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  • 201. Tacchi, S.
    et al.
    Anh Nguyen, T. N.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik. Vietnam National University, Viet Nam.
    Gubbiotti, G.
    Madami, M.
    Carlotti, G.
    Pini, M. G.
    Rettori, A.
    Fallahi, V.
    Dumas, R. K.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    [Co/Pd]-CoFeB exchange spring magnets with tunable gap of spin wave excitations2014Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 47, nr 49, s. 495004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Exchange spring magnets, consisting of a [Co(0.5 nm)/Pd(1 nm)](5) multilayer with perpendicular magnetic anisotropy and a Co20Fe60B20 film with easy plane anisotropy, of variable thickness t(CFB), are investigated using Brillouin light scattering. On reducing t(CFB) in the range 0.8-2.3 nm, the spin-wave frequency gap displays a remarkable increase from nearly 4-48 GHz, reflecting the corresponding rapid growth of the tilting angle of the magnetization with respect to the film normal. These findings are interpreted using a one-dimensional model in which each atomic layer is assumed to be uniformly magnetized, subjected to an effective out-of-plane or easy-plane anisotropy depending on the layer position in the stack, and exchange coupled to its two nearest neighbour atomic layers. With respect to previously investigated [Co/Pd]-NiFe hybrid magnets, a largest frequency tunability, restricted to a narrower range of the soft layer thickness, is observed.

  • 202. Tiwari, Dhananjay
    et al.
    Sisodia, Naveen
    Sharma, Raghav
    Durrenfeld, P.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    Muduli, P. K.
    Enhancement of spin-torque diode sensitivity in a magnetic tunnel junction by parametric synchronization2016Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 108, nr 8, artikkel-id 082402Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate enhanced radio frequency (RF) detection sensitivity in a magnetic tunnel junction based spin torque oscillator (STO) using parametric synchronization. The parametric synchronization is observed above the auto-oscillation threshold of the STO and enhances the RF sensitivity at 2f(0), where f(0) is the auto-oscillation frequency. The maximum RF sensitivity for parametric synchronization at 2f(0) similar or equal to 9GHz is 16 mV/mW, while the maximum RF sensitivity at f(0) similar or equal to 4: 5GHz without parametric synchronization is 12 mV/mW. Macrospin simulations corroborate the experimental results.

  • 203. Tryputen, Larysa
    et al.
    Guo, Feng
    Liu, Frank
    Nguyen, Tu N Anh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik. Vietnam National University, Vietnam.
    Mohseni, Seyed Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Shahid Beheshti University, Iran.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    Fang, Yeyu
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    McMichael, R. D.
    Ross, Caroline A.
    Magnetic structure and anisotropy of [Co/Pd](5)/NiFe multilayers2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, nr 1, s. 014407-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The magnetization behavior, magnetic anisotropy, and domain configurations of Co/Pd multilayers with perpendicular magnetic anisotropy capped with permalloy is investigated using magnetometry, magnetic force microscopy, and ferromagnetic resonance. The thickness of the Ni80Fe20 layer in [Co/Pd](5)/NiFe (t) was varied from t = 0 to 80 nm in order to study the interplay between the anisotropy and magnetization directions of Co/Pd and NiFe. By varying the thickness of the NiFe layer, the net anisotropy changes sign, but domains with plane- normal magnetization are present even for the thickest NiFe. Ferromagnetic resonance measurements show a decrease in damping with increasing NiFe thickness. The results demonstrate how the magnetic behavior of mixed- anisotropy thin films can be controlled.

  • 204.
    Törne, Karin
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. St Jude Medical Systems AB, Sweden.
    Larsson, Mariann
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Norlin, Anna
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Degradation of zinc in saline solutions, plasma, and whole blood2016Inngår i: Journal of Biomedical Materials Research. Part B - Applied biomaterials, ISSN 1552-4973, E-ISSN 1552-4981, Vol. 104, nr 6, s. 1141-1151Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The initial degradation of zinc has been investigated through exposures to simulated and real body fluids of increasing complexity: phosphate buffered saline (PBS), Ringer's saline solution, human plasma, and whole blood. Real body fluids were used to close the electrolyte gap between simulated and in vivo environment. Polarization of zinc in whole blood show a passive response not present in other electrolytes. The analysis shows a decrease in corrosion rate with time for plasma and whole blood and an increase for PBS and Ringer's. During exposure to plasma and whole blood a bi-layered corrosion product with poor adherence was formed over a uniformly corroding surface. The corrosion products comprise a mixture of inorganic material and biomolecules. Samples degrading in PBS were prone to localized corrosion and formed thick porous corrosion products of primarily zinc phosphates while in Ringer's solution a gel like layer of zinc carbonate was formed over an interface with shallow pits. The use of whole blood or plasma as electrolytes for short term in vitro evaluation of potential biodegradable metals may provide an improved understanding of the behavior in vivo, while Ringer's solution is preferred over PBS for long term degradation studies of zinc.

