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  • 1.
    Adshead, Mason
    et al.
    Photon Science Institute, Department of Electrical and Electronic Engineering, University of Manchester, Manchester, M13 9PL, UK.
    Sanaee, Maryam
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Blight, Daniel
    Photon Science Institute, Department of Electrical and Electronic Engineering, University of Manchester, Manchester, M13 9PL, UK.
    Prencipe, Alessandro
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Curry, Richard J.
    Photon Science Institute, Department of Electrical and Electronic Engineering, University of Manchester, Manchester, M13 9PL, UK.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Erbium implantation in thin film Lithium Niobate2023In: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023, Institute of Electrical and Electronics Engineers (IEEE) , 2023Conference paper (Refereed)
    Abstract [en]

    Lithium niobate on insulator (LNOI), thanks to its electro-optic properties and second order nonlinearity, is one of the most promising photonic materials for on-chip implementation of a complex photonic integrated circuit (PIC) [1]. Integration of rare earth ion emitters (RIE), characterized by high coherent transitions in both optical and microwave domains, into LNOI is a very attractive perspective to fully exploit the potential of this material in quantum optics applications and for on chip light generation and amplification. By choosing Erbium ions these functionalities can be implemented at telecom wavelengths (~1550 nm). Erbium integration in LNOI can be achieved using the smart cut technique [2]. However, this approach implies heating the material up to ~1100 ºC, approaching the Curie temperature of lithium niobate (~1200 ºC). Ion implantation also permits the incorporation of RIE into the lithium niobate (LN) crystal structure, operating at lower temperature with high spatial precision of the doped region in a complex PIC.

  • 2.
    Al-Shammari, Rusul M.
    et al.
    School of Physics, University College Dublin, Belfield, Dublin, 4, Ireland, Belfield; Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin, 4, Ireland, Belfield.
    Kassem, Ahmed
    School of Veterinary Medicine, University College Dublin, Belfield, Dublin, 4, Ireland, Belfield; School of Veterinary Medicine, University of Kufa, Iraq.
    Al-attar, Nebras
    Laser and Optoelectronic Engineering Department, University of Technology -Iraq, Baghdad, Iraq; School of Chemistry, Trinity College Dublin, The University of Dublin, Dublin, 4, Ireland.
    Manzo, Michele
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Whyte, Paul
    School of Veterinary Medicine, University College Dublin, Belfield, Dublin, 4, Ireland, Belfield.
    Rice, James H.
    School of Physics, University College Dublin, Belfield, Dublin, 4, Ireland, Belfield.
    Rodriguez, Brian J.
    School of Physics, University College Dublin, Belfield, Dublin, 4, Ireland, Belfield; Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin, 4, Ireland, Belfield.
    Antibacterial properties of lithium niobate crystal substrates2023In: International Journal of Optomechatronics, ISSN 1559-9612, Vol. 17, no 1, article id 2250400Article in journal (Refereed)
    Abstract [en]

    The bactericidal properties of chemically patterned lithium niobate substrates under a super-bandgap UV light source is established. UV irradiation of lithium niobate surfaces inoculated with bacteria leads to antimicrobial activity compared to a glass substrate under similar conditions, as determined by surface enhanced Raman spectroscopy and corroborated with a fluorescence-based live/dead assay. This finding may expand the possible biomedical applications of lithium niobate.

  • 3.
    An, Junxue
    et al.
    Uppsala Univ, Dept Pharm, Uppsala, Sweden..
    Forchheimer, Daniel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Sävmarker, Jonas
    Orexo AB, Pharmaceut Dev, Uppsala, Sweden..
    Brulls, Mikael
    AstraZeneca, Early Prod Dev & Mfg Pharmaceut Sci, R&D, Gothenburg, Sweden..
    Frenning, Goran
    Uppsala Univ, Dept Pharm, Uppsala, Sweden..
    Nanoscale characterization of PEGylated phospholipid coatings formed by spray drying on silica microparticles2020In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 577, p. 92-100Article in journal (Refereed)
    Abstract [en]

    Phospholipids constitute biocompatible and safe excipients for pulmonary drug delivery. They can retard the drug release and, when PEGylated, also prolong the residence time in the lung. The aim of this work was to assess the structure and coherence of phospholipid coatings formed by spray drying on hydrophilic surfaces (silica microparticles) on the nanoscale and, in particular, the effect of addition of PEGylated lipids thereon. Scanning electron microscopy showed the presence of nanoparticles of varying sizes on the microparticles with different PEGylated lipid concentrations. Atomic force microscopy confirmed the presence of a lipid coating on the spray-dried microparticles. It also revealed that the lipid-coated microparticles without PEGylated lipids had a rather homogenous coating whereas those with PEGylated lipids had a very heterogeneous coating with defects, which was corroborated by confocal laser scanning microscopy. All coated microparticles had good dispersibility without agglomerate formation, as indicated by particle size measurements. This study has demonstrated that coherent coatings of phospholipids on hydrophilic surfaces can be obtained by spray drying. However, the incorporation of PEGylated lipids in a one-step spray-drying process to prepare lipid coated microparticles with both controlled-release and stealth properties is very challenging.

  • 4. Andersson, Gustav
    et al.
    Jolin, Shan Williams
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Scigliuzzo, Marco
    Borgani, Riccardo
    Tholen, Mats O.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. Intermodulation Products AB, Segersta SE-82393, Sweden.
    Rivera Hernández, Juan Carlos
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Shumeiko, Vitaly
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Delsing, Per
    Squeezing and Multimode Entanglement of Surface Acoustic Wave Phonons2022In: PRX Quantum, E-ISSN 2691-3399, Vol. 3, no 1, article id 010312Article in journal (Refereed)
    Abstract [en]

    Exploiting multiple modes in a quantum acoustic device could enable applications in quantum information in a hardware-efficient setup, including quantum simulation in a synthetic dimension and continuous-variable quantum computing with cluster states. We develop a multimode surface acoustic wave (SAW) resonator with a superconducting quantum interference device (SQUID) integrated in one of the Bragg reflectors. The interaction with the SQUID-shunted mirror gives rise to coupling between the more than 20 accessible resonator modes. We exploit this coupling to demonstrate two-mode squeezing of SAW phonons, as well as four-mode multipartite entanglement. Our results open avenues for continuous-variable quantum computing in a compact hybrid quantum system.

  • 5.
    Andersson, Sebastian
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Spin-diode effect and thermally controlled switching in magnetic spin-valves2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis demonstrates two new device concepts that are based on the tunneling and giant magnetoresistance effects. The first is a semiconductor-free asymmetric magnetic double tunnel junction that is shown to work as a diode, while at the same time exhibiting a record high magnetoresistance. It is experimentally verified that a diode effect, with a rectification ratio of at least 100, can be obtained in this type of system, and that a negative magnetoresistance of nearly 4000% can be measured at low temperature. The large magnetoresistance is attributed to spin resonant tunneling, where the parallel and antiparallel orientation of the magnetic moments shifts the energy levels in the middle electrode, thereby changing their alignment with the conduction band in the outer electrodes. This resonant tunneling can be useful when scaling down magnetic random access memory; eliminating the need to use external diodes or transistors in series with each bit.

