost and compact 2PP systems. © 2020 Optical Society of America
    view abstract10.1364/OL.401738
  • Biomimetic structural coloration with tunable degree of angle-independence generated by two-photon polymerization
    Zyla, G. and Kovalev, A. and Heisterkamp, S. and Esen, C. and Gurevich, E.L. and Gorb, S. and Ostendorf, A.
    Optical Materials Express 9 (2019)
    A successful realization of photonic systems with characteristics of the Morpho butterfly coloration is reported using two-photon polymerization. Submicron structure features have been fabricated through the interference of the incident beam and the reflected beam in a thin polymer film. Furthermore, the influence of the lateral microstructure organization on the color formation has been studied in detail. The design of the polymerized structures was validated by scanning electron microscopy. The optical properties were analyzed using an angleresolved spectrometer. Tunable angle-independence, based on reflection intensity modulation, has been investigated by using photonic structures with less degree of symmetry. Finally, these findings were used to demonstrate the high potential of two-photon polymerization in the field of biomimetic research and for technical application, e.g. for sensing and anti-counterfeiting. © 2019 Optical Society of America.
    view abstract10.1364/OME.9.002630
  • Effects of femtosecond laser shock peening in distilled water on the surface characterizations of NiTi shape memory alloy
    Wang, H. and Pöhl, F. and Yan, K. and Decker, P. and Gurevich, E.L. and Ostendorf, A.
    Applied Surface Science 471 (2019)
    NiTi shape memory alloy was processed by femtosecond laser shock peening (FLSP) without protective coating in distilled water to modify its surface characterizations. The surface topography, microhardness, microstructure and scratch testing were studied before and after FLSP treatment. The experimental results show that FLSP with different laser scanning speeds and passes can change the surface roughness and microhardness due to laser ablation and high pressure of shock wave. The average microhardness value of the specimens FLSPed in distilled water increased. Grain refinement was observed in the surface layer of FLSPed NiTi alloy. The scratch testing revealed that FLSP process can decrease the frictional force and coefficient of friction, and it also demonstrated that the FLSP technique is beneficial to enhance the surface wear property of NiTi alloy. © 2018 Elsevier B.V.
    view abstract10.1016/j.apsusc.2018.12.087
  • Femtosecond laser patterning of graphene electrodes for thin-film transistors
    Kasischke, M. and Subaşı, E. and Bock, C. and Pham, D.-V. and Gurevich, E.L. and Kunze, U. and Ostendorf, A.
    Applied Surface Science 478 (2019)
    The aim of this study is to assess femtosecond laser patterning of graphene in air and in vacuum for the application as source and drain electrodes in thin-film transistors (TFTs). The analysis of the laser-patterned graphene with scanning electron microscopy, atomic force microscopy and Raman spectroscopy showed that processing in vacuum leads to less debris formation and thus re-deposited carbonaceous material on the sample compared to laser processing in air. It was found that the debris reduction due to patterning in vacuum improves the TFT characteristics significantly. Hysteresis disappears, the mobility is enhanced by an order of magnitude and the subthreshold swing is reduced from S sub = 2.5 V/dec to S sub = 1.5 V/dec. © 2019 Elsevier B.V.
    view abstract10.1016/j.apsusc.2019.01.198
  • Laser metal deposition of compositionally graded TiZrNbTa refractory high-entropy alloys using elemental powder blends
    Dobbelstein, H. and Gurevich, E.L. and George, E.P. and Ostendorf, A. and Laplanche, G.
    Additive Manufacturing 25 (2019)
    In the present study, laser metal deposition (LMD) was used to produce compositionally graded refractory high-entropy alloys (HEAs) for screening purposes by in-situ alloying of elemental powder blends. A compositional gradient from Ti25Zr50Nb0Ta25 to Ti25Zr0Nb50Ta25 is obtained by incrementally substituting Zr powder with Nb powder. A suitable strategy was developed to process the powder blend despite several challenges such as the high melting points of the refractory elements and the large differences in melting points among them. The influence of the LMD process on the final chemical composition was analyzed in detail and the LMD process was optimized to obtain a well-defined compositional gradient. Microstructures, textures, chemical compositions and mechanical properties were characterized using SEM, EBSD, EDX, and microhardness testing, respectively. Compositions between Ti25Zr0Nb50Ta25 and Ti25Zr25Nb25Ta25 were found to be single-phase bcc solid solutions with a coarse grain microstructure. Increasing the Zr to Nb ratio beyond the equiatomic composition results in finer and harder multiphase microstructures. The results shown in the present study clearly show for the first time that LMD is a suitable processing tool to screen HEAs over a range of chemical compositions. © 2018 The Authors
    view abstract10.1016/j.addma.2018.10.042
  • Optimization of femtosecond laser processing in liquids
    Hoppius, J.S. and Maragkaki, S. and Kanitz, A. and Gregorčič, P. and Gurevich, E.L.
    Applied Surface Science 467-468 (2019)
    In this paper we analyze femtosecond laser processing of metals in liquids searching for optimal conditions for predictable ablation. Incident laser pulses are stretched or compressed, self-focused and scattered on bubbles and on surface waves in the liquid environment. Influence of these effects on the laser intensity distribution on the target surface is discussed and optimal processing parameters are suggested. © 2018 Elsevier B.V.
    view abstract10.1016/j.apsusc.2018.10.121
  • Pump-probe microscopy of femtosecond laser ablation in air and liquids
    Kanitz, A. and Förster, D.J. and Hoppius, J.S. and Weber, R. and Ostendorf, A. and Gurevich, E.L.
    Applied Surface Science 475 (2019)
    The ablation process of femtosecond laser pulses of iron in air and different liquids was investigated for fluences of 0.5 J/cm2 and 2 J/cm2 by means of femtosecond pump-probe microscopy. Measurements of the relative change in reflectivity suggest that the surrounding liquid has a significant impact on the ablation process. During the heating phase of the metal within the first picoseconds after laser beam impact, the change in reflectivity in air and liquids is similar. Afterwards, the vapor and melt expulsion in air leads to a strong decrease in reflectivity, while the change in reflectivity in the liquids shows a more complex fluence and time-dependent behavior. This behavior is suggested to be triggered by the expansion of the molten surface and chemical reactions on the picosecond timescale. © 2018 Elsevier B.V.
    view abstract10.1016/j.apsusc.2018.12.184
  • Review on experimental and theoretical investigations of the early stage, femtoseconds to microseconds processes during laser ablation in liquid-phase for the synthesis of colloidal nanoparticles
    Kanitz, A. and Kalus, M.-R. and Gurevich, E.L. and Ostendorf, A. and Barcikowski, S. and Amans, D.
    Plasma Sources Science and Technology 28 (2019)
    Laser ablation in liquid-phase (LAL) has been developed since the 1990s, but the interest in laser synthesis of colloids has emerged in the last decade due to a significant improvement in the production rate, proven comparative advantages in biomedical and catalysis applications, and recent commercialization. However, the method relies on highly transient phenomena, so that the fundamental understanding lacks behind the LAL synthesis refinement research. The complexity of the physics and chemistry involved has led to experimental and theoretical investigations that attempt to provide a basic description of the underlying processes but face the challenge of temporal and spatial resolution as well as non-equilibrium conditions. It appears that the processes occurring at the early time scales, ranging from femtoseconds to several microseconds are critical in the definition of the final product. The review is mainly dedicated to the comprehensive description of the processes occurring at early time scales, which include the description of laser-matter interaction for ultrashort and short laser pulses, plasma formation processes as well as comparison of the measured plasma parameters at these time scales, and subsequent description of the cavitation bubble dynamics. Furthermore, the plasma and cavitation bubble chemistry are addressed, and their impact on the nanoparticle formation is emphasized. © 2019 IOP Publishing Ltd.
    view abstract10.1088/1361-6595/ab3dbe
  • Selective Delamination of Thin Films from Ceramic Surfaces upon Femtosecond Laser Ablation
    Kiel, F. and Bulgakova, N.M. and Ostendorf, A. and Gurevich, E.L.
