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- ItemDirectly Anodized Sulfur-Doped TiO2 Nanotubes as Improved Anodes for Li-ion Batteries(Basel : MDPI, 2020) Sabaghi, Davood; Madian, Mahmoud; Omar, Ahmad; Oswald, Steffen; Uhlemann, Margitta; Maghrebi, Morteza; Baniadam, Majid; Mikhailova, DariaTiO2 represents one of the promising anode materials for lithium ion batteries due to its high thermal and chemical stability, relatively high theoretical specific capacity and low cost. However, the electrochemical performance, particularly for mesoporous TiO2, is limited and must be further developed. Elemental doping is a viable route to enhance rate capability and discharge capacity of TiO2 anodes in Li-ion batteries. Usually, elemental doping requires elevated temperatures, which represents a challenge, particularly for sulfur as a dopant. In this work, S-doped TiO2 nanotubes were successfully synthesized in situ during the electrochemical anodization of a titanium substrate at room temperature. The electrochemical anodization bath represented an ethylene glycol-based solution containing NH4F along with Na2S2O5 as the sulfur source. The S-doped TiO2 anodes demonstrated a higher areal discharge capacity of 95 µAh·cm−2 at a current rate of 100 µA·cm−2 after 100 cycles, as compared to the pure TiO2 nanotubes (60 µAh·cm−2). S-TiO2 also exhibited a significantly improved rate capability up to 2500 µA·cm−2 as compared to undoped TiO2. The improved electrochemical performance, as compared to pure TiO2 nanotubes, is attributed to a lower impedance in S-doped TiO2 nanotubes (STNTs). Thus, the direct S-doping during the anodization process is a promising and cost-effective route towards improved TiO2 anodes for Li-ion batteries.
- ItemTowards Bacteria Counting in DI Water of Several Microliters or Growing Suspension Using Impedance Biochips(Basel : MDPI, 2020) Kiani, Mahdi; Tannert, Astrid; Du, Nan; Hübner, Uwe; Skorupa, Ilona; Bürger, Danilo; Zhao, Xianyue; Blaschke, Daniel; Rebohle, Lars; Cherkouk, Charaf; Neugebauer, Ute; Schmidt, Oliver G.; Schmidt, HeidemarieWe counted bacterial cells of E. coli strain K12 in several-microliter DI water or in several-microliter PBS in the low optical density (OD) range (OD = 0.05–1.08) in contact with the surface of Si-based impedance biochips with ring electrodes by impedance measurements. The multiparameter fit of the impedance data allowed calibration of the impedance data with the concentration cb of the E. coli cells in the range of cb = 0.06 to 1.26 × 109 cells/mL. The results showed that for E. coli in DI water and in PBS, the modelled impedance parameters depend linearly on the concentration of cells in the range of cb = 0.06 to 1.26 × 109 cells/mL, whereas the OD, which was independently measured with a spectrophotometer, was only linearly dependent on the concentration of the E. coli cells in the range of cb = 0.06 to 0.50 × 109 cells/mL.
- ItemViscous Flow of Supercooled Liquid in a Zr-Based Bulk Metallic Glass Synthesized by Additive Manufacturing(Basel : MDPI, 2020) Kosiba, Konrad; Deng, Liang; Scudino, SergioThe constraint in sample size imposed by the critical cooling rate necessary for glass formation using conventional casting techniques is possibly the most critical limitation for the extensive use of bulk metallic glasses (BMGs) in structural applications. This drawback has been recently overcome by processing glass-forming systems via additive manufacturing, finally enabling the synthesis of BMGs with no size limitation. Although processing by additive manufacturing allows fabricating BMG objects with virtually no shape limitation, thermoplastic forming of additively manufactured BMGs may be necessary for materials optimization. Thermoplastic forming of BMGs is carried out above the glass transition temperature, where these materials behave as highly viscous liquids; the analysis of the viscosity is thus of primary importance. In this work, the temperature dependence of viscosity of the Zr52.5Cu17.9Ni14.6Al10Ti5 metallic glass fabricated by casting and laser powder bed fusion (LPBF) is investigated. We observed minor differences in the viscous flow of the specimens fabricated by the different techniques that can be ascribed to the higher porosity of the LPBF metallic glass. Nevertheless, the present results reveal a similar overall variation of viscosity in the cast and LPBF materials, which offers the opportunity to shape additively manufactured BMGs using already developed thermoplastic forming techniques.
- ItemStress and Microstructure Evolution in Mo Thin Films without or with Cover Layers during Thermal-Cycling(Basel : MDPI, 2020) Park, Eunmi; Seifert, Marietta; Rane, Gayatri K.; Menzel, Siegfried B.; Gemming, Thomas; Nielsch, KorneliusThe intrinsic stress behavior and microstructure evolution of Molybdenum thin films were investigated to evaluate their applicability as a metallization in high temperature microelectronic devices. For this purpose, 100 nm thick Mo films were sputter-deposited without or with an AlN or SiO2 cover layer on thermally oxidized Si substrates. The samples were subjected to thermal cycling up to 900 °C in ultrahigh vacuum; meanwhile, the in-situ stress behavior was monitored by a laser based Multi-beam Optical Sensor (MOS) system. After preannealing at 900 °C for 24 h, the uncovered films showed a high residual stress at room temperature and a plastic behavior at high temperatures, while the covered Mo films showed an almost entirely elastic deformation during the thermal cycling between room temperature and 900 °C with hardly any plastic deformation, and a constant stress value during isothermal annealing without a notable creep. Furthermore, after thermal cycling, the Mo films without as well as with a cover layer showed low electrical resistivity (≤10 μΩ·cm).
