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  • 151. Peters, Lars
    et al.
    Ghosh, Saurabh
    Sanyal, Biplab
    van Dijk, Chris
    Bowlan, John
    de Heer, Walt
    Delin, Anna
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Uppsala Universitet, Sweden.
    Di Marco, Igor
    Eriksson, Olle
    Katsnelson, Mikhail I.
    Johansson, Borje
    Kirilyuk, Andrei
    Magnetism and exchange interaction of small rare-earth clusters; Tb as a representative2016Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, artikkel-id 19676Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Here we follow, both experimentally and theoretically, the development of magnetism in Tb clusters from the atomic limit, adding one atom at a time. The exchange interaction is, surprisingly, observed to drastically increase compared to that of bulk, and to exhibit irregular oscillations as a function of the interatomic distance. From electronic structure theory we find that the theoretical magnetic moments oscillate with cluster size in exact agreement with experimental data. Unlike the bulk, the oscillation is not caused by the RKKY mechanism. Instead, the inter-atomic exchange is shown to be driven by a competition between wave-function overlap of the 5d shell and the on-site exchange interaction, which leads to a competition between ferromagnetic double-exchange and antiferromagnetic super-exchange. This understanding opens up new ways to tune the magnetic properties of rare-earth based magnets with nano-sized building blocks.

  • 152.
    Pevere, Federico
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Bruhn, Benjamin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Sangghaleh, Fatemeh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Hormozan, Yashar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Effect of X-ray irradiation on the blinking of single silicon nanocrystals2015Inngår i: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 212, nr 12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Photoluminescence (PL) intermittency (blinking) observed for single silicon nanocrystals (Si-NCs) embedded in oxide is usually attributed to trapping/de-trapping of carriers in the vicinity of the NC. Following this model, we propose that blinking could be modified by introducing new trap sites, for example, via X-rays. In this work, we present a study of the effect of X-ray irradiation (up to 65 kGy in SiO) on the blinking of single Si-NCs embedded in oxide nanowalls. We show that the luminescence characteristics, such as spectrum and life-time, are unaffected by X-rays. However, substantial changes in ON-state PL intensity, switching frequency, and duty cycle emerge from the blinking traces, while the ON- and OFF- time distributions remain of mono-exponential character. Although we do not observe a clear monotonic dependence of the blinking parameters on the absorbed dose, our study suggests that, in the future, Si-NCs could be blinking-engineered via X-ray irradiation.

  • 153.
    Pevere, Federico
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sangghaleh, Fatemeh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Fucikova, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Biexciton Emission as a Probe of Auger Recombination in Individual Silicon Nanocrystals2015Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, nr 13, s. 7499-7505Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Biexciton emission from individual silicon nanocrystals was detected at room temperature by time-resolved, single-particle luminescence measurements. The efficiency of this process, however, was found to be very low, about 10-20 times less than the single exciton emission efficiency. It decreases even further at low temperature, explaining the lack of biexciton emission line observations in silicon nanocrystal single-dot spectroscopy under high excitation. The poor efficiency of the biexciton emission is attributed to the dominant nonradiative Auger process. Corresponding measured biexciton decay times then represent Auger lifetimes, and the values obtained here, from tens to hundreds of nanoseconds, reveal strong dot-to-dot variations, while the range compares well with recent calculations taking into account the resonant nature of the Auger process in semiconductor nanocrystals.

  • 154. Polley, C. M.
    et al.
    Dziawa, P.
    Reszka, A.
    Szczerbakow, A.
    Minikayev, R.
    Domagala, J. Z.
    Safaei, S.
    Kacman, P.
    Buczko, R.
    Adell, J.
    Hårdensson Berntsen, Magnus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Wojek, Bastian M.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Tjernberg, Oscar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Kowalski, B. J.
    Story, T.
    Balasubramanian, T.
    Observation of topological crystalline insulator surface states on (111)-oriented Pb1-xSnxSe films2014Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 7, s. 075317-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present angle-resolved photoemission spectroscopy measurements of the surface states on in-situ grown (111) oriented films of Pb1-xSnxSe, a three-dimensional topological crystalline insulator. We observe surface states with Dirac-like dispersion at (Gamma) over bar and (M) over bar in the surface Brillouin zone, supporting recent theoretical predictions for this family of materials. We study the parallel dispersion isotropy and Dirac-point binding energy of the surface states, and perform tight-binding calculations to support our findings. The relative simplicity of the growth technique is encouraging, and suggests a clear path for future investigations into the role of strain, vicinality, and alternative surface orientations in (Pb,Sn)Se solid solutions.