    2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings (2019)
    Experimental observation of selective delamination of YSZ ceramics upon femtosecond laser processing of its surface is reported. The delamination mechanism is identified as an interplay between beam defocusing by laser-generated free-electron plasma and Kerr nonlinearity. © 2019 The Author(s) 2019 OSA.
    view abstract10.23919/CLEO.2019.8750200
  • Selective Delamination upon Femtosecond Laser Ablation of Ceramic Surfaces
    Kiel, F. and Bulgakova, N.M. and Ostendorf, A. and Gurevich, E.L.
    Physical Review Applied 11 (2019)
    We report on the experimental observation of selective delamination of semitransparent materials on the example of yttria-stabilized zirconia ceramics upon femtosecond laser processing of its surface with a low numerical aperture lens. The delamination of a ceramic layer of dozens of micrometers takes place as a side effect of surface processing and is observed above the surface ablation threshold. The onset of delamination (delamination threshold) depends on the degree of overlap of the irradiation spots from consecutive laser pulses upon beam scanning over material surface. Analysis of the delaminated layer indicates that the material undergoes melting on both of its surfaces. The mechanism of delamination is identified as a complex interplay between the optical response of laser-generated free-electron plasma and nonlinear effects upon laser beam propagation in semitransparent ceramics. The discovered effect enables controllable laser microslicing of brittle ceramic materials. © 2019 American Physical Society.
    view abstract10.1103/PhysRevApplied.11.024038
  • Femtosecond laser crystallization of amorphous titanium oxide thin films
    Hoppius, J.S. and Bialuschewski, D. and Mathur, S. and Ostendorf, A. and Gurevich, E.L.
    Applied Physics Letters 113 (2018)
    In this paper, we demonstrate experimentally that crystalline phases appear in amorphous titanium oxide upon processing with ultrafast laser pulses. Amorphous titanium thin films were produced by plasma-enhanced chemical vapor deposition and exposed to femtosecond laser pulses. Formation of a rutile phase was confirmed by X-ray diffraction, Raman measurements, and electron backscattering diffraction. A range of processing parameters for the crystallization is reported, and possible background mechanisms are discussed. © 2018 Author(s).
    view abstract10.1063/1.5027899
  • Femtosecond laser shock peening of galvanized stainless steel
    Pickhardt, F. and Hoppius, J.S. and Gurevich, E.L.
    Procedia CIRP 74 (2018)
    In this paper a SUS316L stainless steel was electroplated with metallic layers and coated with polymer films. A sub-100fs ultrashort laser pulse with a central wavelength of λ=800nm was utilized to process the layer. The aim was to generate shock waves due to ablation of the deposited sacrificial layers. Generated shockwaves propagate and penetrate the lower stainless-steel sample and increase its mechanical hardness (Laser Shock Peening). The sacrificial layer protects the sample from ablation damage and determines the shock wave coupling. To achieve maximal peening, we compare different sacrificial layers and laser processing parameters. © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.
    view abstract10.1016/j.procir.2018.08.124
  • Laser metal deposition of a refractory TiZrNbHfTa high-entropy alloy
    Dobbelstein, H. and Gurevich, E.L. and George, E.P. and Ostendorf, A. and Laplanche, G.
    Additive Manufacturing 24 (2018)
    Refractory elements have high melting points and are difficult to melt and cast. In this study it is successfully demonstrated for the first time that laser metal deposition can be used to produce TiZrNbHfTa high-entropy alloy from a blend of elemental powders by in-situ alloying. Columnar specimens with a height of 10 mm and a diameter of 3 mm were deposited with a pulsed Nd:YAG laser. The built-up specimen has near-equiatomic composition, nearly uniform grain size, equiaxed grain shape, is bcc single phase and exhibits a high hardness of 509 HV0.2. © 2018 The Authors
    view abstract10.1016/j.addma.2018.10.008
  • Laser-Textured Metal Substrates as Photoanodes for Enhanced PEC Water Splitting Reactions
    Bialuschewski, D. and Hoppius, J.S. and Frohnhoven, R. and Deo, M. and Gönüllü, Y. and Fischer, T. and Gurevich, E.L. and Mathur, S.
    Advanced Engineering Materials 20 (2018)
    We demonstrate the effect of femtosecond laser structuring of titanium substrates to increase the absorption, photoconversion, and overall photoelectrochemical water splitting (PEC) performance compared to pristine metal substrates, independent of any additional top coat layers. The influence of ultra short laser pulse patterning on PEC efficiency is investigated toward spectroscopic (UV-Vis), microscopic (SEM), crystallographic (XRD), and compositional (XPS) properties. The beneficial effect of a periodically patterned substrate is attributed to enhanced specific surface area and improved in-plane light trapping when compared to flat surfaces. Photoanodes for water splitting experiments fabricated by titanium and iron oxide films on laser pre-patterned Ti substrates are also found to show enhanced PEC efficiency (0.057 mA cm−2) when compared to unpatterened substrates (0.028 mA cm−2). The lower absolute PEC efficiencies are due to extreme thin films. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/adem.201800167
  • On femtosecond laser shock peening of stainless steel AISI 316
    Hoppius, J.S. and Kukreja, L.M. and Knyazeva, M. and Pöhl, F. and Walther, F. and Ostendorf, A. and Gurevich, E.L.
    Applied Surface Science 435 (2018)
    In this paper we report on the competition in metal surface hardening between the femtosecond shock peening on the one hand, and formation of laser-induced periodic surface structures (LIPSS) and surface oxidation on the other hand. Peening of the stainless steel AISI 316 due to shock loading induced by femtosecond laser ablation was successfully demonstrated. However, for some range of processing parameters, surface erosion due to LIPSS and oxidation seems to dominate over the peening effect. Strategies to increase the peening efficiency are discussed. © 2017 Elsevier B.V.
    view abstract10.1016/j.apsusc.2017.11.145
  • Printing structural colors via direct laser writing
    Zyla, G. and Kovalev, A. and Gurevich, E.L. and Esen, C. and Ostendorf, A. and Gorb, S.
    Proceedings of SPIE - The International Society for Optical Engineering 10544 (2018)
    Most common colors in our world as we see them, for example, in crystals, pigments, metals and salt solutions are the result from light scattering properties of electrons in atoms and molecules. Nevertheless, colors can also result from light interference effects, which are of great importance in the life of organisms. The structural colors of living organisms, e.g., the wings of some birds, insects and butteries, are often more intense and almost angle-independent. Understanding this specific color formation is of great interest for biology and for engineered materials with a broad range of biomimetic real world applications due to forgoing of toxic dyes and pigments. Therefore, the generation of artificial color formation with lithographic methods offers many advantages not available in coated multilayer systems because it avoids multiple complex fabrication steps. In the present work, we report an effortless fabrication method to generate structural coloration based on microand nano-structures using 3d-laser writing technique. The uniform micro- A nd nano-structures were produced in a thin polymer film with an refractive index of 1.51. The single structures are aligned in an array to create a blue color field. The identification of the influence of the structures on the artificial color formation was performed using scanning electron microscopy. The optical properties of the blue color was analyzed via an angle-resolved spectrometer. © 2018 SPIE.
    view abstract10.1117/12.2289820
  • Simultaneous nanopatterning and reduction of graphene oxide by femtosecond laser pulses
    Kasischke, M. and Maragkaki, S. and Volz, S. and Ostendorf, A. and Gurevich, E.L.
