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  • 1.
    Ahmadi, Mazaher
    et al.
    Bu Ali Sina Univ, Fac Chem, Hamadan, Iran..
    Moein, Mohammad Mahdi
    Karolinska Inst, Ctr Psychiat Res, Dept Clin Neurosci, SE-17176 Stockholm, Sweden.;Stockholm Cty Council, SE-17176 Stockholm, Sweden..
    Madrakian, Tayyebeh
    Bu Ali Sina Univ, Fac Chem, Hamadan, Iran..
    Afkhami, Abbas
    Bu Ali Sina Univ, Fac Chem, Hamadan, Iran..
    Bahar, Soleiman
    Univ Kurdistan, Fac Sci, Dept Chem, Sanandaj, Iran..
    Abdel-Rehim, Mohamed
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Karolinska Inst, Ctr Psychiat Res, Dept Clin Neurosci, SE-17176 Stockholm, Sweden.;Stockholm Cty Council, SE-17176 Stockholm, Sweden..
    Reduced graphene oxide as an efficient sorbent in microextraction by packed sorbent: Determination of local anesthetics in human plasma and saliva samples utilizing liquid chromatography-tandem mass spectrometry2018In: Journal of chromatography. B, ISSN 1570-0232, E-ISSN 1873-376X, Vol. 1095, p. 177-182Article in journal (Refereed)
    Abstract [en]

    Herein, reduced graphene oxide (RGO) has been utilized as an efficient sorbent in microextraction by packed sorbent (MEPS). The combination of MEPS and liquid chromatography-tandem mass spectrometry has been used to develop a method for the extraction and determination of three local anesthetics (i.e. lidocaine, prilocaine, and ropivacaine) in human plasma and saliva samples. The results showed that the utilization of RGO in MEPS could minimize the matrix effect so that no interfering peaks at the retention times of the analytes or internal standard was observed. The high extraction efficiency of this method was approved by mean recoveries of 97.26-106.83% and 95.21-105.83% for the studied analytes in plasma and saliva samples, respectively. Intra- and inter-day accuracies and precisions for all analytes were in good accordance with the international regulations. The accuracy values (as percentage deviation from the nominal value) of the quality control samples were between - 2.1 to 13.9 for lidocaine, - 4.2 to 11.0 for prilocaine and between - 4.5 to - 2.4 for ropivacaine in plasma samples while the values were ranged from - 4.6 to 1.6 for lidocaine, from - 4.2 to 15.5 for prilocaine and from - 3.3 to - 2.3 for ropivacaine in human saliva samples. Lower and upper limit of quantification (LLOQ, ULOQ) were set at 5 and 2000 nmol L-1 for all of the studied drugs. The correlation coefficients values were >= 0.995. The limit of detection values were obtained 4 nmol L-1 for lidocaine and prilocaine, and 2 nmol L-1 for ropivacaine.

  • 2. Al-Naamani, Laila
    et al.
    Muthukrishnan, Thirumahal
    Dutta, Joydeep
    KTH, School of Engineering Sciences (SCI), Applied Physics, Functional Materials, FNM. KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Dobretsov, Sergey
    Antifouling properties or chitosan coatings on plastic substrates2019In: Journal of Agricultural and Marine Sciences, Vol. 23, no 1, p. 92-98Article in journal (Refereed)
  • 3.
    Andersson, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material- och nanofysik.
    Delin, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material- och nanofysik.
    A quality process for assessing mathematics in a study programme2018In: Proceedings från 6:e utvecklingskonferensen för Sveriges ingenjörsutbildningar / [ed] Lena Petersson, Kristina Edström, Oskar Gedda, Fredrik Georgsson, Liselott Lycke och Marie Arehag, 2018Conference paper (Refereed)
    Abstract [en]

    We present two methodologies to assess the use of mathematics in a study programme. Firstly, we use a relatively simple methodology to assess how students show their ability to use mathematics in their degree project reports. Secondly, we present a methodology to assess how mathematics is used during a study programme. We have applied the first methodology on the mathematics content in 114 randomly chosen bachelor degree reports from 6 different study programmes within the fields of electrical engineering and computer engineering at KTH. For the 3-year bachelor degree programmes in computer engineering, we find clear deficits in the way students use mathematics in their bachelor degree reports as compared to the other programmes in our study. Through the second methodology, we were able to relate the deficits in the bachelor degree reports to a programme structure where skills in mathematics have not been sufficiently demanded in the engineering courses of the programme. 

  • 4.
    Andersson, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Weurlander, Maria
    KTH, School of Industrial Engineering and Management (ITM), Learning.
    Peer review of laboratory reports for engineering students2018In: European Journal of Engineering Education, ISSN 0304-3797, E-ISSN 1469-5898, p. 1-12Article in journal (Refereed)
    Abstract [en]

    Here, we present a module to introduce student peer review of laboratoryreports to engineering students. Our findings show that students werepositive and felt that they had learnt quite a lot from this experience.The most important part of the module was the classification scheme.The scheme was constructed to mimic the way an expert would arguewhen making a fair judgement of a laboratory report. Hence, our resultsmay suggest that the success of the module design comes from activelyengaging students in work that is more related to ‘arguing like anexpert’ than to only supply feedback to peers, which in such a casewould implicate a somewhat new direction for feedback research. Forpractitioners, our study suggests that important issues to consider in thedesign are (i) a clear and understandable evaluation framework, (ii)anonymity in the peer-review process and (iii) a small external motivation.

  • 5.
    Banuazizi, S. Amir Hossein
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Microwave probe stations with throw-dimensional control of the magnetic field to study high-frequency dynamic in nanoscale devices2018In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 89, no 6, article id 064701Article in journal (Refereed)
    Abstract [en]

    We present two microwave probe stations with motorized rotary stages for adjusting the magnitude and angle of the applied magnetic field. In the first system, the magnetic field is provided by an electromagnet and can be adjusted from 0 to similar to 1.4 T while its polar angle (theta) can be varied from 0 degrees to 360 degrees. In the second system the magnetic field is provided by a Halbach array permanent magnet, which can be rotated and translated to cover the full range of polar (theta) and azimuthal (phi) angles with a tunable field magnitude up to similar to 1 T. Both systems are equipped with microwave probes, bias-Ts, amplifiers, and spectrum analyzers, to allow for microwave characterization up to 40 GHz, as well as software to automatically perform continuous large sets of electrical and microwave measurements.

  • 6.
    Banuazizi, Seyed Amir Hossein
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Determining and Optimizing the Current and Magnetic Field Dependence of Spin-Torque and Spin Hall Nano-Oscillators: Toward Next-Generation Nanoelectronic Devices and Systems2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Spin-torque and spin Hall nano-oscillators are nanoscale devices (about 100 nm) capable of producing tunable broadband high-frequency microwave signals ranging from 0.1 GHz to over 65 GHz that several research groups trying to reach up to 200 - 300 GHz. Their development is ongoing for applications in high-frequency nanoelectronic devices and systems, such as mobile phones, wireless networks, base stations, vehicle radars, and even medical applications.

    This thesis covers a wide range of characterizations of spin-torque and spin Hall nano-oscillator devices that aim to investigate their current and magnetic field dependency, as well as to suggest improvements in these devices to optimize their application in spintronics and magnonics. The work is primarily based on experimental methods for characterizing these devices by building up new measurement systems, but it also includes numerical and micromagnetic simulations.

    Experimental techniques: In order to characterize the fabricated nanodevices in a detailed and accurate manner through their electrical and microwave responses, new measurement systems capable of full 3D control over the external magnetic fields will be described. In addition, a new method of probing an operational device using magnetic force microscopy (MFM) will be presented.

    Spin-torque nano-oscillators: We will describe remarkable improvements in the performance of spin-torque nano-oscillators (STNOs) that enhance their integration capability with applications in microwave systems. In nanocontact (NC-)STNOs made from a conventional spin-valve stack, though with thicker bottom electrodes, it is found the auto-oscillations can be excited with higher frequencies at lower threshold currents, and with higher output powers. We also find that this idea is useful for tuning spin-wave resonance and also controlling the thermal budget. Furthermore, a detailed study of magnetic droplet solitons and spin-wave dynamics in NC-STNOs will be described. Finally, we demonstrate ultra-high frequency tunability in low-current STNOs based on perpendicular magnetic tunnel junctions(p-MTJs).