  • 155. Puliafito, Vito
    et al.
    Pogoryelov, Yevgen
    Azzerboni, Bruno
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Finocchio, Giovanni
    Hysteretic Synchronization in Spin-Torque Nanocontact Oscillators: A Micromagnetic Study2014Inngår i: IEEE transactions on nanotechnology, ISSN 1536-125X, E-ISSN 1941-0085, Vol. 13, nr 3, s. 532-536Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several experiments report the presence of finite jumps in the properties of spin-torque oscillators at room temperature, such as oscillation frequency and power as functions of current or field. On the basis of micromagnetic simulations, this paper links those experimental discontinuities to the changes in the curve slope numerically observed in the absence of thermal effects. Our numerical results show the key ingredient triggering this behavior is the presence of abrupt changes in the oscillation axis of the magnetization precession. We also predict that by fixing the bias point of the oscillator near those critical regions, it is possible to observe hysteretic synchronization. This result should be a key point in the design of nanoscale on-chip phase-locked loop receivers with improved sensitivity.

  • 156.
    Qejvanaj, Fatjon
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH.
    A PHEB magnetometer with record thick multiexchange-biased sensor layerManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    In this paper, we develop material stacks for the fabrication of a magnetometer with multiple exchange-biased layers reaching thicknesses exceeding previous attempts in the literature. The benets of such thick sensor layers is demonstrated in terms of the low noise based on the decreasing resistance without an eect on device sensitivity. The thick sensor layers of [IrMn(15nm)/NiFe(150nm)]7/IrMn(15nm), as a novel multiple-biasing scheme, is able to stabilize up to fourteenfold biased interfaces. We measured the sensitivity and noise of these devices and report a eld detectivity of 600 pT/pHz at 2 Hz. Our results describe a reliable technique for the fabrication of thick prototype magnetometers based on the exchange-bias mechanism.

  • 157.
    Qejvanaj, Fatjon
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH.
    Fabrication and Characterization of magnetometer for space applications2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The present rapid increase in the number of space missions demands a decrease in the cost of satellite equipment, but also requires the development of instruments that have low power consumption, low weight, and small size.Anisotropic magnetoresistance (AMR) sensors can answer these needs on account of their small size, weight, and power consumption. AMR sensors also produce lower noise than either giant magnetoresistance (GMR) or tunnel magnetoresistance (TMR) devices and are thus more suitable for space applications.The type of AMR sensor developed in this study was a Planar Hall EffectBridge (PHEB) sensor. The FM layer was also coupled with an AFM layer in order to fix the internal magnetization of the FM layer.One technique that was employed in order to meet the low-noise requirement was to make the FM layer thicker than has previously been attempted.In doing so, the exchange bias field between the AFM layer and the FMlayer is no longer high enough to bias the thicker FM layer, so in order to correct this unwanted effect, the material stack was upgraded to two AFM–FM interfaces. With this configuration, it became possible to increase the exchange field by up to 60%. Stronger exchange bias leads to a thicker FMlayer and so to lower noise in the device performance. Another strategy that was used to lower the resistance of the device was to implement an NiFeX alloy instead of the standard NiFe. NiFeX consists of an alloy of NiFe andCu, Ag, or Au; the last of these is known to have very low resistivity.This solution leads to a significant lowering of the device’s resistance. A recent technological advance used to fabricate devices with lower resistance is to deposit a multilayer of AFM–FM.

  • 158.
    Qejvanaj, Fatjon
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH.
    Gamma radiation hardness of PHEB magnetometersManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We study planar Hall eect bridge (PHEB) sensors under gamma ray irradiation to investigate their potential use in space applications. We fabricate and characterize a wide range of PHEBs with dierent geometries to evaluate the eects of irradiation. We observe no signicant change in performance for the sensors irradiated by gamma rays with doses up to 100 krad. However, a dramatic increase in sensor noise and a corresponding loss in detectivity are observed after 300 krad of radiation. Our results indicate that PHEB magnetometers can operate for at least 5 years in orbit.