  • 205.
    Törne, Karin
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Örnberg, A.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    The influence of buffer system and biological fluids on the degradation of magnesium2017Inngår i: Journal of Biomedical Materials Research. Part B - Applied biomaterials, ISSN 1552-4973, E-ISSN 1552-4981, Vol. 105, nr 6, s. 1490-1502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of frequently used buffer system 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) compared to CO2/HCO3- on the corrosion of magnesium is investigated. Samples were immersed in simulated body fluid (m-SBF) while monitored by electrochemical impedance spectroscopy (EIS) for up to 30 days. In CO2/HCO3- the initial corrosion rate was 0.11 mm yr-1. An inner protective layer of magnesium oxide was formed within the first 30 min exposure and subsequently covered by an outer layer of apatite within 24 h. The corrosion mechanism thereafter is best described as passive pitting with a porosity of ∼10%. Using HEPES as buffer agent increased the corrosion rate to 3.37 mm yr-1. Cross sectional microscopy show a porous outer corrosion layer allowing rapid diffusion of aggressive ions through the film. Here the EIS results are best described by an active pitting model with an inner layer 5 to 10 times less protective compared to the inner layer formed without HEPES. Further the suitability of human whole blood and plasma as in vitro models for Mg degradation was evaluated. Mg corrosion caused coagulation after 24 h in both biological fluids. The corrosion during the first 24 h is similar to the corrosion in m-SBF with HEPES.

  • 206. Ulman, Kanchan
    et al.
    Narasimhan, Shobhana
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Tuning spin transport properties and molecular magnetoresistance through contact geometry2014Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, nr 4, s. 044716-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Molecular spintronics seeks to unite the advantages of using organic molecules as nanoelectronic components, with the benefits of using spin as an additional degree of freedom. For technological applications, an important quantity is the molecular magnetoresistance. In this work, we show that this parameter is very sensitive to the contact geometry. To demonstrate this, we perform ab initio calculations, combining the non-equilibrium Green's function method with density functional theory, on a dithienylethene molecule placed between spin-polarized nickel leads of varying geometries. We find that, in general, the magnetoresistance is significantly higher when the contact is made to sharp tips than to flat surfaces. Interestingly, this holds true for both resonant and tunneling conduction regimes, i.e., when the molecule is in its "closed" and "open" conformations, respectively. We find that changing the lead geometry can increase the magnetoresistance by up to a factor of similar to 5. We also introduce a simple model that, despite requiring minimal computational time, can recapture our ab initio results for the behavior of magnetoresistance as a function of bias voltage. This model requires as its input only the density of states on the anchoring atoms, at zero bias voltage. We also find that the non-resonant conductance in the open conformation of the molecule is significantly impacted by the lead geometry. As a result, the ratio of the current in the closed and open conformations can also be tuned by varying the geometry of the leads, and increased by similar to 400%.

  • 207.
    Usman, Muhammad
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar. Quaid I Azam Univ, Pakistan.
    Suvanam, Sethu Saveda
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Yazdi, Milad Ghadami
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sultan, Muhammad
    Hallén, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Stoichiometry of the ALD-Al2O3/4H-SiC interface by synchrotron-based XPS2016Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, nr 25, artikkel-id 255308Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The interface of Al2O3 with 4H-SiC is investigated with synchrotron-based high-resolution x-ray photoelectron spectroscopy to clarify the effect of post-dielectric deposition annealing processes (rapid thermal annealing (RTA) and furnace annealing (FA)) involved in device fabrication. Our results show that post-deposition annealing of Al2O3/4H-SiC up to 1100 degrees C forms a thin interfacial layer of SiO2 between Al2O3 and SiC, which possibly improves the dielectric properties of the system by reducing oxide charges and near-interface traps. Moreover, the formation of SiO2 at the interface gives additional band offset to the dielectric system. We have also observed that the RTA and FA processes have similar results at a high temperature of 1100 degrees C. Therefore, we propose that high-temperature post-oxide (Al2O3) deposition annealing of up to 1100 degrees C may be used in device processing, which can improve overall dielectric properties and consequently the device performance.

  • 208. Visniakova, Sigita
    et al.
    Urbanaviciute, Indre
    Dauksaite, Lauryna
    Janulevicius, Matas
    Lenkeviciute, Brone
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Arlauskas, Ketutis
    Zilinskas, Albinas
    Luminescent benzo- and naphthoquinolines: Synthesis and investigation of photophysical properties2015Inngår i: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 167, s. 261-267Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study was to synthesise new luminescent small molecular weight benzo- and naphthoquinoline derivatives (based on already known synthons) with different substituents (chlorine, tetrazole, iminophosphorane and amine), to characterize them by ultraviolet photoelectron spectroscopy in air (UPS), luminescence and absorption photospectrometry and to investigate the changes in these properties resulted by differences of molecular structure. Measured values of the HOMO, the LUMO energy levels and optical band gap (E-g_opt) were in range E-HOMO = [ - 5, 9; - 5, 5] eV, E-LUMO = [ 3, 6; - 3] eV, E-g_opt = [2; 2, 8] eV. Most of the examined materials showed high intensity fluorescence reaching quantum yields of 49%. Fluorescence peaks of thermally evaporated layers distributed in range of lambda(Layer)=[477; 596] nm - from blue to orange colour while in chloroform solution remained in blue-green interval lambda(Solution)=[471;537] nm. Primary study results of electroluminescence indicate that the materials have a potential to be used in organic optoelectronics.

