2019, Bateni, A., Erdem, E., Häßler, W., Somer, M.

Nano sized magnesium diboride (MgB2) samples were synthesized using various high-quality nano-B precursor powders. The microscopic defect structures of MgB2 samples were systematically investigated using X-ray powder diffraction, Raman, resistivity measurements and electron paramagnetic resonance spectroscopy. A significant deviation in the critical temperature Tc was observed due to defects and crystal distortion. The symmetry effect of the latter is also reflected on the vibrational modes in the Raman spectra. Scanning electron microscopy analysis demonstrate uniform and ultrafine morphology for the modified MgB2. Defect center in particular Mg vacancies influence the connectivity and the conductivity properties which are crucial for the superconductivity applications.

2019, Yang, W., Velkos, G., Liu, F., Sudarkova, S.M., Wang, Y., Zhuang, J., Zhang, H., Li, X., Zhang, X., Büchner, B., Avdoshenko, S.M., Popov, A.A., Chen, N.

A new class of single-molecule magnets (SMMs) based on Dy-oxide clusterfullerenes is synthesized. Three isomers of Dy2O@C82 with Cs(6), C3v(8), and C2v(9) cage symmetries are characterized by single-crystal X-ray diffraction, which shows that the endohedral Dy−(µ2-O)−Dy cluster has bent shape with very short Dy−O bonds. Dy2O@C82 isomers show SMM behavior with broad magnetic hysteresis, but the temperature and magnetization relaxation depend strongly on the fullerene cage. The short Dy−O distances and the large negative charge of the oxide ion in Dy2O@C82 result in the very strong magnetic anisotropy of Dy ions. Their magnetic moments are aligned along the Dy−O bonds and are antiferromagnetically (AFM) coupled. At low temperatures, relaxation of magnetization in Dy2O@C82 proceeds via the ferromagnetically (FM)-coupled excited state, giving Arrhenius behavior with the effective barriers equal to the AFM-FM energy difference. The AFM-FM energy differences of 5.4–12.9 cm−1 in Dy2O@C82 are considerably larger than in SMMs with {Dy2O2} bridges, and the Dy∙∙∙Dy exchange coupling in Dy2O@C82 is the strongest among all dinuclear Dy SMMs with diamagnetic bridges. Dy-oxide clusterfullerenes provide a playground for the further tuning of molecular magnetism via variation of the size and shape of the fullerene cage.

2004, Shepherd, M., Fricke-Begemann, C.

Zonal mean daytime temperatures from the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) and nightly temperatures from a potassium (K) lidar are employed in the study of the tidal variations in mesospheric temperature at low and mid latitudes in the Northern Hemisphere. The analysis is applied to observations at 89 km height for winter solstice, December to February (DJF), at 55° N, and for May and November at 28° N. The WINDII results are based on observations from 1991 to 1997. The K-lidar observations for DJF at Kühlungsborn (54° N) were from 1996-1999, while those for May and November at Tenerife 28° N were from 1999. To avoid possible effects from year-to-year variability in the temperatures observed, as well as differences due to instrument calibration and observation periods, the mean temperature field is removed from the respective data sets, assuming that only tidal and planetary scale perturbations remain in the temperature residuals. The latter are then binned in 0.5 h periods and the individual data sets are fitted in a least-mean square sense to 12-h and 8-h harmonics, to infer semidiurnal and terdiurnal tidal parameters. Both the K-lidar and WINDII independently observed a strong semidiurnal tide in November, with amplitudes of 13 K and 7.4 K, respectively. Good agreement was also found in the tidal parameters derived from the two data sets for DJF and May. It was recognized that insufficient local time coverage of the two separate data sets could lead to an overestimation of the semidiurnal tidal amplitude. A combined ground-based/satellite data set with full diurnal local time coverage was created which was fitted to 24 h+ 12 h+8 h harmonics and a novel method applied to account for possible differences between the daytime and nighttime means. The results still yielded a strong semidiurnal tide in November at 28° N with an amplitude of 8.8 K which is twice the SD amplitude in May and DJF. The diurnal tidal parameters were practically the same at 28° N and 55° N, in November and DJF, respectively, with an amplitude of 6.5 K and peaking at ∼9h. The diurnal and semidiurnal amplitudes in May were about the same, 4 K, and 4.6 K, while the terdiurnal tide had the same amplitudes and phases in May and November at 28° N. Good agreement is found with other experimental data while models tend to underestimate the amplitudes.

2018, Ren, W., Zhu, H., Zhu, Q., Saparamadu, U., He, R., Liu, Z., Mao, J., Wang, C., Nielsch, K., Wang, Z., Ren, Z.

Conversion efficiency and output power are crucial parameters for thermoelectric power generation that highly rely on figure of merit ZT and power factor (PF), respectively. Therefore, the synergistic optimization of electrical and thermal properties is imperative instead of optimizing just ZT by thermal conductivity reduction or just PF by electron transport enhancement. Here, it is demonstrated that Nb0.95Hf0.05FeSb has not only ultrahigh PF over ≈100 µW cm−1 K−2 at room temperature but also the highest ZT in a material system Nb0.95M0.05FeSb (M = Hf, Zr, Ti). It is found that Hf dopant is capable to simultaneously supply carriers for mobility optimization and introduce atomic disorder for reducing lattice thermal conductivity. As a result, Nb0.95Hf0.05FeSb distinguishes itself from other outstanding NbFeSb-based materials in both the PF and ZT. Additionally, a large output power density of ≈21.6 W cm−2 is achieved based on a single-leg device under a temperature difference of ≈560 K, showing the realistic prospect of the ultrahigh PF for power generation.

