13 results
Search Results
Now showing 1 - 10 of 13
- ItemElectrically-Pumped Wavelength-Tunable GaAs Quantum Dots Interfaced with Rubidium Atoms(Washington, DC : ACS, 2017) Huang, Huiying; Trotta, Rinaldo; Huo, Yongheng; Lettner, Thomas; Wildmann, Johannes S.; MartÃn-Sánchez, Javier; Huber, Daniel; Reindl, Marcus; Zhang, Jiaxiang; Zallo, Eugenio; Schmidt, Oliver G.; Rastelli, ArmandoWe demonstrate the first wavelength-tunable electrically pumped source of nonclassical light that can emit photons with wavelength in resonance with the D2 transitions of 87Rb atoms. The device is fabricated by integrating a novel GaAs single-quantum-dot light-emitting diode (LED) onto a piezoelectric actuator. By feeding the emitted photons into a 75 mm long cell containing warm 87Rb vapor, we observe slow-light with a temporal delay of up to 3.4 ns. In view of the possibility of using 87Rb atomic vapors as quantum memories, this work makes an important step toward the realization of hybrid-quantum systems for future quantum networks.
- ItemTuning the magneto-optical response of TbPc2 single molecule magnets by the choice of the substrate(London [u.a.] : RSC, 2015) Robaschik, Peter; Fronk, Michael; Toader, Marius; Klyatskaya, Svetlana; Ganss, Fabian; Siles, Pablo F.; Schmidt, Oliver G.; Albrecht, Manfred; Hietschold, Michael; Ruben, Mario; Zahn, Dietrich R.T.; Salvan, GeorgetaIn this work, we investigated the magneto-optical response of thin films of TbPc2 on substrates which are relevant for (spin) organic field effect transistors (SiO2) or vertical spin valves (Co) in order to explore the possibility of implementing TbPc2 in magneto-electronic devices, the functionality of which includes optical reading. The optical and magneto-optical properties of TbPc2 thin films prepared by organic molecular beam deposition (OMBD) on silicon substrates covered with native oxide were investigated by variable angle spectroscopic ellipsometry (VASE) and magneto-optical Kerr effect (MOKE) spectroscopy at room temperature. The magneto-optical activity of the TbPc2 films can be significantly enhanced by one to two orders of magnitude upon changing the molecular orientation (from nearly standing molecules on SiO2/Si substrates to nearly lying molecules on perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) templated SiO2/Si substrates) or by using metallic ferromagnetic substrates (Co).
- ItemMagnetooptical response of permalloy multilayer structures on different substrate in the IR-VIS-UV spectral range(Bristol : IOP Publ., 2019) Patra, Rajkumar; Mattheis, Roland; Stöcker, Hartmut; Monecke, Manuel; Salvan, Georgeta; Schäfer, Rudolf; Schmidt, Oliver G.; Schmidt, HeidemarieThe magnetooptical (MO) response of Ru/Py/Ta thin film stacks with 4, 8, and 17 nm thick Ni81Fe19 permalloy (Py) films on a SiO2/Si and a ZnO substrate was measured by vector magnetooptical generalized ellipsometry. The MO response from VMOGE was modelled using a 4  ×  4 Mueller matrix algorithm. The wavelength-dependent, substrate-independent and thickness-independent complex MO coupling constant (Q) of Py in the Ru/Py/Ta thin film stacks was extracted by fitting Mueller matrix difference spectra in the spectral range from 300 nm to 1000 nm. Although the composition-dependent saturation magnetization of NixFe1−x alloys (x  =  0.0...1.0), e.g. of Ni81Fe19, is predictable from the two saturation magnetization end points, the MO coupling constant of NixFe1−x is not predictable from the two Q end points. However, in a small alloy range (0.0  <  x  <  0.2 and 0.8  <  x  <  1.0) the composition-dependent Q of NixFe1−x can be interpolated from a sufficiently high number of analyzed NixFe1−x alloys. The available complex MO coupling constants of six different NixFe1−x (x  =  1.0 to 0.0) alloys were used to interpolate MO response of binary NixFe1−x alloys in the range from x  =  0.0 to x  =  1.0.