  • 209. Wang, C.
    et al.
    Xiao, D.
    Zhou, Y.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Liu, Y.
    Phase-locking of multiple magnetic droplets by a microwave magnetic field2017Inngår i: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 7, nr 5, artikkel-id 056019Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Manipulating dissipative magnetic droplet is of great interest for both the fundamental and technological reasons due to its potential applications in the high frequency spin-torque nano-oscillators. In this paper, a magnetic droplet pair localized in two identical or non-identical nano-contacts in a magnetic thin film with perpendicular anisotropy can phase-lock into a single resonance state by using an oscillating microwave magnetic field. This resonance state is a little away from the intrinsic precession frequency of the magnetic droplets. We found that the phase-locking frequency range increases with the increase of the microwave field strength. Furthermore, multiple droplets with a random initial phase can also be synchronized by a microwave field.

  • 210. Wang, Q.
    et al.
    Rajabi, M.
    Karim, A.
    Almqvist, S.
    Bakowski, M.
    Savage, S.
    Jan, Y. A.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Yu, S.
    Gustafsson, Oscar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Hammar, Mattias
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Asplund, C.
    Surface states characterization and simulation of type-II In(Ga)Sb quantum dot structures for processing optimization of LWIR detectors2013Inngår i: Proceedings of SPIE, Infrared Technology and Applications XXXIX, SPIE - International Society for Optical Engineering, 2013, s. 870433-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Quantum structures base on type-II In(Ga)Sb quantum dots (QDs) embedded in an InAs matrix were used as active material for achieving long-wavelength infrared (LWIR) photodetectors in this work. Both InAs and In(Ga)Sb are narrow band semiconductor materials and known to possess a large number of surface states, which apparently play significant impact for the detector's electrical and optical performance. These surface states are caused not only by material or device processing induced defects but also by surface dangling bonds, oxides, roughness and contaminants. To experimentally analyze the surface states of the QD structures treated by different device fabrication steps, atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) measurements were performed. The results were used to optimize the fabrication process of the LWIR photodetectors in our ongoing project. The dark current and its temperature dependence of the fabricated IR photodetectors were characterized in temperature range 10 K to 300 K, and the experiment results were analyzed by a theoretic modeling obtained using simulation tool MEDICI.

  • 211. Wang, Qin
    et al.
    Li, Xun
    Zhang, Andy
    Acreo, Sweden.
    Almqvist, Susanne
    Karim, Amir
    Noharet, Bertrand
    Andersson, Jan Y.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Yu, Shun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Gustafsson, Oscar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Hammar, Mattias
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Asplund, Carl
    Gothelid, Emmanuelle
    Analysis of surface oxides on narrow bandgap III-V semiconductors leading towards surface leakage free IR photodetectors2012Inngår i: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 8353, s. 835311-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Narrow bandgap semiconductors GaSb, InAs, and InSb are important building blocks for infrared photodetectors based on type-II InSb quantum dots or an InAs/GaSb strained layer superlattice. Understanding the surface chemical composition of these materials can provide valuable information that enables optimization of device surface passivation techniques leading towards surface leakage free IR photodetectors. We report on an investigation into Ga-, In-, Sb-, and As-oxides and other chemical species on the surface of untreated, dry etched and thermally treated GaSb, InAs and InSb samples by x-ray photoelectron spectroscopy. The experimental results reveal the presence of Sb- and Ga-oxides on the surfaces of the untreated and treated GaSb samples. Both Sb- and In-oxides were observed on the surface of all InSb samples, and especially the dry etched sample had thicker oxide layers. In the case of the InAs samples, not only In-and As-oxides XPS signals were obtained, but also AsCl species were found on the ICP dry etched sample. These results helped to analyze the dark current of our fabricated IR detectors.

  • 212. Wei, Yajun
    et al.
    Akansel, Serkan
    Thersleff, Thomas
    Harward, Ian
    Brucas, Rimantas
    Ranjbar, Mojtaba
    Jana, Somnath
    Lansaker, Pia
    Pogoryelov, Yevgen
    Dumas, Randy K.
    Leifer, Klaus
    Karis, Olof
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    Celinski, Zbigniew
    Svedlindh, Peter
    Exponentially decaying magnetic coupling in sputtered thin film FeNi/Cu/FeCo trilayers2015Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, nr 4, artikkel-id 042405Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetic coupling in trilayer films of FeNi/Cu/FeCo deposited on Si/SiO2 substrates have been studied. While the thicknesses of the FeNi and FeCo layers were kept constant at 100 angstrom, the thickness of the Cu spacer was varied from 5 to 50 angstrom. Both hysteresis loop and ferromagnetic resonance results indicate that all films are ferromagnetically coupled. Micromagnetic simulations well reproduce the ferromagnetic resonance mode positions measured by experiments, enabling the extraction of the coupling constants. Films with a thin Cu spacer are found to be strongly coupled, with an effective coupling constant of 3 erg/cm(2) for the sample with a 5 angstrom Cu spacer. The strong coupling strength is qualitatively understood within the framework of a combined effect of Ruderman-Kittel-Kasuya-Yosida and pinhole coupling, which is evidenced by transmission electron microscopy analysis. The magnetic coupling constant surprisingly decreases exponentially with increasing Cu spacer thickness, without showing an oscillatory thickness dependence. This is partially connected to the substantial interfacial roughness that washes away the oscillation. The results have implications on the design of multilayers for spintronic applications.

