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- ItemMagnetic Nanoparticle Chains in Gelatin Ferrogels: Bioinspiration from Magnetotactic Bacteria(Weinheim : Wiley-VCH, 2019) Sturm, Sebastian; Siglreitmeier, Maria; Wolf, Daniel; Vogel, Karin; Gratz, Micha; Faivre, Damien; Lubk, Axel; Büchner, Bernd; Sturm, Elena V.; Cölfen, HelmutInspired by chains of ferrimagnetic nanocrystals (NCs) in magnetotactic bacteria (MTB), the synthesis and detailed characterization of ferrimagnetic magnetite NC chain-like assemblies is reported. An easy green synthesis route in a thermoreversible gelatin hydrogel matrix is used. The structure of these magnetite chains prepared with and without gelatin is characterized by means of transmission electron microscopy, including electron tomography (ET). These structures indeed bear resemblance to the magnetite assemblies found in MTB, known for their mechanical flexibility and outstanding magnetic properties and known to crystallographically align their magnetite NCs along the strongest <111> magnetization easy axis. Using electron holography (EH) and angular dependent magnetic measurements, the magnetic interaction between the NCs and the generation of a magnetically anisotropic material can be shown. The electro- and magnetostatic modeling demonstrates that in order to precisely determine the magnetization (by means of EH) inside chain-like NCs assemblies, their exact shape, arrangement and stray-fields have to be considered (ideally obtained using ET). © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemA magnetocaloric booster unit for energy-efficient air-conditioning(Basel : MDPI AG, 2019) Krautz, M.; Beyer, M.; Jäschke, C.; Schinke, L.; Waske, A.; Seifert, J.A concept for the application of a magnetocaloric device in energy-efficient air conditioners is introduced. In order to evaluate this concept, a test stand has been developed equipped with a magnetic field source providing about a 1.5-T flux density change into which different regenerator geometries can be implemented and evaluated. A processing route for the production of profiled magnetocaloric LaFeSiMn-based composite plates by tape casting is presented. The processed plates show a maximum isothermal entropy change of about 3.8 J kg −1 K −1 at a magnetic field change of 1.5 T at 285 K. The hydraulic and thermal performance of regenerator geometries that can be realized by profiled plates is assessed by calculations. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemEvolution of the charge carrier plasmon in the one-dimensional metal TTF-TCNQ as a function of temperature and momentum(Bristol : Institute of Physics Publishing, 2019) Kovbasa, N.; Graf, L.; Knupfer, M.We have investigated the charge carrier plasmon in the quasi one-dimensional metal TTF-TCNQ using electron energy-loss spectroscopy. Our data reveal a negative plasmon dispersion with a slope that is independent of temperature, which is in agreement to predictions from model calculations and previous room temperature data. A plasmon energy shift upon temperature is observed, and we discuss possible contributions to this shift. The spectral width of the plasmon is rather temperature independent, but increases clearly above a momentum value of about 0.3 Å-1.
- ItemCombining carbon nanotubes and chitosan for the vectorization of methotrexate to lung cancer cells(Basel : MDPI AG, 2019) Cirillo, G.; Vittorio, O.; Kunhardt, D.; Valli, E.; Voli, F.; Farfalla, A.; Curcio, M.; Spizzirri, U.G.; Hampel, S.A hybrid system composed of multi-walled carbon nanotubes coated with chitosan was proposed as a pH-responsive carrier for the vectorization of methotrexate to lung cancer. The effective coating of the carbon nanostructure by chitosan, quantified (20% by weight) by thermogravimetric analysis, was assessed by combined scanning and transmission electron microscopy, and X-ray photoelectron spectroscopy (N1s signal), respectively. Furthermore, Raman spectroscopy was used to characterize the interaction between polysaccharide and carbon counterparts. Methotrexate was physically loaded onto the nanohybrid and the release profiles showed a pH-responsive behavior with higher and faster release in acidic (pH 5.0) vs. neutral (pH 7.4) environments. Empty nanoparticles were found to be highly biocompatible in either healthy (MRC-5) or cancerous (H1299) cells, with the nanocarrier being effective in reducing the drug toxicity on MRC-5 while enhancing the anticancer activity on H1299.