    The second device concept is a thermally controlled spin-switch; a novel way to control the free-layer switching and magnetoresistance in spin-valves. By exchange coupling two ferromagnetic films through a weakly ferromagnetic Ni-Cu alloy, the coupling is controlled by changes in temperature. At room temperature, the alloy is weakly ferromagnetic and the two films are exchange coupled through the alloy. At a temperature higher than the Curie point, the alloy is paramagnetic and the two strongly ferromagnetic films decouple. Using this technique, the read out signal from a giant magnetoresistance element is controlled using both external heating and internal Joule heating. No degradation of device performance upon thermal cycling is observed. The change in temperature for a full free-layer reversal is shown to be 35 degrees Celsius for the present Ni-Cu alloy. It is predicted that this type of switching theoretically can lead to high frequency oscillations in current, voltage, and temperature, where the frequency is controlled by an external inductor or capacitor. This can prove to be useful for applications such as voltage controlled oscillators in, for example, frequency synthesizers and function generators. Several ways to optimize the thermally controlled spin switch are discussed and conceptually demonstrated with experiments.

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  • 6.
    Andersson, Sebastian
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Exchange coupling and magnetoresistance in CoFe/NiCu/CoFe spin valves near the Curie point of the spacer2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 107, no 9, p. 09D711-Article in journal (Refereed)
    Abstract [en]

    Thermal control of exchange coupling between two strongly ferromagnetic layers through a weakly ferromagnetic Ni-Cu spacer and the associated magnetoresistance is investigated. The spacer, having a Curie point slightly above room temperature, can be cycled between its paramagnetic and ferromagnetic states by varying the temperature externally or using joule heating. It is shown that the giant magnetoresistance vanishes due to a strong reduction in the mean free path in the spacer at above similar to 30% Ni concentration-before the onset of ferromagnetism. Finally, a device is proposed which combines thermally controlled exchange coupling and large magnetoresistance by separating the switching and the readout elements.

  • 7.
    Andersson, Sebastian
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Thermoelectrically Controlled Spin-Switch2010In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 46, no 6, p. 2140-2143Article in journal (Refereed)
    Abstract [en]

    The search for novel spintronic devices brings about new ways to control switching in magnetic thin-films. In this work we experimentally demonstrate a device based on thermoelectrically controlled exchange coupling. The read out signal from a giant magnetoresistance element is controlled by exchange coupling through a weakly ferromagnetic Ni-Cu alloy. This exchange coupling is shown to vary strongly with changes in temperature, and both internal Joule heating and external heating is used to demonstrate magnetic switching. The device shows no degradation upon thermal cycling. Ways to further optimize the device performance are discussed. Our experimental results show a new way to thermoelectrically control magnetic switching in multilayers.

  • 8.
    Ankel, Martin
    et al.
    Chalmers University of Technology,Department of Microtechnology and Nanoscience,Sweden;Surveillance, Saab, Research and Concepts, Sweden.
    Jonsson, Robert S.
    Chalmers University of Technology,Department of Microtechnology and Nanoscience,Sweden;Surveillance, Saab, Research and Concepts, Sweden.
    Tholen, Mats O.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. Intermodulation Products AB, Sweden.
    Bryllert, Tomas
    Chalmers University of Technology,Department of Microtechnology and Nanoscience,Sweden;Surveillance, Saab, Research and Concepts, Sweden.
    Ulander, Lars M.H.
    Chalmers University of Technology,Earth and Environment, Geoscience and Remote Sensing,Department of Space,Sweden.
    Delsing, Per
    Chalmers University of Technology,Department of Microtechnology and Nanoscience,Sweden.
    Experimental Evaluation of Moving Target Compensation in High Time-Bandwidth Noise Radar2023In: Proceedings 20th European Radar Conference (EuRAD), Institute of Electrical and Electronics Engineers (IEEE) , 2023, p. 213-216Conference paper (Refereed)
    Abstract [en]

    In this article, the effect a moving target has on the signal-to-interference-plus-noise-ratio (SINR) for high time-bandwidth noise radars is investigated. To compensate for cell migration we apply a computationally efficient stretch processing algorithm that is tailored for batched processing and suitable for implementation onto a real-time radar processor. The performance of the algorithm is studied using experimental data. In the experiment, pseudorandom noise, with a bandwidth of 100 MHz, is generated and transmitted in real-time. An unmanned aerial vehicle (UAV), flown at a speed of 11.5 m/s, is acting as a target. For an integration time of 1 s, the algorithm is shown to yield an increase in SINR of roughly 13 dB, compared to no compensation. It is also shown that coherent integration times of 2.5 s can be achieved.

  • 9.
    Ankel, Martin
    et al.
    Department of Microtechnology and Nanoscience Chalmers University of Technology Göteborg Sweden;New Concepts and System Studies, Surveillance Saab Göteborg Sweden.
    Tholen, Mats O.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. Intermodulation Products AB Segersta Sweden.
    Bryllert, Tomas
    Department of Microtechnology and Nanoscience Chalmers University of Technology Göteborg Sweden;New Concepts and System Studies, Surveillance Saab Göteborg Sweden.
    Ulander, Lars M. H.
    Department of Space, Earth and Environment Chalmers University of Technology Göteborg Sweden.
    Delsing, Per
    Department of Microtechnology and Nanoscience Chalmers University of Technology Göteborg Sweden.
    Implementation of a coherent real‐time noise radar system2023In: IET radar, sonar & navigation, ISSN 1751-8784, E-ISSN 1751-8792Article in journal (Refereed)
    Abstract [en]

    The utilisation of continuous random waveforms for radar, that is, noise radar, has been extensively studied as a candidate for low probability of intercept operation. However, compared with the more traditional pulse-Doppler radar, noise radar systems are significantly more complicated to implement, which is likely why few systems exist. If noise radar systems are to see the light of day, system design, implementation, limitations etc., must be investigated. Therefore, the authors examine and detail the implementation of a real-time noise radar system on a field programmable gate array. The system is capable of operating with 100% duty cycle, 200 MHz bandwidth, and 268 ms integration time while processing a range of about 8.5 km. Additionally, the system can perform real-time moving target compensation to reduce cell migration. System performance is primarily limited by the memory bandwidth of the off-chip dynamic random access memory.

  • 10. Aurino, P. P.
    et al.
    Kalabukhov, A.
    Borgani, Riccardo
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Bauch, T.
    Lombardi, F.
    Claeson, T.
    Winkler, D.
    Retention of Electronic Conductivity in LaAlO3/SrTiO3 Nanostructures Using a SrCuO2 Capping Layer2016In: PHYSICAL REVIEW APPLIED, ISSN 2331-7019, Vol. 6, no 2, article id 024011Article in journal (Refereed)
    Abstract [en]

    The interface between two wide band-gap insulators, LaAlO3 and SrTiO3 (LAO/STO) offers a unique playground to study the interplay and competitions between different ordering phenomena in a strongly correlated two- dimensional electron gas. Recent studies of the LAO/STO interface reveal the inhomogeneous nature of the 2DEG that strongly influences electrical-transport properties. Nanowires needed in future applications may be adversely affected, and our aim is, thus, to produce a more homogeneous electron gas. In this work, we demonstrate that nanostructures fabricated in the quasi-2DEG at the LaAlO3/SrTiO3 interface, capped with a SrCuO2 layer, retain their electrical resistivity and mobility independent of the structure size, ranging from 100 nm to 30 mu m. This is in contrast to noncapped LAO/STO structures, where the room-temperature electrical resistivity significantly increases when the structure size becomes smaller than 1 mu m. High-resolution intermodulation electrostatic force microscopy reveals an inhomogeneous surface potential with "puddles" of a characteristic size of 130 nm in the noncapped samples and a more uniform surface potential with a larger characteristic size of the puddles in the capped samples. In addition, capped structures show superconductivity below 200 mK and nonlinear currentvoltage characteristics with a clear critical current observed up to 700 mK. Our findings shed light on the complicated nature of the 2DEG at the LAO/STO interface and may also be used for the design of electronic devices.