    Spin Hall nano-oscillators: Characterizations of spin Hall nano-oscillator(SHNO) devices based on different structures and materials with both conventional and novel methods will be described. A detailed study of the current, temperature, and magnetic field profiles of nanogap SHNOs will be presented. In addition, we show the current and magnetic field dependence of nanoconstriction-based SHNOs.Moreover, it is shown that multiple SHNOs can be serially synchronized, thereby increasing their output power and enhancing the usage of these devices in applications such as neuromorphic computing. We show synchronization of multiple nanoconstriction SHNOs in the presence of a low in-plane magnetic field. Finally, there is a demonstration of the results of a novel method for probing an operationalSHNO using MFM.

  • 7.
    Banuazizi, Seyed Amir Hossein
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Houshang, Afshin
    A. Awad, Ahmad
    Belova, Lyubov M
    Åkerman, Johan
    Magnetic force microscopy of an operational nanodeviceManuscript (preprint) (Other academic)
    Abstract [en]

    We present a new method for probing the spatial profile of an operational magnetic nanodevice using magnetic force microscopy (MFM). We have developed an MFM system by adding a microwave probe station equipped with microwave probe, bias-T, and amplifier to allow electrical and microwave characterization up to 40 GHz during the MFM process. The nanoscale spintronic devices---spin Hall nano-oscillators (SHNOs) based on Pt/NiFe bilayers with a specific design compatible with the developed system---were fabricated and scanned using a Co magnetic force microscopy tip with 10 nm spatial resolution, while a DC current sufficient to exert auto-oscillation flowed. Our results show that this method of developed provides a promising path for the characterization of the spatial profiles of operational nano-oscillators.

  • 8.
    Banuazizi, Seyed Amir Hossein
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Mohseni, Seyed Majid
    R. Sani, Sohrab
    Eklund, Anders
    A. M. Naiini, Maziar
    Malm, B. Gunnar
    Åkerman, Johan
    Control of thermal budget in nanocontact spin-torque nano-oscillatorsManuscript (preprint) (Other academic)
    Abstract [en]

    We investigate the influence of the bottom Cu electrode thickness (tCu) in nanocontact spin-torque nano-oscillators (NC-STNOs) based on Si/SiO2/Pd(8)/Cu(tCu)/Co(8)/Cu(7)/NiFe(4.5)/Cu(3)/Pd(3) GMR stacks on the thermal budget of the magnetodynamically active region. Increasing tCu from 10 to 70 nm results in a ~50% reduction in Joule heating in both the Co and NiFe layers, which directly improves the microwave output stability and linewidth. Numerical simulations of the NC-STNO current distribution suggest that this improvement originates from a strongly reduced lateral current spread in the top ferromagnetic layer and a reduction in the device's resistance.

  • 9.
    Banuazizi, Seyed Amir Hossein
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Åkerman, Johan
    Microwave probe stations with three-dimensional control of the magnetic field to study high frequency dynamics in nanoscale devices2018In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623Article in journal (Refereed)
    Abstract [en]

    We present two microwave probe stations with motorized rotary stages for adjusting the magnitude and angle of the applied magnetic field. In the first system, the magnetic field is provided by an electromagnet and can be adjusted from 0 to ~ 1.4 T while its polar angle (θ) can be varied from 0o to 360o. In the second system the magnetic field is provided by a Halbach array permanent magnet, which can be rotated and translated to cover the full range of polar (θ) and azimuthal (φ) angles with a tunable field magnitude up to ~ 1 T. Both systems are equipped with microwave probes, bias-Ts, amplifiers, and spectrum analyzers, to allow for microwave characterization up to 40 GHz, as well as software to automatically perform continuous large sets of electrical and microwave measurements.

  • 10.
    Benedek, Peter
    et al.
    Swiss Fed Inst Technol, Dept Informat Technol & Elect Engn, CH-8092 Zurich, Switzerland..
    Yazdani, Nuri
    Swiss Fed Inst Technol, Dept Informat Technol & Elect Engn, CH-8092 Zurich, Switzerland..
    Chen, Hungru
    Univ Bath, Dept Chem, Bath BA2 7AY, Avon, England..
    Wenzler, Nils
    Swiss Fed Inst Technol, Dept Informat Technol & Elect Engn, CH-8092 Zurich, Switzerland..
    Juranyi, Fanni
    Paul Scherrer Inst, Lab Neutron Scattering & Imaging, CH-5232 Villigen, Switzerland..
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Islam, M. Saiful
    Univ Bath, Dept Chem, Bath BA2 7AY, Avon, England..
    Wood, Vanessa C.
    Swiss Fed Inst Technol, Dept Informat Technol & Elect Engn, CH-8092 Zurich, Switzerland..
    Surface phonons of lithium ion battery active materials2019In: SUSTAINABLE ENERGY & FUELS, ISSN 2398-4902, Vol. 3, no 2, p. 508-513Article in journal (Refereed)
    Abstract [en]

    Surfaces of active materials are understood to play an important role in the performance and lifetime of lithium-ion batteries, but they remain poorly characterized and therefore cannot yet be systematically designed. Here, we combine inelastic neutron scattering and ab initio simulations to demonstrate that the structure of the surface of active materials differs from the interior of the particle. We use LiFePO4 (LFP) as a model system, and we find that carbon coating influences the Li-O bonding on the (010) LFP surface relative to the bulk. Our results highlight how coatings can be used to systematically engineer the vibrations of atoms at the surface of battery active materials, and thereby impact lithium ion transport, charge transfer, and surface reactivity.

  • 11.
    Berglund, Lars
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Li, Yuanyuan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Fu, Qiliang
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Yang, Min
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Modification of transparent wood for photonics functions2018In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 255Article in journal (Other academic)
  • 12.
    Borlenghi, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Boman, Magnus
    KTH, School of Electrical Engineering and Computer Science (EECS), Software and Computer systems, SCS. RISE SICS, Electrum 229, SE-16429 Kista, Sweden..
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Modeling reservoir computing with the discrete nonlinear Schrodinger equation2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, no 5, article id 052101Article in journal (Refereed)
    Abstract [en]

    We formulate, using the discrete nonlinear Schrodinger equation (DNLS), a general approach to encode and process information based on reservoir computing. Reservoir computing is a promising avenue for realizing neuromorphic computing devices. In such computing systems, training is performed only at the output level by adjusting the output from the reservoir with respect to a target signal. In our formulation, the reservoir can be an arbitrary physical system, driven out of thermal equilibrium by an external driving. The DNLS is a general oscillator model with broad application in physics, and we argue that our approach is completely general and does not depend on the physical realization of the reservoir. The driving, which encodes the object to be recognized, acts as a thermodynamic force, one for each node in the reservoir. Currents associated with these thermodynamic forces in turn encode the output signal from the reservoir. As an example, we consider numerically the problem of supervised learning for pattern recognition, using as a reservoir a network of nonlinear oscillators.

  • 13.
    Borlenghi, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Delin, Anna
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Stochastic Thermodynamics of Oscillators' Networks2018In: Entropy, ISSN 1099-4300, E-ISSN 1099-4300, Vol. 20, no 12, article id 992Article in journal (Refereed)
    Abstract [en]

    We apply the stochastic thermodynamics formalism to describe the dynamics of systems of complex Langevin and Fokker-Planck equations. We provide in particular a simple and general recipe to calculate thermodynamical currents, dissipated and propagating heat for networks of nonlinear oscillators. By using the Hodge decomposition of thermodynamical forces and fluxes, we derive a formula for entropy production that generalises the notion of non-potential forces and makes transparent the breaking of detailed balance and of time reversal symmetry for states arbitrarily far from equilibrium. Our formalism is then applied to describe the off-equilibrium thermodynamics of a few examples, notably a continuum ferromagnet, a network of classical spin-oscillators and the Frenkel-Kontorova model of nano friction.