- ItemInfluencing Martensitic Transition in Epitaxial Ni-Mn-Ga-Co Films with Large Angle Grain Boundaries(Basel : MDPI, 2020) Lünser, Klara; Diestel, Anett; Nielsch, Kornelius; Fähler, SebastianMagnetocaloric materials based on field-induced first order transformations such as Ni-Mn-Ga-Co are promising for more environmentally friendly cooling. Due to the underlying martensitic transformation, a large hysteresis can occur, which in turn reduces the efficiency of a cooling cycle. Here, we analyse the influence of the film microstructure on the thermal hysteresis and focus especially on large angle grain boundaries. We control the microstructure and grain boundary density by depositing films with local epitaxy on different substrates: Single crystalline MgO(0 0 1), MgO(1 1 0) and Al2O3(0 0 0 1). By combining local electron backscatter diffraction (EBSD) and global texture measurements with thermomagnetic measurements, we correlate a smaller hysteresis with the presence of grain boundaries. In films with grain boundaries, the hysteresis is decreased by about 30% compared to single crystalline films. Nevertheless, a large grain boundary density leads to a broadened transition. To explain this behaviour, we discuss the influence of grain boundaries on the martensitic transformation. While grain boundaries act as nucleation sites, they also lead to different strains in the material, which gives rise to various transition temperatures inside one film. We can show that a thoughtful design of the grain boundary microstructure is an important step to optimize the hysteresis.
- ItemCatechol Containing Polyelectrolyte Complex Nanoparticles as Local Drug Delivery System for Bortezomib at Bone Substitute Materials(Basel : MDPI, 2020) Vehlow, David; Wong, Jeremy P.H.; Urban, Birgit; Weißpflog, Janek; Gebert, Annett; Schumacher, Matthias; Gelinsky, Michael; Stamm, Manfred; Müller, MartinThe proteasome inhibitor bortezomib (BZM) is one of the most potent anti-cancer drugs in the therapy of multiple myeloma. In this study, an adhesive drug delivery system (DDS) for BZM was developed. Therefore, we extended the present DDS concept of polyelectrolyte complex (PEC) nanoparticle (NP) based on electrostatic interactions between charged drug and polyelectrolyte (PEL) to a DDS concept involving covalent bonding between PEL and uncharged drugs. For this purpose, 3,4-dihydroxyphenyl acetic acid (DOPAC) was polymerized via an oxidatively induced coupling reaction. This novel chemo-reactive polyanion PDOPAC is able to temporarily bind boronic acid groups of BZM via its catechol groups, through esterification. PDOPAC was admixed to poly(l-glutamic acid) (PLG) and poly(l-lysine) (PLL) forming a redispersible PEC NP system after centrifugation, which is advantageous for further colloid and BZM loading processing. It was found that the loading capacity (LC) strongly depends on the PDOPAC and catechol content in the PEC NP. Furthermore, the type of loading and the net charge of the PEC NP affect LC and the residual content (RC) after release. Release experiments of PDOPAC/PEC coatings were performed at medically relevant bone substitute materials (calcium phosphate cement and titanium niobium alloy) whereby the DDS worked independently of the surface properties. Additionally, in contrast to electrostatically based drug loading the release behavior of covalently bound, uncharged BZM is independent of the ionic strength (salt content) in the release medium.
- ItemSpin-Dependent Phenomena in Semiconductor Micro-and Nanoparticles - From Fundamentals to Applications(Basel : MDPI, 2020) Fomin, Vladimir M.; Timoshenko, Victor Y.The present overview of spin-dependent phenomena in nonmagnetic semiconductor microparticles (MPs) and nanoparticles (NPs) with interacting nuclear and electron spins is aimed at covering a gap between the basic properties of spin behavior in solid-state systems and a tremendous growth of the experimental results on biomedical applications of those particles. The first part of the review represents modern achievements of spin-dependent phenomena in the bulk semiconductors from the theory of optical spin orientation under indirect optical injection of carriers and spins in the bulk crystalline silicon (c-Si)—via numerous insightful findings in the realm of characterization and control through the spin polarization—to the design and verification of nuclear spin hyperpolarization in semiconductor MPs and NPs for magnetic resonance imaging (MRI) diagnostics. The second part of the review is focused on the electron spin-dependent phenomena in Si-based nanostructures, including the photosensitized generation of singlet oxygen in porous Si and design of Si NPs with unpaired electron spins as prospective contrast agents in MRI. The experimental results are analyzed by considering both the quantum mechanical approach and several phenomenological models for the spin behavior in semiconductor/molecular systems. Advancements and perspectives of the biomedical applications of spin-dependent properties of Si NPs for diagnostics and therapy of cancer are discussed.