Search Results
Laser-induced surface modification of biopolymers - Micro/nanostructuring and functionalization
2018, Stankova, N.E., Atanasov, P.A., Nedyalkov, N.N., Tatchev, Dr., Kolev, K.N., Valova, E.I., Armyanov, St.A., Grochowska, K., Śliwiński, G., Fukata, N., Hirsch, D., Rauschenbach, B.
The medical-grade polydimethylsiloxane (PDMS) elastomer is a widely used biomaterial in medicine for preparation of high-tech devices because of its remarkable properties. In this paper, we present experimental results on surface modification of PDMS elastomer by using ultraviolet, visible, and near-infrared ns-laser system and investigation of the chemical composition and the morphological structure inside the treated area in dependence on the processing parameters - wavelength, laser fluence and number of pulses. Remarkable chemical transformations and changes of the morphological structure were observed, resulting in the formation of a highly catalytically active surface, which was successfully functionalized via electroless Ni and Pt deposition by a sensitizing-activation free process. The results obtained are very promising in view of applying the methods of laser-induced micro- and nano-structuring and activation of biopolymers' surface and further electroless metal plating to the preparation of, e.g., multielectrode arrays (MEAs) devices in neural and muscular surface interfacing implantable systems.
SERS analysis of Ag nanostructures produced by ion-beam deposition
2018, Atanasov, P.A., Nedyalkov, N.N., Nikov, Ru.G., Grüner, Ch., Rauschenbach, B., Fukata, N.
This study deals with the development of a novel technique for formation of advanced Ag nanostructures (NSs) to be applied to high-resolution analyses based on surface enhanced Raman scattering (SERS). It has direct bearing on human health and food quality, e.g., monitoring small amount or traces of pollutants or undesirable additives. Three types of nanostructured Ag samples were produced using ion-beam deposition at glancing angle (GLAD) on quartz. All fabricated structures were covered with BI-58 pesticide (dimethoate) or Rhodamine 6G (R6G) for testing their potential for use as substrates for (SERS).
Laser structuring of thin layers for flexible electronics by a shock wave-induced delamination process
2014, Lorenz, P., Ehrhardt, M., Zimmer, K.
The defect-free laser-assisted structuring of thin films on flexible substrates is a challenge for laser methods. However, solving this problem exhibits an outstanding potential for a pioneering development of flexible electronics. Thereby, the laser-assisted delamination method has a great application potential. At the delamination process: the localized removal of the layer is induced by a shock wave which is produced by a laser ablation process on the rear side of the substrate. In this study, the thin-film patterning process is investigated for different polymer substrates dependent on the material and laser parameters using a KrF excimer laser. The resultant structures were studied by optical microscopy and white light interferometry (WLI). The delamination process was tested at different samples (indium tin oxide (ITO) on polyethylene terephthalate (PET), epoxy-based negative photoresist (SU8) on polyimide (PI) and indium tin oxide/copper indium gallium selenide/molybdenum (ITO/CIGS/Mo) on PI.
In-process evaluation of electrical properties of CIGS solar cells scribed with laser pulses of different pulse lengths
2014, Zimmer, K., Wang, X., Lorenz, P., Bayer, L., Ehrhardt, M., Scheit, C., Braun, A.
The optimization of laser scribing for the interconnection of CIGS solar cells is a current focus of laser process development. In addition to the geometry of the laser scribes the impact of the laser patterning to the electrical properties of the solar cells has to be optimized with regards to the scribing process and the laser sources. In-process measurements provide an approach for reliable evaluation of the electrical characteristics. In particular, the parallel resistance Rp that was calculated from the measured I-V curves was measured in dependence on the scribing parameters of a short-pulsed ns laser in comparison to a standard ps laser at a wavelength of 1.06 μm. With low pulse overlap of ∼ 20% a reduction of Rp to 2/3 of the initial value has been achieved for ns laser pulses. In comparison to ps laser slightly more defects were observed at the investigated parameter range.
Preparation and characterisation of carbon-free Cu(111) films on sapphire for graphene synthesis
2018, Lehnert, J., Spemann, D., Surjuse, S., Mensing, M., Grüner, C., With, P., Schumacher, P., Finzel, A., Hirsch, D., Rauschenbach, B.