  • 14.
    Boucly, Anthony
    et al.
    Sorbonne Univ, CNRS UMR 7614, Lab Chim Phys Matiere & Rayonnement, 4 Pl Jussieu, F-75252 Paris 05, France..
    Rochet, Francois
    Sorbonne Univ, CNRS UMR 7614, Lab Chim Phys Matiere & Rayonnement, 4 Pl Jussieu, F-75252 Paris 05, France.;Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France..
    Arnoux, Quentin
    Sorbonne Univ, CNRS UMR 7614, Lab Chim Phys Matiere & Rayonnement, 4 Pl Jussieu, F-75252 Paris 05, France..
    Gallet, Jean-Jacques
    Sorbonne Univ, CNRS UMR 7614, Lab Chim Phys Matiere & Rayonnement, 4 Pl Jussieu, F-75252 Paris 05, France.;Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France..
    Bournel, Fabrice
    Sorbonne Univ, CNRS UMR 7614, Lab Chim Phys Matiere & Rayonnement, 4 Pl Jussieu, F-75252 Paris 05, France.;Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France..
    Tissot, Heloise
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Sorbonne Univ, CNRS UMR 7614, Lab Chim Phys Matiere & Rayonnement, 4 Pl Jussieu, F-75252 Paris 05, France.;Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France.
    Marry, Virginie
    Sorbonne Univ, CNRS UMR 8234, Physicochim Electrolyses & Nanosyst Interfaciaux, 4 Pl Jussieu, F-75252 Paris 05, France..
    Dubois, Emmanuelle
    Sorbonne Univ, CNRS UMR 8234, Physicochim Electrolyses & Nanosyst Interfaciaux, 4 Pl Jussieu, F-75252 Paris 05, France..
    Michot, Laurent
    Sorbonne Univ, CNRS UMR 8234, Physicochim Electrolyses & Nanosyst Interfaciaux, 4 Pl Jussieu, F-75252 Paris 05, France..
    Soft X-ray Heterogeneous Radiolysis of Pyridine in the Presence of Hydrated Strontium-Hydroxyhectorite and its Monitoring by Near-Ambient Pressure Photoelectron Spectroscopy2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 6164Article in journal (Refereed)
    Abstract [en]

    The heterogeneous radiolysis of organic molecules in clays is a matter of considerable interest in astrochemistry and environmental sciences. However, little is known about the effects of highly ionizing soft X-rays. By combining monochromatized synchrotron source irradiation with in situ Near Ambient Pressure X-ray Photoelectron Spectroscopy (in the mbar range), and using the synoptic view encompassing both the gas and condensed phases, we found the water and pyridine pressure conditions under which pyridine is decomposed in the presence of synthetic Sr2+-hydroxyhectorite. The formation of a pyridine/water/Sr2+ complex, detected from the Sr 3d and N 1s core-level binding energies, likely presents a favorable situation for the radiolytic breaking of the O-H bond of water molecules adsorbed in the clay and the subsequent decomposition of the molecule. However, decomposition stops when the pyridine pressure exceeds a critical value. This observation can be related to a change in the nature of the active radical species with the pyridine loading. This highlights the fact that the destruction of the molecule is not entirely determined by the properties of the host material, but also by the inserted organic species. The physical and chemical causes of the present observations are discussed.

  • 15.
    Burgos-Parra, E.
    et al.
    Univ Exeter, Coll Engn Math & Phys Sci, Exeter EX4 4QL, Devon, England..
    Bukin, N.
    Univ Exeter, Coll Engn Math & Phys Sci, Exeter EX4 4QL, Devon, England..
    Redjai Sani, Sohrab
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Figueroa, A. I.
    Diamond Light Source, Magnet Spect Grp, Didcot, Oxon, England..
    Beutier, G.
    Univ Grenoble Alpes, CNRS, Genoble INP, SIMaP, Grenoble, France..
    Dupraz, M.
    Univ Grenoble Alpes, CNRS, Genoble INP, SIMaP, Grenoble, France..
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Duerrenfeld, P.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Le, Q. Tuan
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Mohseni, S. M.
    Shahid Beheshti Univ, Fac Phys, Tehran 19839, Iran..
    Houshang, A.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, Electrum 205, S-16440 Kista, Sweden..
    Cavill, S. A.
    Univ York, Dept Phys, York YO10 5DD, N Yorkshire, England..
    Hicken, R. J.
    Univ Exeter, Coll Engn Math & Phys Sci, Exeter EX4 4QL, Devon, England..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, Electrum 205, S-16440 Kista, Sweden..
    van der Laan, G.
    Diamond Light Source, Magnet Spect Grp, Didcot, Oxon, England..
    Ogrin, F. Y.
    Univ Exeter, Coll Engn Math & Phys Sci, Exeter EX4 4QL, Devon, England..
    Investigation of magnetic droplet solitons using x-ray holography with extended references2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 11533Article in journal (Refereed)
    Abstract [en]

    A dissipative magnetic soliton, or magnetic droplet, is a structure that has been predicted to exist within a thin magnetic layer when non-linearity is balanced by dispersion, and a driving force counteracts the inherent damping of the spin precession. Such a soliton can be formed beneath a nano-contact (NC) that delivers a large spin-polarized current density into a magnetic layer with perpendicular magnetic anisotropy. Although the existence of droplets has been confirmed from electrical measurements and by micromagnetic simulations, only a few attempts have been made to directly observe the magnetic landscape that sustains these structures, and then only for a restricted set of experimental parameter values. In this work we use and x-ray holography technique HERALDO, to image the magnetic structure of the [ Co/ Ni] x4 multilayer within a NC orthogonal pseudo spin-valve, for different range of magnetic fields and injected electric currents. The magnetic configuration imaged at -33 mA and 0.3 T for devices with 90 nm NC diameter reveals a structure that is within the range of current where the droplet soliton exist based on our electrical measurements and have it is consistent with the expected size of the droplet (similar to 100 nm diameter) and its spatial position within the sample. We also report the magnetisation configurations observed at lower DC currents in the presence of fields (0-50 mT), where it is expected to observe regimes of the unstable droplet formation.

  • 16.
    Calil Kores, Cristine
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Ismail, Nur
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Geskus, Dimitri
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Dijkstra, M.
    Bernhardi, Edward H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Temperature dependence of the resonance line of optically pumped distributed-feedback lasers2018In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2018Conference paper (Refereed)
    Abstract [en]

    We characterize experimentally and theoretically a distributed-feedback laser resonator subject to a thermal chirp. The total accumulated phase shift determines the resonance wavelength. The reflectivities (outcoupling losses) at the resonance wavelength govern the resonance linewidth.

  • 17.
    Carrasco, Irene
    et al.
    Univ Surrey, Adv Technol Inst, Dept Elect & Elect Engn, Guildford GU2 7XH, Surrey, England..
    Agazzi, Laura
    Univ Twente, MESA Inst, Integrated Opt Micro Syst, POB 217, NL-7500 AE Enschede, Netherlands..
    Loiko, Pavel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Surrey, Adv Technol Inst, Dept Elect & Elect Engn, Guildford GU2 7XH, Surrey, England.;Univ Twente, MESA Inst, Integrated Opt Micro Syst, POB 217, NL-7500 AE Enschede, Netherlands.
    Energy-Transfer Processes Among Non-Homogeneously Distributed Rare-Earth Ions and Impact on Amplification and Lasing2018In: 20th International Conference on Transparent Optical Networks, ICTON / [ed] Jaworski, M Marciniak, M, Institute of Electrical and Electronics Engineers (IEEE), 2018, article id 8473493Conference paper (Refereed)
    Abstract [en]

    Energy-transfer processes such as energy-transfer upconversion are often detrimental to the performance of rareearth- doped amplifiers and lasers on the typical luminescence transitions in the near-infrared spectral region between 1-2 mu m. In order to quantify the influence of these interionic processes on amplification and lasing, not only luminescence decay curves have to be measured, but also the population dynamics of the electronic level scheme need to be modeled. The usually encountered non-homogeneous ion distributions complicate the situation. Here we present a stochastic model of energy-transfer processes that takes a statistical ion distribution into account. The influence of energy-transfer upconversion and cross-relaxation on amplification and lasing on the 1.06 mm transition in Nd3+, the 1.53 mm transition in Er3+, or the 1.84 mm transition in Tm3+ under these conditions is investigated.

  • 18.
    Cheng, Dan-Chen
    et al.
    Fudan Univ, Dept Opt Sci & Engn, Shanghai 200433, Peoples R China.;Fudan Univ, Shanghai Ultra Precis Opt Mfg Engn Ctr, Shanghai 200433, Peoples R China..
    Hao, Hong-Chen
    Fudan Univ, Dept Opt Sci & Engn, Shanghai 200433, Peoples R China.;Fudan Univ, Shanghai Ultra Precis Opt Mfg Engn Ctr, Shanghai 200433, Peoples R China..
    Zhang, Miao
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Royal Inst Technol KTH, S-16440 Kista, Sweden..
    Shi, Wei
    Fudan Univ, Dept Opt Sci & Engn, Shanghai 200433, Peoples R China.;Fudan Univ, Shanghai Ultra Precis Opt Mfg Engn Ctr, Shanghai 200433, Peoples R China..
    Lu, Ming
    Fudan Univ, Dept Opt Sci & Engn, Shanghai 200433, Peoples R China.;Fudan Univ, Shanghai Ultra Precis Opt Mfg Engn Ctr, Shanghai 200433, Peoples R China..
    Improving Si solar cell performance using Mn:ZnSe quantum dot-doped PLMA thin film2013In: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 8, article id 291Article in journal (Refereed)
    Abstract [en]

    Poly(lauryl methacrylate) (PLMA) thin film doped with Mn:ZnSe quantum dots (QDs) was spin-deposited on the front surface of Si solar cell for enhancing the solar cell efficiency via photoluminescence (PL) conversion. Significant solar cell efficiency enhancements (approximately 5% to 10%) under all-solar-spectrum (AM0) condition were observed after QD-doped PLMA coatings. Furthermore, the real contribution of the PL conversion was precisely assessed by investigating the photovoltaic responses of the QD-doped PLMA to monochromatic and AM0 light sources as functions of QD concentration, combined with reflectance and external quantum efficiency measurements. At a QD concentration of 1.6 mg/ml for example, among the efficiency enhancement of 5.96%, about 1.04% was due to the PL conversion, and the rest came from antireflection. Our work indicates that for the practical use of PL conversion in solar cell performance improvement, cautions are to be taken, as the achieved efficiency enhancement might not be wholly due to the PL conversion.