  • 159.
    Qejvanaj, Fatjon
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH.
    Order of magnitude increase in AMR sensor layer thickness through multi-interface exchange biasingManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We demonstrate an order of magnitude increase in total ferromagnetic layer thickness in magnetron sputtered and exchange-biased multilayers of [IrMn(15nm)/NiFe(t)]N/IrMn(15nm) with t=50{200 nm and N=1{7. Wend a strong exchange-bias eld (Heb) and a low coercivity (Hc) in all multilayers, with a gradual improvement with increasing number of multilayer repetitions. All stacks with t=50{150 nm exhibit single-step switching,while the stacks with the thickest NiFe show signs of multistep switching. Four-point magnetotransport measurements show values for the anisotropic magnetoresistance (AMR) of about 3% in all stacks. We determine the lm roughness and mean grain size using Atomic Force Microscopy and nd a direct correlation between Heb and the grain size on the one hand, and Hc and the inverse of the roughness on the other. Our results directly demonstrate the feasibility

  • 160.
    Qejvanaj, Fatjon
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mazraati, Hamid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Jiang, S.
    Persson, A.
    Sani, Sohrab Redjai
    Chung, S.
    Magnusson, F.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik. Göteborg univ.
    Planar Hall-Effect Bridge Sensor With NiFeX (X = Cu, Ag, and Au) Sensing Layer2015Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 51, nr 11, artikkel-id 4005404Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a new material alloy for planar Hall-effect bridge (PHEB) sensors and the accurate analysis of the resistance and sensitivity of these materials. The sensing layer is based on NiFeX (X = Cu, Ag, and Au). These alloys have a lower resistance without a significant loss of sensitivity. The presented PHEB sensors with NiFeX sensing layer show a coercivity of 1.7 Oe, lower than that of PHEB sensors with NiFe sensing layers, which have coercivities of 2.2 Oe.

  • 161. Qejvanaj, Fatjon
    et al.
    Zubair, M.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Persson, A.
    Mohseni, S. M.
    Fallahi, V.
    Sani, Sohrab Redjai
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Le, Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Magnusson, F.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Thick Double-Biased IrMn/NiFe/IrMn Planar Hall Effect Bridge Sensors2014Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, nr 11, artikkel-id 4006104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we present a new material stack for planar Hall effect bridge (PHEB) sensors and a detailed investigation of the sensitivity and noise properties of PHEB sensors made from these. The sputter deposited material stack was based on a ferromagnetic (FM) NiFe sensing layer surrounded by two layers of anti-FM IrMn. This material stack enables implementation of a thick NiFe layer without loss of sensitivity. We present an improvement in detectivity in the PHEB by changing the shape and the materials of the corners between the sensors in a meander shape. A significant reduction of noise also comes from the thick NiFe layer, due to the reduced resistance of the sensor.

  • 162. Qi, B.
    et al.
    Shayestehaminzadeh, S.
    Ólafsson, S.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Gislason, H. P.
    Formation and nitridation of InGa composite droplets on Si(111): In-situ study by high resolution X-ray photoelectron spectroscopy2014Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 303, s. 297-305Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate applying synchrotron radiation based high resolution X-ray photoelectron spectroscopy as a versatile in-situ tool to study the step-wise formation and nitridation of indium gallium (InGa) composite droplets on Si(1 1 1) 7 x 7. This includes analysis of initial interactions of Ga and In with Si(1 1 1)7x7, and characterization of formation and nitridation of InGa droplets. The results show that after stabilization of Si(1 1 1) 7 x 7 structure with Ga and In at 750 degrees C and formation of Ga nanodroplets as the bases, the InGa composite droplets (In:Ga approximate to 3:1) were formed at RT and 200 degrees C in a coverage range 3-14 monolayers. The nitridation efficiency and structure of the droplets/Si(1 1 1) with NH3 were temperature dependent. At or below 350 degrees C, the droplets were hardly nitridated. At 670 degrees C, the nitridation of InGa was more completed, which however caused an unavoidable nitridation of Si surface. The optimum nitridation occurred around 480 degrees C and proceed in a 2D mode. Further simultaneous growth and nitridation of the InGa droplets on the 2D nitridated surface at 400 degrees C resulted in a complex surface composition and structure. An ex-situ atomic force microscopy reveals both the aligned metallic droplet-island assemblies and the fractured nitridated island bases with small droplets on top for the final surface.