    Applied Surface Science 445 (2018)
    This paper presents a novel one-step method for the periodical nanopatterning and reduction of graphene oxide (GO). Self-organized periodic structures of reduced graphene oxide (rGO) appear on GO surfaces upon processing with a femtosecond laser at fluences slightly higher than the fluence needed for reduction of the GO. This indicates that the periodic pattern is formed either simultaneously with or due to the reduction of the GO. The laser-induced reduction of GO was identified by sheet resistance measurements, Raman and X-ray photoelectron spectroscopy. This fast and simple method to both reduce and periodically structure GO offers a variety of possible applications in printed and flexible electronics. © 2018 Elsevier B.V.
    view abstract10.1016/j.apsusc.2018.03.086
  • Generation of bioinspired structural colors via two-photon polymerization
    Zyla, G. and Kovalev, A. and Grafen, M. and Gurevich, E.L. and Esen, C. and Ostendorf, A. and Gorb, S.
    Scientific Reports 7 (2017)
    Colors of crystals, pigments, metals, salt solutions and bioluminescence occur in nature due to the optical properties of electrons in atoms and molecules. However, colors can also result from interference effects on nanostructures. In contrast to artificial coloration, which are caused by well-defined regular structures, the structural colors of living organisms are often more intense and almost angle-independent. In this paper, we report the successful manufacturing of a lamellar nanostructure that mimics the ridge shape of the Morpho butterfly using a 3d-direct laser writing technique. The viewing angle dependency of the color was analyzed via a spectrometer and the structure was visualized using a scanning electron microscope. The generated nano-and micro-structures and their optical properties were comparable to those observed in the Morpho butterfly. © 2017 The Author(s).
    view abstract10.1038/s41598-017-17914-w
  • Graphene oxide reduction induced by femtosecond laser irradiation
    Kasischke, M. and Maragkaki, S. and Volz, S. and Gurevich, E.L. and Ostendorf, A.
    Proceedings of SPIE - The International Society for Optical Engineering 10356 (2017)
    A promising fabrication method for graphene is the reduction of graphene oxide (GO), this can be achieved photochemically by laser irradiation. In this study, we examine the results of latter method by a femtosecond fiber laser (1030 nm, 280 fs). The chemical properties of the irradiated areas were analyzed by Raman and X-ray photoelectron spectroscopy (XPS) and electrical properties were evaluated using sheet resistance measurements. We found that, within a wide range of fluences (8.5 mJ/cm2to 57.8 mJ/cm2) at high overlapping rates (>99.45 %), photochemical oxygen reduction can be achieved. However, hybridization transition of sp3 to sp2 graphene-like structures only takes place at upper fluences of the mentioned range. © 2017 SPIE.
    view abstract10.1117/12.2274976
  • Impact of liquid environment on femtosecond laser ablation
    Kanitz, A. and Hoppius, J.S. and Fiebrandt, M. and Awakowicz, P. and Esen, C. and Ostendorf, A. and Gurevich, E.L.
    Applied Physics A: Materials Science and Processing 123 (2017)
    The ablation rate by femtosecond laser processing of iron in different liquids is investigated for fluences up to 5 J/cm2. The resulting fluence dependency is modeled by an approach derived from the two-temperature model. In our experiments, the liquid environment strongly affects the effective penetration depth, e.g, the ablation rate in water is almost ten times higher than in toluene. This effect is discussed and introduced phenomenologically into the model. Additional reflectivity measurements and plasma imaging provide improved insight into the ablation process. © 2017, Springer-Verlag GmbH Germany.
    view abstract10.1007/s00339-017-1280-z
  • Influence of solvent mixture on the ablation rate of iron using femtosecond laser pulses
    Kanitz, A. and Hoppius, J.S. and Ostendorf, A. and Gurevich, E.L.
    Proceedings of SPIE - The International Society for Optical Engineering 10092 (2017)
    Ultrashort pulse laser ablation has become an important tool for material processing. Adding liquids to the process can be beneficial for a reduced debris and heat affected zone width. Another application is the production of ligand-free nanoparticles. By measuring the ablation rate of iron for femtosecond pulsed laser ablation in different solvents and solvent-mixtures, the influence of the solvent properties on the ablation process is studied. The ablation efficiency is quantified by measuring the ablation rate in dependency of the fluence from 0.05 J/cm2 up to 5 J/cm2 in water-ethanol and water-acetone mixtures which are varied in 25 % steps. The ablation rate is significantly influenced by the solvent-mixtures. © 2017 SPIE.
    view abstract10.1117/12.2254444
  • Optical assembly of microsnap-fits fabricated by two-photon polymerization
    Köhler, J. and Kutlu, Y. and Zyla, G. and Ksouri, S.I. and Esen, C. and Gurevich, E.L. and Ostendorf, A.
    Optical Engineering 56 (2017)
    To respond to current demands of nano- and microtechnologies, e.g., miniaturization and integration, different bottom-up strategies have been developed. These strategies are based on picking, placing, and assembly of multiple components to produce microsystems with desired features. This paper covers the fabrication of arbitrary-shaped microcomponents by two-photon polymerization and the trapping, moving, and aligning of these structures by the use of a holographic optical tweezer. The main focus is on the assembly technique based on a cantilever microsnap-fit. More precisely, mechanical properties are characterized by optical forces and a suitable geometry of the snap-fit is designed. As a result of these investigations, a fast and simple assembly technique is developed. Furthermore, disassembly is provided by an optimized design. These findings suggest that the microsnap-fit is suitable for the assembly of miniaturized systems and could broaden the application opportunities of bottom-up strategies. © 2017 Society of Photo-Optical Instrumentation Engineers (SPIE).
    view abstract10.1117/1.OE.56.10.105105
  • Orientation of ripples induced by ultrafast laser pulses on copper in different liquids
    Maragkaki, S. and Elkalash, A. and Gurevich, E.L.
    Applied Physics A: Materials Science and Processing 123 (2017)
    Formation of laser-induced periodic surface structures (LIPSS or ripples) was studied on a metallic surface of polished copper using irradiation with multiple femtosecond laser pulses in different environmental conditions (air, water, ethanol and methanol). Uniform LIPSS have been achieved by controlling the peak fluence and the overlapping rate. Ripples in both orientations, perpendicular and parallel to laser polarization, were observed in all liquids simultaneously. The orientation of these ripples in the center of the ablated line was changing with the incident light intensity. For low intensities the orientation of the ripples is perpendicular to the laser polarization, whereas for high intensities it turns parallel to it without considerable changes in the period. Multi-directional LIPSS formation was also observed for moderate peak fluence in liquid environments. © 2017, Springer-Verlag GmbH Germany.
    view abstract10.1007/s00339-017-1336-0
  • Role of the temperature dynamics in formation of nanopatterns upon single femtosecond laser pulses on gold
    Gurevich, E. L. and Levy, Y. and Gurevich, S. V. and Bulgakova, N. M.