  • 11.
    Balatsky, Alexander V.
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Institute for Materials Science, Los Alamos National Laboratory, Los Alamos, NM, United States .
    Balatsky, Galina I.
    Borysov, Stanislav S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Resource Demand Growth and Sustainability Due to Increased World Consumption2015In: Sustainability, E-ISSN 2071-1050, Vol. 7, no 3, p. 3430-3440Article in journal (Refereed)
    Abstract [en]

    The paper aims at continuing the discussion on sustainability and attempts to forecast the impossibility of the expanding consumption worldwide due to the planet's limited resources. As the population of China, India and other developing countries continue to increase, they would also require more natural and financial resources to sustain their growth. We coarsely estimate the volumes of these resources (energy, food, freshwater) and the gross domestic product (GDP) that would need to be achieved to bring the population of India and China to the current levels of consumption in the United States. We also provide estimations for potentially needed immediate growth of the world resource consumption to meet this equality requirement. Given the tight historical correlation between GDP and energy consumption, the needed increase of GDP per capita in the developing world to the levels of the U.S. would deplete explored fossil fuel reserves in less than two decades. These estimates predict that the world economy would need to find a development model where growth would be achieved without heavy dependence on fossil fuels.

  • 12. Balkashin, O. P.
    et al.
    Fisun, V. V.
    Korovkin, I. A.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Ferromagnetic resonance in copper-permalloy point contacts2014In: Fizika Nizkih Temperatur, ISSN 0132-6414, E-ISSN 1816-0328, Vol. 40, no 10, p. 1187-1197Article in journal (Refereed)
    Abstract [en]

    The systematic investigations of the response signal of Copper-Permalloy (Ni80Fe20) point contacts to microwave irradiation (8-12 GHz) are performed. The influence of external magnetic field strength, transport current flowing through the contact, the intensity and frequency of the RF exposure on the measured signal is studied. The contributions to the contacts resistance from the effects of giant and anisotropic magnetoresistance are analyzed. It is established experimentally that the position of resonance features is in good agreement with the Kittel formula calculation for FMR in the film at a parallel H field. The resonance signal was observed on the background of an additional contribution due to the rectification of RF current on the nonlinear contact IV-curve. It is found that there are two mechanisms for the resonant response are revealed: a synchronous self-detection by means of mixing of RF current with temporal variations of resistance and a bolometric mechanism associated with a steady-state change of contact resistance under excitation of magnetization precession (a bolometric response). It is found that the resonance signal amplitude is linearly proportional to transport current through the contact and microwave irradiation intensity.

  • 13. Balkashin, O. P.
    et al.
    Fisun, V. V.
    Korovkin, I. A.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Ferromagnetic resonance in copper-permalloy point contacts2014In: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 40, no 10, p. 929-936Article in journal (Refereed)
    Abstract [en]

    The response of copper-permalloy (Ni80Fe20) point microcontacts to microwave irradiation (8-12 GHz) is investigated systematically. The effects of the external magnetic field strength, transport current flowing through the contact, and microwave intensity and frequency on the measured signal are studied. The contributions to the contact electrical resistance owing to giant and anisotropic magnetoresistance are analyzed. The experimentally determined positions of the resonance features are in good agreement with Kittel's formula for FMR in films in parallel magnetic fields. The resonance signal is observed against the background of an additional contribution owing to rectification of the rf field on the nonlinear current-voltage characteristic of the contact. Two mechanisms for the resonance response are discovered: synchronous self-detection from mixing of the rf current with temporal variations in the resistance and a bolometric response associated with the steady-state variation in the contact resistance when magnetization precession is excited. The amplitude of the resonance signal is linearly proportional to the transport current through the contact and to the intensity of the microwave irradiation.

  • 14. Balkashin, O. P.
    et al.
    Fisun, V. V.
    Triputen, L. Yu
    Andersson, Sebastian
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Naidyuk, Yu G.
    Spin-valve effects in point contacts to exchange biased Co40Fe40B20 films2014In: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 40, no 10, p. 915-918Article in journal (Refereed)
    Abstract [en]

    Nonlinear current-voltage characteristics and magnetoresistance of point contacts between a normal metal (N) and films of amorphous ferromagnet (F) Co40Fe40B20 of different thickness, exchange-biased by antiferromagnetic Mn80Ir20 are studied. A surface spin valve effect in the conductance of such F-N contacts is observed. The effect of exchange bias is found to be inversely proportional to the Co40Fe40B20 film thickness. This behavior as well as other magneto-transport effects we observe on single exchange-pinned ferromagnetic films are similar in nature to those found in conventional three-layer spin-valves.

  • 15.
    Balkashin, O. P.
    et al.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, .
    Fisun, V. V.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, .
    Triputen, L.Yu.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, .
    Andersson, Samir
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Naidyuk, Yu.G.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, .
    Spin-valve effects in point contacts to exchange biased Сo 40Fe 40B 20 films2014In: Fizika Nizkih Temperatur, ISSN 0132-6414, E-ISSN 1816-0328, Vol. 40, no 10, p. 1170-1174Article in journal (Refereed)
    Abstract [en]

    Nonlinear current-voltage characteristics and magnetoresistance of point contacts between a normal metal (N) and films of amorphous ferromagnet (F) Co40Fe40B20 of different thickness, exchange-biased by antiferromagnetic Mn80Ir20 are studied. A surface spin valve effect in the conductance of such F-N contacts is observed. The effect of exchange bias is found to be inversely proportional to the Co40Fe40B20 film thickness. This behavior as well as other magneto-transport effects we observe on single exchange-pinned ferromagnetic films are similar in nature to those found in conventional three-layer spin-valves. 

  • 16. Balkashin, O. P.
    et al.
    Fisun, V. V.
    Yanson, I. K.
    Triputen, L. Yu
    Konovalenko, Alexander
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Nonstationary magnetization dynamics of point contacts with a single ferromagnetic film2009In: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 35, no 8-9, p. 693-701Article in journal (Refereed)
    Abstract [en]

    The electric conductivity of point nanocontacts between 5, 10, and 100 nm thick ferromagnetic (F) cobalt films and a nonmagnetic (N) metal (copper or silver) needle is investigated. Two fundamentally different mechanisms for the formation of the response, signal to microwave irradiation have been observed for the first time. One mechanism is due to the effect of the rectification of high frequency ac current on the nonlinearity of the current-voltage characteristics due to the precession of the magnetization under the action of a constant transport current flowing through the contact. The second one is associated with the resonance excitation of the precession of the magnetization vector at the fundamental frequency and its harmonic by an external high-frequency field. The experimental results support a previous contention that a "surface spin valve" whose static and dynamic properties are similar to conventional F-1-N-F-2 spin valve [Nano Letters 7, 927 (2007)] is formed in the experimental F-N nanocontacts.

  • 17.
    Balkashin, O. P.
    et al.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    Fisun, V. V.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Yanson, I. K.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    Triputen, L. Yu.
    B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine.
    Konovalenko, Alexander
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Spin dynamics in point contacts to single ferromagnetic films2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 9, p. 092419-1-092419-4Article in journal (Refereed)
    Abstract [en]

    Excitation of magnons or spin waves driven by nominally unpolarized transport currents in point contacts of normal and ferromagnetic metals is probed by irradiating the contacts with microwaves. Two characteristic dynamic effects are observed: a suppression of spin-wave nonlinearities in the point contact conductance by off-resonance microwave irradiation and a resonant stimulation of spin-wave peaks in the differential resistance of the nanocontacts by the microwave field. These observations provide direct evidence that the magnetoresistance peaks observed are due to gigahertz spin dynamics at the ferromagnetic interface driven by the spin transfer torque effect of the transport current.