  • 213.
    Weissenrieder, Jonas
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Gustafson, Johan
    Stacchiola, Dario
    Reactivity and Mass Transfer of Low-Dimensional Catalysts2014Inngår i: The chemical record, ISSN 1527-8999, E-ISSN 1528-0691, Vol. 14, nr 5, s. 857-868Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Understanding the mechanisms governing chemical and morphological changes induced by an ambient-pressure gas and how such changes influence the activity of heterogeneous catalysts is central to the formation of a predictive capability for structure-reactivity relationships. With techniques such as ambient-pressure photoelectron spectroscopy, scanning tunneling microscopy, and surface X-ray diffraction, active phases and reaction intermediates can be probed in situ on relevant samples to form a comprehensive picture of this dynamic interplay between gases and surfaces. Of particular interest is the interaction of oxygen and carbon monoxide with catalysts. We will describe how model systems of increased complexity can be used to investigate gas-mediated mass transfer processes that may occur even at relatively modest temperatures. Furthermore, we will discuss how the morphology may be tailored to study specific contributions from defect sites and charge transfer to catalytic activity.

  • 214.
    Wojek, Bastian M.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Comment on "Probing two- and three-dimensional electrons in MgB2 with soft x-ray angle-resolved photoemission"Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    A recent article by Sassa et al. [Phys. Rev. B 91, 045114 (2015)] reports on a soft-xray angle-resolved photoemission study of MgB2. The analysis and/or presentation of the collected data and the corresponding calculations appear to be partially inconsistent. The aim of this comment is to provide a guide to these inconsistencies and to discuss their influence on the presented conclusions.

  • 215.
    Wojek, Bastian M.
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Dziawa, P.
    Kowalski, B. J.
    Szczerbakow, A.
    Black-Schaffer, A. M.
    Hårdensson Berntsen, Magnus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Balasubramanian, T.
    Story, T.
    Tjernberg, Oskar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Band inversion and the topological phase transition in (Pb,Sn)Se2014Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, nr 16, s. 161202-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The recent discovery of a topological phase transition in IV-VI narrow-gap semiconductors has revitalized the decades-old interest in the bulk band inversion occurring in these materials. Here we systematically study the (001) surface states of Pb1-xSnxSe mixed crystals by means of angle-resolved photoelectron spectroscopy in the parameter space 0 <= x <= 0.37 and 300 K >= T >= 9 K. Using the surface-state observations, we monitor directly the topological phase transition in this solid solution and gain valuable information on the evolution of the underlying fundamental band gap of the system. In contrast to common model expectations, the band-gap evolution appears to be nonlinear as a function of the studied parameters, resulting in the measuring of a discontinuous band-inversion process. This finding signifies that the anticipated gapless bulk state is in fact not a stable configuration and that the topological phase transition therefore exhibits features akin to a first-order transition.

  • 216.
    Wojek, Bastian M.
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Hårdensson Berntsen, M.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Jonsson, Viktor
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Szczerbakow, A.
    Dziawa, P.
    Kowalski, B. J.
    Story, T.
    Tjernberg, Oscar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Direct observation and temperature control of the surface Dirac gap in a topological crystalline insulator2015Inngår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, artikkel-id 8463Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Since the advent of topological insulators hosting Dirac surface states, efforts have been made to gap these states in a controllable way. A new route to accomplish this was opened up by the discovery of topological crystalline insulators where the topological states are protected by crystal symmetries and thus prone to gap formation by structural changes of the lattice. Here we show a temperature-driven gap opening in Dirac surface states within the topological crystalline insulator phase in (Pb,Sn) Se. By using angle-resolved photoelectron spectroscopy, the gap formation and mass acquisition is studied as a function of composition and temperature. The resulting observations lead to the addition of a temperature-and composition-dependent boundary between massless and massive Dirac states in the topological phase diagram for (Pb,Sn) Se (001). Overall, our results experimentally establish the possibility to tune between massless and massive topological states on the surface of a topological system.

  • 217. Xiao, Dun
    et al.
    Liu, Yaowen
    Zhou, Y.
    Mohseni, Seyed Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik (Stängd 20120101), Materialfysik, MF (Stängd 20120101). University of Gothenburg, Sweden; Shahid Beheshti University, Tehran, Iran.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    Merging droplets in double nanocontact spin torque oscillators2016Inngår i: Physical Review B, ISSN 2469-9950, Vol. 93, nr 9, artikkel-id 094431Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate how magnetic droplet soliton pairs, nucleated by two separated nanocontact (NC) spin torque oscillators, can merge into a single droplet soliton. A detailed description of the magnetization dynamics of this merger process is obtained by micromagnetic simulations: A droplet pair with a steady-state in-phase spin precession is generated through the spin-transfer torque effect underneath two separate NCs, followed by a gradual expansion of the droplets' volume and the out-phase of magnetization on the inner side of the two droplets, resulting in the droplets merging into a larger droplet. This merger occurs only when the NC separation is smaller than a critical value. A transient breathing mode is observed before the merged droplet stabilizes into a steady precession state. The precession frequency of the merged droplet is lower than that of the droplet pair, consistent with its larger size. Merged droplets can again break up into droplet pairs at high enough magnetic field with a strong hysteretic response.