- ItemMo-La2O3 multilayer metallization systems for high temperature surface acoustic wave sensor devices(Basel : MDPI AG, 2019) Menzel, S.B.; Seifert, M.; Priyadarshi, A.; Rane, G.K.; Park, E.; Oswald, S.; Gemming, T.Developing advanced thin film materials is the key challenge in high-temperature applications of surface acoustic wave sensor devices. One hundred nanometer thick (Mo-La2O3) multilayer systems were fabricated at room temperature on thermally oxidized (100) Si substrates (SiO2/Si) to study the effect of lanthanum oxide on the electrical resistivity of molybdenum thin films and their high-temperature stability. The multilayer systems were deposited by the magnetron sputter deposition of extremely thin (≤1 nm) La interlayers in between adjacent Mo layers. After deposition of each La layer the process was interrupted for 25 to 60 min to oxidize the La using the residual oxygen in the high vacuum of the deposition chamber. The samples were annealed at 800 °C in high vacuum for up to 120 h. In case of a 1 nm thick La interlayer in-between the Mo a continuous layer of La2O3 is formed. For thinner La layers an interlayer between adjacent Mo layers is observed consisting of a (La2O3-Mo) mixed structure of molybdenum and nm-sized lanthanum oxide particles. Measurements show that the (Mo-La2O3) multilayer systems on SiO2/Si substrates are stable at least up to 800 °C for 120 h in high vacuum conditions.
- ItemElectroless-deposited platinum antennas for wireless surface acousticwave sensors(Basel : MDPI AG, 2019) Brachmann, E.; Seifert, M.; Neumann, N.; Alshwawreh, N.; Uhlemann, M.; Menzel, S.B.; Acker, J.; Herold, S.; Hoffmann, V.; Gemming, T.In an effort to develop a cost-efficient technology for wireless high-temperature surface acoustic wave sensors, this study presents an evaluation of a combined method that integrates physical vapor deposition with electroless deposition for the fabrication of platinum-based planar antennas. The proposed manufacturing process becomes attractive for narrow, thick, and sparse metallizations for antennas in the MHz to GHz frequency range. In detail, narrow platinum-based lines of a width down to 40 μm were electroless-deposited on γ -Al2O3 substrates using different seed layers. At first, the electrolyte chemistry was optimized to obtain the highest deposition rate. Films with various thickness were prepared and the electrical resistivity, microstructure, and chemical composition in the as-prepared state and after annealing at temperatures up to 1100 °C were evaluated. Using these material parameters, the antenna was simulated with an electromagnetic full-wave simulation tool and then fabricated. The electrical parameters, including the S-parameters of the antenna, were measured. The agreement between the simulated and the realized antenna is then discussed.
- ItemThe influence of partial replacement of Cu with Ga on the corrosion behavior of Ti40Zr10Cu36PD14 metallic glasses(Bristol : IOP Publishing, 2019) Wei, Qi; Gostin, Petre Flaviu; Addison, Owen; Reed, Daniel; Calin, Mariana; Bera, Supriya; Ramasamy, Parthiban; Davenport, AlisonTiZrCuPdGa metallic glasses are under consideration for small dental biomedical implants. There is interest in replacing some of the Cu with Ga to improve the glass-forming ability and biocompatibility. Ti40Zr10Cu36-xPd14Gax (x = 0, 1, 2, 4, 8 and 10 at.%) metallic glasses in rod and ribbon forms were fabricated by mould casting and melt spinning, respectively, and electrochemically tested in a 0.9wt.% NaCl (0.154 M) solution. It has been shown that for both rod and ribbon samples Ga levels up to 8% have no significant effect on passive current density, pitting potential or cathodic reactivity in 0.9% NaCl at 37°C. Different pitting potential and corrosion potential values were found when ribbon and rod samples of the same composition were compared for all compositions apart from the one containing the highest Ga level (10%). This was attributed to structural relaxation occurring as a result of the slower cooling rates during casting rods compared with melt-spinning ribbons. Substitution of Ga for Cu in these metallic glasses therefore expected to have no significant effect on corrosion susceptibility. © The Author(s) 2019.