    Physical Review B 95 (2017)
    In this paper we investigate the role of two-temperature heating dynamics for formation of periodic structures on metal surfaces exposed to single ultrashort laser pulses. The results of two-temperature model (TTM) twodimensional simulations are presented on the irradiation of gold by a single 800-nm femtosecond laser pulse the intensity of which is modulated in order to reproduce an initial electron temperature perturbation, which can arise from incoming and scattered surface wave interference. The growing (unstable) modes of the lattice temperature distribution along the surface may be significant in the laser induced periodic surface structures formation. After the end of the laser pulse and before the complete coupling between lattice and electrons occurs, the evolution of the amplitude of the subsequent modulation in the lattice temperature reveals different tendencies depending on the spatial period of the initial modulation. This instabilitylike behavior is shown to arise due to the perturbation of the electronic temperature which relaxes slower for bigger spatial periods and thus imparts more significant modulations to the lattice temperature. Small spatial periods of the order of 100 nm and smaller experience stabilization and fast decay from the more efficient lateral heat diffusion which facilitates the relaxation of the electronic temperature amplitude due to in-depth diffusion. An analytical instability analysis of a simplified version of the TTM set of equations supports the lattice temperature modulation behavior obtained in the simulations and reveals that in-depth diffusion length is a determining parameter in the dispersion relation of unstable modes. Finally, it is discussed how the change in optical properties can intensify the modulation-related effects.
    view abstract10.1103/PhysRevB.95.054305
  • Synthesis of Magnetic Nanoparticles by Ultrashort Pulsed Laser Ablation of Iron in Different Liquids
    Kanitz, A. and Hoppius, J.S. and del Mar Sanz, M. and Maicas, M. and Ostendorf, A. and Gurevich, E.L.
    ChemPhysChem 18 (2017)
    Magnetic nanoparticles were generated by ultrashort pulsed laser ablation of an iron target in water, methanol, ethanol, acetone and toluene. The relationship between ablation rate, liquid properties and the physical and chemical properties of the nanoparticles was studied. Composition, morphology and magnetic properties were investigated by TEM, XPS and vibrating-sample (VSM) and SQUID magnetometry. The properties of the generated nanoparticle ensembles reflected the influence of the liquid environment on the particle formation process. For example, the composition was strongly dependent on the carbon to oxygen ratio within the molecules of the liquid. In contrast to short pulsed laser ablation in liquids, the nanoparticles generated by ultrashort pulses had a higher level of polycrystallinity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/cphc.201601252
  • Wavelength dependence of picosecond laser-induced periodic surface structures on copper
    Maragkaki, S. and Derrien, T.J.-Y. and Levy, Y. and Bulgakova, N.M. and Ostendorf, A. and Gurevich, E.L.
    Applied Surface Science 417 (2017)
    The physical mechanisms of the laser-induced periodic surface structures (LIPSS) formation are studied in this paper for single-pulse irradiation regimes. The change in the LIPSS period with wavelength of incident laser radiation is investigated experimentally, using a picosecond laser system, which provides 7-ps pulses in near-IR, visible, and UV spectral ranges. The experimental results are compared with predictions made under the assumption that the surface-scattered waves are involved in the LIPSS formation. Considerable disagreement suggests that hydrodynamic mechanisms can be responsible for the observed pattern periodicity. © 2017 Elsevier B.V.
    view abstract10.1016/j.apsusc.2017.02.068
  • Characterization of azimuthal and radial velocity fields induced by rotors in flows with a low Reynolds number
    Köhler, J. and Friedrich, J. and Ostendorf, A. and Gurevich, E.L.
    Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 93 (2016)
    We theoretically and experimentally investigate the flow field that emerges from a rodlike microrotor rotating about its center in a nonaxisymmetric manner. A simple theoretical model is proposed that uses a superposition of two rotlets as a fundamental solution to the Stokes equation. The predictions of this model are compared to measurements of the azimuthal and radial microfluidic velocity field components that are induced by a rotor composed of fused microscopic spheres. The rotor is driven magnetically and the fluid flow is measured with the help of a probe particle fixed by an optical tweezer. We find considerable deviations of the mere azimuthal flow pattern induced by a single rotating sphere as it has been reported by Di Leonardo et al. [Phys. Rev. Lett. 96, 134502 (2006)PRLTAO0031-900710.1103/PhysRevLett.96.134502]. Notably, the presence of a radial velocity component that manifests itself by an oscillation of the probe particle with twice the rotor frequency is observed. These findings open up a way to discuss possible radial transport in microfluidic devices. © 2016 American Physical Society.
    view abstract10.1103/PhysRevE.93.023108
  • Direct metal deposition of refractory high entropy alloy MoNbTaW
    Dobbelstein, H. and Thiele, M. and Gurevich, E.L. and George, E.P. and Ostendorf, A.
    Physics Procedia 83 (2016)
    Alloying of refractory high entropy alloys (HEAs) such as MoNbTaW is usually done by vacuum arc melting (VAM) or powder metallurgy (PM) due to the high melting points of the elements. Machining to produce the final shape of parts is often needed after the PM process. Casting processes, which are often used for aerospace components (turbine blades, vanes), are not possible. Direct metal deposition (DMD) is an additive manufacturing technique used for the refurbishment of superalloy components, but generating these components from the bottom up is also of current research interest. MoNbTaW possesses high yield strength at high temperatures and could be an alternative to state-of-the-art materials. In this study, DMD of an equimolar mixture of elemental powders was performed with a pulsed Nd:YAG laser. Single wall structures were built, deposition strategies developed and the microstructure of MoNbTaW was analyzed by back scattered electrons (BSE) and energy dispersive X-ray (EDX) spectroscopy in a scanning electron microscope. DMD enables the generation of composition gradients by using dynamic powder mixing instead of pre-alloyed powders. However, the simultaneous handling of several elemental or pre-alloyed powders brings new challenges to the deposition process. The influence of thermal properties, melting point and vapor pressure on the deposition process and chemical composition will be discussed. © 2016 The Authors.
    view abstract10.1016/j.phpro.2016.08.065
  • Influence of the liquid on femtosecond laser ablation of iron
    Kanitz, A. and Hoppius, J.S. and Gurevich, E.L. and Ostendorf, A.
    Physics Procedia 83 (2016)
    Ultrashort pulse laser ablation has become a very important industrial method for highly precise material removal ranging from sensitive thin film processing to drilling and cutting of metals. Over the last decade, a new method to produce pure nanoparticles emerged from this technique: Pulsed Laser Ablation in Liquids (PLAL). By this method, the ablation of material by a laser beam is used to generate a metal vapor within the liquid in order to obtain nanoparticles from its recondensation process. It is well known that the liquid significantly alters the ablation properties of the substrate, in our case iron. For example, the ablation rate and crater morphology differ depending on the used liquid. We present our studies on the efficiency and quality of ablated grooves in water, methanol, acetone, ethanol and toluene. The produced grooves are investigated by means of white-light interferometry, EDX and SEM. © 2016 The Authors.
    view abstract10.1016/j.phpro.2016.08.022
  • Investigation on femto-second laser irradiation assisted shock peening of medium carbon (0.4% C) steel
    Majumdar, J.D. and Gurevich, E.L. and Kumari, R. and Ostendorf, A.
    Applied Surface Science 364 (2016)
    In the present study, the effect of femtosecond laser irradiation on the peening behavior of 0.4% C steel has been evaluated. Laser irradiation has been conducted with a 100 μJ and 300 fs laser with multiple pulses under varied energy. Followed by laser irradiation, a detailed characterization of the processed zone was undertaken by scanning electron microscopy, and X-ray diffraction technique. Finally, the residual stress distribution, microhardness and wear resistance properties of the processed zone were also evaluated. Laser processing leads to shock peening associated with plasma formation and its expansion, formation of martensite and ferrito-pearlitic phase in the microstructure. Due to laser processing, there is introduction of residual stress on the surface which varies from high tensile (140 MPa) to compressive (-335 MPa) as compared to 152 MPa of the substrate. There is a significant increase in microhardness to 350-500 VHN as compared to 250 VHN of substrate. The fretting wear behavior against hardened steel ball shows a significant reduction in wear depth due to laser processing. Finally, a conclusion of the mechanism of wear has been established. © 2015 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.apsusc.2015.12.058
  • Mechanisms of femtosecond LIPSS formation induced by periodic surface temperature modulation
    Gurevich, E.L.