  • 218. Xu, Fang
    et al.
    Mudiyanselage, Kumudu
    Baber, Ashleigh E.
    Soldemo, Markus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    White, Michael G.
    Stacchiola, Dario J.
    Redox-Mediated Reconstruction of Copper during Carbon Monoxide Oxidation2014Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 29, s. 15902-15909Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Copper has excellent initial activity for the oxidation of CO, yet it rapidly deactivates under reaction conditions. In an effort to obtain a full picture of the dynamic morphological and chemical changes occurring on the surface of catalysts under CO oxidation conditions, a complementary set of in situ ambient pressure (AP) techniques that include scanning tunneling microscopy, infrared reflection absorption spectroscopy (IRRAS), and X-ray photoelectron spectroscopy were conducted. Herein, we report in situ AP CO oxidation experiments over Cu(111) model catalysts at room temperature. Depending on the CO:O-2 ratio, Cu presents different oxidation states, leading to the coexistence of several phases. During CO oxidation, a redox cycle is observed on the substrate's surface, in which Cu atoms are oxidized and pulled from terraces and step edges and then are reduced and rejoin nearby step edges. IRRAS results confirm the presence of under-coordinated Cu atoms during the reaction. By using control experiments to isolate individual phases, it is shown that the rate for CO oxidation decreases systematically as metallic copper is fully oxidized.

  • 219. Yang, Zhenyu
    et al.
    De los Reyes, Glenda B.
    Titova, Lyubov V.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Dasog, Mita
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Hegmann, Frank A.
    Veinot, Jonathan G. C.
    Evolution of the Ultrafast Photoluminescence of Colloidal Silicon Nanocrystals with Changing Surface Chemistry2015Inngår i: ACS Photonics, E-ISSN 2330-4022, Vol. 2, nr 5, s. 595-605Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The role of surface species in the optical properties of silicon nanocrystals (SiNCs) is the subject of intense debate. Changes in photoluminescence (PL) energy following hydrosilylation of SiNCs with alkyl-terminated surfaces are most often ascribed to enhanced quantum confinement in the smaller cores of oxidized NCs or to oxygen-induced defect emission. We have investigated the PL properties of alkyl-functionalized SiNCs prepared using two related methods: thermal and photochemical hydrosilylation. Photochemically functionalized SiNCs exhibit higher emission energies than the thermally functionalized equivalent. While microsecond lifetime emission attributed to carrier recombination within the NC core was observed from all samples, much faster, size-independent nanosecond lifetime components were only observed in samples prepared using photochemical hydrosilylation that possessed substantial surface oxidation. In addition, photochemically modified SiNCs exhibit higher absolute photoluminescent quantum yields (AQY), consistent with radiative recombination processes occurring at the oxygen-based defects. Correlating spectrally- and time-resolved PL measurements and XPS-derived relative surface oxidation for NCs prepared using different photoassisted hydrosilylation reaction times provides evidence the PL blue-shift as well as the short-lived PL emission observed for photochemically functionalized SiNCs are related to the relative concentration of oxygen surface defects.

  • 220. Yin, Yuli
    et al.
    Pan, Fan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Ahlberg, Martina
    Ranjbar, Mojtaba
    Duerrenfeld, Philipp
    Houshang, Afshin
    Haidar, Mohammad
    Bergqvist, Lars
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Zhai, Ya
    Dumas, Randy K.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Åkerman, Johan
    University of Gothenburg, Sweden.
    Tunable permalloy-based films for magnonic devices2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, nr 2, artikkel-id 024427Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using both broadband ferromagnetic resonance (FMR) spectroscopy and ab initio calculations, we study the magnetodynamic properties of permalloy (Py, Ni80Fe20) and Py100-x M-x films with M as platinum (Pt), gold (Au), or silver (Ag). From the uniform FMR mode, we extract the saturation magnetization (M-S), damping (alpha), and inhomogeneous broadening (Delta H-0); from the first perpendicular standing spin-wave (PSSW) mode, we extract the exchange stiffness (A). M-S and A are found to decrease with increasing alloying, most strongly for Au and less so for Pt. On the other hand, alpha increases rapidly with both Pt and Au content, while being virtually independent of Ag content. The physical origins of the observed trends in alpha, M-S, and A are analyzed and explained using density functional theory calculations in the coherent potential approximation. The calculated trends quantitatively agree with the experimental observations. The drastically different impacts of Pt, Au, and Ag on the various fundamental magnetodynamic properties will allow for significant design freedom, where different properties can be varied independently of others through careful combinations of the Pt, Au, and Ag contents of Py100-x M-x films. By empirical approximations of each property's concentration dependence, we can dial in any desired combination of magnetodynamic properties within this parameter space. As a proof-of-principle demonstration we design a set of Py100-x-yPtxAgy films, where the saturation magnetization stays constant throughout the set and the damping can be tuned by a factor of 4.

