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- ItemComparative study of sculptured metallic thin films deposited by oblique angle deposition at different temperatures(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2018) Liedtke, Susann; Grüner, Christoph; Gerlach, Jürgen W.; Rauschenbach, BerndMetals with a wide range of melting points are deposited by electron beam evaporation under oblique deposition geometry on thermally oxidized Si substrates. During deposition the sample holder is cooled down to 77 K. It is observed that all obliquely deposited metals grow as tilted, high aspect ratio columns and hence with a similar morphology. A comparison of such columns with those deposited at room temperature (300 K) reveals that shadowing dominates the growth process for columns deposited at 77 K, while the impact of surface diffusion is significantly increased at elevated substrate temperatures. Furthermore, it is discussed how the incidence angle of the incoming particle flux and the substrate temperature affect the columnar tilt angles and the porosity of the sculptured thin films. Exemplarily for tilted Al columns deposited at 77 K and at 300 K, in-plane pole figure measurements are carried out. A tendency to form a biaxial texture as well as a change in the crystalline structure depending on the substrate temperature is found for those films.
- ItemTiO2 as Photosensitizer and Photoinitiator for Synthesis of Photoactive TiO2-PEGDA Hydrogel Without Organic Photoinitiator(Lausanne : Frontiers Media, 2018-8-7) Glass, Sarah; Trinklein, Betsy; Abel, Bernd; Schulze, AgnesThe replacement of potentially toxic photoinitiators is of increasing interest regarding the synthesis of biomaterials by photopolymerization. Therefore, we present a new method for the preparation of UV polymerized hydrogels with TiO2 as a photoinitiator. Titania is known to be an excellent photoactive compound which is non-toxic, inert, and cheap. The so-formed hydrogels possess excellent mechanical properties, a high swelling ratio, and high thermal stability. Furthermore, no TiO2 is released from the hydrogels. Thus, the material is highly suitable for medical applications. Additionally, the present TiO2 in the hydrogels remains photoactive as demonstrated by degradation of methylene blue. This enables the application of TiO2-hydrogels in photodynamic therapy.
- ItemTarget ion and neutral spread in high power impulse magnetron sputtering(New York, NY : Inst., 2022) Hajihoseini, H.; Brenning, N.; Rudolph, M.; Raadu, M.A.; Lundin, D.; Fischer, J.; Minea, T. M.; Gudmundsson, J.T.In magnetron sputtering, only a fraction of the sputtered target material leaving the ionization region is directed toward the substrate. This fraction may be different for ions and neutrals of the target material as the neutrals and ions can exhibit a different spread as they travel from the target surface toward the substrate. This difference can be significant in high power impulse magnetron sputtering (HiPIMS) where a substantial fraction of the sputtered material is known to be ionized. Geometrical factors or transport parameters that account for the loss of produced film-forming species to the chamber walls are needed for experimental characterization and modeling of the magnetron sputtering discharge. Here, we experimentally determine transport parameters for ions and neutral atoms in a HiPIMS discharge with a titanium target for various magnet configurations. Transport parameters are determined to a typical substrate, with the same diameter (100 mm) as the cathode target, and located at a distance 70 mm from the target surface. As the magnet configuration and/or the discharge current are changed, the transport parameter for neutral atoms ζ tn remains roughly the same, while transport parameters for ions ζ ti vary greatly. Furthermore, the relative ion-to-neutral transport factors, ζ ti / ζ tn, that describe the relative deposited fractions of target material ions and neutrals onto the substrate, are determined to be in the range from 0.4 to 1.1.
- ItemIncreased biocompatibility and bioactivity after energetic PVD surface treatments(Basel : MDPI, 2009) Mändl, S.Ion implantation, a common technology in semiconductor processing, has been applied to biomaterials since the 1960s. Using energetic ion bombardment, a general term which includes conventional ion implantation plasma immersion ion implantation (PIII) and ion beam assisted thin film deposition, functionalization of surfaces is possible. By varying and adjusting the process parameters, several surface properties can be attuned simultaneously. Extensive research details improvements in the biocompatibility, mainly by reducing corrosion rates and increasing wear resistance after surface modification. Recently, enhanced bioactivity strongly correlated with the surface topography and less with the surface chemistry has been reported, with an increased roughness on the nanometer scale induced by self-organisation processes during ion bombardment leading to faster cellular adhesion processes. © 2009 by the authors;.