  • 163. Ranjbar, M.
    et al.
    Durrenfeld, P.
    Haidar, M.
    Iacocca, E.
    Balinskiy, M.
    Le, T. Q.
    Fazlali, M.
    Houshang, A.
    Awad, A. A.
    Dumas, R. K.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Goteborgs Universitet, Department of Physics, Goteborg, Sweden .
    CoFeB-Based Spin Hall Nano-Oscillators2014Inngår i: IEEE Magnetics Letters, ISSN 1949-307X, E-ISSN 1949-3088, Vol. 5, s. 3000504-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate magnetization auto-oscillations driven by pure spin currents in spin Hall nano-oscillators based on CoFeB/Pt bilayers. Despite the very low anisotropic magnetoresistance of CoFeB, a substantial microwave signal power can be detected, even at room temperature, indicating that a sizable spin wave amplitude is generated. Spin torque ferromagnetic resonance measurements reveal that the generated auto-oscillation frequency lies below the ferromagnetic resonance frequency of CoFeB and is therefore well described by a self-localized spin wave bullet mode.

  • 164. Ranjbar, M.
    et al.
    Sbiaa, R.
    Dumas, R. K.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Piramanayagam, S. N.
    Spin reorientation via antiferromagnetic coupling2014Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, nr 17, s. 4852076-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spin reorientation in antiferromagnetically coupled (AFC) Co/Pd multilayers, wherein the thickness of the constituent Co layers was varied, was studied. AFC-Co/Pd multilayers were observed to have perpendicular magnetic anisotropy even for a Co sublayer thickness of 1 nm, much larger than what is usually observed in systems without antiferromagnetic coupling. When similar multilayer structures were prepared without antiferromagnetic coupling, this effect was not observed. The results indicate that the additional anisotropy energy contribution arising from the antiferromagnetic coupling, which is estimated to be around 6 × 106 ergs/cm3, induces the spin-reorientation.

  • 165.
    Rapp, Östen
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Reinterpretation of the zero-temperature conductivity in icosahedral AlPdRe2016Inngår i: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, nr 2, artikkel-id 024202Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The zero-temperature conductivity sigma(0) of icosahedral (i)-AlPdRe has been found to be simply related to the resistance ratio R = rho(4.2 K)/rho(295 K) by a power law, sigma(0) similar to R (1.74), over four orders of magnitude in sigma(0). This relation includes metallic single grain samples, and polygrain samples of different morphologies which are metallic for small R values, and insulatinglike at large R. Electronic transport properties of single grain i-AlPdRe samples are thus found to be on common ground with polygrain i-AlPdRe. The relation between R and sigma(0) can be qualitatively understood from published band-structure calculations on quasicrystalline approximants.

  • 166.
    Redjai Sani, Sohrab
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Dürrenfeld, Philipp
    Mohseni, Seyed Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Microwave Signal Generation in Single-Layer Nano-Contact Spin Torque Oscillators2013Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 49, nr 7, s. 4331-4334Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate spin transfer torque (STT) driven microwave signal generation, from about 250 MHz to above 3 GHz, in single perm alloy layers underneath a nano-contact with diameter of 100 nm. The threshold current for signal generation is found to be strongly hysteretic, the microwave signal shows a number of harmonics, zero-field operation is straightforward, and the microwave frequency increases quasi-linearly with drive current. All observations are consistent with STT driven motion of a vortex-antivortex pair nucleated by the Oersted field underneath the nano-contact. While the generated power is about 10 dB smaller than the best GMR based nano-contact spin torque oscillators, the linewidth of 6-100 MHz is of the same order.