  • 18. Ban, S.
    et al.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Pattern storage and recognition using ferrofluids2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 99, no 8Article in journal (Refereed)
    Abstract [en]

    An implementation of an associative memory based on a ferromagnetic nanocolloid is proposed. The design contains inductive input and output units for training the ferrofluid as well as sensors incorporated into the output units for performing recall. Using Monte Carlo simulations of the system we demonstrate the possibility of creating nanoparticle configurations that can serve to associate input/output pattern pairs.

  • 19.
    Batili, Hazal
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Hamawandi, Bejan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Ergül, Adem Björn
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Toprak, Muhammet
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova. KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    On the electrophoretic deposition of Bi2Te3 nanoparticles through electrolyte optimization and substrate design2022In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 649, p. 129537-, article id 129537Article in journal (Refereed)
    Abstract [en]

    Assembly of thermoelectric nanostructures with pre-defined morphology and surface chemistry on solid sub-strates has been one of the challenges for in-plane TE devices. Electrophoretic deposition (EPD) has the potential to be used for this purpose, where the use of non-conductive substrates is required to enable a reliable evaluation of the transport property of electrically active films. Bi2Te3 nanoparticles, which were synthesized using microwave-assisted hydrothermal route, were used for the EPD of thermoelectric films on glass substrates. A special substrate was fabricated using maskless photolithography, to evaluate the electronic transport properties of the TE films without the interference of the substrate. Electrolyte composition was optimized for high mobility of the suspended nanoparticles, and Bi2Te3 EPD films were fabricated with a high deposition rate, reaching 10 mu m/min. Initial EPD films showed high resistivity, ascribed to the surface oxide layer and capping ligands. The resistance was significantly reduced by the addition of a dithiol molecular linker, capable of interconnecting the Bi2Te3 nanoparticles through ligand-exchange. Seebeck coefficient in the range-150 to-180 mu V/K was measured, revealing the transport through the deposited films. Finally, a power factor of 169 nW/K-2.m was estimated, revealing the potential for the application of this technology to large area TE films as active coatings using the developed EPD process.

  • 20. Bergqvist, J.
    et al.
    Tress, W.
    Forchheimer, Daniel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Melianas, A.
    Tang, Z.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Inganäs, O.
    New method for lateral mapping of bimolecular recombination in thin-film organic solar cells2016In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 24, no 8, p. 1096-1108Article in journal (Refereed)
    Abstract [en]

    The best organic solar cells are limited by bimolecular recombination. Tools to study these losses are available; however, they are only developed for small area (laboratory-scale) devices and are not yet available for large area (production-scale) devices. Here we introduce the Intermodulation Light Beam-Induced Current (IMLBIC) technique, which allows simultaneous spatial mapping of both the amount of extracted photocurrent and the bimolecular recombination over the active area of a solar cell. We utilize the second-order non-linear dependence on the illumination intensity as a signature for bimolecular recombination. Using two lasers modulated with different frequencies, we record the photocurrent response at each modulation frequency and the bimolecular recombination in the second-order intermodulation response at the sum and difference of the two frequencies. Drift-diffusion simulations predict a unique response for different recombination mechanisms. We successfully verify our approach by studying solar cells known to have mainly bimolecular recombination and thus propose this method as a viable tool for lateral detection and characterization of the dominant recombination mechanisms in organic solar cells. We expect that IMLBIC will be an important future tool for characterization and detection of recombination losses in large area organic solar cells.

  • 21.
    Bondarenko, Artem
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Nonlinear dynamics of strongly-bound magnetic vortex pairs2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work is a study of nonlinear phenomena in vertically stacked pairs of magnetic vortices. New dynamic regimes are uncovered with a decrease in the inter-vortex separation to below the lateral vortex-core size. These include linear, non-linear, and chaos dynamics of the coupled vortex cores, as well as core-core coupling/decoupling driven by resonant microwave fields. In addition to the direct advantages gained from the favorable symmetry of the system, which includes the fringing flux closure, new ways of exciting and controlling the motion of the vortex cores are shown. The dynamics of the vortex stack show promising improvements over those of a single vortex, in particular the characteristic speed of operation can be increased by an order of magnitude. The system therefore is viewed to have the potential for applications in data storage and oscillators.

    A combination of experimental, analytical, and numerical methods is used. A theoretical framework based on the quasiparticle Thiele-equation approach, extended to thermally driven dynamics by using the Monte Carlo method, is constructed and extensively tested experimentally and numerically. In-depth micromagnetic simulations are performed and show consistency with the results obtained analytically, both successfully validated against the measured data collected in a series of experiments on spin vortex pairs. Among these are microwave spectroscopy, transient dynamics, thermal decay, and pinning spectroscopy measurements.

    In particular, it is shown that the nonlinear frequency response of a two-vortex system exhibits a fold-over and an isolated rotational core-core resonance. A parametric inter-modal interaction is shown to induce hybrid dynamic regimes of the vortex-core oscillation when the system is subject to high excitation amplitudes.

    An intrinsic bi-stability of the core positions in the structure is found and investigated as a candidate for a memory element. The bi-stability is pronounced at lower temperatures. The rates of thermal switching were investigated in order to find the optimum operating DC-bias conditions.

    It is found that parametric interactions play a big role in the otherwise frustrated dynamics of essentially a 1D system. The parameters of the short excitation pulses for switching between the core-core states are optimized to achieve switching probabilities of over 90% in the experiment, with the pulses only a few nanoseconds long.

    Vortex pairs are demonstrated to be sensitive to the presence of defects in the ferromagnetic layers of the nanostructure. It is shown that the key factor in this sensitivity lies in the vortex' flux closure. Binding of a core-core pair to a defect is observed experimentally. A model is developed to describe the changes in the dynamical characteristics of the defect-pinned vortex pair. The capabilities of the model for characterizing magnetic and morphological defects in nanostructures are demonstrated.

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    Bondarenko-thesis
  • 22.
    Bondarenko, Artem
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Holmgren, Erik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Koop, Björn C.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Descamps, Thomas
    KTH.
    Ivanov, B. A.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Stochastic dynamics of strongly-bound magnetic vortex pairs2017In: AIP Advances, E-ISSN 2158-3226, Vol. 7, no 5, article id 056007Article in journal (Refereed)
    Abstract [en]

    We demonstrate that strongly-bound spin-vortex pairs exhibit pronounced stochastic behaviour. Such dynamics is due to collective magnetization states originating from purely dipolar interactions between the vortices. The resulting thermal noise exhibits telegraph-like behaviour, with random switching between different oscillation regimes observable at room temperature. The noise in the system is further studied by varying the external field and observing the related changes in the frequency of switching and the probability for different magnetic states and regimes. Monte Carlo simulations are used to replicate and explain the experimental observations.

  • 23.
    Bondarenko, Artem
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Holmgren, Erik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Li, Zhong Wei
    Ivanov, B. A.
    Institute of Magnetism, National Academy of Science, 03142 Kiev, Ukraine; National University of Science and Technology “MISiS”, Moscow 119049, Russian Federation..
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Chaotic dynamics in spin-vortex pairs2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, article id 054402Article in journal (Refereed)
    Abstract [en]

    We report on spin-vortex pair dynamics measured at temperatures low enough to suppress stochastic core motion, thereby uncovering the highly nonlinear intrinsic dynamics of the system. Our analysis shows that the decoupling of the two vortex cores is resonant and can be enhanced by dynamic chaos. We detail the regions of the relevant parameter space, in which the various mechanisms of the resonant core-core dynamics are activated. We show that the presence of chaos can reduce the thermally induced spread in the decoupling time by up to two orders of magnitude.