This work presents an investigation of carbon formed on polycrystalline Cu(111) thin films prepared by ion beam sputtering at room temperature on c-plane Al2O3 after thermal treatment in a temperature range between 300 and 1020°C. The crystallinity of the Cu films was studied by XRD and RBS/channeling and the surface was characterised by Raman spectroscopy, XPS and AFM for each annealing temperature. RBS measurements revealed the diffusion of the Cu into the Al2O3 substrate at high temperatures of > 700°C. Furthermore, a cleaning procedure using UV ozone treatment is presented to remove the carbon from the surface which yields essentially carbon-free Cu films that open the possibility to synthesize graphene of well-controlled thickness (layer number).
Incorporation of nitrogen into TiO2 thin films during PVD processes
2014, Asenova, I., Manova, D., Mändl, S.
In this paper we investigate the possibility of incorporating nitrogen into amorphous, photocatalytic TiO2 thin films, prepared at room temperature, during the growth process. The aim is to reduce the bandgap of the UV active thin films. Physical vapor deposition experiments employing a titanium vacuum arc with gas backfill ranging from pure oxygen to pure nitrogen, are carried out. The resulting films are characterized for chemical composition, phase composition, optical properties and hydrophilicity in order to determine a correlation between gas composition and thin film properties. The experimental results point that a visible change in the band structure of the deposited layers is achieved.
Pattern transfer of sub-micrometre-scaled structures into solid copper by laser embossing
2014, Ehrhardt, M., Lorenz, P., Lotnyk, A., Romanus, H., Thelander, E., Zimmer, K.
Laser embossing allows the micron and submicron patterning of metal substrates that is of great interest in a wide range of applications. This replication process enables low-cost patterning of metallic materials by non-thermal, high-speed forming which is driven by laser-induced shock waves. In this study the surface topography characteristics as well as the material structure at laser embossing of sub-micrometre gratings into solid copper is presented. The topography of the laser-embossed copper pattern is analysed with atomic force microscopy (AFM) in comparison to the master surface. The height of the embossed structures and the replicated pattern fidelity increases up to a laser fluence of F ∼ 10 J/cm2. For higher laser fluences the height of the embossed structures saturates at 75% of the master pattern height and the shape is adequate to the master. Structural modifications in the copper mono crystals after the laser embossing process were investigated with transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). Almost no modifications were detected. The residual stress after laser embossing of 32 MPa (F = 30 J/cm2) has only a limited influence on the surface pattern formation.
Evidence for Efficient Pathway to Produce Slow Electrons by Ground-state Dication in Clusters
2017, You, Daehyun, Fukuzawa, Hironobu, Sakakibara, Yuta, Takanashi, Tsukasa, Ito, Yuta, Maliyar, Gianluigi G., Motomura, Koji, Nagaya, Kiyonobu, Nishiyama, Toshiyuki, Asa, Kazuki, Sato, Yuhiro, Saito, Norio, Oura, Masaki, Schöffler, Markus, Kastirke, Gregor, Hergenhahn, Uwe, Stumpf, Vasili, Gohkberg, Kirill, Kuleff, Alexander I., Cederbaum, Lorenz S., Ueda, Kiyoshi
We present an experimental evidence for a so-far unobserved, but potentially very important step relaxation cascades following inner-shell ionization of a composite system: Multiply charged ionic states created after Auger decay may be neutralized by electron transfer from a neighboring species, producing at the same time a low-energy free electron. This electron transfer-mediated decay (ETMD) called process is effective even after Auger decay into the dicationic ground state. Here, we report the ETMD of Ne2+ produced after Ne 1s photoionization in Ne-Kr mixed clusters.
Laser-Induced front Side Etching: An Easy and Fast Method for Sub-μm Structuring of Dielectrics
2012, Lorenz, P., Ehrhardt, M., Zimmer, K.
Laser-induced front side etching (LIFE) is a method for the nanometer-precision structuring of dielectrics, e.g. fused silica, using thin metallic as well as organic absorber layer attached to the laser-irradiated front side of the sample. As laser source an excimer laser with a wavelength of 248 nm and an pulse duration of 25 ns was used. For sub-μm patterning a phase mask illuminated by the top hat laser beam was projected by a Schwarzschild objective. The LIFE process allows the fabrication of well-defined and smooth surface structures with sub-μm lateral etching regions (Δx < 350 nm) and vertical etching depths from 1 nm to sub-mm.
Laser Patterning of CIGS thin Films with 1550 nm Nanosecond Laser Pulses
2016, Ehrhardt, Martin, Lorenz, Pierre, Bayer, Lukas, Zagoranskiy, Igor, Zimmer, Klaus
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.