    Applied Surface Science 374 (2016)
    Here we analyze the formation of laser-induced periodic surface structures (LIPSS) on metal surfaces upon single femtosecond laser pulses. Most of the existing models of the femtosecond LIPSS formation discuss only the appearance of a periodic modulation of the electron and ion temperatures. However the mechanism how the inhomogeneous surface temperature distribution induces the periodically-modulated surface profile under the conditions corresponding to ultrashort-pulse laser ablation is still not clear. Estimations made on the basis of different hydrodynamic instabilities allow to sort out mechanisms, which can bridge the gap between the temperature modulation and the LIPSS. The proposed theory shows that the periodic structures can be generated by single ultrashort laser pulses due to ablative instabilities. The Marangoni and Rayleigh-Bénard convection on the contrary cannot cause the LIPSS formation.
    view abstract10.1016/j.apsusc.2015.09.091
  • Relaxation dynamics of femtosecond-laser-induced temperature modulation on the surfaces of metals and semiconductors
    Levy, Y. and Derrien, T. J. Y. and Bulgakova, N. M. and Gurevich, E. L. and Mocek, T.
    Applied Surface Science 374 (2016)
    Formation of laser-induced periodic surface structures (LIPSS) is a complicated phenomenon which involves periodic spatial modulation of laser energy absorption on the irradiated surface, transient changes in optical response, surface layer melting and/or ablation. The listed processes strongly depend on laser fluence and pulse duration as well as on material properties. This paper is aimed at studying the spatiotemporal evolution of a periodic modulation of the deposited laser energy, once formed upon irradiation of metal (Ti) and semiconductor (Si) surfaces. Assuming that the incoming laser pulse interferes with a surface electromagnetic wave, the resulting sinusoidal modulation of the absorbed laser energy is introduced into a two-dimensional two-temperature model developed for titanium and silicon. Simulations reveal that the lattice temperature modulation on the surfaces of both materials following from the modulated absorption remains significant for longer than 50 ps after the laser pulse. In the cases considered here, the partially molten phase exists 10 ps in Ti and more than 50 ps in Si, suggesting that molten matter can be subjected to temperature-driven relocation toward LIPSS formation, due to the modulated temperature profile on the material surfaces. Molten phase at nanometric distances (nano-melting) is also revealed. (C) 2015 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.apsusc.2015.10.159
  • Throughput optimization for laser micro structuring
    Hoppius, J.S. and Kanitz, A. and Gurevich, E.L. and Ostendorf, A.
    Proceedings of SPIE - The International Society for Optical Engineering 9736 (2016)
    Laser pulses in the picosecond and femtosecond regime enable nearly non-thermal material processing where heat effects like molten pools and thermal tensions are often significantly reduced. However, a residual amount of laser energy transforms into heat. As a consequence cumulative multiple shot processing leads to heat accumulation and subsequently lower manufacturing accuracy. To increase the processing throughput without losing quality, it is important to optimize the laser pulse properties and the ablation strategy to further reduce thermal effects. Due to a low heat capacity in small structures, it is necessary to consider the substrate dimensions while performing micro- and nanoprocessing. In contrast to bulk material ablation, the heat dissipation is confined by the small heat capacity of microstructures. Especially for complex structures, it is time-consuming to find efficient processing parameters manually. For this reason, an in-situ evaluation system based on electrical resistivity measurements for on-line control of the ablation process was developed to optimize the laser parameters. In the work presented, the efficiency of 35 femtosecond pulsed laser ablation was evaluated on copper structures in the micrometer range. Furthermore, these results have been compared and evaluated with surface profiles measured by white-light interferometry. © 2016 SPIE.
    view abstract10.1117/12.2216849
  • Graphene-intercalated Fe2O3/TiO2 heterojunctions for efficient photoelectrolysis of water
    Kaouk, A. and Ruoko, T.-P. and Gönüllü, Y. and Kaunisto, K. and Mettenbörger, A. and Gurevich, E. and Lemmetyinen, H. and Ostendorf, A. and Mathur, S.
    RSC Advances 5 (2015)
    Interfacial modification of α-Fe2O3/TiO2 multilayer photoanodes by intercalating few-layer graphene (FLG) was found to improve water splitting efficiency due to superior transport properties, when compared to individual iron and titanium oxides and heterojunctions thereof. Both metal oxides and graphene sheets were grown by plasma-enhanced chemical vapor deposition. Compared to the onset potential achieved for α-Fe2O3 films (1 V vs. RHE), the α-Fe2O3/TiO2 bilayer structure yielded a better onset potential (0.3 V vs. RHE). Heterojunctioned bilayers exhibited a higher photocurrent density (0.32 mA cm-2 at 1.23 V vs. RHE) than the single α-Fe2O3 layer (0.22 mA cm-2 at 1.23 V vs. RHE), indicating more efficient light harvesting and higher concentration of photogenerated charge carriers. For more efficient charge transport at the interface, a few layer graphene sheet was intercalated into the α-Fe2O3/TiO2 interface, which substantially increased the photocurrent density to 0.85 mA cm-2 (1.23 V vs. RHE) and shifted the onset potential (0.25 V vs. RHE). Ultrafast transient absorption spectroscopy studies indicated that the incorporation of FLG between the α-Fe2O3 and TiO2 layers resulted in reduced recombination in the α-Fe2O3 layer. The results showed that graphene intercalation improved the charge separation and the photocurrent density of the FTO/α-Fe2O3/FLG/TiO2 system. © The Royal Society of Chemistry.
    view abstract10.1039/c5ra18330h
  • Comparison of in situ and ex situ methods for synthesis of two-photon polymerization polymer nanocomposites
    Guo, Q. and Ghadiri, R. and Weigel, T. and Aumann, A. and Gurevich, E.L. and Esen, C. and Medenbach, O. and Cheng, W. and Chichkov, B. and Ostendorf, A.
    Polymers 6 (2014)
    This article reports about nanocomposites, which refractive index is tuned by adding TiO2 nanoparticles. We compare in situ/ex situ preparation of nanocomposites. Preparation procedure is described, properties of nanocomposites are compared, and especially we examine the applicability of two-photon polymerization (2PP) of synthesized nanocomposites. All prepared samples exhibit suitable optical transparency at specific laser wavelengths. Three-dimensional structures were generated by means of two-photon polymerization effect induced by a femtosecond laser. © 2014 by the authors; licensee MDPI.
    view abstract10.3390/polym6072037
  • Correction to Comparison of in Situ and ex Situ methods for synthesis of two-photon polymerization polymer nanocomposites [Polymers, 6, (2014) 2037-2050]
    Guo, Q. and Ghadiri, R. and Weigel, T. and Aumann, A. and Gurevich, E.L. and Esen, C. and Medenbach, O. and Cheng, W. and Chichkov, B. and Ostendorf, A.
    Polymers 6 (2014)
    view abstract10.3390/polym6092433
  • Ex-situ preparation of high-conductive polymer/SWNTs nanocomposites for structure fabrication
    Guo, Q. and Ghadiri, R. and Weigel, T. and Aumann, A. and Gurevich, E.L. and Esen, C. and Li, Y. and Cheng, W. and Chichkov, B. and Ostendorf, A.