  • 24.
    Borgani, Riccardo
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Probing nonlinear electrical properties at the nanoscale: Studies in multifrequency AFM2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nanostructured materials promise great advances in diverse and active research fields such as energy harvesting and storage, corrosion prevention and high-density memories. Electrical characterization at the nanometer scale is key to understanding and optimizing the performance of these materials, and therefore central to the progress of nanotechnology. One of the most versatile tools for this purpose is the atomic force microscope (AFM), thanks to its ability to image surfaces with high spatial resolution.

    In this thesis we present several multifrequency techniques for AFM. Intermodulation electrostatic force microscopy (ImEFM) measures the potential of a surface with low noise and high spatial resolution. In contrast to traditionally available methods, ImEFM does not use a feedback-controlled bias to measure the surface potential, and is therefore suitable to measurements in liquid environments. Removing feedback allows the applied bias to be used for investigating charge injection and extraction on nanocomposite materials. Intermodulation conductive AFM (ImCFM) measures the current-voltage characteristic of a sample at every point of an AFM image. ImCFM is able to separate the galvanic and displacement contributions to the measured current, improving the measurement speed by four orders of magnitude compared to previously available methods. We finally demonstrate an alternative approach to pump-probe spectroscopy, which allows the AFM to measure electrical charge dynamics with a time resolution approaching the nanosecond range.

    These techniques are based on intermodulation spectroscopy, and they demonstrate the power and flexibility of measuring and analyzing nonlinear response in the frequency domain. The nonlinearity of the tip-surface force is used to concentrate response in a narrow band around the resonance of the AFM cantilever, where force measurement sensitivity is at the thermal limit. In this narrow band, we perform coherent measurements at multiple frequencies by exploiting the stability of a single reference oscillation. The power of the multifrequency approach is nicely demonstrated in a general method for measuring and compensating background forces, i.e. long-range linear forces that act on the body of the AFM probe. This compensation is necessary to reveal the the true force between the surface and the AFM tip. We show the effect of the compensation on soft polymer materials, where the background forces are typically strongest.

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    fulltext
  • 25.
    Borgani, Riccardo
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Sensing photo-induced surface charges on OrganicPhoto-Voltaic materials using Atomic Force Microscopy2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
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    fulltext
  • 26.
    Borgani, Riccardo
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Forchheimer, Daniel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Bergqvist, Jonas
    Thorén, Per-Anders
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Inganas, Olle
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Intermodulation electrostatic force microscopy for imaging surface photo-voltage2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 14, p. 143113-Article in journal (Refereed)
    Abstract [en]

    We demonstrate an alternative to Kelvin Probe Force Microscopy for imaging surface potential. The open-loop, single-pass technique applies a low-frequency AC voltage to the atomic force microscopy tip while driving the cantilever near its resonance frequency. Frequency mixing due to the nonlinear capacitance gives intermodulation products of the two drive frequencies near the cantilever resonance, where they are measured with high signal to noise ratio. Analysis of this intermodulation response allows for quantitative reconstruction of the contact potential difference. We derive the theory of the method, validate it with numerical simulation and a control experiment, and we demonstrate its utility for fast imaging of the surface photo-voltage on an organic photovoltaic material.

  • 27.
    Borgani, Riccardo
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Gilzad Kohan, Mojtaba
    Department of Engineering Sciences and Mathematics, Luleå University of Technology, 97187 Luleå, Sweden.
    Vomiero, Alberto
    Department of Engineering Sciences and Mathematics, Luleå University of Technology, 97187 Luleå, Sweden.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Fast multifrequency measurement of nonlinear conductanceManuscript (preprint) (Other academic)
    Abstract [en]

    Low noise measurement of small currents in nanometer-scale junctions is of central importance to the characterization of novel high-performance devices and materials for applications ranging from energy harvesting and energy conversion to topological materials for quantum computers. The high resistance of these junctions and the stray capacitance of their measurement leads impose speed limitations (tens of seconds) on the traditional methods of measuring their nonlinear conductance, making detailed investigations of change with external fields or maps of variation over a surface impractical, if not impossible. Here we demonstrate fast (milliseconds) reconstruction of nonlinear current-voltage characteristics from phase-coherent multifrequency lock-in data using the inverse Fourier transform. The measurement technique allows for separation of the galvanic and displacement currents in the junction and easy cancellation of parasitic displacement current due to the measurement leads. We use the method to reveal nanometer-scale variations in the electrical transport properties of organic photovoltaic and semiconducting thin films. The method has broad applicability and its wide-spread implementation promises advancement in high-speed and high-resolution characterization for nanotechnology.

  • 28.
    Borgani, Riccardo
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Intermodulation spectroscopy as an alternative to pump-probe for the measurement of fast dynamics at the nanometer scaleManuscript (preprint) (Other academic)
    Abstract [en]

    We present an alternative approach to pump-probe spectroscopy for measuring fast charge dynamics with an atomic force microscope (AFM). Our approach is based on coherent multifrequency lock-in measurement of the intermodulation between a mechanical drive and an optical or electrical excitation. In response to the excitation, the charge dynamics of the sample is reconstructed by fitting a theoretical model to the measured frequency spectrum of the electrostatic force near resonance of the AFM cantilever. We discuss the time resolution, which in theory is limited only by the measurement time, but in practice is of order one nanosecond for standard cantilevers and imaging speeds. We verify the method with simulations and demonstrate it with a control experiment, achieving a time resolution of 20 ns in ambient conditions, limited by thermal noise.

  • 29.
    Borgani, Riccardo
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Intermodulation spectroscopy as an alternative to pump-probe for the measurement of fast dynamics at the nanometer scale2019In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 90, no 1, article id 013705Article in journal (Refereed)
    Abstract [en]

    We present an alternative approach to pump-probe spectroscopy for measuring fast charge dynamics with an atomic force microscope (AFM). Our approach is based on coherent multifrequency lock-in measurement of the intermodulation between a mechanical drive and an optical or electrical excitation. In response to the excitation, the charge dynamics of the sample is reconstructed by fitting a theoretical model to the measured frequency spectrum of the electrostatic force near resonance of the AFM cantilever. We discuss the time resolution, which in theory is limited only by the measurement time, but in practice is of order 1 ns for standard cantilevers and imaging speeds. We verify the method with simulations and demonstrate it with a control experiment, achieving a time resolution of 30 ns in ambient conditions, limited by thermal noise.

  • 30.
    Borgani, Riccardo
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Kohan, Mojtaba Gilzad
    Lulea Univ Technol, Dept Engn Sci & Math, SE-97187 Lulea, Sweden..
    Vomiero, Alberto
    Lulea Univ Technol, Dept Engn Sci & Math, SE-97187 Lulea, Sweden..
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Fast Multifrequency Measurement of Nonlinear Conductance2019In: Physical Review Applied, E-ISSN 2331-7019, Vol. 11, no 4, article id 044062Article in journal (Refereed)
    Abstract [en]

    We describe a phase-coherent multifrequency lock-in measurement technique that uses the inverse Fourier transform to reconstruct the nonlinear current-voltage characteristic of a nanoscale junction. The method provides separation of the galvanic and displacement currents in the junction and easy cancellation of the parasitic displacement current from the measurement leads. These two features allow us to overcome traditional limitations imposed by the low conductance of the junction and the high capacitance of the leads, thus providing an increase in measurement speed of several orders of magnitude. We demonstrate the method in the context of conductive atomic force microscopy, acquiring current-voltage characteristics at every pixel while scanning at standard imaging speed.