- ItemFemtosecond laser induced step-like structures inside transparent hydrogel due to laser induced threshold reduction(San Francisco, California, US : PLOS, 2019) Saerchen, Emanuel; Liedtke-Gruener, Susann; Kopp, Maximilian; Heisterkamp, Alexander; Lubatschowski, Holger; Ripken, TammoIn the area of laser material processing, versatile applications for cutting glasses and transparent polymers exist. However, parasitic effects such as the creation of step-like structures appear when laser cutting inside a transparent material. To date, these structures were only described empirically. This work establishes the physical and chemical mechanisms behind the observed effects and describes the influence of process and material parameters onto the creation of step-like structures in hydrogel, Dihydroxyethylmethacrylat (HEMA). By focusing laser pulses in HEMA, reduced pulse separation distance below 50 nm and rise in pulse energy enhances the creation of unintended step-like structures. Spatial resolved Raman-spectroscopy was used to measure the laser induced chemical modification, which results into a reduced breakdown threshold. The reduction in threshold influences the position of optical breakdown for the succeeding laser pulses and consequently leads to the step-like structures. Additionally, the experimental findings were supplemented with numerical simulations of the influence of reduced damage threshold onto the position of optical breakdown.
- ItemDeposition of exchange-coupled dinickel complexes on gold substrates utilizing ambidentate mercapto-carboxylato ligands(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2017) Börner, Martin; Blömer, Laura; Kischel, Marcus; Richter, Peter; Salvan, Georgeta; Zahn, Dietrich R. T.; Siles, Pablo F.; Fuentes, Maria E. N.; Bufon, Carlos C. B.; Grimm, Daniel; Schmidt, Oliver G.; Breite, Daniel; Abel, Bernd; Kersting, BertholdThe chemisorption of magnetically bistable transition metal complexes on planar surfaces has recently attracted increased scientific interest due to its potential application in various fields, including molecular spintronics. In this work, the synthesis of mixed-ligand complexes of the type [NiII2L(L’)](ClO4), where L represents a 24-membered macrocyclic hexaazadithiophenolate ligand and L’ is a ω-mercapto-carboxylato ligand (L’ = HS(CH2)5CO2− (6), HS(CH2)10CO2− (7), or HS(C6H4)2CO2− (8)), and their ability to adsorb on gold surfaces is reported. Besides elemental analysis, IR spectroscopy, electrospray ionization mass spectrometry (ESIMS), UV–vis spectroscopy, and X-ray crystallography (for 6 and 7), the compounds were also studied by temperature-dependent magnetic susceptibility measurements (for 7 and 8) and (broken symmetry) density functional theory (DFT) calculations. An S = 2 ground state is demonstrated by temperature-dependent susceptibility and magnetization measurements, achieved by ferromagnetic coupling between the spins of the Ni(II) ions in 7 (J = +22.3 cm−1) and 8 (J = +20.8 cm−1; H = −2JS1S2). The reactivity of complexes 6–8 is reminiscent of that of pure thiolato ligands, which readily chemisorb on Au surfaces as verified by contact angle, atomic force microscopy (AFM) and spectroscopic ellipsometry measurements. The large [Ni2L] tail groups, however, prevent the packing and self-assembly of the hydrocarbon chains. The smaller film thickness of 7 is attributed to the specific coordination mode of the coligand. Results of preliminary transport measurements utilizing rolled-up devices are also reported.