    Proceedings of SPIE - The International Society for Optical Engineering 9277 (2014)
    This paper reports ex-situ preparation of conductive polymer/single-walled carbon nanotubes (SWNTs) nanocomposites by adding high conductive SWNTs to the polymer matrix. Sonication methods were used to disperse the SWNTs in the polymer. The conductivity of the nanocomposites is tuned by increasing the concentration of SWNTs. Furthermore, we present two-photon polymerization (2PP) method to fabricate structures on the basis of conductive photosensitive composites. The conductive structures were successfully generated by means of 2PP effect induced by a femtosecond laser. © 2014 SPIE.
    view abstract10.1117/12.2071870
  • Generation of microfluidic flow using an optically assembled and magnetically driven microrotor
    Köhler, J. and Ghadiri, R. and Ksouri, S.I. and Guo, Q. and Gurevich, E.L. and Ostendorf, A.
    Journal of Physics D: Applied Physics 47 (2014)
    The key components in microfluidic systems are micropumps, valves and mixers. Depending on the chosen technology, the realization of these microsystems often requires rotational and translational control of subcomponents. The manufacturing of such active components as well as the driving principle are still challenging tasks. A promising all-optical approach could be the combination of laser direct writing and actuation based on optical forces. However, when higher actuation velocities are required, optical driving might be too slow. Hence, a novel approach based on optical assembling of microfluidic structures and subsequent magnetic actuation is proposed. By applying the optical assembly of microspherical building blocks as the manufacturing method and magnetic actuation, a microrotor was successfully fabricated and tested within a microfluidic channel. The resulting fluid flow was characterized by introducing an optically levitated measuring probe particle. Finally, a freely moving tracer particle visualizes the generated flow. The tracer particle analysis shows average velocities of 0.4-0.5 μm s-1 achieved with the presented technology. © 2014 IOP Publishing Ltd Printed.
    view abstract10.1088/0022-3727/47/50/505501
  • Generation of NiTi nanoparticles by femtosecond laser ablation in liquid
    Chakif, M. and Essaidi, A. and Gurevich, E. and Ostendorf, A. and Prymak, O. and Epple, M.
    Journal of Materials Engineering and Performance 23 (2014)
    NiTi was investigated as a model system for a binary alloy where the properties strongly depend on the relative proportion of the two elements and on the grain size. The NiTi nanoparticles were generated by laser ablation in water. For the analysis of the particle size distribution, we used transmission electron microscopy and dynamic light scattering. Here, we found a broad particle size distribution (10-200 nm). Furthermore, the temperature-resolved x-ray powder diffraction and differential scanning calorimetry (DSC) were used to evaluate the phase transition behavior of the generated NiTi nanoparticles. Here, we found an interesting effect. During the heating by DSC, an austenite phase transition and a weak martensite phase transition in the NiTi nanoparticles appeared. Moreover, the phase transformation temperature was about 40 K lower than that of the bulk target. © 2014 ASM International.
    view abstract10.1007/s11665-014-1007-7
  • Impact of solvent mixture on iron nanoparticles generated by laser ablation
    Chakif, M. and Prymak, O. and Slota, M. and Heintze, E. and Gurevich, E.L. and Esen, C. and Bogani, L. and Epple, M. and Ostendorf, A.
    Progress in Biomedical Optics and Imaging - Proceedings of SPIE 8955 (2014)
    The present work reveals the structural and magnetic properties of iron oxide (FexOy) nanoparticles (NPs) prepared by femtosecond laser ablation. The FexOy-NPs were produced in solutions consisting of different ratios of water and acetone. Laser ablation in water yields agglomerates and that in acetone yields chain structures whereas that in water/acetone show a mixture of both. We observe significant fabrication dependent properties such as different crystallinities and magnetic behaviors. The structural characterization shows a change from iron (Fe) to a Fe xOy state of the NPs which depends on the solution composition. Furthermore, transmission electron microscopy measurements exhibit a broad particle size distribution in all samples but with significant differences in the mean sizes. Using magnetic measurements we show that nanoparticles fabricated in pure acetone have lower coercive fields which come along with a smaller mean particle size and therefore increasing superparamagnetic behavior. © 2014 SPIE.
    view abstract10.1117/12.2037682
  • Laser Induced Periodic Surface Structures induced by surface plasmons coupled via roughness
    Gurevich, E.L. and Gurevich, S.V.
    Applied Surface Science 302 (2014)
    In this paper the formation mechanisms of the femtosecond laser-induced periodic surface structures (LIPSS) are discussed. One of the most frequently used theories explains the structures by interference between the incident laser beam and surface plasmon-polariton waves. The latter is most commonly attributed to the coupling of the incident laser light to the surface roughness. We demonstrate that this excitation of surface plasmons contradicts the results of laser-ablation experiments. As an alternative approach to the excitation of LIPSS we analyse development of hydrodynamic instabilities in the melt layer. © 2013 Elsevier B.V.
    view abstract10.1016/j.apsusc.2013.10.141
  • Optical tweezers as manufacturing and characterization tool in microfluidics
    Köhler, J. and Ghadiri, R. and Ksouri, S.I. and Gurevich, E.L. and Ostendorf, A.
    Proceedings of SPIE - The International Society for Optical Engineering 9164 (2014)
    Pumping and mixing of small volumes of liquid samples are basic processes in microfluidic applications. Among the number of different principles for active transportation of the fluids microrotors have been investigated from the beginning. The main challenge in microrotors, however, has been the driving principle. In this work a new approach for a very simple magnetic driving principle has been realized. More precisely, we take advantage of optical grippers to fabricate various microrotors and introduce an optical force method to characterize the fluid flow generated by rotating the structures through magnetic actuation. The microrotors are built of silica and magnetic microspheres which are initially coated with Streptavidin or Biotin molecules. Holographic optical tweezers (HOT) are used to trap, to position, and to assemble the microspheres with the chemical interaction of the biomolecules leading to a stable binding. Using this technique, complex designs of microrotors can be realized. The magnetic response of the magnetic microspheres enables the rotation and control of the structures through an external magnetic field. The generated fluid flow around the microrotor is measured optically by inserting a probe particle next to the rotor. While the probe particle is trapped by optical forces the flow force leads to a displacement of the particle from the trapping position. This displacement is directly related to the flow velocity and can be measured and calibrated. Variations of the microrotor design and rotating speed lead to characteristic flow fields. © 2014 SPIE.
    view abstract10.1117/12.2063080
  • Polydisperse NiTi nanoparticles investigated by X-ray standing waves and electron microscopy - A comparative study
    Brücher, M. and Chakif, M. and Gurevich, E.L. and Hergenröder, R.
    Spectrochimica Acta - Part B Atomic Spectroscopy 98 (2014)
    A polydisperse mixture of nickel-titanium nanoparticles generated by femtosecond-laser ablation was investigated by the application of different analytical methods in order to characterize the distribution of particle sizes. Images obtained with scanning and transmission electron microscopy and intensity curves of fluorescence excited by X-ray standing waves (XSW) were evaluated and the resulting distributions were plotted in several histograms. Based on the differences found in the results, the possibilities, limitations and appropriate criteria of application of the respective technique are discussed. The principles of the XSW technique and the evaluation procedure are explained in more detail. The respective analytical methods were compared in terms of spatial resolution, information content, the risk of artifacts, the statistics of the evaluation and the availability of experimental facilities. © 2014 Elsevier B.V.
    view abstract10.1016/j.sab.2014.05.004
  • Resolution and aspect ratio in two-photon lithography of positive photoresist
    Aumann, A. and Isabelle Ksouri, S. and Guo, Q. and Sure, C. and Gurevich, E.L. and Ostendorf, A.
