Zeitschriftenaufsätze

Atomic-scale spatial characteristics of a phthalocyanine orbital and skeleton are obtained on a metal surface with a scanning tunneling microscope and a CO-functionalized tip. Intriguingly, the high spatial resolution of the intramolecular electronic patterns is achieved without resonant tunneling into the orbital and despite the hybridization of the molecule with the reactive Cu substrate. The resolution can be fine-tuned by the tip-molecule distance, which controls the p-wave and s-wave contribution of the molecular probe to the imaging process. The detailed structure is deployed to minutely track the translation of the molecule in a reversible interconversion of rotational variants and to quantify relaxations of the adsorption geometry. Entering into the Pauli repulsion imaging mode, the intramolecular contrast loses its orbital character and reflects the molecular skeleton instead. The assignment of pyrrolic-hydrogen sites becomes possible, which in the orbital patterns remains elusive.

The carbon fullerene C60 is an anti-inflammatory substance that reduces cellular stress levels. In this study, C60 fullerenes were deposited on complex dental implants to improve cell attachment and vitality. For the first time, fullerene C60 films were deposited via high-vacuum sublimation on complex-shaped Ti-6Al-4V dental implants with a threaded-screw design. The “as-deposited” fullerene C60 films were compared with fullerene C60 films on dental Ti-6Al-4V implants using a threaded-screw design after three weeks of incubation in Hank's balanced salt solution (HBSS). It was proven by Raman spectroscopy that the incubation in potassium and alkali-ion rich HBSS at 37 ˚C resulted in a reduction of monomeric fullerene C60 fraction and an increase in dimer, linear chain and polymerized C60 molecules. Furthermore, the structure of the C60 films differed depending on the measurement position on dental implants with a threaded-screw design. The fraction of monomeric fullerene C60 was highest on top of the trapezoidal thread, which had a micropatterned topography. Nano-indentations were performed at this position with a maximum load of 1000 μN. The fullerene C60 films showed a nano-hardness of 0.3 ± 0.1 GPa and a Young's modulus of 7.6 ± 3.6 GPa at this position, which is typical for monomeric fullerene C60 with weak interatomic interaction in the face-centred-cubic crystal structure. The murine embryonal calvarial stem-cell line MC3T3-E1 (ECACC, UK), which is driven toward osteogenic differentiation, spread out extremely well on the fullerene C60 film, with improved cell morphology compared to uncoated Ti-6Al-4V. Cell nuclei density were determined to be 237.5 cell nuclei per mm2 for the Ti-6Al-4V dental implants with a threaded-screw design with fullerene C60 coating in “as-deposited” condition. This was approximately 40 % better than that of uncoated Ti-6Al-4V dental implants with a threaded-screw design.

Using silicon in multijunction photocells leads to promising device structures for direct photoelectrochemical water splitting. In this regard, photoelectron spectra of silicon surfaces are used to investigate the energetic condition of contact formation. It is shown that the Fermi-level position at the surface differs from the values expected from their bulk doping concentrations, indicating significant surface band bending which may limit the overall device efficiency. In this study, the influence of different surface preparation procedures for p- and n-doped Si wafers on surface band bending is investigated. With the help of photoemission and X-ray absorption spectroscopy, Si dangling bonds are identified as dominating defect centers at Si surfaces. These defects lead to an occupied defect band in the lower half and an unoccupied defect band in the upper half of the Si bandgap. However, partial oxidation of the defect centers causes a shift of defect bands, with only donor states remaining in the Si bandgap. Source-induced photovoltages at cryogenic temperatures indicate that partial surface oxidation also decreases the recombination activity of these defect centers. It is shown that defect distribution, defect concentration, and source-induced photovoltages need to be considered when analyzing Fermi-level pinning at Si surfaces.

During continuous casting process, the internal molten steel flow pattern of the mold is one of the important factors affecting the quality of slab products. The application of electromagnetic braking (EMBr) technology in the slab caster provides an effective solution to improve the molten steel flow pattern in the mold. In the current research, one of the commonly used EMBr technology is studied, namely the Ruler-EMBr technology. In detail, the effect of magnetic flux density on the behavior of the molten steel jet flow, heat transfer, and solidification in a 1450 mm × 230 mm slab mold is numerically simulated through a Reynolds-averaged Navier-Stokes (RANS) turbulence model together with an enthalpy-porosity approach. The simulation results indicate that the electromagnetic force generated by the Ruler-EMBr can significantly suppress the diffusion of the impinging jet to the narrow face of the mold with the increase of magnetic flux density. By that, the impact of the upward backflow on the meniscus region in the mold is suppressed. Correspondingly, the uniformity of the temperature distribution in the mold is effectively improved. The parametric studies suggest that the optimized magnetic flux density is 0.3 T to ensure the improvement of steel quality with a casting speed of 1.6 m/min. By applying the magnetic flux density of 0.3 T, the Ruler-EMBr has a better capability to reduce the maximum amplitude of the surface velocity by 24.5% and increase the average surface temperature of the molten steel by 0.25% when compared to the case of No-EMBr. With this electromagnetic parameter, the Ruler-EMBr technology can well prevent the mold flux entrapment and promote solidified shell uniform growth along the casting direction.

Sufficient energy consumption for conventional information processing makes it necessary to look for new computational methods. One of the possible solutions to this problem is neuromorphic computations using memristive devices. Memristors based on molybdenum disulfide (MoS2) are a promising way to provide a sizeable amount of hysteresis at low energy costs. Herein, different configurations of MoS2 memristors as well as the mechanisms involved in hysteresis formation are shown. Bottom gated configuration is beneficial in terms of hysteresis area and energy efficiency. The impact of device channel dimensions on the hysteresis area and energy consumption is discussed. Different operation conditions with triangular, rectangular, sinusoidal, and sawtooth drain-to-source pulses are simulated, and rectangular pulses demonstrate the highest energy efficiency. The study shows the potential to realize low-power neuromorphic systems using MoS2 memristive devices.