  • 31.
    Borgani, Riccardo
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Pallon, Love
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hedenqvist, Mikael S.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Gedde, Ulf W.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Haviland, David
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Local Charge Injection and Extraction on Surface-Modified Al2O3Nanoparticles in LDPE2016In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, no 9, p. 5934-5937, article id 10.1021/acs.nanolett.6b02920Article in journal (Refereed)
    Abstract [en]

    We use a recently developed scanning probe technique to image with high spatial resolution the injection and extraction of charge around individual surface-modified aluminum oxide nanoparticles embedded in a low-density polyethylene (LDPE) matrix. We find that the experimental results are consistent with a simple band structure model where localized electronic states are available in the band gap (trap states) in the vicinity of the nanoparticles. This work offers experimental support to a previously proposed mechanism for enhanced insulating properties of nanocomposite LDPE and provides a powerful experimental tool to further investigate such properties.

  • 32.
    Borgani, Riccardo
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Thorén, Per-Anders
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Forchheimer, Daniel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Dobryden, Illia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Sah, Si Mohamed
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Claesson, Per Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Background-Force Compensation in Dynamic Atomic Force Microscopy2017In: Physical Review Applied, E-ISSN 2331-7019, Vol. 7, no 6, article id 064018Article in journal (Refereed)
    Abstract [en]

    Background forces are linear long-range interactions of the cantilever body with its surroundings that must be compensated for in order to reveal tip-surface force, the quantity of interest for determining material properties in atomic force microscopy. We provide a mathematical derivation of a method to compensate for background forces, apply it to experimental data, and discuss how to include background forces in simulation. Our method, based on linear-response theory in the frequency domain, provides a general way of measuring and compensating for any background force and it can be readily applied to different force reconstruction methods in dynamic AFM.

  • 33.
    Borynskyi, V. Yu
    et al.
    NAS Ukraine, Inst Magnetism, 36-b Akad Vernadsky Blvd, UA-03142 Kiev, Ukraine.;MES Ukraine, 36-b Akad Vernadsky Blvd, UA-03142 Kiev, Ukraine..
    Polishchuk, Dmytr
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. NAS Ukraine, Inst Magnetism, 36-b Akad Vernadsky Blvd, UA-03142 Kiev, Ukraine.;MES Ukraine, 36-b Akad Vernadsky Blvd, UA-03142 Kiev, Ukraine..
    Melnyk, A. K.
    NAS Ukraine, Inst Sorpt & Problems Endoecol, 13 Naumov Str, UA-03164 Kiev, Ukraine..
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. NAS Ukraine, Inst Magnetism, 36-b Akad Vernadsky Blvd, UA-03142 Kiev, Ukraine.;MES Ukraine, 36-b Akad Vernadsky Blvd, UA-03142 Kiev, Ukraine..
    Tovstolytkin, A. , I
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Higher-order ferromagnetic resonances in periodic arrays of synthetic-antiferromagnet nanodisks2021In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 119, no 19, article id 192402Article in journal (Refereed)
    Abstract [en]

    We investigate spin dynamics in nanodisk arrays of synthetic-antiferromagnets (SAF) made of Py/NiCu/Py trilayers, where the NiCu spacer undergoes a Curie transition at about 200 K. The observed ferromagnetic resonance spectra have three distinct resonance modes at room temperature, which are fully recreated in our micromagnetic simulations, showing also how the intra-SAF asymmetry can be used to create and control the higher-order resonances in the structure. Below the Curie temperature of the spacer, the system effectively transitions into a single-layer nanodisk array with only two resonance modes. Our results show how multilayering of nanoarrays can add tunable GHz functionality relevant for such rapidly developing fields as magnetic metamaterials, magnonic crystals, arrays of spin-torque oscillators, and neuromorphic junctions.

  • 34.
    Borynskyi, V. Yu
    et al.
    Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, Kyiv 03142, Ukraine.
    Polishchuk, Dmytr
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, Kyiv 03142, Ukraine.
    Savina, Yu O.
    B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, Kharkiv 61103, Ukraine.
    Pashchenko, V. O.
    B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, Kharkiv 61103, Ukraine.
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, Kyiv 03142, Ukraine.
    Tovstolytkin, A. I.
    Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, Kyiv 03142, Ukraine.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Thermomagnetic transition in nanoscale synthetic antiferromagnets Py/NiCu/Py2023In: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 49, no 7, p. 863-869Article in journal (Refereed)
    Abstract [en]

    Using the method of SQUID magnetometry, the features of the antiferromagnet-ferromagnet thermomagnetic transition in arrays of the nanosized disks of Py/NiCu/Py synthetic antiferromagnets (SAFs) have been investigated. The effective interlayer interaction in individual SAFs “ferromagnet/diluted ferromagnet/ferromagnet” (F2/f/F1) changes from high-temperature antiferromagnetic to low-temperature ferromagnetic upon the transition at the Curie temperature T C f of the interlayer f. Temperature dependence of the magnetic parameters of individual layers and their effect on the features of the thermomagnetic transition are determined. The observed properties are important for the development of temperature-controlled nanoscale SAFs and multilayer nanostructures based on them.

  • 35.
    Borynskyi, Vladyslav
    et al.
    Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, Department of Physics of Films, Kyiv, Ukraine.
    Kravets, Anatolii
    Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, Department of Physics of Films, Kyiv, Ukraine.
    Polishchuk, Dmytr
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Tovstolytkin, Alexandr
    Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, Department of Physics of Films, Kyiv, Ukraine.
    Sharai, Iryna
    Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, Department of Physics of Films, Kyiv, Ukraine.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Melnyk, Andrii
    Center for the collective use of scientific equipment 'EPR spectroscopy' Institute for Sorption and Problems of Endoecology of the NAS of Ukraine, Kyiv, Ukraine.
    Spin-wave Resonance in Arrays of Nanoscale Synthetic-antiferromagnets2022In: Proceedings of the 2022 IEEE 12th International Conference "Nanomaterials: Applications and Properties", NAP 2022, Institute of Electrical and Electronics Engineers (IEEE) , 2022Conference paper (Refereed)
    Abstract [en]

    The study concerns dynamics of standing spin waves in arrays of sub-100 nm elliptic synthetic-antiferromagnet (SAF) nanodisks. We performed a detailed ferromagnetic resonance analysis in conjunction with micro magnetic modeling to find out several prominent traits of such systems. One broad line is shown to be the sole resonant response for a SAF of the considered sizes. We demonstrate that this mode is degenerated, and its excitation map resembles a superposition of in-center and edge-type oscillations. We also show how this hybrid excitation leads to almost twofold enhancement in the shape-induced anisotropy of the mode.

  • 36.
    Borysov, Stanislav
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Roudi, Yasser
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. The Kavli Institute for Systems Neuroscience, NTNU, Trondheim, Norway.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Institute for Materials Science, Los Alamos National Laboratory, Los Alamos, NM, United States.
    U.S. stock market interaction network as learned by the Boltzmann machine2015In: European Physical Journal B: Condensed Matter Physics, ISSN 1434-6028, E-ISSN 1434-6036, Vol. 88, no 12, p. 1-14Article in journal (Refereed)
    Abstract [en]

    We study historical dynamics of joint equilibrium distribution of stock returns in the U.S. stock market using the Boltzmann distribution model being parametrized by external fields and pairwise couplings. Within Boltzmann learning framework for statistical inference, we analyze historical behavior of the parameters inferred using exact and approximate learning algorithms. Since the model and inference methods require use of binary variables, effect of this mapping of continuous returns to the discrete domain is studied. The presented results show that binarization preserves the correlation structure of the market. Properties of distributions of external fields and couplings as well as the market interaction network and industry sector clustering structure are studied for different historical dates and moving window sizes. We demonstrate that the observed positive heavy tail in distribution of couplings is related to the sparse clustering structure of the market. We also show that discrepancies between the model’s parameters might be used as a precursor of financial instabilities.