  • 167.
    Redjai Sani, Sohrab
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Persson, J.
    Mohseni, Seyed Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Pogoryelov, Ye
    Muduli, P. K.
    Eklund, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Malm, Gunnar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Dmitriev, A.
    Käll, M.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mutually synchronized bottom-up multi-nanocontact spin-torque oscillators2013Inngår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 4, s. 2731-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spin-torque oscillators offer a unique combination of nanosize, ultrafast modulation rates and ultrawide band signal generation from 100 MHz to close to 100 GHz. However, their low output power and large phase noise still limit their applicability to fundamental studies of spin-transfer torque and magnetodynamic phenomena. A possible solution to both problems is the spin-wave-mediated mutual synchronization of multiple spin-torque oscillators through a shared excited ferromagnetic layer. To date, synchronization of high-frequency spin-torque oscillators has only been achieved for two nanocontacts. As fabrication using expensive top-down lithography processes is not readily available to many groups, attempts to synchronize a large number of nanocontacts have been all but abandoned. Here we present an alternative, simple and cost-effective bottom-up method to realize large ensembles of synchronized nanocontact spin-torque oscillators. We demonstrate mutual synchronization of three high-frequency nanocontact spin-torque oscillators and pairwise synchronization in devices with four and five nanocontacts.

  • 168. Richters, J. -P
    et al.
    Dev, Apurba
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Bremen, Germany.
    Ronning, C.
    Gutowski, J.
    Voss, T.
    Functional ZnO/polymer core-shell nanowires fabricated by oxidative chemical vapour deposition2014Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 47, nr 39, artikkel-id 394004Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Functional ZnO-nanowire/polymer core-shell heterostructures were realized using oxidative chemical vapour deposition (oCVD). This dry and versatile technique allows uniform coating of semiconductor nanowires with polymers and simultaneous doping control of the shell. Here, 100 nm thick, p-doped shells of poly(3,4-ethylenedioxythiophene) (PEDOT) were deposited around n-conductive ZnO nanowires. Energy-dispersive x-ray spectroscopy confirms the incorporation of Br dopants into the PEDOT shell, and the resulting p-conductivity of the polymer shell is demonstrated by electrical measurements on nanowire arrays. Photoluminescence spectroscopy points to reactions of Br with the ZnO surface but proves that the nanowires show only little degradation of their optical properties.

  • 169.
    Råsander, Mikael
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Bergqvist, Lars
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Electronic structure and lattice dynamics in the FeSb3 skutterudite from density functional theory2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, nr 1, artikkel-id 014303Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have performed density functional calculations of the electronic structure and lattice dynamics of the binary skutterudite FeSb3. We find that the ground state of FeSb3 is a near half-metallic ferromagnet with T-c = 175 K. Furthermore, we find that FeSb3 is softer than CoSb3 based on an analysis of the relation of the elastic constants and the shape of the phonon density of states in the two systems, which is in agreement with experimental observation. Based on these observations we find it plausible that FeSb3 will have a lower thermal conductivity than CoSb3. Additionally, our calculations indicate that FeSb3 may be stable towards decomposition into FeSb2 and Sb. Furthermore, for ferromagnetic FeSb3 we obtain real-valued phonon frequencies and also a c44 greater than zero, indicating that the system is mechanically as well as dynamically stable.

  • 170.
    Sangghaleh, Fatemeh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Carrier Dynamics in Single Luminescent Silicon Quantum Dots2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Bulk silicon as an indirect bandgap semiconductor is a poor light emitter. In contrast, silicon nanocrystals (Si NCs) exhibit strong emission even at room temperature, discovered initially at 1990 for porous silicon by Leigh Canham. This can be explained by the indirect to quasi-direct bandgap modification of nano-sized silicon according to the already well-established model of quantum confinement.

    In the absence of deep understanding of numerous fundamental optical properties of Si NCs, it is essential to study their photoluminescence (PL) characteristics at the single-dot level. This thesis presents new experimental results on various photoluminescence mechanisms in single silicon quantum dots (Si QDs).

    The visible and near infrared emission of Si NCs are believed to originate from the band-to-band recombination of quantum confined excitons. However, the mechanism of such process is not well understood yet. Through time-resolved PL decay spectroscopy of well-separated single Si QDs, we first quantitatively established that the PL decay character varies from dot-to-dot and the individual lifetime dispersion results in the stretched exponential decays of ensembles. We then explained the possible origin of such variations by studying radiative and non-radiative decay channels in single Si QDs. For this aim the temperature dependence of the PL decay were studied. We further demonstrated a model based on resonance tunneling of the excited carriers to adjacent trap sites in single Si QDs which explains the well-known thermal quenching effect.