- ItemPhotoluminescence investigation of strictly ordered Ge dots grown on pit-patterned Si substrates(Bristol : IOP Publ., 2015) Brehm, Moritz; Grydlik, Martyna; Tayagaki, Takeshi; Langer, Gregor; Schäffler, Friedrich; Schmidt, Oliver G.We investigate the optical properties of ordered Ge quantum dots (QDs) by means of micro-photoluminescence spectroscopy (PL). These were grown on pit-patterned Si(001) substrates with a wide range of pit-periods and thus inter QD-distances (425–3400 nm). By exploiting almost arbitrary inter-QD distances achievable in this way we are able to choose the number of QDs that contribute to the PL emission in a range between 70 and less than three QDs. This well-defined system allows us to clarify, by PL-investigation, several points which are important for the understanding of the formation and optical properties of ordered QDs. We directly trace and quantify the amount of Ge transferred from the surrounding wetting layer (WL) to the QDs in the pits. Moreover, by exploiting different pit-shapes, we reveal the role of strain-induced activation energy barriers that have to be overcome for charge carriers generated outside the dots. These need to diffuse between the energy minimum of the WL in and between the pits, and the one in the QDs. In addition, we demonstrate that the WL in the pits is already severely intermixed with Si before upright QDs nucleate, which further enhances intermixing of ordered QDs as compared to QDs grown on planar substrates. Furthermore, we quantitatively determine the amount of Ge transferred by surface diffusion through the border region between planar and patterned substrate. This is important for the growth of ordered islands on patterned fields of finite size. We highlight that the Ge WL-facets in the pits act as PL emission centres, similar to upright QDs.
- ItemMagnetism in curved geometries(Bristol : IOP Publ., 2016) Streubel, Robert; Fischer, Peter; Kronast, Florian; Kravchuk, Volodymyr P.; Sheka, Denis D.; Gaididei, Yuri; Schmidt, Oliver G.; Makarov, DenysExtending planar two-dimensional structures into the three-dimensional space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring the geometry of an object, e.g. its local curvature. In a generic electronic system, curvature results in the appearance of scalar and vector geometric potentials inducing anisotropic and chiral effects. In the specific case of magnetism, even in the simplest case of a curved anisotropic Heisenberg magnet, the curvilinear geometry manifests two exchange-driven interactions, namely effective anisotropy and antisymmetric exchange, i.e. Dzyaloshinskii–Moriya-like interaction. As a consequence, a family of novel curvature-driven effects emerges, which includes magnetochiral effects and topologically induced magnetization patterning, resulting in theoretically predicted unlimited domain wall velocities, chirality symmetry breaking and Cherenkov-like effects for magnons. The broad range of altered physical properties makes these curved architectures appealing in view of fundamental research on e.g. skyrmionic systems, magnonic crystals or exotic spin configurations. In addition to these rich physics, the application potential of three-dimensionally shaped objects is currently being explored as magnetic field sensorics for magnetofluidic applications, spin-wave filters, advanced magneto-encephalography devices for diagnosis of epilepsy or for energy-efficient racetrack memory devices. These recent developments ranging from theoretical predictions over fabrication of three-dimensionally curved magnetic thin films, hollow cylinders or wires, to their characterization using integral means as well as the development of advanced tomography approaches are in the focus of this review.
- ItemHigh-performance giant magnetoresistive sensorics on flexible Si membranes(Melville, NY : American Inst. of Physics, 2015) Pérez, Nicolás; Melzer, Michael; Makarov, Denys; Ueberschär, Olaf; Ecke, Ramona; Schulz, Stefan E.; Schmidt, Oliver G.We fabricate high-performance giant magnetoresistive (GMR) sensorics on Si wafers, which are subsequently thinned down to 100 μm or 50 μm to realize mechanically flexible sensing elements. The performance of the GMR sensors upon bending is determined by the thickness of the Si membrane. Thus, bending radii down to 15.5 mm and 6.8 mm are achieved for the devices on 100 μm and 50 μm Si supports, respectively. The GMR magnitude remains unchanged at the level of (15.3 ± 0.4)% independent of the support thickness and bending radius. However, a progressive broadening of the GMR curve is observed associated with the magnetostriction of the containing Ni81Fe19 alloy, which is induced by the tensile bending strain generated on the surface of the Si membrane. An effective magnetostriction value of λs = 1.7 × 10−6 is estimated for the GMR stack. Cyclic bending experiments showed excellent reproducibility of the GMR curves during 100 bending cycles.
- ItemOptical properties of individual site-controlled Ge quantum dots(Melville, NY : American Inst. of Physics, 2015) Grydlik, Martyna; Brehm, Moritz; Tayagaki, Takeshi; Langer, Gregor; Schmidt, Oliver G.; Schäffler, FriedrichWe report photoluminescence (PL) experiments on individual SiGe quantum dots (QDs) that were epitaxially grown in a site-controlled fashion on pre-patterned Si(001) substrates. We demonstrate that the PL line-widths of single QDs decrease with excitation power to about 16 meV, a value that is much narrower than any of the previously reported PL signals in the SiGe/Si heterosystem. At low temperatures, the PL-intensity becomes limited by a 25 meV high potential-barrier between the QDs and the surrounding Ge wetting layer (WL). This barrier impedes QD filling from the WL which collects and traps most of the optically excited holes in this type-II heterosystem. This work was supported by the Austrian Science Funds (FWF) via Schrödinger Scholarship J3328-N19 and the Project Nos. F2502-N17 and F2512-N17 of SFB025: IRON. M.G. and O.G.S. acknowledge support from the Center for Advancing Electronics Dresden, CfAED. T.T. was supported by the ICR-KU International Short-term Exchange Program for Young Researchers. The authors thank T. Fromherz and F. Hackl for helpful discussions.