2014, Bogusz, A., Müller, A.D., Blaschke, D., Skorupa, I., Bürger, D., Scholz, A., Schmidt, O.G., Schmidt, H.

We report a unipolar, nonvolatile resistive switching in polycrystalline YMnO3 thin films grown by pulsed laser deposition and sandwiched between Au top and Ti/Pt bottom electrodes. The ratio of the resistance in the OFF and ON state is larger than 103. The observed phenomena can be attributed to the formation and rupture of conductive filaments within the multiferroic YMnO3 film. The generation of conductive paths under applied electric field is discussed in terms of the presence of grain boundaries and charged domain walls inherently formed in hexagonal YMnO3. Our findings suggest that engineering of the ferroelectric domains might be a promising route for designing and fabrication of novel resistive switching devices.

2019, Potapov, P., Lubk, A.

STEM XEDS spectrum images can be drastically denoised by application of the principal component analysis (PCA). This paper looks inside the PCA workflow step by step on an example of a complex semiconductor structure consisting of a number of different phases. Typical problems distorting the principal components decomposition are highlighted and solutions for the successful PCA are described. Particular attention is paid to the optimal truncation of principal components in the course of reconstructing denoised data. A novel accurate and robust method, which overperforms the existing truncation methods is suggested for the first time and described in details.

2010, Granzer, T., Weber, M., Strassmeier, K.G.

Since May 2006, the two STELLA robotic telescopes at the Izaa observatory in Tenerife, Spain, delivered an almost uninterrupted stream of scientific data. To achieve such a high level of autonomous operation, the replacement of all troubleshooting skills of a regular observer in software was required. Care must be taken on error handling issues and on robustness of the algorithms used. In the current paper, we summarize the approaches we followed in the STELLA observatory. Copyright © 2010 Thomas Granzer et al.

2019, Li, F., Wang, J., Liu, L., Qu, J., Li, Y., Bandari, V.K., Karnaushenko, D., Becker, C., Faghih, M., Kang, T., Baunack, S., Zhu, M., Zhu, F., Schmidt, O.G.

The rapid development of microelectronics has equally rapidly increased the demand for miniaturized energy storage devices. On-chip microsupercapacitors (MSCs), as promising power candidates, possess great potential to complement or replace electrolytic capacitors and microbatteries in various applications. However, the areal capacities and energy densities of the planar MSCs are commonly limited by the low voltage window, the thin layer of the electrode materials and complex fabrication processes. Here, a new-type three-dimensional (3D) tubular asymmetric MSC with small footprint area, high potential window, ultrahigh areal energy density, and long-term cycling stability is fabricated with shapeable materials and photolithographic technologies, which are compatible with modern microelectronic fabrication procedures widely used in industry. Benefiting from the novel architecture, the 3D asymmetric MSC displays an ultrahigh areal capacitance of 88.6 mF cm−2 and areal energy density of 28.69 mW h cm−2, superior to most reported interdigitated MSCs. Furthermore, the 3D tubular MSCs demonstrate remarkable cycling stability and the capacitance retention is up to 91.8% over 12 000 cycles. It is believed that the efficient fabrication methodology can be used to construct various integratable microscale tubular energy storage devices with small footprint area and high performance for miniaturized electronics.

2010, Strassmeier, K.G., Granzer, T., Weber, M., Woche, M., Popow, E., Jrvinen, A., Bartus, J., Bauer, S.-M., Dionies, F., Fechner, T., Bittner, W., Paschke, J.

The Astrophysical Institute Potsdam (AIP) and the Instituto de Astrofísica de Canarias (IAC) inaugurated the robotic telescopes STELLA-I and STELLA-II (STELLar Activity) on Tenerife on May 18, 2006. The observatory is located on the Izaa ridge at an elevation of 2400m near the German Vacuum Tower Telescope. STELLA consists of two 1.2m alt-az telescopes. One telescope fiber feeds a bench-mounted high-resolution echelle spectrograph while the other telescope feeds a wide-field imaging photometer. Both scopes work autonomously by means of artificial intelligence. Not only that the telescopes are automated, but the entire observatory operates like a robot, and does not require any human presence on site. Copyright © 2010 Klaus G. Strassmeier et al.

2020, Feng, Le, Freudenberger, Jens, Mix, Torsten, Nielsch, Kornelius, Woodcock, Thomas George

Rare-earth-free MnAl-C-Ni permanent magnets have been produced for the first time by extruding powders milled from bulk. The resulting materials, fabricated using different conditions, contained a large volume fraction (> 0.92) of the desired τ-phase. In terms of the maximum energy product, the best performance obtained for a whole, transverse section of the extruded material was (BH)max = 46 kJm−3, and was (BH)max = 49 kJm−3 for a sample taken from near the edge of this section. Analysis showed that this material was comparable to the long-established benchmark, comprising MnAl-C-based magnets extruded in industry from bulk or from gas-atomised powder. Such materials are no longer available. The microstructure of the materials produced here consisted of fine, recrystallised grains, which exhibited an <001> fibre texture with intermediate texture quality and of larger, non-recrystallised regions, which contained hierarchical twinning and a high density of defects. The volume fraction and size of the non-recrystallised regions was greatly reduced by decreasing the size of the initial powder particles. This led to a large increase in the squareness factor of the demagnetisation curve and consequently to the high (BH)max values observed.