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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.
- ItemActively Tunable Collective Localized Surface Plasmons by Responsive Hydrogel Membrane(Weinheim : Wiley-VCH, 2019) Quilis, Nestor Gisbert; van Dongen, Marcel; Venugopalan, Priyamvada; Kotlarek, Daria; Petri, Christian; Cencerrado, Alberto Moreno; Stanescu, Sorin; Herrera, Jose Luis Toca; Jonas, Ulrich; Möller, Martin; Mourran, Ahmed; Dostalek, JakubCollective (lattice) localized surface plasmons (cLSP) with actively tunable and extremely narrow spectral characteristics are reported. They are supported by periodic arrays of gold nanoparticles attached to a stimuli-responsive hydrogel membrane, which can on demand swell and collapse to reversibly modulate arrays period and surrounding refractive index. In addition, it features a refractive index-symmetrical geometry that promotes the generation of cLSPs and leads to strong suppression of radiative losses, narrowing the spectral width of the resonance, and increasing of the electromagnetic field intensity. Narrowing of the cLSP spectral band down to 13 nm and its reversible shifting by up to 151 nm is observed in the near infrared part of the spectrum by varying temperature and by solvent exchange for systems with a poly(N-isopropylacrylamide)-based hydrogel membrane that is allowed to reversibly swell and collapse in either one or in three dimensions. The reported structures with embedded periodic gold nanoparticle arrays are particularly attractive for biosensing applications as the open hydrogel structure can be efficiently post-modified with functional moieties, such as specific ligands, and since biomolecules can rapidly diffuse through swollen polymer networks. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemSelf-Assembled Flexible and Integratable 3D Microtubular Asymmetric Supercapacitors(Chichester : John Wiley and Sons Ltd, 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.
- ItemSingle Molecule Magnetism with Strong Magnetic Anisotropy and Enhanced Dy∙∙∙Dy Coupling in Three Isomers of Dy-Oxide Clusterfullerene Dy2O@C82(Chichester : John Wiley and Sons Ltd, 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.
- ItemOptimal principal component analysis of stem xeds spectrum images(Heidelberg : Springer Verlag, 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.
- ItemNovel concept for VCSEL enhanced silicon photonic coherent transceiver(New York, NY : American Inst. of Physics, 2019) Seiler, Pascal M.; Ronniger, Gregor; Troppenz, Ute; Sigmund, Ariane; Moehrle, Martin; Peczek, Anna; Zimmermann, LarsWe present a novel concept for an integrated silicon photonic coherent transceiver using vertical-emitting laser sources at 1550 nm. In a state of the art external modulation configuration, we deploy a VCSEL on the transmit and a HCSEL on the receive side. We demonstrate the feasibility of this approach by externally modulating the VCSEL with QPSK at up to 28 Gbaud. We also perform experiments with the VCSEL-HCSEL configuration in a slave-master optical injection locking setup for future data center interconnects. The results show stable locking conditions and the VCSEL is detuned to perform predominant phase modulation. To the best of our knowledge, this is the first time direct phase modulation of a VCSEL under optical injection locking was demonstrated using two vertically emitting laser sources as master - and slave laser. © 2019 Author(s).