  • 37.
    Borysov, Stanislav S.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Cross-Correlation Asymmetries and Causal Relationships between Stock and Market Risk2014In: PLOS ONE, E-ISSN 1932-6203, Vol. 9, no 8, p. e105874-Article in journal (Refereed)
    Abstract [en]

    We study historical correlations and lead-lag relationships between individual stock risk (volatility of daily stock returns) and market risk (volatility of daily returns of a market-representative portfolio) in the US stock market. We consider the cross-correlation functions averaged over all stocks, using 71 stock prices from the Standard & Poor's 500 index for 1994-2013. We focus on the behavior of the cross-correlations at the times of financial crises with significant jumps of market volatility. The observed historical dynamics showed that the dependence between the risks was almost linear during the US stock market downturn of 2002 and after the US housing bubble in 2007, remaining at that level until 2013. Moreover, the averaged cross-correlation function often had an asymmetric shape with respect to zero lag in the periods of high correlation. We develop the analysis by the application of the linear response formalism to study underlying causal relations. The calculated response functions suggest the presence of characteristic regimes near financial crashes, when the volatility of an individual stock follows the market volatility and vice versa.

  • 38.
    Borysov, Stanislav S.
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Forchheimer, Daniel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Dynamic calibration of higher eigenmode parameters of a cantilever in atomic force microscopy by using tip-surface interactions2014In: Beilstein Journal of Nanotechnology, ISSN 2190-4286, Vol. 5, p. 1899-1904Article in journal (Refereed)
    Abstract [en]

    We present a theoretical framework for the dynamic calibration of the higher eigenmode parameters (stiffness and optical lever inverse responsivity) of a cantilever. The method is based on the tip-surface force reconstruction technique and does not require any prior knowledge of the eigenmode shape or the particular form of the tip-surface interaction. The calibration method proposed requires a single-point force measurement by using a multimodal drive and its accuracy is independent of the unknown physical amplitude of a higher eigenmode.

  • 39.
    Borysov, Stanislav S.
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Platz, Daniel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    de Wijn, Astrid S.
    Forchheimer, Daniel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Tolén, Eric A.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Reconstruction of tip-surface interactions with multimodal intermodulation atomic force microscopy2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 11, p. 115405-Article in journal (Refereed)
    Abstract [en]

    We propose a theoretical framework for reconstructing tip-surface interactions using the intermodulation technique when more than one eigenmode is required to describe the cantilever motion. Two particular cases of bimodal motion are studied numerically: one bending and one torsional mode, and two bending modes. We demonstrate the possibility of accurate reconstruction of a two-dimensional conservative force field for the former case, while dissipative forces are studied for the latter.

  • 40.
    Cherepov, Sergiy
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Resonant switching and vortex dynamics in spin-flop bi-layers2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is a study of the static and dynamic behavior of the magne-tization in spin-flop bi-layers, which consist of two soft ferromagnetic layerscoupled by dipolar forces through a thin nonmagnetic spacer. The focus ofthe work is three fold: collective spin dynamics in the anti-parallel groundstate; resonant switching in the presence of thermal agitation; and static anddynamic behavior of the system in the vortex-pair state, with a particularemphasis on the interlayer core-core interaction.

    Two collective spin-flop resonance modes are observed and interpreted asacoustical and optical spin precessions, in which the moments of the two lay-ers oscillate in phase and out of phase, respectively. An analytical macrospinmodel is developed to analyze the experimental results and is found to ac-curately predict the resonance frequencies and their field dependence in thelow-field anti-parallel state and the high-field near saturated state. A micro-magnetic model is developed and successfully explains the static and dynamicbehavior of the system in the entire field range, including the C- and S-typespin-perturbed scissor state of the bi-layer at intermediate fields.

    The optical spin-flop resonance at 3-4 GHz is used to demonstrate resonantswitching in the system, in the range of the applied field where quasi-staticswitching is forbidden. An off-axis field of relatively small amplitude canexcite large-angle scissor-like oscillations at the optical resonance frequency,which can result in a full 180-degree reversal, with the two moments switchingpast each other into the mirror anti-parallel state. It is found that the switch-ing probability increases with increasing the duration of the microwave fieldpulse, which shows that the resonant switching process is affected by thermalagitation. Micromagnetic modeling incorporating the effect of temperature isperformed and is in good agreement with the experimental results.

    Vortex pair states in spin-flop bi-layers are produced using high amplitudefield pulses near the optical spin resonance in the system. The stable vortex-pair states, 16 in total, of which 4 sub-classes are non-degenerate in energy, areidentified and investigated using static and dynamic applied fields. For AP-chirality vortex-pair states, the system can be studied while the two vortexcores are coupled and decoupled in a single field sweep. It is found thatthe dynamics of the AP-chirality vortex pairs is critically determined by thepolarizations of the two vortex cores and the resulting attractive or repulsivecore-core interaction. The measured spin resonance modes in the system areinterpreted as gyrational, rotational, and vibrational resonances with the helpof the analytical and micromagnetic models developed herein.

    A significant effort during this project was made to build two instrumentsfor surface and transport characterization of magnetic nanostructures: a high-current Scanning Tunneling Microscope for studying transport in magneticpoint contacts, and a Current In Plane Tunneling instrument for characteriz-ing unpatterned magnetic tunnel junctions. The design and implementationof the instruments as well as the test data are presented.

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  • 41.
    Cherepov, Sergiy
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Dzhezherya, Yu. I.
    Worledge, D. C.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Resonant Activation of a Synthetic Antiferromagnet2011In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, no 7, p. 077202-Article in journal (Refereed)
    Abstract [en]

    The magnetic decay time of a synthetic antiferromagnet comprised of two closely spaced magnetic dipoles is measured in the presence of microwave excitation. The system is known to be highly stable with respect to switching between its two antiparallel ground states under quasistatic magnetic fields. We show that an order of magnitude lower field can switch the pair, provided the field is applied in resonance with the optical eigenmode of the collective spin dynamics in the system. We furthermore show that thermal agitation can play an essential role in spin-flop switching for resonant excitations of near-or subcritical amplitude.

  • 42.
    Cherepov, Sergiy
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Konovalenko, Alexander
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Worledge, D. C.
    IBM T.J. Watson Researh Center.
    Micromagnetics of Spin-Flop Bilayers: S, C, and Vortex Spin States2010In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 46, no 6, p. 2124-2127Article in journal (Refereed)
    Abstract [en]

    Spin-flop tunnel junctions subjected to strong gigahertz excitations are found to exhibit highly stable resistance states, intermediate between the two spin-uniform ground states of high and low resistance. The associated spin distributions are necessarily nonuniform and differ significantly from the ground-state anti-parallel spin configuration in their static and dynamic properties. Detailed micromagnetic modeling reveals that inplane spin vortices in dipole-coupled thin-film bilayers are stable spin configurations, where the orientation of the vortex cores and the vortex chirality play an important role in the response of the system to external magnetic fields.