  • 19.
    Chung, Sunjae
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. Department of Physics, University of Gothenburg.
    Jiang, Sheng
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Eklund, Anders
    KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits.
    Iacocca, Ezio
    Department of Applied Mathematics, University of Colorado.
    Le, Quang Tuan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Mazraati, Hamid
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Mohseni, Seyed Majid
    Department of Physics, Shahid Beheshti University, Tehran 19839, Iran.
    Sani, Sohrab Redjai
    Department of Physics and Astronomy, Uppsala University,.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Effect of canted magnetic field on magnetic droplet nucleation boundariesManuscript (preprint) (Other academic)
    Abstract [en]

    The influence on magnetic droplet nucleation boundaries by canted magnetic elds are investigated and reported. The nucleation boundary condition, In = αAH + BH + C, is determined at different canted angles (0°< θH<20°) using magnetoresistance (MR) and microwave measurements in nanocontact spintorque oscillators (NC-STOs). As θH increased, the nucleation boundary shifts gradually towards higher In and H. The coefficient B of the nucleation boundary equation also nearly doubled as θH increases. On theother hand, the coefficient αA remained constant for all values of θH. These observations can be explained by considering the drift instability of magnetic droplets and the different tilt behaviour of the Co fixed layer induced by different θH.

  • 20. Fan, W.
    et al.
    Fu, Q.
    Qian, Q.
    Chen, Q.
    Liu, W.
    Zhou, X.
    Yuan, H.
    Yue, J.
    Huang, Z.
    Jiang, Sheng
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Southeast University, China.
    Kou, Z.
    Zhai, Y.
    Investigation of magnetization dynamics damping in Ni80Fe20/Nd-Cu bilayer at room temperature2018In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 8, no 5, article id 056325Article in journal (Refereed)
    Abstract [en]

    Focusing on the Ni80Fe20 (Py)/Nd-Cu bilayers, the magnetization dynamic damping from spin pumping effect is investigated systematically by doping itinerant Cu in rear earth metal Nd. Various Ta/Py/Nd1-xCux/Ta/Si films with x = 0%, 16%, 38%, 46% and 58% are prepared by magnetron sputtering. For every content of Cu, the thickness of Nd-Cu layer is changed from 1 nm to 32 nm. The damping coefficient increases with increasing the thickness of Nd-Cu layer, which shows the trend of the spin pumping behavior. Also, with increasing Cu concentration in the Nd-Cu layer, the damping coefficient decreases, implying that the spin-orbit coupling in Nd-Cu layer is indeed cut down by high itinerant of Cu dopants. It is interesting that the spin diffusion length (λSD) in the Nd-Cu layer for different Cu dopants is not found to increase monotonously.

  • 21. Fazlali, Masoumeh
    et al.
    Banuazizi, Seyed Amir Hossein
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Ahlberg, Martina
    Dvornik, Mykola
    R. Sani, Sohrab
    Mohseni, Seyed Majid
    Åkerman, Johan
    Tuning exchange-dominated spin-waves using lateral current spread in nanocontact spin-torque nano-oscillators2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118Article in journal (Refereed)
    Abstract [en]

    We present an efficient method to tailor propagating spin waves in quasi-confined systems. We use nanocontact spin-torque nano-oscillators based on NiFe/Cu/Co spin-valves and study the ferromagnetic and spin-wave resonances (FMR and SWR) of both layers. We employ homodyne-detected ferromagnetic resonance spectroscopy, resembling spin-torque FMR, to detect the magnetodynamics. The external field is applied in-plane, giving a parallel configuration of the magnetic layers, which do not provide any spin-transfer torque. Instead, the excitation is caused by the Oersted-field. By varying the thickness of the bottom Cu electrode of the devices, we tune the current distribution in the samples, and thereby the Oersted field, which governs the spin wave characteristics.

  • 22.
    Forslund, Ola Kenji
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Andreica, D.
    Sassa, Y.
    Nozaki, H.
    Umegaki, I.
    Nocerino, Elisabetta
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Jonsson, Viktor
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Guguchia, Z.
    Shermadini, Z.
    Khasanov, R.
    Isobe, M.
    Takagi, H.
    Ueda, Y.
    Sugiyama, J.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Magnetic phase diagram of K 2 Cr 8 O 16 clarified by high-pressure muon spin spectroscopy2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, no 1, article id 1141Article in journal (Refereed)
    Abstract [en]

    The K 2 Cr 8 O 16 compound belongs to a series of quasi-1D compounds with intriguing magnetic properties that are stabilized through a high-pressure synthesis technique. In this study, a muon spin rotation, relaxation and resonance (μ + SR) technique is used to investigate the pressure dependent magnetic properties up to 25 kbar. μ + SR allows for measurements in true zero applied field and hereby access the true intrinsic material properties. As a result, a refined temperature/pressure phase diagram is presented revealing a novel low temperature/high pressure (p C1 = 21 kbar) transition from a ferromagnetic insulating to a high-pressure antiferromagnetic insulator. Finally, the current study also indicates the possible presence of a quantum critical point at p C2 ~ 33 kbar where the magnetic order in K 2 Cr 8 O 16 is expected to be fully suppressed even at T = 0 K.

  • 23.
    Geskus, Dimitri
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Centro de Lasers e Aplicações, IPEN/SP, Av. Prof. Lineu Prestes, São Paulo, SP, 2242, Brazil.
    Jakutis-Neto, J.
    Spence, D. J.
    Pask, H. M.
    Wetter, N. U.
    Extreme Linewidth Broadening in a Nd: YLiF 4 -KGW Intracavity Raman Laser2019In: Proceedings 2015 European Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, CLEO/Europe-EQEC 2015, Optical Society of America, 2019Conference paper (Refereed)
  • 24.
    Geskus, Dimitri
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Yong, Y. S.
    Bernhardi, E. H.
    Agazzi, L.
    García-Blanco, S. M.
    Aravazhi, S.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Concentration dependence of optical gain in Yb 3+ -doped potassium double tungstate channel waveguides2019In: Proceedings 2015 European Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, CLEO/Europe-EQEC 2015, Optical Society of America, 2019Conference paper (Refereed)
  • 25. Haidar, Mohammad
    et al.
    Awad, Ahmad A.
    Dvornik, Mykola
    Khymyn, Roman
    Houshang, Afshin
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    A single layer spin-orbit torque nano-oscillator2019In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 2362Article in journal (Refereed)
    Abstract [en]

    Spin torque and spin Hall effect nano-oscillators generate high intensity spin wave auto-oscillations on the nanoscale enabling novel microwave applications in spintronics, magnonics, and neuromorphic computing. For their operation, these devices require externally generated spin currents either from an additional ferromagnetic layer or a material with a high spin Hall angle. Here we demonstrate highly coherent field and current tunable microwave signals from nano-constrictions in single 15-20 nm thick permalloy layers with oxide interfaces. Using a combination of spin torque ferromagnetic resonance measurements, scanning micro-Brillouin light scattering microscopy, and micromagnetic simulations, we identify the auto-oscillations as emanating from a localized edge mode of the nano-constriction driven by spin-orbit torques. Our results pave the way for greatly simplified designs of auto-oscillating nano-magnetic systems only requiring single ferromagnetic layers with oxide interfaces.