- ItemStress-Induced 3D Chiral Fractal Metasurface for Enhanced and Stabilized Broadband Near-Field Optical Chirality(Weinheim : Wiley-VCH Verlag, 2019) Tseng M.L.; Lin Z.-H.; Kuo H.Y.; Huang T.-T.; Huang Y.-T.; Chung T.L.; Chu C.H.; Huang J.-S.; Tsai D.P.Metasurfaces comprising 3D chiral structures have shown great potential in chiroptical applications such as chiral optical components and sensing. So far, the main challenges lie in the nanofabrication and the limited operational bandwidth. Homogeneous and localized broadband near-field optical chirality enhancement has not been achieved. Here, an effective nanofabrication method to create a 3D chiral metasurface with far- and near-field broadband chiroptical properties is demonstrated. A focused ion beam is used to cut and stretch nanowires into 3D Archimedean spirals from stacked films. The 3D Archimedean spiral is a self-similar chiral fractal structure sensitive to the chirality of light. The spiral exhibits far- and near-field broadband chiroptical responses from 2 to 8 µm. With circularly polarized light (CPL), the spiral shows superior far-field transmission dissymmetry and handedness-dependent near-field localization. With linearly polarized excitation, homogeneous and highly enhanced broadband near-field optical chirality is generated at a stably localized position inside the spiral. The effective yet straightforward fabrication strategy allows easy fabrication of 3D chiral structures with superior broadband far-field chiroptical response as well as strongly enhanced and stably localized broadband near-field optical chirality. The reported method and chiral metasurface may find applications in broadband chiral optics and chiral sensing. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemColloidal Self-Assembly Concepts for Plasmonic Metasurfaces(Weinheim : Wiley-VCH, 2019) Mayer, Martin; Schnepf, Max J.; König, Tobias A.F.; Fery, AndreasMetallic nanostructures exhibit strong interactions with electromagnetic radiation, known as the localized surface plasmon resonance. In recent years, there is significant interest and growth in the area of coupled metallic nanostructures. In such assemblies, short- and long-range coupling effects can be tailored and emergent properties, e.g., metamaterial effects, can be realized. The term “plasmonic metasurfaces” is used for this novel class of assemblies deposited on planar surfaces. Herein, the focus is on plasmonic metasurfaces formed from colloidal particles. These are formed by self-assembly and can meet the demands of low-cost manufacturing of large-area, flexible, and ultrathin devices. The advances in high optical quality of the colloidal building blocks and methods for controlling their self-assembly on surfaces will lead to novel functional devices for dynamic light modulators, pulse sharpening, subwavelength imaging, sensing, and quantum devices. This progress report focuses on predicting optical properties of single colloidal building blocks and their assemblies, wet-chemical synthesis, and directed self-assembly of colloidal particles. The report concludes with a discussion of the perspectives toward expanding the colloidal plasmonic metasurfaces concept by integrating them with quantum emitters (gain materials) or mechanically responsive structures. © 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemThe equivalent circuit approach for the electrical diagnostics of dielectric barrier discharges: The classical theory and recent developments(Basel : MDPI AG, 2019) Pipa, Andrei V.; Brandenburg, RonnyMeasurements of current and voltage are the basic diagnostics for electrical discharges. However, in the case of dielectric barrier discharges (DBDs), the measured current and voltage waveforms are influenced by the discharge reactor geometry, and thus, interpretation of measured quantities is required to determine the discharge properties. This contribution presents the main stages of the development of electrical diagnostics of DBDs, which are based on lumped electrical elements. The compilation and revision of the contributions to the equivalent circuit approach are targeted to indicate: (1) the interconnection between the stage of development, (2) its applicability, and (3) the current state-of-the-art of this approach. © 2019 by the authors.
- ItemResonant terahertz light absorption by virtue of tunable hybrid interface phonon-plasmon modes in semiconductor nanoshells(Basel : MDPI AG, 2019) Nika, D.L.; Pokatilov, E.P.; Fomin, V.M.; Devreese, J.T.; Tempere, J.Metallic nanoshells have proven to be particularly versatile, with applications in biomedical imaging and surface-enhanced Raman spectroscopy. Here, we theoretically demonstrate that hybrid phonon-plasmon modes in semiconductor nanoshells offer similar advantages in the terahertz regime. We show that, depending on tm,n,nhe doping of the semiconductor shells, terahertz light absorption in these nanostructures can be resonantly enhanced due to the strong coupling between interface plasmons and phonons. A threefold to fourfold increase in the absorption peak intensity was achieved at specific values of electron concentration. Doping, as well as adapting the nanoshell radius, allowed for fine-tuning of the absorption peak frequencies.