    Despite the long PL lifetime of Si NCs, which limits them for optoelectronics applications, they are ideal candidates for biomedical imaging, diagnostic purposes, and phosphorescence applications, due to the non-toxicity, biocompability and material abundance of silicon. Therefore, measuring quantum efficiency of Si NCs is of great importance, while a consistency in the reported values is still missing. By direct measurements of the optical absorption cross-section for single Si QDs, we estimated a more precise value of internal quantum efficiency (IQE) for single dots in the current study. Moreover, we verified IQE of ligand-passivated Si NCs to be close to 100%, due to the results obtained from spectrally-resolved PL decay studies. Thus, ligand-passivated silicon nanocrystals appear to differ substantially from oxide-encapsulated particles, where any value from 0 % to 100 % could be measured. Therefore, further investigation on passivation parameters is strongly suggested to optimize the efficiency of silicon nanocrystals systems.

  • 171.
    Sangghaleh, Fatemeh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Bruhn, Benjamin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Schmidt, Torsten
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Exciton lifetime measurements on single silicon quantum dots2013Inngår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 24, nr 22, s. 225204-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We measured the exciton lifetime of single silicon quantum dots, fabricated by electron beam lithography, reactive ion etching and oxidation. The observed photoluminescence decays are of mono-exponential character with a large variation (5-45 mu s) from dot to dot, even for the same emission energy. We show that this lifetime variation may be the origin of the heavily debated non-exponential (stretched) decays typically observed for ensemble measurements.

  • 172.
    Sangghaleh, Fatemeh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Bruhn, Benjamin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Optical absorption cross section and quantum efficiency of a single silicon quantum dot2013Inngår i: Nanotechnology VI, SPIE - International Society for Optical Engineering, 2013, s. 876607-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Direct measurements of the optical absorption cross section (sigma) and exciton lifetime are performed on a single silicon quantum dot fabricated by electron beam lithography (EBL), reactive ion etching (RIE) and oxidation. For this aim, single photon counting using, an avalanche photodiode detector (APD) is applied to record photoluminescence (PL) intensity traces under pulsed excitation. The PL decay is found to be of a mono-exponential character with a lifetime of 6.5 mu s. By recording the photoluminescence rise time at different photon fluxes the absorption cross could be extracted yielding a value of 1.46x10(-14)cm(2) under 405 nm excitation wavelength. The PL quantum efficiency is found to be about 9% for the specified single silicon quantum dot.

  • 173.
    Sangghaleh, Fatemeh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Bruhn, Benjamin
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Non-radiative decay in Si/SiO2 quantum dots in transition from dark to bright exciton statesManuskript (preprint) (Annet vitenskapelig)
  • 174.
    Sangghaleh, Fatemeh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Yang, Zhenyu
    Veinot, Jonathan G C
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Near-Unity Internal Quantum Efficiency of Luminescent Silicon Nanocrystals with Ligand Passivation.2015Inngår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 9, nr 7, s. 7097-7104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spectrally resolved photoluminescence (PL) decays were measured for samples of colloidal, ligand-passivated silicon nanocrystals. These samples have PL emission energies with peak positions in the range 1.4-1.8 eV and quantum yields of 30-70%. Their ensemble PL decays are characterized by a stretched-exponential decay with a dispersion factor of 0.8, which changes to an almost monoexponential character at fixed detection energies. The dispersion factors and decay rates for various detection energies were extracted from spectrally resolved curves using a mathematical approach that excluded the effect of homogeneous line width broadening. Since nonradiative recombination would introduce a random lifetime variation, leading to a stretched-exponential decay for an ensemble, we conclude that the observed monoexponential decay in size-selected ensembles signifies negligible nonradiative transitions of a similar strength to the radiative one. This conjecture is further supported as extracted decay rates agree with radiative rates reported in the literature, suggesting 100% internal quantum efficiency over a broad range of emission wavelengths. The apparent differences in the quantum yields can then be explained by a varying fraction of "dark" or blinking nanocrystals.