- ItemReduction of biofouling of a microfiltration membrane using amide functionalities-Hydrophilization without changes in morphology(Basel : MDPI, 2020) Breite, Daniel; Went, Marco; Prager, Andrea; Kühnert, Mathias; Schulze, AgnesA major goal of membrane science is the improvement of the membrane performance and the reduction of fouling effects, which occur during most aqueous filtration applications. Increasing the surface hydrophilicity can improve the membrane performance (in case of aqueous media) and decelerates membrane fouling. In this study, a PES microfiltration membrane (14,600 L m−2 h−1 bar−1) was hydrophilized using a hydrophilic surface coating based on amide functionalities, converting the hydrophobic membrane surface (water contact angle, WCA: ~90°) into an extremely hydrophilic one (WCA: ~30°). The amide layer was created by first immobilizing piperazine to the membrane surface via electron beam irradiation. Subsequently, a reaction with 1,3,5-benzenetricarbonyl trichloride (TMC) was applied to generate an amide structure. The presented approach resulted in a hydrophilic membrane surface, while maintaining permeance of the membrane without pore blocking. All membranes were investigated regarding their permeance, porosity, average pore size, morphology (SEM), chemical composition (XPS), and wettability. Soxhlet extraction was carried out to demonstrate the stability of the applied coating. The improvement of the modified membranes was demonstrated using dead-end filtration of algae solutions. After three fouling cycles, about 60% of the initial permeance remain for the modified membranes, while only ~25% remain for the reference.
- ItemFinishing of metal optics by ion beam technologies(Bellingham, Wash. : SPIE, 2019) Bauer, Jens; Frost, Frank; Lehmann, Antje; Ulitschka, Melanie; Li, Yaguo; Arnold, ThomasUltraprecise mirror devices show considerable potential with view to applications in the visible and the ultraviolet spectral ranges. Aluminum alloys gather good mechanical and excellent optical properties and thus they emerge as important mirror construction materials. However, ultraprecision machining and polishing of optical aluminum surfaces are challenging, which originates from the high chemical reactivity and the heterogeneous matrix structure. Recently, several ion beam-based techniques have been developed to qualify aluminum mirrors for short-wavelength applications. We give an overview of the state-of-the-art ion beamprocessing techniques for figure error correction and planarization, either by direct aluminum machining or with the aid of polymer or inorganic, amorphous surface films. © The Authors.
- ItemTailoring morphology in titania nanotube arrays by implantation: experiments and modelling on designed pore size—and beyond(London [u.a.] : Taylor & Francis, 2021) Kupferer, Astrid; Mändl, Stephan; Mayr, Stefan G.Titania nanotube arrays are an exceptionally adaptable material for various applications ranging from energy conversion to biomedicine. Besides electronic properties, structural morphology on nanometre scale is essential. It is demonstrated that ion implantation constitutes a versatile method for the synthesis of tailored nanotube morphologies. Experimental-phenomenological observations reveal a successive closing behaviour of nanotubes upon ion implantation. Employing molecular dynamics calculations in combination with analytical continuum models, the physical origins of this scenario are unravelled by identifying ion bombardment induced viscous flow driven by capillarity as its underlying mechanism besides minor contributions from sputtering and redeposition. These findings enable the tailoring of nanotube arrays suitable for manifold applications.
- ItemCharge Separating Microfiltration Membrane with pH-Dependent Selectivity(Basel : MDPI, 2018-12-20) Breite, Daniel; Went, Marco; Prager, Andrea; Kuehnert, Mathias; Schulze, AgnesMembrane filters are designed for selective separation of components from a mixture. While separation by size might be the most common approach, other characteristics like charge can also be used for separation as presented in this study. Here, a polyether sulfone membrane was modified to create a zwitterionic surface. Depending on the pH value of the surrounding solution the membrane surface will be either negatively or positively charged. Thus, the charged state can be easily adjusted even by small changes of the pH value of the solution. Charged polystyrene beads were used as model reagent to investigate the pH dependent selectivity of the membrane. It was found that electrostatic forces are dominating the interactions between polystyrene beads and membrane surface during the filtration. This enables a complete control of the membrane’s selectivity according to the electrostatic interactions. Furthermore, differently charged beads marked with fluorescent dyes were used to investigate the selectivity of mixtures of charged components. These different components were successfully separated according to their charged state proving the selectivity of the invented membrane.