    Journal of Laser Applications 26 (2014)
    In this work, the authors report on investigations of two-photon lithography of positive photoresist. The dependency of the pattern linewidth on variation in the processing parameters, like the laser patterning velocity or power of the femtosecond laser oscillator, is presented. The influence of the scan velocity between 0.38 and 1.90 mm/s on the resolution is discussed for a layer thickness of 3.5 μm. By using a commercial positive photoresist, an aspect ratio of 5 has been realized for grid structures and the qualities of the produced structures are discussed. © 2014 Laser Institute of America.
    view abstract10.2351/1.4857275
  • Selective Ablation Of Thin Films By Pulsed Laser
    Ostendorf, A. and Gurevich, E.L. and Shizhou, X.
    Springer Series in Materials Science 195 (2014)
    Laser direct patterning of thin films with minimal substrate damage is receiving attention in many industrial applications, e.g., photovoltaic or flat displays. Substantial progress has been made in understanding of the laser-matter interactions and reveals that laser-induced thermal effects are significantly critical in most of laser ablation processes. The thermal penetration depth, determined by the optical absorption and subsequently the thermal diffusion length, are heavily dependent on the applied laser pulse duration. The ratios between the film thickness, the thermal and the optical penetration depths separate the ablation to be film-like or bulk-like behavior of the thin-film ablation. © Springer International Publishing Switzerland 2014.
    view abstract10.1007/978-3-319-05987-7_9
  • On the influence of surface plasmon-polariton waves on pattern formation upon laser ablation
    Gurevich, E.L.
    Applied Surface Science 278 (2013)
    Here we analyze whether the laser-induced periodic surface structures (LIPSS), which appear on solid surfaces exposed to single-pulse femtosecond laser radiation, can be explained by excitation of surface plasmon-polariton waves. We demonstrate that excitation of the surface plasmons is impossible in the laser-ablation experiments, since the excitation conditions are not fulfilled. Moreover, properties and morphology of the observed periodic patterns contradict to the theory of the plasmonic nature of the LIPSS. The results are illustrated with experimental examples. © 2012 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.apsusc.2013.01.103
  • Development of a novel dielectric barrier microhollow cathode discharge for gaseous atomic emission spectroscopy
    Meyer, C. and Demecz, D. and Gurevich, E.L. and Marggraf, U. and Jestel, G. and Franzke, J.
    Journal of Analytical Atomic Spectrometry 27 (2012)
    The present research demonstrates a novel microhollow cathode discharge based on the dielectric barrier discharge principle (DB-MHCD) for application as an analytical microplasma gas detector. The plasma is formed inside a microfabricated multilayer structure and is mainly confined in a bore with a diameter of 100-250 μm. The DB-MHCD operates with alternating rectangular voltages of 1-2 kV pp and a frequency of 50 kHz. The insulation of the electrodes by the dielectric layer prevents deterioration of the electrodes and eliminates contamination of the gaseous analyte with electrode material. This enables long-term operation of the DB-MHCD device over several days. The analytical performance of the DB-MHCD is demonstrated with halogenated hydrocarbons leading to an excellent detection limit of 27 ppb for gaseous Cl in He. © The Royal Society of Chemistry 2012.
    view abstract10.1039/c2ja10225k
  • Experimental and numerical study of surface alloying by femtosecond laser radiation
    Gurevich, E.L. and Kittel, S. and Hergenröder, R.
    Applied Surface Science 258 (2012)
    Here we report on experimental studies of femtosecond laser induced surface metal alloying. We demonstrate that layers of different metals can be mixed in a certain range of laser pulse energies. Numeric simulations demonstrate that the sub-surface melting and mixing is advantaged through the difference in the electron-phonon coupling constants of the metals in the multi-layer system. Dependence of the depth of the mixed layer on the number of laser pulses per unit area is studied. Numeric simulations illustrate physical picture of the laser alloying process. © 2011 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.apsusc.2011.10.094
  • Experimental estimation of the surface charge density in micro dielectric barrier discharges
    Meyer, C. and Franzke, J. and Gurevich, E.L.
    Journal of Physics D: Applied Physics 45 (2012)
    Here we report on the experimental studies of discharge processes in micro dielectric barrier gas discharge cells (μ-DBD). We propose a method, which allows us to measure the average surface charge density on the dielectric barriers of the discharge cell. The method is based on the measurement of the delay time between the polarity change of the applied voltage and the peak of the active discharge current. This procedure is applicable for cells of different sizes and geometries. It is especially advantageous for micro discharge cells, in which direct measurements are not applicable. © 2012 IOP Publishing Ltd.
    view abstract10.1088/0022-3727/45/35/355205
  • Incubation effect and its influence on laser patterning of ITO thin film
    Xiao, S. and Gurevich, E.L. and Ostendorf, A.
    Applied Physics A: Materials Science and Processing 107 (2012)
    Results are presented on the surface damage thresholds of ITO thin films induced by single-and multipulse laser irradiation at a pulse duration of 10 ps and a wavelength of 1064 nm. For multi-pulse ablation the incubation effect results in a reduction of the damage threshold, especially apparent at low pulse numbers and very small film thicknesses. The incubation effect attributes to the accumulation of defect sites and/or the storage of thermal stressstrain energy induced by the incident laser pulses. An incubation coefficient of S = 0.82 has been obtained which is independent on the film thickness in the range of 10-100 nm. In practical applications, the incubation effect determines the laser patterning structure of ITO films while increasing the pulse overlapping rate. The width of the patterned line can be predicted by the proposed model involving the laser fluence, the overlapping rate and the incubation coefficient. © 2012 Springer-Verlag.
    view abstract10.1007/s00339-012-6820-y
  • Analytical features of particle counting sensor based on plasmon assisted microscopy of nano objects
    Gurevich, E.L. and Temchura, V.V. and Überla, K. and Zybin, A.
    Sensors and Actuators, B: Chemical 160 (2011)
    We present a new analytical method for concentration measurements of nano objects of different nature such as polystyrene nanoparticles or viruses. The method is based on counting single particles of interest bound to a functionalized sensor surface. The counting rate was used for concentration measurements. For polystyrene particles, the counting rate was found to be in good agreement with the theoretically predicted one. Binding of human immunodeficiency virus (HIV) virus-like particles (VLPs) to the sensor surface functionalized with antibodies was observed. The concentration of HIV-VLP was estimated by means of well-characterized solutions of artificial nanoparticles as a reference material. The results are in a good agreement with standard enzyme-linked immunosorbent assay (ELISA) analysis. Factors are discussed which determine the detection power of the method. © 2011 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.snb.2011.09.050
  • Dielectric barrier discharges in analytical chemistry
    Meyer, C. and Müller, S. and Gurevich, E.L. and Franzke, J.
    Analyst 136 (2011)
    The present review reflects the importance of dielectric barrier discharges in analytical chemistry. Special about this discharge is - and in contrast to usual discharges with direct current - that the plasma is separated from one or two electrodes by a dielectric barrier. This gives rise to two main features of the dielectric barrier discharges; it can serve as dissociation and excitation device and as ionization mechanism, respectively. The article portrays the various application fields for dielectric barrier discharges in analytical chemistry, for example the use for elemental detection with optical spectrometry or as ionization source for mass spectrometry. Besides the introduction of different kinds of dielectric barrier discharges used for analytical chemistry from the literature, a clear and concise classification of dielectric barrier discharges into capacitively coupled discharges is provided followed by an overview about the characteristics of a dielectric barrier discharge concerning discharge properties and the ignition mechanism. © 2011 The Royal Society of Chemistry.
    view abstract10.1039/c0an00994f
  • GPGPU-based realtime detection of nano-objects using plasmon-assisted microscopy
    Weichert, F. and Timm, C. and Gaspar, M. and Zybin, A. and Gurevich, E.L. and Müller, H. and Marwedel, P.