  • 221.
    Yu, Shun
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Ahmadi, Sareh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sun, Chenghua
    The University of Queensland.
    Tabib Zadeh Adibi, Pooya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chow, Winnie
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Pietzsch, Annette
    Lund University.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Inhomogeneous charge transfer within monolayer zinc phthalocyanine absorbed on TiO2(110)2012Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, nr 15, s. 154703-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The d-orbital contribution from the transition metal centers of phthalocyanine brings difficulties to understand the role of the organic ligands and their molecular frontier orbitals when it adsorbs on oxide surfaces. Here we use zinc phthalocyanine (ZnPc)/TiO2(110) as a model system where the zinc d-orbitals are located deep below the organic orbitals leaving room for a detailed study of the interaction between the organic ligand and the substrate. A charge depletion from the highest occupied molecular orbital is observed, and a consequent shift of N1s and C1s to higher binding energy in photoelectron spectroscopy (PES). A detailed comparison of peak shifts in PES and near-edge X-ray absorption fine structure spectroscopy illustrates a slightly uneven charge distribution within the molecular plane and an inhomogeneous charge transfer screening between the center and periphery of the organic ligand: faster in the periphery and slower at the center, which is different from other metal phthalocyanine, e. g., FePc/TiO2. Our results indicate that the metal center can substantially influence the electronic properties of the organic ligand at the interface by introducing an additional charge transfer channel to the inner molecular part.

  • 222.
    Zabel, Thomas
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Reuterskiöld Hedlund, Carl
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Gustafsson, O.
    Karim, A.
    Berggren, Jesper
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Wang, Q.
    Ernerheim Jokumsen, Christopher
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    Soldemo, Markus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Gotelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Hammar, Mattias
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Auger recombination in In(Ga)Sb/InAs quantum dots2015Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, nr 1, s. 013103-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the epitaxial formation of type II In0.5Ga0.5Sb/InAs and InSb/InAs quantum dot ensembles using metal organic vapor phase epitaxy. Employing scanning tunneling spectroscopy, we determine spatial quantum dot dimensions smaller than the de Broglie wavelength of InGaSb, which strongly indicates a three dimensional hole confinement. Photoluminescence spectroscopy at low temperatures yields an enhanced radiative recombination in the mid-infrared regime at energies of 170-200 meV. This luminescence displays a strong excitation power dependence with a blueshift indicating a filling of excited quantum dot hole states. Furthermore, a rate equation model is used to extract the Auger recombination coefficient from the power dependent intensity at 77 K yielding values of 1.35 x 10(-28) cm(6)/s for In0.5Ga0.5Sb/InAs quantum dots and 1.47 x 10(-27) cm(6)/s for InSb/InAs quantum dots, which is about one order of magnitude lower as previously obtained values for InGaSb superlattices.

  • 223. Zeng, Tui
    et al.
    Zhou, Yan
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Lai, P. T.
    Pong, Philip W. T.
    Linear Phase Tuning of Spin Torque Oscillators Using In-Plane Microwave Fields2014Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, nr 1, s. 1400104-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate numerically and analytically that a nano-pillar spin torque oscillator (STO), operating either with in-plane or out-ofplane free-layer precession, locks to a microwave field (H-ac) having the same frequency as the STO. By varying the spatial direction of the microwave field, we further show the preferred phase shift (Delta Phi(0)) between the STO and H-ac can be tuned in a linear fashion. We explain this phenomenon by using a magnetic-energy-based analysis. Our results provide a way to synchronize serially connected STOs by tuning the phase shift of each individual STO with external microwave field, which may enhance the locking efficiency, the locking range, and the output power of the serially connected STOs.

  • 224.
    Zhang, Miao
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Schmidt, Torsten
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Jemt, Anders
    KTH, Skolan för bioteknologi (BIO), Genteknologi. KTH, Centra, Science for Life Laboratory, SciLifeLab.
    Sahlén, Pelin
    KTH, Skolan för bioteknologi (BIO), Genteknologi. KTH, Centra, Science for Life Laboratory, SciLifeLab.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Lundeberg, Joakim
    KTH, Skolan för bioteknologi (BIO), Genteknologi. KTH, Centra, Science for Life Laboratory, SciLifeLab.
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Nanopore arrays in a silicon membrane for parallel single-molecule detection: DNA translocation2015Inngår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 26, nr 31, artikkel-id 314002Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Optical nanopore sensing offers great potential in single-molecule detection, genotyping, or DNA sequencing for high-throughput applications. However, one of the bottle-necks for fluorophore-based biomolecule sensing is the lack of an optically optimized membrane with a large array of nanopores, which has large pore-to-pore distance, small variation in pore size and low background photoluminescence (PL). Here, we demonstrate parallel detection of single-fluorophore-labeled DNA strands (450 bps) translocating through an array of silicon nanopores that fulfills the above-mentioned requirements for optical sensing. The nanopore array was fabricated using electron beam lithography and anisotropic etching followed by electrochemical etching resulting in pore diameters down to similar to 7 nm. The DNA translocation measurements were performed in a conventional wide-field microscope tailored for effective background PL control. The individual nanopore diameter was found to have a substantial effect on the translocation velocity, where smaller openings slow the translocation enough for the event to be clearly detectable in the fluorescence. Our results demonstrate that a uniform silicon nanopore array combined with wide-field optical detection is a promising alternative with which to realize massively-parallel single-molecule detection.