  • 43.
    Cherepov, Sergiy
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Koop, Björn
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Galkin, A. Yu.
    Khymyn, R.S.
    Institute of Magnetism, Ukrainian Academy of Science.
    Ivanov, B. A.
    Institute of Magnetism, Ukrainian Academy of Science.
    Worledge, D. C.
    IBM T.J. Watson Researh Center.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Core-Core Dynamics in Spin Vortex Pairs2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, no 9, p. 097204-Article in journal (Refereed)
    Abstract [en]

    We investigate nanopillars in which two thin ferromagnetic particles are separated by a nanometer thin nonmagnetic spacer and can be set into stable spin vortex-pair configurations. We find that the previously unexplored limit of strong vortex core-core coupling can dominate the spin dynamics in the system. We observe experimentally and explain analytically and numerically how the 0.2 GHz gyrational resonance modes of the individual vortices are transformed into a 2 GHz collective rotational resonance mode in the configurations where the two cores form a bound pair.

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  • 44.
    Cherepov, Sergiy
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Korenivski, Vladislav
    Worledge, D. C.
    IBM T.J. Watson Researh Center.
    Resonant activation of asynthetic antiferromagnetManuscript (preprint) (Other academic)
  • 45.
    Cherepov, Sergiy
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Worledge, D. C.
    IBM T.J. Watson Researh Center.
    Resonant Switching of Two Dipole-Coupled Nanomagnets2010In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 46, no 6, p. 2112-2115Article in journal (Refereed)
    Abstract [en]

    The storage layer of recently developed spin-flop magnetic random-access memory consists of two closely spaced dipole-coupled nanomagnets and is highly stable in the ground state as well as in quasistatic fields applied off the easy axis. We show experimentally and confirm by using micromagnetic simulations that these spin-flop bilayers can be switched relatively easily by dynamic fields, applied at the frequency of the optical spin resonance of the bilayer. The field amplitude sufficient for this resonant switching can be an order of magnitude lower than the fields necessary for quasistatic reversal. Our data and micromagnetic analysis suggest that thermal agitation can play a role in the observed resonant switching behavior.

  • 46.
    Claesson, Per M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden.
    Dobryden, Illia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Li, Gen
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    He, Yunjuan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Huang, Hui
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Thorén, Per-Anders
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    From force curves to surface nanomechanical properties2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 35, p. 23642-23657Article in journal (Refereed)
    Abstract [en]

    Surface science, which spans the fields of chemistry, physics, biology and materials science, requires information to be obtained on the local properties and property variations across a surface. This has resulted in the development of different scanning probe methods that allow the measurement of local chemical composition and local electrical and mechanical properties. These techniques have led to rapid advancement in fundamental science with applications in areas such as composite materials, corrosion protection and wear resistance. In this perspective article, we focussed on the branch of scanning probe methods that allows the determination of surface nanomechanical properties. We discussed some different AFM-based modes that were used for these measurements and provided illustrative examples of the type of information that could be obtained. We also discussed some of the difficulties encountered during such studies.

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  • 47.
    Corlevi, Silvia
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Guichard, Wiebke
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Cooper pair transistor in a tunable environment2006In: Quantum Computing in Solid State Systems, Springer-Verlag New York, 2006, p. 63-69Chapter in book (Other academic)
    Abstract [en]

    We report an experimental study on the effect of high impedance environment on a Cooper pair transistor (CPT). The CPT consists of two small capacitance Josephson tunnel junctions in series with a gate electrode coupled through a capacitance Cg to a central island. In small-capacitance CPT the charging energy EC = e2/2C, where C ∼ 2CJ+Cg is the total capacitance of the island, becomes relevant at low temperature, and charging effects influence the transport properties.

  • 48. Crippa, Federica
    et al.
    Thorén, Per-Anders
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Forchheimer, Daniel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Borgani, Riccardo
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Rothen-Rutishauser, Barbara
    Petri-Fink, Alke
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Probing nano-scale viscoelastic response in air and in liquid with dynamic atomic force microscopy2018In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 14, no 19, p. 3998-4006Article in journal (Refereed)
    Abstract [en]

    We perform a comparative study of dynamic force measurements using an Atomic Force Microscope (AFM) on the same soft polymer blend samples in both air and liquid environments. Our quantitative analysis starts with calibration of the same cantilever in both environments. Intermodulation AFM (ImAFM) is used to measure dynamic force quadratures on the same sample. We validate the accuracy of the reconstructed dynamic force quadratures by numerical simulation of a realistic model of the cantilever in liquid. In spite of the very low quality factor of this resonance, we find excellent agreement between experiment and simulation. A recently developed moving surface model explains the measured force quadrature curves on the soft polymer, in both air and liquid.

  • 49.
    Demchenko, Lesya
    et al.
    Stockholm University, Department of Materials and Environmental Chemistry, Stockholm, Sweden; National Technical University of Ukraine, 'Igor Sikorsky Kyiv Polytechnic Institute', Department of Materials Science and Heat Treatment, Kyiv, Ukraine.
    Titenko, Anatoliy
    Institute of Magnetism of NAS and MES of Ukraine, Department of Physics of Films, Kyiv, Ukraine.
    Kozlova, Larysa
    Institute of Magnetism of NAS and MES of Ukraine, Department of Physics of Meso- and Nanocrystalline Magnetic Structures, Kyiv, Ukraine.
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. Institute of Magnetism of NAS and MES of Ukraine, Department of Physics of Films, Kyiv, Ukraine.
    Babanli, Mustafa
    Azerbaijan State University of Oil and Industry, Machine-building and Materials Science Department, Baku, Azerbaijan.
    Structural and Magnetic Transitions in Aged Shape Memory Cu-Al-Mn and Cu-Al-Mn-Fe Alloys2023In: Proceedings of the 2023 IEEE 13th International Conference Nanomaterials: Applications and Properties, NAP 2023, Institute of Electrical and Electronics Engineers (IEEE) , 2023, p. NMM041-NMM044Conference paper (Refereed)
    Abstract [en]

    A comparative analysis of the structural and magnetic behavior of Cu-Al-Mn and Cu-Al-Mn-Fe alloys depending on their heat treatment is carried out. The influence of low-temperature aging on the behavior of temperature induced martensitic transformation was established. The difference in magnetic behavior of alloys is a consequence of the formation of the ferromagnetic (Cu,Mn)3Al and (Fe,Mn)3Al Heusler phases during isothermal aging and the transition to a superparamagnetic state. In alloys doped with iron, antiferromagnetic ordering can prevail over ferromagnetic. The precipitates create a significant cumulative effect on the character and characteristic temperature of thermoelastic martensite transformation (MT), as well as on mechanical and magnetic behavior.

  • 50.
    Dobryden, Illia
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. Division of Materials Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden .
    Borgani, Riccardo
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Rigoni, Federica
    Division of Materials Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden; Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Venezia Mestre, Italy .
    Ghamgosar, Pedram
    Division of Materials Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden .
    Concina, Isabella
    Division of Materials Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden .
    Almqvist, Nils
    Division of Materials Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden .
    Vomiero, Alberto
    Division of Materials Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden ;Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Venezia Mestre, Italy. .
    Nanoscale characterization of an all-oxide core-shell nanorod heterojunction using intermodulation atomic force microscopy (AFM) methods2021In: Nanoscale Advances, E-ISSN 2516-0230, Vol. 3, no 15, p. 4388-4394Article in journal (Refereed)
    Abstract [en]

    The electrical properties of an all-oxide core-shell ZnO-Co3O4nanorod heterojunction were studied in the dark and under UV-vis illumination. The contact potential difference and current distribution maps were obtained utilizing new methods in dynamic multifrequency atomic force microscopy (AFM) such as electrostatic and conductive intermodulation AFM. Light irradiation modified the electrical properties of the nanorod heterojunction. The new techniques are able to follow the instantaneous local variation of the photocurrent, giving a two-dimensional (2D) map of the current-voltage curves and correlating the electrical and morphological features of the heterostructured core-shell nanorods.

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