    Informatik aktuell (2011)
    view abstract10.1007/978-3-642-19335-4_10
  • Radiofrequency driven and low cost fabricated microhollow cathode discharge for gaseous atomic emission spectrometry
    Meyer, C. and Heming, R. and Gurevich, E.L. and Marggraf, U. and Okruss, M. and Florek, S. and Franzke, J.
    Journal of Analytical Atomic Spectrometry 26 (2011)
    The current research presents a microhollow cathode discharge (MHCD) used as an analytical microplasma gas detector combining the advantages of a hollow cathode geometry in a miniaturized system offering atmospheric pressure operation. The plasma is driven by a homemade resonant radiofrequency generator (f = 1-10 MHz) reducing the electrode sputtering by a factor of 6.5 compared to common direct current operation leading to an extension of the lifetime of the microplasma chip of the same range. This paper aims further for the development of a novel low priced and therefore replaceable MHCD chip exchanging formerly used Pt electrodes by thin Cu electrodes. The analytical performance of the low cost Cu-MHCD with lifetime enhancing radiofrequency operation is demonstrated by atomic emission spectrometry with halogenated hydrocarbons with the Cl emission line at 912.114 nm. This leads to an excellent detection limit of 15 ppb v/v gaseous Cl in He making this microplasma chip suitable for lab on a chip application. © 2011 The Royal Society of Chemistry.
    view abstract10.1039/c0ja00216j
  • Self-organized nanopatterns in thin layers of superheated liquid metals
    Gurevich, E.L.
    Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 83 (2011)
    In this paper experimental observations of self-organized patterns in resolidified thin films of liquid superheated metals are reported. The superheated melt layers represent an example of a system driven far from equilibrium, which undergoes explosive boiling and solidifies afterward. The melts appear in the course of single-shot femtosecond laser heating of metal samples. Self-organized cells, solitonlike structures, periodic stripes, and transient patterns are observed. Pattern properties and mechanisms leading to the pattern formation as well as possible applications for nanotechnology are discussed. © 2011 American Physical Society.
    view abstract10.1103/PhysRevE.83.031604
  • Wetting morphologies and their transitions in grooved substrates
    Seemann, R. and Brinkmann, M. and Herminghaus, S. and Khare, K. and Law, B.M. and McBride, S. and Kostourou, K. and Gurevich, E. and Bommer, S. and Herrmann, C. and Michler, D.
    Journal of Physics Condensed Matter 23 (2011)
    When exposed to a partially wetting liquid, many natural and artificial surfaces equipped with complex topographies display a rich variety of liquid interfacial morphologies. In the present article, we focus on a few simple paradigmatic surface topographies and elaborate on the statics and dynamics of the resulting wetting morphologies. It is demonstrated that the spectrum of wetting morphologies increases with increasing complexity of the groove structure. On elastically deformable substrates, additional structures in the liquid morphologies can be observed, which are caused by deformations of the groove geometry in the presence of capillary forces. The emergence of certain liquid morphologies in grooves can be actively controlled by changes in wettability and geometry. For electrically conducting solid substrates, the apparent contact angle can be varied by electrowetting. This allows, depending on groove geometry, a reversible or irreversible transport of liquid along surface grooves. In the case of irreversible liquid transport in triangular grooves, the dynamics of the emerging instability is sensitive to the apparent hydrodynamic slip at the substrate. On elastic substrates, the geometry can be varied in a straightforward manner by stretching or relaxing the sample. The imbibition velocity in deformable grooves is significantly reduced compared to solid grooves, which is a result of the microscopic deformation of the elastic groove material close to the three phase contact line. © 2011 IOP Publishing Ltd.
    view abstract10.1088/0953-8984/23/18/184108
  • Modification of GaAs surface by low-current Townsend discharge
    Gurevich, E.L. and Kittel, S. and Hergenröder, R. and Astrov, Y.A. and Portsel, L.M. and Lodygin, A.N. and Tolmachev, V.A. and Ankudinov, A.V.
    Journal of Physics D: Applied Physics 43 (2010)
    The influence of stationary spatially homogeneous Townsend discharge on the (1 0 0) surface of semi-insulating GaAs samples is studied. Samples exposed to both electrons and ions in a nitrogen discharge at a current density j = 60 μA cm-2 are studied by means of x-ray photoelectron spectroscopy, ellipsometry and atomic force microscopy. It is shown that an exposure to low-energy ions (< 1 eV) changes the crystal structure of the semiconductor for a depth of up to 10-20 nm, although the stoichiometric composition does not change. The exposure to low-energy electrons (< 10 eV) forms an oxide layer, which is 5-10 nm thick. Atomic force microscopy demonstrates that the change in the surface potential of the samples may exceed 100 mV, for both discharge polarities, while the surface roughness does not increase. © 2010 IOP Publishing Ltd.
    view abstract10.1088/0022-3727/43/27/275302
  • Real-time detection of single immobilized nanoparticles by surface plasmon resonance imaging
    Zybin, A. and Kuritsyn, Y.A. and Gurevich, E.L. and Temchura, V.V. and Überla, K. and Niemax, K.
    Plasmonics 5 (2010)
    In this manuscript, a new approach in surface plasmon resonance microscopy is presented. The method provides optical real-time detection of single nanoparticles on surfaces. The potential of the method is demonstrated recording spherical dielectric particles as small as 40 nm in diameter and single HIV virus-like particles having diameters of ~100 nm both immobilized on functionalized surfaces. The surface plasmon resonance signal in the binding spots was found to be almost linearly proportional to the size of the particles and, therefore, surpasses the intensity of Mie scattering on spherical particle (dependence ~r-6) by orders of magnitude for small objects. The physical reason leading to this strong effect is discussed. © Springer Science+Business Media, LLC 2009.
    view abstract10.1007/s11468-009-9111-5
  • Signal analysis and classification for surface plasmon assisted microscopy of nanoobjects
    Weichert, F. and Gaspar, M. and Timm, C. and Zybin, A. and Gurevich, E.L. and Engel, M. and Müller, H. and Marwedel, P.
    Sensors and Actuators, B: Chemical 151 (2010)
    The need for portable and on site screening methods for viruses is evident in face of virus infections that can spread fastly in a heavily connected world. A robust and efficient method for detecting viruses is a novel technique called Plasmon Assisted Microscopy of Nanoobjects. It is based on the acquisition of images from a sensor surface exploiting the behavior of surface plasmons in the presence of nanoobjects. In this paper an efficient image analysis approach with respect to the requirements of the sensor is presented and an embedded image processing system for this purpose is introduced. The processing pipeline comprises three steps and starts with restorating the images by removing the background and filtering artifacts. The acquired image series is analyzed pixel by pixel in a second pipeline step in order to detect pixels containing nanoobjects. In a last step pixels are aggregated to nanoobject structures. The paper introduces in the context of this virus detection method a configurable embedded system that was used for rapid prototyping of the image analysis algorithms in a flexible way. © 2010 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.snb.2010.08.005
  • lasers

  • nanoparticles

  • plasmons

  • thin films

  • ultrashort pulses

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