  • 225.
    Zhang, Miao
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Schmidt, Torsten
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sangghaleh, Fatemeh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Roxhed, Niclas
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Oxidation of nanopores in a silicon membrane: self-limiting formation of sub-10nm circular openings2014Inngår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 25, nr 35, s. 355302-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We describe a simple but reliable approach to shrink silicon nanopores with nanometer precision for potential high throughput biomolecular sensing and parallel DNA sequencing. Here, nanopore arrays on silicon membranes were fabricated by a self-limiting shrinkage of inverted pyramidal pores using dry thermal oxidation at 850 degrees C. The shrinkage rate of the pores with various initial sizes saturated after 4 h of oxidation. In the saturation regime, the shrinkage rate is within +/- 2 nm h(-1). Oxidized pores with an average diameter of 32 nm were obtained with perfect circular shape. By careful design of the initial pore size, nanopores with diameters as small as 8 nm have been observed. Statistics of the pore width show that the shrinkage process did not broaden the pore size distribution; in most cases the distribution even decreased slightly. The progression of the oxidation and the deformation of the oxide around the pores were characterized by focused ion beam and electron microscopy. Cross-sectional imaging of the pores suggests that the initial inverted pyramidal geometry is most likely the determining factor for the self-limiting shrinkage.

  • 226.
    Zhang, Miao
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Schmidt, Thorsten
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Optical detection of two-color-fluorophore barcode for nanopore DNA sensing2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A simple schematic on parallel optical detection of two-fluorophore barcode for single-molecule nanopore sensing is presented. The chosen two fluorophores, ATTO-532 and DY-521-XL, emitting in well-separated spectrum range can be excited at the same wavelength. A beam splitter was employed to separate signals from the two fluorophores and guide them to the same CCD camera. Based on a conventional microscope, sources of background in the nanopore sensing system, including membranes, compounds in buffer solution, and a detection cell was characterized. By photoluminescence excitation measurements, it turned out that silicon membrane has a negligible photoluminescence under the examined excitation from 440 nm to 560 nm, in comparison with a silicon nitrite membrane. Further, background signals from the detection cell were suppressed. Brownian motion of 450 bps DNA labelled with single ATTO-532 or DY-521-XL was successfully recorded by our optical system.

  • 227.
    Zhao, Yichen
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sugunan, Abhilash
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. SP Tech Res Inst Sweden, Chem Mat & Surfaces Unit, Sweden.
    Schmidt, Torsten
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Fornara, Andrea
    Toprak, Muhammet S.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Muhammed, Mamoun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Relaxation is the key to longer life: suppressed degradation of P3HT films on conductive substrates2014Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 2, nr 33, s. 13270-13276Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Here we show the dependence of the degree of degradation of poly-3-hexylthiophene (P3HT) films on the conductivity of the supporting substrate. P3HT is widely used for organic solar cells and electronic devices because it allows simple, low cost fabrication and has potential for the fabrication of flexible devices. However, P3HT is known to have a relatively low photostability, and investigating the photodegradation mechanism is an active research field. We find that P3HT films on conductive substrates show significantly retarded degradation and retain their chemical and morphological features when compared to similar films on glass substrates. This 'substrate effect' in retarding the degradation of P3HT films is evident even upon prolonged exposure to air for up to five months.

  • 228. Zhou, Y.
    et al.
    Iacocca, E.
    Awad, A. A.
    Dumas, R. K.
    Zhang, F. C.
    Braun, H. B.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    Dynamically stabilized magnetic skyrmions2015Inngår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, artikkel-id 8193Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetic skyrmions are topologically non-trivial spin textures that manifest themselves as quasiparticles in ferromagnetic thin films or noncentrosymmetric bulk materials. So far attention has focused on skyrmions stabilized either by the Dzyaloshinskii-Moriya interaction (DMI) or by dipolar interaction, where in the latter case the excitations are known as bubble skyrmions. Here we demonstrate the existence of a dynamically stabilized skyrmion, which exists even when dipolar interactions and DMI are absent. We establish how such dynamic skyrmions can be nucleated, sustained and manipulated in an effectively lossless medium under a nanocontact. As quasiparticles, they can be transported between two nanocontacts in a nanowire, even in complete absence of DMI. Conversely, in the presence of DMI, we observe that the dynamical skyrmion experiences strong breathing. All of this points towards a wide range of skyrmion manipulation, which can be studied in a much wider class of materials than considered so far.