- ItemLayered manganese bismuth tellurides with GeBi4Te7- and GeBi6Te10-type structures: Towards multifunctional materials(London : RSC Publ., 2019) Souchay, Daniel; Nentwig, Markus; Günther, Daniel; Keilholz, Simon; de Boor, Johannes; Zeugner, Alexander; Isaeva, Anna; Ruck, Michael; Wolter, Anja U.B.; Büchnerde, Bernd; Oeckler, OliverThe crystal structures of new layered manganese bismuth tellurides with the compositions Mn0.85(3)Bi4.10(2)Te7 and Mn0.73(4)Bi6.18(2)Te10 were determined by single-crystal X-ray diffraction, including the use of microfocused synchrotron radiation. These analyses reveal that the layered structures deviate from the idealized stoichiometry of the 12P-GeBi4Te7 (space group P3m1) and 51R-GeBi6Te10 (space group R3m) structure types they adopt. Modified compositions Mn1-xBi4+2x/3Te7 (x = 0.15-0.2) and Mn1-xBi6+2x/3Te10 (x = 0.19-0.26) assume cation vacancies and lead to homogenous bulk samples as confirmed by Rietveld refinements. Electron diffraction patterns exhibit no diffuse streaks that would indicate stacking disorder. The alternating quintuple-layer [M2Te3] and septuple-layer [M3Te4] slabs (M = mixed occupied by Bi and Mn) with 1 : 1 sequence (12P stacking) in Mn0.85Bi4.10Te7 and 2 : 1 sequence (51R stacking) in Mn0.81Bi6.13Te10 were also observed in HRTEM images. Temperature-dependent powder diffraction and differential scanning calorimetry show that the compounds are high-temperature phases, which are metastable at ambient temperature. Magnetization measurements are in accordance with a MnII oxidation state and point at predominantly ferromagnetic coupling in both compounds. The thermoelectric figures of merit of n-type conducting Mn0.85Bi4.10Te7 and Mn0.81Bi6.13Te10 reach zT = 0.25 at 375 °C and zT = 0.28 at 325 °C, respectively. Although the compounds are metastable, compact ingots exhibit still up to 80% of the main phases after thermoelectric measurements up to 400 °C. © The Royal Society of Chemistry 2019.
- ItemElectrical and magnetic properties of NiTiO3 nanoparticles synthesized by the sol-gel synthesis method and microwave sintering(Amsterdam : Elsevier B.V., 2019) Pavithra, C.; Madhuri, W.In this paper, we focused on microwave sintered NiTiO3 nanoparticles synthesized via sol-gel method. The crystal structure was determined by the X-ray diffraction. Vibrational bands related to Ni-O and Ti-O bands were confirmed using the Fourier transform infrared spectrum. These NiTiO3 ceramics obeyed semiconductor behavior of Arrhenius type. The activation energy was found to be 0.04 μeV. The M-H curve exhibited superparamagnetic behavior at room temperature.
- ItemMicrostructure and elastic deformation behavior of β-type Ti-29Nb-13Ta-4.6Zr with promising mechanical properties for stent applications(Amsterdam : Elsevier B.V., 2019) Plaine, A.H.; Silva, M.R.D.; Bolfarini, C.In this paper, an attempt was made to combine theoretical composition design and thermo-mechanical treatments to produce a metastable β-type titanium alloy with mechanical compatibility for self-expandable stent applications. Metastable β-type Ti-29Nb-13Ta-4.6â»Zr (wt.%) thin-wires with an elastic modulus of 46â»GPa and a yield strength of 920â»MPa were successfully fabricated by cold rolling and low temperature aging. This combination of high yield strength and comparatively low elastic modulus resulted in enhanced elastic recoverable strain of 1.9%, which is much higher than that of the conventional metallic stent materials. The microstructure responsible for the much sought-after mechanical properties was observed to be mainly consisted of a homogeneous distribution of nanometer-sized α-precipitates in a β-phase matrix obtained via a spinodal decomposition of the pre-existed α″-martensite phase through α″â»→â»α″ leanâ»+â»α″ richâ»→â»αâ»+â»β. The α-precipitates increase the strength of the material by hindering the motion of dislocations (spinodal hardening) while the β-matrix with relatively low content of β-stabilizers gives rise to the observed low elastic modulus. More broadly, these findings could be extended to developing advanced metastable β-type titanium alloys for implant and other engineering applications.
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