- ItemShapeable magnetoelectronics(Melville, NY : American Inst. of Physics, 2016) Makarov, Denys; Melzer, Michael; Karnaushenko, Daniil; Schmidt, Oliver G.Inorganic nanomembranes are shapeable (flexible, printable, and even stretchable) and transferrable to virtually any substrate. These properties build the core concept for new technologies, which transform otherwise rigid high-speed devices into their shapeable counterparts. This research is motivated by the eagerness of consumer electronics towards being thin, lightweight, flexible, and even wearable. The realization of this concept requires all building blocks as we know them from rigid electronics (e.g., active elements, optoelectronics, magnetoelectronics, and energy storage) to be replicated in the form of (multi)functional nanomembranes, which can be reshaped on demand after fabrication. There are already a variety of shapeable devices commercially available, i.e., electronic displays, energy storage elements, and integrated circuitry, to name a few. From the beginning, the main focus was on the fabrication of shapeable high-speed electronics and optoelectronics. Only very recently, a new member featuring magnetic functionalities was added to the family of shapeable electronics. With their unique mechanical properties, the shapeable magnetic field sensor elements readily conform to ubiquitous objects of arbitrary shapes including the human skin. This feature leads electronic skin systems beyond imitating the characteristics of its natural archetype and extends their cognition to static and dynamic magnetic fields that by no means can be perceived by human beings naturally. Various application fields of shapeable magnetoelectronics are proposed. The developed sensor platform can equip soft electronic systems with navigation, orientation, motion tracking, and touchless control capabilities. A variety of novel technologies, such as smart textiles, soft robotics and actuators, active medical implants, and soft consumer electronics, will benefit from these new magnetic functionalities. This review reflects the establishment of shapeable magnetic sensorics, describing the entire development from the first attempts to verify the functional concept to the realization of ready-to-use highly compliant and strain invariant sensor devices with remarkable robustness.
- ItemPrintable magnetoelectronics(Hoboken, NJ : Wiley, 2013) Makarov, Denys; Karnaushenko, Daniil; Schmidt, Oliver G.The field of printable electronics is well developed. A large variety of electronic components assembled as printable optoelectronic devices and communication modules are already available. However, the element responding to a magnetic field, which is highly demanded for the concept of printable electronics has only been realized very recently. A printable magnetic sensing device has been one of the remaining missing building blocks crucial to realize the concept of entirely printable electronics. Here, we position the novel topic of printable magnetic sensorics in a family of printable electronics and highlight possible application directions of this technology.
- ItemReal-Time IR Tracking of Single Reflective Micromotors through Scattering Tissues(Weinheim : Wiley-VCH, 2019) Aziz, Azaam; Medina-Sánchez, Mariana; Koukourakis, Nektarios; Wang, Jiawei; Kuschmierz, Robert; Radner, Hannes; Czarske, Jürgen W.; Schmidt, Oliver G.Medical micromotors have the potential to lead to a paradigm shift in future biomedicine, as they may perform active drug delivery, microsurgery, tissue engineering, or assisted fertilization in a minimally invasive manner. However, the translation to clinical treatment is challenging, as many applications of single or few micromotors require real-time tracking and control at high spatiotemporal resolution in deep tissue. Although optical techniques are a popular choice for this task, absorption and strong light scattering lead to a pronounced decrease of the signal-to-noise ratio with increasing penetration depth. Here, a highly reflective micromotor is introduced which reflects more than tenfold the light intensity of simple gold particles and can be precisely navigated by external magnetic fields. A customized optical IR imaging setup and an image correlation technique are implemented to track single micromotors in real-time and label-free underneath phantom and ex vivo mouse skull tissues. As a potential application, the micromotors speed is recorded when moving through different viscous fluids to determine the viscosity of diverse physiological fluids toward remote cardiovascular disease diagnosis. Moreover, the micromotors are loaded with a model drug to demonstrate their cargo-transport capability. The proposed reflective micromotor is suitable as theranostic tool for sub-skin or organ-on-a-chip applications. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.