  • 229. Zhu, Jian-Xin
    et al.
    Janoschek, Marc
    Chaves, D. S.
    Cezar, J. C.
    Durakiewicz, Tomasz
    Ronning, Filip
    Sassa, Yasmine
    Månsson, Martin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Scott, B. L.
    Wakeham, N.
    Bauer, Eric D.
    Thompson, J. D.
    Electronic correlation and magnetism in the ferromagnetic metal Fe3GeTe22016Inngår i: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, nr 14, artikkel-id 144404Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Motivated by the search for design principles of rare-earth-free strong magnets, we present a study of electronic structure and magnetic properties of the ferromagnetic metal Fe3GeTe2 within the local-density approximation (LDA) of the density-functional theory, and its combination with dynamical mean-field theory (DMFT). To compare these calculations, we measure magnetic and thermodynamic properties as well as x-ray magnetic circular dichroism and the photoemission spectrum of single-crystal Fe3GeTe2. We find that the experimentally determined Sommerfeld coefficient is enhanced by an order of magnitude with respect to the LDA value. This enhancement can be partially explained by LDA+DMFT. In addition, the inclusion of dynamical electronic correlation effects provides the experimentally observed magnetic moments, and the spectral density is in better agreement with photoemission data. These results establish the importance of electronic correlations in this ferromagnet.

  • 230. Zubritskaya, Irina
    et al.
    Lodewijks, Kristof
    Maccaferri, Nicolo
    Mekonnen, Addis
    Dumas, Randy K.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    Vavassori, Paolo
    Dmitriev, Alexandre
    Active Magnetoplasmonic Ruler2015Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 15, nr 5, s. 3204-3211Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plasmon rulers are an emerging concept in which the strong near-field coupling of plasmon nanoantenna elements is employed to Obtain structural information at the nanoscale. Here, we combine nanoplasmonics and nano-magnetism to conceptualize a magnetoplasmonic dimer nanoantenna that would be able to report nanoscale distances While optimizing its own spatial orientation. The latter constitutes an active operation in which a dynamically optimized optical response per measured unit length allows for the measurement of small and large nanoscale distances With about 2 orders of magnitude higher precision than current state-of-the-art plasmon rulers. We further propose,a concept to Optically measure the nanoscale response to the controlled application of force with a magnetic field.

  • 231.
    Önsten, Anneli
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Stoltz, Dunja
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Palmgren, Pål
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Yu, Shun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Claesson, Thomas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Karlsson, Ulf O.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    SO2 interaction with Zn(0001) and ZnO(0001) and the influence of water2013Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 608, s. 31-43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Photoelectron spectroscopy has been used to study room temperature adsorption of sulfur dioxide on clean and water exposed (0001) surfaces of zinc and zinc oxide. Water has no significant effect either on clean or on SO2 exposed Zn(0001) at the low water pressures used (p < 10(-7) mbar). In the Case of the zinc-terminated ZnO(0001) surface, however, water adsorbs dissociatively and OH groups are shown to have a considerable effect on SO2 surface reactions. A strong oxidation reaction occurs between Zn(0001) and SO2 giving various sulfur containing species. On ZnO(0001), SO2 interacts mainly with oxygen sites giving SO3 or SO4 species. It is shown that the ZnO(0001) sample preparation procedure can have large effects on surface chemical and physical properties. Samples cleaned by four different preparation procedures are investigated, namely sputtering only and sputtering followed by annealing at 450 degrees C, 530 degrees C and 600-650 degrees C. Annealing at 600 degrees C leads to a transition from a partly OH-terminated surface to a triangularly structured surface free from OH groups. Adsorption of SO2 on the latter surface leads to a decreased surface conductivity, which hampers photoemission measurements. Water is shown to block SO2 adsorption sites on both 450 degrees C and 530 degrees C annealed samples. On the latter sample. SO2 reduction has been observed to a small extent on the clean surface and to a larger extent when the surface is prehydroxylated. Here, we speculate that water, similar to hydrogen, generates surface zinc clusters on ZnO(0001). Zinc clusters could enable charge transfer to the antibonding LUMO of the SO2 molecule and subsequent dissociation.

  • 232.
    Önsten, Anneli
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Stoltz, Dunja
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Yu, Shun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Karlsson, Ulf O.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Role of defects in surface chemistry on Cu2O(111)2013Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 38, s. 19357-19364Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-resolution photoemission spectroscopy and scanning tunneling microscopy (STM) have been used to investigate defects on Cu2O(111) and their interaction with water and sulfur dioxide (SO2). Two types of point defects, i.e., oxygen and copper vacancies, are identified. Copper vacancies are believed to be the most important defects in both water and SO2 surface chemistry. Multiply coordinatively unsaturated oxygen anions (OMCUS) such as oxygen anions adjacent to copper vacancies are believed to be adsorption sites for both water and SO2 reaction products. Water adsorption at 150 K results in both molecular and dissociated water. Molecular water leaves the surface at 180 K. At 300 K and even more at 150 K, SO2 interacts with oxygen sites at the surface forming SO 3 species. However, thermal treatment up to 280 K of Cu 2O(111)/SO2 prepared at 150 K renders only SO4 on the surface.

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