  • 26.
    Horio, M.
    et al.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Hauser, K.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Sassa, Y.
    Uppsala Univ, Dept Phys & Astron, SE-75121 Uppsala, Sweden..
    Mingazheva, Z.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Sutter, D.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Kramer, K.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Cook, A.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Nocerino, Elisabetta
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Forslund, Ola Kenji
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Tjernberg, Oscar
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Kobayashi, M.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Chikina, A.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Schroter, N. B. M.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Krieger, J. A.
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland.;Swiss Fed Inst Technol, Lab Festkorperphys, CH-8093 Zurich, Switzerland..
    Schmitt, T.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Strocov, V. N.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Pyon, S.
    Univ Tokyo, Dept Adv Mat, Kashiwa, Chiba 2778561, Japan..
    Takayama, T.
    Univ Tokyo, Dept Adv Mat, Kashiwa, Chiba 2778561, Japan..
    Takagi, H.
    Univ Tokyo, Dept Adv Mat, Kashiwa, Chiba 2778561, Japan..
    Lipscombe, O. J.
    Univ Bristol, HH Wills Phys Lab, Bristol BS8 1TL, Avon, England..
    Hayden, S. M.
    Univ Bristol, HH Wills Phys Lab, Bristol BS8 1TL, Avon, England..
    Ishikado, M.
    CROSS, Tokai, Ibaraki 3191106, Japan..
    Eisaki, H.
    Natl Inst Adv Ind Sci & Technol, Elect & Photon Res Inst, Tsukuba 3058568, Japan..
    Neupert, T.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Matt, C. E.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland.;Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland.;Harvard Univ, Dept Phys, Cambridge, MA 02138 USA..
    Chang, J.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Three-Dimensional Fermi Surface of Overdoped La-Based Cuprates2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 7, article id 077004Article in journal (Refereed)
    Abstract [en]

    We present a soft x-ray angle-resolved photoemission spectroscopy study of overdoped high-temperature superconductors. In-plane and out-of-plane components of the Fermi surface are mapped by varying the photoemission angle and the incident photon energy. No k(z) dispersion is observed along the nodal direction, whereas a significant antinodal k(z) dispersion is identified for La-based cuprates. Based on a tight-binding parametrization, we discuss the implications for the density of states near the van Hove singularity. Our results suggest that the large electronic specific heat found in overdoped La2-xSrxCuO4 cannot be assigned to the van Hove singularity alone. We therefore propose quantum criticality induced by a collapsing pseudogap phase as a plausible explanation for observed enhancement of electronic specific heat.

  • 27.
    Hårdensson Berntsen, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Götberg, Olof
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Reinvestigation of the giant Rashba-split states on Bi-covered Si(111)2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 12, article id 125148Article in journal (Refereed)
    Abstract [en]

    We study the electronic and spin structures of the giant Rashba-split surface states of the Bi/Si(111)-(root 3 x root 3)R30 degrees trimer phase by means of spin- and angle-resolved photoelectron spectroscopy (spin-ARPES). Supported by tight-binding calculations of the surface state dispersion and spin orientation, our findings show that the spin experiences a vortexlike structure around the (Gamma) over bar point of the surface Brillouin zone-in accordance with the standard Rashba model. Moreover, we find no evidence of a spin vortex around the (K) over bar point in the hexagonal Brillouin zone and thus no peculiar Rashba split around this point, something that has been suggested by previous works. Rather the opposite, our results show that the spin structure around (K) over bar can be fully understood by taking into account the symmetry of the Brillouin zone and the intersection of spin vortices centered around the (Gamma) over bar points in neighboring Brillouin zones. As a result, the spin structure is consistently explained within the standard framework of the Rashba model although the spin-polarized surface states experience a more complex dispersion compared to free-electron-like parabolic states.

  • 28.
    Ismail, Nur
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Kores, Cristine Calil
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Geskus, Dimitri
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Mode profiles and Airy distributions of Fabry-Perot resonators with frequency-dependent mirror reflectivity2017In: Laser Resonators, Microresonators, and Beam Control XIX / [ed] Kudryashov, AV Paxton, AH Ilchenko, VS, SPIE - International Society for Optical Engineering, 2017, Vol. 10090, article id UNSP 1009011-1Conference paper (Refereed)
    Abstract [en]

    We thoroughly investigate the Fabry-Perot resonator, avoid approximations, and derive its generic Airy distribution, equaling the internal resonance enhancement, and all related Airy distributions, such as the commonly known transmission. We verify that the sum of the mode profiles of all longitudinal modes is the fundamental physical function characterizing the Fabry-Perot resonator and generating the Airy distributions. We investigate the influence of frequency-dependent mirror reflectivities on the mode profiles and the resulting Airy distributions. The mode profiles then deviate from simple Lorentzian lines and exhibit peaks that are not located at resonant frequencies. Our simple, yet accurate analysis greatly facilitates the characterization of Fabry-Perot resonators with strongly frequency-dependent mirror reflectivities.

  • 29.
    Jiang, Sheng
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Engineering Magnetic Droplets in Nanocontact Spin-Torque Nano-Oscillators2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Spin-torque nano-oscillators (STNOs) are nanoscale spintronic devices capable of generating highly tunable broadband microwave signals. In this thesis, I study nanocontact (NC)-based STNOs using strong perpendicular magnetic anisotropy(PMA) free layers, where a novel magnetic soliton—a magnetic droplet—exists. This work is devoted to further understanding the characteristics of the magnetic droplet in diverse magnetic structures, including orthogonal and all-perpendicular(all-PMA) spin valves (SVs) and orthogonal magnetic tunnel junctions (MTJs). The nucleation, transition, and collapse of magnetic droplets are observed, tailored, and analyzed by engineering the magnetic properties of the thin films’ stacks. This thesis consists of three main parts: Orthogonal SVs with [Co/Ni]/Cu/CoxNiFe1−x: Magnetic droplets were first observed in orthogonal SV STNOs. We engineered the fixed layer magnetization Ms,p by cosputtering different compositions of CoxNiFe1−x (x = 0−1). The nucleation boundaries of a magnetic droplet in a current-field phase shift to a lower region as Ms,p decreases. The nucleation boundary is also examined under canted fields in order to better understand the drift instability of the droplets. The observations not only confirm the theoretical predictions of nucleation boundary, but suggest a method for controlling the nucleation boundary. All-PMA SVs with [Co/Ni]/Cu/[Co/Pd]: In contrast to orthogonal SVs,all-PMA NC-STNOs show many novel features. First, thanks to the dramatic improvement in droplet stability that results from using a [Co/Pd] PMA fixed layer, the droplets are directly imaged by a scanning transmission x-ray microscopy(STXM). The transition between the static bubble and magnetic droplet is also observed and imaged. Moreover, to investigate the effect of PMA, He+ irradiation is conducted on the all-PMA NC-STNOs, progressively tuning the PMA. The transitions of the normal FMR-like mode and droplet mode are demonstrated. The behavior of frequency tunability versus PMA is systematically studied. These investigations of all-PMA and irradiated NC-STNOs show that it is feasible to engineer the magnetic properties of STNOs through He+ irradiation. Besides, the dynamic droplets and static bubbles have great potential applications in next-generation information carriers. Orthogonal MTJs with CoFeB/MgO/CoFe: The existence of droplets in orthogonal MTJs is still debated. Instead, the magnetodynamics are investigated here. Very importantly, we find that the frequency tunability is determined by the spin-transfer torque (STT), the voltage-controlled magnetic anisotropy (VCMA), and thermal heating. This paves the way to improving tunability by combining these contributions. This study will contribute greatly to real applications, such as microwave generators and detectors.

  • 30.
    Jiang, Sheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Ahlberg, Martina
    Department of Physics, University of Gothenburg.
    Afshin, Houshang
    Department of Physics, University of Gothenburg.
    Ferreira, R.
    International Iberian Nanotechnology Laboratory (INL), Braga, Portugal.
    Freitas, P. P.
    International Iberian Nanotechnology Laboratory (INL), Braga, Portugal.
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Department of Physics, University of Gothenburg.
    Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctionsManuscript (preprint) (Other academic)
    Abstract [en]

    We demonstrate the magnetodynamics of nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions, with a strong perpendicular magnetic anisotropy free layer and an easy-plane reference layer. First, the static magnetic properties are studied by conducting hysteresis loop and magnetoresistance measurements. Then, we characterize the generated microwave signals by applying dc currents. Field-sweep signals at xed current show a typical FMR-like frequency dependence. Interestingly, for current-sweep measurements, the plot of frequency versus dc current can be fitted well with a symmetric parabolic and an asymmetric linear term. The symmetric behavior is ascribed to the current-induced Joule heating and Oersted elds. The asymmetric dependence is due to the linear perpendicular spin torque (or eld-like torque) and the voltage-controlled magnetic anisotropy. Our observation hints at a route to improving the frequency tunability in future spintronic applications by selectively adding all these contributions.

