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- ItemHigh-quality MgB2 nanocrystals synthesized by using modified amorphous nano-boron powders: Study of defect structures and superconductivity properties(College Park, MD : American Institute of Physics, 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.
- ItemTuning emission energy and fine structure splitting in quantum dots emitting in the telecom O-band(College Park, MD : American Institute of Physics, 2019) Höfer, B.; Olbrich, F.; Kettler, J.; Paul, M.; Höschele, J.; Jetter, M.; Portalupi, S.L.; Ding, F.; Michler, P.; Schmidt, O.G.We report on optical investigations of MOVPE-grown InGaAs/GaAs quantum dots emitting at the telecom O-band that were integrated onto uniaxial piezoelectric actuators. This promising technique, which does not degrade the emission brightness of the quantum emitters, enables us to tune the quantum dot emission wavelengths and their fine-structure splitting. By spectrally analyzing the emitted light with respect to its polarization, we are able to demonstrate the cancelation of the fine structure splitting within the experimental resolution limit. This work represents an important step towards the high-yield generation of entangled photon pairs at telecommunication wavelength, together with the capability to precisely tune the emission to target wavelengths.
- ItemComputer modeling of single-layer nanocluster formation in a thin SiO2 layer buried in Si by ion mixing and thermal phase decomposition(College Park, MD : American Institute of Physics, 2019) Prüfer, T.; Möller, W.; Heinig, K.-H.; Wolf, D.; Engelmann, H.-J.; Xu, X.; Von Borany, J.A single sheet of Si nanoclusters with an average diameter of about 2 nm has been formed in a 30 nm Si/7 nm SiO2/Si layer stack by 50 and 60 keV Si+ ion-beam mixing at room temperature and fluences between 8.5 ⋯ 1015 and 2.6 ⋯ 1016 ions/cm2 and by subsequent thermal annealing at a temperature above 1000 °C. Computer modeling of the process is accomplished by TRIDYN dynamic ballistic simulation of ion mixing and subsequent lattice kinetic Monte Carlo simulation of the phase decomposition of substoichiometric silicon oxide into Si nanoclusters in a SiO2 matrix. The simulation algorithms are briefly described with special emphasis on the choice of governing parameters for the present system. In comparison to the experimental results, it is concluded that the predicted ion mixing profiles overestimate the interface broadening. This discrepancy is attributed to the neglect of chemical driving forces in connection with thermal-spike induced diffusion, which tends to reconstitute the Si/SiO2 interfaces. With a corresponding correction and a suitable number of Monte Carlo steps, the experimentally obtained areal densities and average diameters of the nanoclusters are successfully reproduced.
- ItemAdvances in magneto-ionic materials and perspectives for their application(College Park, MD : American Institute of Physics, 2021) Nichterwitz, M.; Honnali Sudheendra, S.; Kutuzau, M.; Guo, S.; Zehner, J.; Nielsch, K.; Leistner, K.The possibility of tuning magnetic material properties by ionic means is exciting both for basic science and, especially in view of the excellentenergy efficiency and room temperature operation, for potential applications. In this perspective, we shortly introduce the functionality ofmagneto-ionic materials and focus on important recent advances in this field. We present a comparative overview of state-of-the-art magneto-ionic materials considering the achieved magnetoelectric voltage coefficients for magnetization and coercivity and the demonstrated timescales for magneto-ionic switching. Furthermore, the application perspectives of magneto-ionic materials in data storage and computing,magnetic actuation, and sensing are evaluated. Finally, we propose potential research directions to push this field forward and tackle thechallenges related to future applications
- ItemPossible experimental realization of a basic Z 2 topological semimetal in GaGeTe(College Park, MD : American Institute of Physics, 2019) Haubold, E.; Fedorov, A.; Pielnhofer, F.; Rusinov, I.P.; Menshchikova, T.V.; Duppel, V.; Friedrich, D.; Weihrich, R.; Pfitzner, A.; Zeugner, A.; Isaeva, A.; Thirupathaiah, S.; Kushnirenko, Y.; Rienks, E.; Kim, T.; Chulkov, E.V.; Büchner, B.; Borisenko, S.We report experimental and theoretical evidence that GaGeTe is a basic Z2 topological semimetal with three types of charge carriers: bulk-originated electrons and holes as well as surface state electrons. This electronic situation is qualitatively similar to the classic 3D topological insulator Bi2Se3, but important differences account for an unprecedented transport scenario in GaGeTe. High-resolution angle-resolved photoemission spectroscopy combined with advanced band structure calculations show a small indirect energy gap caused by a peculiar band inversion at the T-point of the Brillouin zone in GaGeTe. An energy overlap of the valence and conduction bands brings both electron and holelike carriers to the Fermi level, while the momentum gap between the corresponding dispersions remains finite. We argue that peculiarities of the electronic spectrum of GaGeTe have a fundamental importance for the physics of topological matter and may boost the material's application potential.
- ItemMagnetoelectric materials, phenomena, and devices(College Park, MD : American Institute of Physics, 2021) Herrera Diez, L.; Kruk, R.; Leistner, K.; Sort, J.[no abstract available]
- ItemMetrological large range magnetic force microscopy(College Park, MD : American Institute of Physics, 2018) Dai, G.; Hu, X.; Sievers, S.; Fernández, Scarioni, A.; Neu, V.; Fluegge, J.; Schumacher, H.W.A new metrological large range magnetic force microscope (Met. LR-MFM) has been developed. In its design, the scanner motion is measured by using three laser interferometers along the x, y, and z axes. Thus, the scanner position and the lift height of the MFM can be accurately and traceably determined with subnanometer accuracy, allowing accurate and traceable MFM measurements. The Met. LR-MFM has a measurement range of 25 mm × 25 mm × 5 mm, larger than conventional MFMs by almost three orders of magnitude. It is capable of measuring samples from the nanoscale to the macroscale, and thus, it has the potential to bridge different magnetic field measurement tools having different spatially resolved scales. Three different measurement strategies referred to as Topo&MFM, MFMXY, and MFMZ have been developed. The Topo&MFM is designed for measuring topography and MFM phase images, similar to conventional MFMs. The MFMXY differs from the Topo&MFM as it does not measure the topography profile of surfaces at the second and successive lines, thus reducing tip wear and saving measurement time. The MFMZ allows the imaging of the stray field in the xz- or yz-planes. A number of measurement examples on a multilayered thin film reference sample made of [Co(0.4 nm)/Pt(0.9 nm)]100 and on a patterned magnetic multilayer [Co(0.4 nm)/Pt(0.9 nm)]10 with stripes with a 9.9 μm line width and 20 μm periodicity are demonstrated, indicating excellent measurement performance.