  • 31.
    Jiang, Sheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. NanOsc AB, S-16440 Kista, Sweden..
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Diez, Liza Herrera
    Univ Paris Saclay, Univ Paris Sud, CNRS, Inst Elect Fondamentale, F-91405 Orsay, France..
    Le, Quang Tuan
    KTH, School of Engineering Sciences (SCI), Applied Physics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.
    Magnusson, Fredrik
    NanOsc AB, S-16440 Kista, Sweden..
    Ravelosona, Dafine
    Univ Paris Saclay, Univ Paris Sud, CNRS, Inst Elect Fondamentale, F-91405 Orsay, France.;Spin Ion Technol, 28 Rue Gen Leclerc, F-78000 Versailles, France..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics. NanOsc AB, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Tuning the magnetodynamic properties of all-perpendicular spin valves using He+ irradiation2018In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 8, no 6, article id 065309Article in journal (Refereed)
    Abstract [en]

    Using He+ ion irradiation, we demonstrate how the magnetodynamic properties of both ferromagnetic layers in all-perpendicular [Co/Pd]/Cu/[Co/Ni] spin valves can be tuned by varying the He+ ion fluence. As the perpendicular magnetic anisotropy of both layers is gradually reduced by the irradiation, different magnetic configurations can be achieved from all-perpendicular (up arrow up arrow), through orthogonal (->up arrow), to all in-plane (paired right arrows). In addition, both the magnetic damping (alpha) and the inhomogeneous broadening (Delta H-0) of the Co/Ni layer improve substantially with increasing fluence. While the GMR of the spin valve is negatively affected, decreasing linearly from an original value of 1.14% to 0.4% at the maximum fluence of 50x10(14) He+/cm(2), most of the Co/Ni layer improvement is achieved already at a fluence of 10x10(14) He+/cm(2), for which GMR only reduces to 0.9%.

  • 32.
    Jiang, Sheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics. Department of Physics and Astronomy, Uppsala University.
    Le, Quang Tuan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Diez, Liza Herrera
    Institut d'Electronique Fondamentale, CNRS, Universite Paris-Sud, Universite Paris-Saclay.
    Houshang, Afshin
    Department of Physics, University of Gothenburg.
    Zahedinejad, Mohammad
    Department of Physics, University of Gothenburg.
    Ravelosona, Dafine
    Institut d'Electronique Fondamentale, CNRS, Universite Paris-Sud, Universite Paris-Saclay.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Department of Physics, University of Gothenburg.
    Experimental evidence of tunable nonlinearity in He+ irradiated spin-torque oscillatorsManuscript (preprint) (Other academic)
    Abstract [en]

    Spin-torque nano-oscillators (STNOs) are among the most promising candidates for nanoscale broadband microwave generators. Before this application can be realized, however, enormous efforts are required of researchers to meet the commercial requirements of high-frequency tunability, high power, and narrow linewidth. As the performance of STNOs is mainly attributed to the nonlinearity on the basis of nonlinear auto-oscillator theory, we here systematically study how this nonlinearity is affected by the free-layer's effective magnetization Meff (i.e., the perpendicular magnetic anisotropy, PMA) in STNOs. The PMA is gradually tuned by using different fluences of He+ irradiation. Consequently, the nonlinearity can be continuously tailored from positive to negative. In addition, due to the almost zero nonlinearity, the linewidth shows an improvement of more than two orders of magnitude. This experimental observation is in strong agreement with the theory of nonlinear auto-oscillators. Our study not only confirms the theoretical prediction of nonlinearity, but also indicates the route to be taken towards realizing commercial microwave generators.

  • 33.
    Jiang, Sheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Le, Quang Tuan
    Mazraati, Hamid
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Houshang, Afshin
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Using magnetic droplet nucleation to determine the spin torque effciency and asymmetry in Cox(NiFe)1-x thin filmsManuscript (preprint) (Other academic)
    Abstract [en]

    We demonstrate how to extract the material dependent spin torque efficiency (ε) and asymmetry(λ) from the eld{current nucleation boundaries of magnetic droplet solitons in orthogonal nanocontacts in-torque oscillators with Cox(Ni80Fe20)1-x, (x=0{1), fixed layers. As the perpendicular component of the xed layer magnetization plays a central role in governing droplet nucleation, the nucleation boundaries exhibit monotonic shifts towards higher perpendicular magnetic elds when the xed layer magnetization μ0Ms,p is tuned from 1.04 to 1.7 T. We then extract ε and λ from tsto the nucleation boundaries and nd that while ε does not vary with composition, λ increases from1.5 to 3 with increasing Co content. The analysis of droplet nucleation boundaries is hence a useful tool for the systematic study of both ε and λ as functions of material composition.

  • 34.
    Jiang, Sheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. NanOsc AB, S-16440 Kista, Sweden..
    Etesami, Seyyed Ruhollah
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics. Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Le, Quang Tuan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Houshang, Afshin
    NanOsc AB, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Impact of the Oersted Field on Droplet Nucleation Boundaries2018In: IEEE Magnetics Letters, ISSN 1949-307X, E-ISSN 1949-3088, Vol. 9, article id 3104304Article in journal (Refereed)
    Abstract [en]

    We investigate how the Oersted field affects the magnetic droplet nucleation boundary in spin-torque nano-oscillators based on orthogonal spin-valve stacks with a perpendicular magnetic anisotropy Co/Ni free layer and an easy-plane anisotropy Ni80Fe20 fixed layer. The current-field nucleation boundary is determined experimentally using both microwave signal and dc resistance measurements. The Oersted field can, in principle, have an impact on droplet nucleation. This effect is considered approximately using an analytical equation for the nucleation boundary, which is extended to cover fields larger than the fixed-layer saturation field. We test the accuracy of this approach by comparing with micromagnetic simulations. Finally, we carry out a numerical fit to experimental data and find good agreement.

  • 35.
    Khymyn, Roman
    et al.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Lisenkov, Ivan
    Oregon State Univ, Dept Elect Engn & Comp Sci, Corvallis, OR 97331 USA.;Northeastern Univ, Elect & Comp Engn Dept, Boston, MA 02464 USA..
    Voorheis, James
    Oakland Univ, Dept Phys, Rochester, MI 48309 USA..
    Sulymenko, Olga
    Taras Shevchenko Natl Univ Kyiv, Fac Radiophys Elect & Comp Syst, UA-01601 Kiev, Ukraine..
    Prokopenko, Oleksandr
    Taras Shevchenko Natl Univ Kyiv, Fac Radiophys Elect & Comp Syst, UA-01601 Kiev, Ukraine..
    Tiberkevich, Vasil
    Oakland Univ, Dept Phys, Rochester, MI 48309 USA..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Slavin, Andrei
    Oakland Univ, Dept Phys, Rochester, MI 48309 USA..
    Ultra-fast artificial neuron: generation of picosecond-duration spikes in a current-driven antiferromagnetic auto-oscillator2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 15727Article in journal (Refereed)
    Abstract [en]

    We demonstrate analytically and numerically, that a thin film of an antiferromagnetic (AFM) material, having biaxial magnetic anisotropy and being driven by an external spin-transfer torque signal, can be used for the generation of ultra-short "Dirac-delta-like" spikes. The duration of the generated spikes is several picoseconds for typical AFM materials and is determined by the inplane magnetic anisotropy and the effective damping of the AFM material. The generated output signal can consist of a single spike or a discrete group of spikes ("bursting"), which depends on the repetition (clock) rate, amplitude, and shape of the external control signal. The spike generation occurs only when the amplitude of the control signal exceeds a certain threshold, similar to the action of a biological neuron in response to an external stimulus. The "threshold" behavior of the proposed AFM spike generator makes possible its application not only in the traditional microwave signal processing but also in the future neuromorphic signal processing circuits working at clock frequencies of tens of gigahertz.

  • 36.
    Kjellgren, Björn
    et al.
    KTH, School of Education and Communication in Engineering Science (ECE), Learning, Language and communication.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Wingård, Lasse
    KTH, School of Industrial Engineering and Management (ITM).
    Andersson, Magnus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Hedin, Björn
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Hjelm, Niclas
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Berglund, Anders
    The Pedagogical Developers Initiative – Sustainable Impact of Falling into Oblivion?2018In: Proceedings of the 14th International CDIO Conference / [ed] Bean Bennedsen, Edström, Hugo, Roslöf, Songer & Yamamoto, Kanazawa: Kanazawa Institute of Technology , 2018, p. 738-747Conference paper (Refereed)
    Abstract [en]

    Between 2014-16, KTH Royal Institute of Technology set aside considerable resources in its biggest pedagogical project to date, the Pedagogical Developers Initiative. The project has been continuously reported on at recent CDIO conferences. While aimed primarily at CDIO Standard 10, enhancement of faculty teaching competence, the project managed, by design as much as through accident, to strengthen many CDIO standards and syllabus items. With the conclusion of the project, the constructive practices and ideas that emerged from the initiative were meant to be incorporated into the regular operations of the university, a task that was delegated to each of KTH’s ten schools. However, even though KTH officially labelled the project a success, the schools have taken a non-uniform approach to this endeavour, as they indeed had done to the project as a whole during its duration. Following up on our earlier reports, and primarily using data from interviews and our own observations, the paper looks at which of the initiative’s ideas and practices have survived the end of the project, in what forms, by what means, and what insights and lessons one can draw from this when designing mechanisms for continuous and sustainable improvement of pedagogical practices at a technical university.

  • 37.
    Kores, Cristine C.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Geskus, Dimitri
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Ismail, Nur
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Dijkstra, Meindert
    Bernhardi, Edward H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    The linewidth of distributed feedback resonators: the combined effect of thermally induced chirp and gain narrowing2017In: Laser Resonators, Microresonators, and Beam Control XIX / [ed] Kudryashov, AV Paxton, AH Ilchenko, VS, SPIE - International Society for Optical Engineering, 2017, article id UNSP 1009014-1Conference paper (Refereed)
    Abstract [en]

    Distributed-feedback (DFB) laser resonators are widely recognized for their advantage of generating laser emission with extremely narrow linewidth. Our investigation concerns ytterbium-doped amorphous Al2O3 channel waveguides with a corrugated homogeneous Bragg grating inscribed into its SiO2 top cladding, in which lambda/4 phase-shift provides a resonance and allows for laser emission with a linewidth as narrow as a few kHz. Pump absorption imposes a thermal chirp of the grating period, which has implications for the spectral characteristics of the resonator. Thermal effects on the spectral response of a DFB passive resonator were investigated via simulations using Coupled Mode Theory by considering (i) a constant deviation of the grating period or (ii) a chirp with a linear profile. We report an increase of the resonance linewidth up to 15%. This result is due to two factors, namely changes of the grating reflectivity at the resonance frequency up to 2.4% and of the shift of resonance frequency up to 61 pm due to an accumulated phase shift imposed on the grating by the chirp profile. The linewidth decrease due to gain is on the order of 106, which is a much larger value. Nevertheless, according to the Schawlow-Townes equation the linewidth increase of the passive resonator due to a thermal chirp quadratically increases the laser linewidth.

  • 38.
    Kores, Cristine Calil
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Geskus, Dimitri
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Ismail, Nur
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Dijkstra, M.
    Bernhardi, E. H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Characterization of Ultranarrow-Linewidth Distributed-Feedback Resonators Below Laser Threshold2016Conference paper (Refereed)
  • 39.
    Kores, Cristine Calil
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Ismail, N.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Geskus, D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Dijkstra, M.
    Univ Twente, MESA Inst, Opt Sci, NL-7500 AE Enschede, Netherlands..
    Bernhardi, E. H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Surrey, Adv Technol Inst, Guildford GU2 7XH, Surrey, England..
    Temperature Dependence of Spectral Characteristics of Distributed-Feedback Resonators2018In: FIBER LASERS AND GLASS PHOTONICS: MATERIALS THROUGH APPLICATIONS / [ed] Taccheo, S Mackenzie, JI Ferrari, M, SPIE-INT SOC OPTICAL ENGINEERING , 2018, article id 106830BConference paper (Refereed)
    Abstract [en]

    The spectral response of a distributed-feedback resonator with a thermal chirp is investigated. An Al2O3 channel waveguide with a surface Bragg grating inscribed into its SiO2 top cladding is studied. A linear temperature gradient along the resonator leads to a corresponding variation of the grating period. We characterize its spectral response with respect to wavelength and linewidth changes of the resonance peak. Simulated results show good agreement with the experimental data, indicating that the resonance wavelength is determined by the total accumulated phase shift. The calculated grating reflectivities at the resonance wavelength largely explain the observed changes of the resonance linewidth. This agreement demonstrates that the linewidth increase is caused by the increase of resonator outcoupling losses.

  • 40.
    Kores, Cristine Calil
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Ismail, Nur
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Bernhardi, E. H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Distributed phase shift and lasing wavelength in distributed-feedback resonators2019Conference paper (Refereed)
  • 41.
    Kores, Cristine Calil
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Ismail, Nur
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Bernhardi, E. H.
    KTH.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ. of Surrey (United Kingdom) .
    Lasing wavelength in dielectric distributed-feedback lasers with a distributed phase shift2019Conference paper (Refereed)
    Abstract [en]

    Distributed-feedback waveguide lasers based on Bragg-grating resonators generate ultranarrow-linewidth emission. Oscillation at the center of the reflection band ensures maximum reflectivity, hence minimum laser linewidth. The required μ/2 phase shift is often introduced by a distributed change in effective refractive index, e.g. by adiabatically widening the waveguide. Despite careful design and fabrication, the experimentally observed resonance wavelength deviates, thereby placing the resonance and laser emission at a position with lower reflectivity inside the reflection band. This effect is usually incorrectly attributed to fabrication errors. Here we show theoretically and experimentally that the decay of light intensity during propagation from the phase-shift center into both sides of the Bragg grating due to (i) reflection by the periodic grating and (ii) the adiabatic refractive-index change causes an incomplete accumulation of designed phase shift, thereby systematically shifting the resonance to a shorter wavelength. Calculations are performed based on the characteristic-matrix approach. Experimental studies are carried out in a distributed-feedback channel-waveguide resonator in amorphous Al2O3 on silicon with a distributed phase shift introduced by adiabatic widening of the waveguide according to a sin2 function. Calculations and experiments show good agreement. Considering in the design the overlap integral between distributed phase shift and light intensity provides the desired performance.

  • 42.
    Kores, Cristine Calil
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Ismail, Nur
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Bernhardi, E. H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ. of Surrey (United Kingdom).
    Spectral behavior of integrated distributed-feedback resonators utilizing a distributed phase shift2019Conference paper (Refereed)
    Abstract [en]

    Bragg-grating-based distributed-feedback waveguide resonators, with a discrete phase shift introduced inside the Bragg grating, exhibit within their grating reflection band a Lorentzian-shaped resonance line with an ultranarrow linewidth. If the phase shift is π/2, the resonance is located at the center of the reflection band, i.e., at the Bragg wavelength, where the grating reflectivity is maximum, hence the resonance linewidth is minimum. Alternatively, the required π/2 phase shift is often introduced by a distributed change in effective refractive index, e.g. by adiabatically widening the waveguide. Despite careful design and fabrication, the experimentally observed resonance wavelength deviates from the designed one. Besides deviations owing to fabrication errors, a fundamental, systematic shift towards shorter wavelengths occurs. We show theoretically and experimentally that the decay of light intensity during propagation from the phase-shift center into both sides of the Bragg grating due to (i) reflection by the periodic grating and (ii) the adiabatic refractive-index change causes an incomplete accumulation of designed phase shift by the oscillating light, thereby systematically shifting the resonance to a shorter wavelength. Calculations are performed based on the characteristic-matrix approach. Experimental studies are carried out in distributed-feedback channel-waveguide resonators in an amorphous aluminum oxide thin film on silicon with a distributed phase shift introduced by adiabatic widening of the waveguide according to a sin2 function. Calculations and experiments show good agreement. Considering in the design the overlap integral between distributed phase shift and light intensity provides a performance that is much closer to the desired value.

  • 43.
    Kores, Cristine Calil
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Ismail, Nur
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Bernhardi, Edward H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Accumulation of distributed phase shift in distributed-feedback lasers2018In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2018Conference paper (Refereed)
    Abstract [en]

    In distributed-feedback lasers, a distributed phase shift of /2, seemingly placing the resonance at the Bragg wavelength, is not accumulated because of light confinement and asymmetry, leading to a systematic resonance shift to shorter wavelengths.

  • 44.
    Kores, Cristine Calil
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Ismail, Nur
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Bernhardi, Edward H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Accumulation of Distributed Phase Shift in Distributed-Feedback Resonators2019In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 11, no 1, article id 1500109Article in journal (Refereed)
    Abstract [en]

    Distributed-feedback waveguide lasers based on Bragg-grating resonators generate ultranarrow-linewidth emission. Oscillation at the center of the reflection band ensures maximum reflectivity, hence minimum linewidth. The required pi/2 phase shift is often introduced by a distributed change in effective refractive index, e.g., by widening the waveguide. Despite careful design and fabrication, the experimentally observed resonance wavelength deviates from the designed wavelength. Even when thermally induced chirp or fabrication errors are negligible, this deviation is still present. Here, we show theoretically and experimentally that this deviation is of fundamental nature. The decay of light intensity during propagation from the phase-shift center into both sides of the Bragg grating due to reflection by the periodic grating and the refractive index change causes an incomplete accumulation of designed phase shift, thereby systematically shifting the resonance to a shorter wavelength. Considering the overlap integral between the distributed phase shift and light intensity in the design provides the desired performance.

  • 45.
    Kores, Cristine Calil
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Ismail, Nur
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Geskus, Dimitri
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Dijkstra, M.
    Bernhardi, Edward H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Pollnau, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Frequency and linewidth dependence of distributed-feedback resonators on thermal chirp2017In: 2017 19th International Conference on Transparent Optical Networks (ICTON), IEEE Computer Society, 2017, article id 8025100Conference paper (Refereed)
    Abstract [en]

    We present an analysis of the spectral characteristics of distributed-feedback (DFB) laser resonators with thermally chirped distributed mirrors. Such DFB resonators have the interesting capability of producing a linewidth as narrow as a few kHz. The investigated devices are ytterbium-doped amorphous Al2O3 channel waveguides with a periodic Bragg grating inscribed into its SiO2 top cladding. The resonance in the spectral response of the resonator results from a distributed λ/4 phase-shift produced by increasing the waveguide width. Its frequency is determined by the period of the Bragg grating, whereas its linewidth is determined by the intrinsic losses and the outcoupling losses of the resonator. When such a device is optically pumped to achieve gain and eventually lasing, the grating period becomes thermally chirped, thereby influencing the spectral characteristics of the resonator. We investigate experimentally and via simulations the frequency and linewidth of the resonance in the presence of a thermally induced linear chirp on the grating profile. Experiments and simulations show good quantitative agreement.

  • 46. Kyaw, H H
    et al.
    Myint, M T Z
    Al-Harthi, S H
    Maekawa, T
    Yanagisawa, K
    Sellai, A
    Dutta, Joydeep
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    The influence of initial gold nanoparticles layer on migration of silver nanoparticles in silver/glass matrix2019In: Thin Solid Films, Vol. 685, p. 216-224Article in journal (Refereed)
    Abstract [en]

    A thin layer of gold nanoparticles (AuNPs) was deposited on glass substrates followed by subsequent deposition of silver nanoparticles (AgNPs) on it. Both AuNPs and AgNPs layers were fabricated by DC magnetron sputtering with inert gas condensation technique. The effect of initial thin layer of AuNPs have on the transformation of AgNPs surface structure by post annealing at 500 degrees C and 600 degrees C in air was investigated. The influence of post annealing temperature on the surface morphology was studied by atomic force microscopy and post annealing at 500 degrees C reduce the size of AgNPs along with the formation of some AgNPs inside the glass matrix. At 600 degrees C, aggregation of AuNPs on the surface was observed and increased in the number of AgNPs that diffused into the glass matrix. X-ray photoelectron spectroscopy was employed to study the surface composition and chemical states. The temperature dependence of Ag diffusion into the glass matrix was characterised and observed by UV-visible absorption spectroscopy and cross sectional transmission electron microscopy. Furthermore, ultraviolet photoelectron spectroscopy revealed a new shoulder related to Au 6 s hybridized with Au 5d and Ag 4d bands in the 1-4 eV regions, which affirmed the metallic character of AgNPs/AuNPs/glass system at higher annealing temperature. By introducing AuNPs on glass prior to AgNPs deposition, novel properties such as limited Ag ion diffusion and evaporation were found and problems previously encountered in AgNPs/glass system were avoided. The proposed AgNPs/AuNPs/glass system can be useful in plasmonic applications such as chroma filters and photonic devices.

  • 47.
    Laxman, Karthik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Kimoto, Daiki
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Sahakyan, Armen
    Dutta, Joydeep
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Nanoparticulate Dielectric Overlayer for Enhanced Electric Fields in a Capacitive Deionization Device2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 6, p. 5941-5948Article in journal (Refereed)
    Abstract [en]

    The magnitude and distribution of the electric field between two conducting electrodes of a capacitive deionization (CDI) device plays an important role in governing the desalting capacity. A dielectric coating on these electrodes can polarize under an applied potential to modulate the net electric field and hence the salt adsorption capacity of the device. Using finite element models, we show the extent and nature of electric field modulation, associated with changes in the size, thickness, and permittivity of commonly used nanostructured dielectric coatings such as zinc oxide (ZnO) and titanium dioxide (TiO2). Experimental data pertaining to the simulation are obtained by coating activated carbon cloth (ACC) with nanoparticles of ZnO and TiO2 and using them as electrodes in a CDI device. The dielectric-coated electrodes displayed faster desalting kinetics of 1.7 and 1.55 mg g(-1) min(-1) and higher unsaturated specific salt adsorption capacities of 5.72 and 5.3 mg g(-1) for ZnO and TiO2, respectively. In contrast, uncoated ACC had a salt adsorption rate and capacity of 1.05 mg g(-1) min(-1) and 3.95 mg g(-1), respectively. The desalting data is analyzed with respect to the electrical parameters of the electrodes extracted from cyclic voltammetry and impedance measurements. Additionally, the obtained results are correlated with the simulation data to ascertain the governing principles for the changes observed and advances that can be achieved through dielectric-based electrode modifications for enhancing the CDI device performance.

  • 48.
    Loiko, P.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Pollnau, M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Surrey, Adv Technol Inst, Guildford GU2 7XH, Surrey, England..
    Stochastic Model of Energy-Transfer Processes Among Rare-Earth Ions2018In: FIBER LASERS AND GLASS PHOTONICS: MATERIALS THROUGH APPLICATIONS / [ed] Taccheo, S Mackenzie, JI Ferrari, M, SPIE-INT SOC OPTICAL ENGINEERING , 2018, article id 106831XConference paper (Refereed)
    Abstract [en]

    Energy-transfer processes strongly affect the performance of lanthanide-doped photonic devices. In this work, we introduce a simple stochastic model of energy-transfer processes and successfully apply it to the example of cross-relaxation (CR) and energy-transfer upconversion (ETU) in amorphous Al2O3:Tm3+ waveguides on silicon intended for lasers operating at similar to 2 mu m. The stochastic model is based on the rate-equation formalism and considers two spectroscopically distinct ion classes, namely single ions and ions with neighbours (pairs and clusters), with the corresponding ion fractions being dependent on the doping concentration. We prove that a more accurate description of the luminescence properties of amorphous Al2O3:Tm3+ is obtained when accounting for the presence of these distinct ion classes. Based on the developed model, we derive microscopic CR and ETU parameters of C-CR = 5.83 x 10(-38) cm(6)s(-1), C-ETU1 = 0.93 x 10(-40) cm(6)s(-1), and C-ETU2 = 7.81 x 10(-40) cm(6)s(-1), and determine the laser quantum efficiency eta(q) of excitation of Tm3+ ions in the upper laser level. For the maximum Tm3+ concentration of 5.0 x 10(20) cm(-3) studied experimentally in this investigation, eta(q) reaches 1.73. Furthermore, the transition cross-sections at the pump and laser wavelengths are determined. For the H-3(6) -> F-3(4) transition, the maximum stimulated-emission cross-section is sigma(e) = 0.47 x 10(-20) cm(2) at 1808 nm.

  • 49. Loiko, Pavel
    et al.
    Bora, Tanujjal
    Serres, JM
    Mateos, Xavier
    Yu, HH
    Baranov, A
    Aguilo, M
    Diaz, F
    Griebner, U
    Petrov, V
    Dutta, Joydeep
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Oriented ZnO Nanorods: A Novel Saturable Absorber for Lasers at 1-2 μm2017In: 2017 European Conference on Lasers and Electro-Optics and European Quantum Electronics Conference, 2017Conference paper (Other academic)
    Abstract [en]

    Nowadays, the development of broadband ultrafast saturable absorbers (SAs) based on carbon nanostructures (e.g., graphene, SWCNTs) and 2D-materials (e.g., MoS2, topological insulators) for passive Q-switching (PQS) and mode-locking (ML) of near-IR lasers (1-2 μm) is attracting a tremendous interest [1]. For PQS, such absorbers can be integrated into compact bulk (microchip) and waveguide lasers providing ns-long pulses at high repetition rates (up to few MHz). Zinc oxide (ZnO) nanostructures exhibit outstanding physical properties and they are used in various photonic applications. In the present work, we demonstrate the potential of ZnO nanorods (NRs) for broadband SAs for near-IR lasers.

  • 50. Luo, Jun-Wei
    et al.
    Li, Shu-Shen
    Sychugov, Ilya
    Pevere, Federico
    Linnros, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material- och nanofysik.
    Zunger, Alex
    Absence of redshift in the direct bandgap of silicon nanocrystals with reduced size2017In: Nature Nanotechnology, ISSN 1748-3387, E-ISSN 1748-3395, Vol. 12, no 10, p. 930-932Article in journal (Refereed)
12 1 - 50 of 84
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