  • 175. Sassa, Y.
    et al.
    Mansson, M.
    Kobayashi, M.
    Gotberg, O.
    Strocov, V. N.
    Schmitt, T.
    Zhigadlo, N. D.
    Tjernberg, Oscar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Batlogg, B.
    Probing two- and three-dimensional electrons in MgB2 with soft x-ray angle-resolved photoemission2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, nr 4, s. 045114-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    electronic band structure of MgB2 involves a unique combination of two-and three-dimensional (3D) electrons derived from the boron sigma and pi states, respectively. We have mapped out the sigma and pi bands over the complete Brillouin zone, including the full disconnected Fermi surface, using high-resolution soft x-ray angle-resolved photoelectron spectroscopy. The measured band structure, which is closely related to that of graphene, is in overall good agreement with the density functional theory-general gradient approximation (DFT-GGA), though differences in Fermi surface volume are seen. Surprisingly, the measured bands are wider than calculated, by similar to 8% for the s and similar to 10-15% for the p bands. This solves the long-standing challenge of establishing the full 3D electronic structure of the model compound MgB2, and it demonstrates the tendency of DFT-GGA to overestimate the band narrowing due to exchange correlations effects.

  • 176. Sbiaa, R.
    et al.
    Al-Omari, I. A.
    Kharel, P. R.
    Ranjbar, M.
    Sellmyer, D. J.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    Piramanayagam, S. N.
    Temperature effect on exchange coupling and magnetization reversal in antiferromagnetically coupled (Co/Pd) multilayers2015Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, nr 6, artikkel-id 063902Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetization reversal of antiferromagnetically coupled (AFC) soft and hard (Co/Pd) multilayers was studied as a function of temperature. While the hard [Co(0.3 nm)/Pd(0.8 nm)](x10) was kept unchanged, the softness of the [Co(t)/Pd(0.8 nm)](x3) was controlled by varying the thickness t of the Co sublayer. Clear two-step hysteresis loops were observed for all the investigated multilayers with t ranging between 0.4 and 1 nm. The spin reorientation of the soft layer magnetization from in-plane direction to out-of-plane direction was investigated from 50 to 300 K. The antiferromagnetic field H-AFC measured from the shift of the minor hysteresis loop reveals a good agreement to the quantum-well model. From the out-of-plane hysteresis loop of the uncoupled soft layer, its magnetization shows an in-plane orientation for t >= 0.6 nm. The strong H-AFC helps to induce an out-of plane orientation of the soft layer with a linear decrease of its coercivity with temperature. These investigated structures show the possibility to reduce the unwanted stray field and improving the out-of-plane anisotropy even for relatively thicker soft layer.

  • 177. Sbiaa, R.
    et al.
    Ranjbar, M.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    Domain structures and magnetization reversal in Co/Pd and CoFeB/Pd multilayers2015Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, nr 17, artikkel-id 17C102Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Domain structures and magnetization reversal of (Co/Pd) and (CoFeB/Pd) multilayers with 7 and 14 repeats were investigated. The Co-based multilayers show much larger coercivities, a better squareness, and a sharper magnetization switching than CoFeB-based multilayers. From magnetic force microscopy observations, both structures show strong reduction in domains size as the number of repeats increases but the magnetic domains for Co-based multilayers are more than one order of magnitude larger than for CoFeB-based multilayers. By imaging domains at different times, breaks in the (CoFeB/Pd) multilayer stripes were observed within only few hours, while no change could be seen for (Co/Pd) multilayers. Although CoFeB single layers are suitable for magnetoresistive devices due to their large spin polarization and low damping constants, their lamination with Pd suffers mainly from thermal instability.

  • 178.
    Schmidt, Torsten
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Zhang, Miao
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Roxhed, Niclas
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Nanopore arrays in a silicon membrane for parallel single-molecule detection: fabrication2015Inngår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 26, nr 31, artikkel-id 314001Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Solid state nanopores enable translocation and detection of single bio-molecules such as DNA in buffer solutions. Here, sub-10 nm nanopore arrays in silicon membranes were fabricated by using electron-beam lithography to define etch pits and by using a subsequent electrochemical etching step. This approach effectively decouples positioning of the pores and the control of their size, where the pore size essentially results from the anodizing current and time in the etching cell. Nanopores with diameters as small as 7 nm, fully penetrating 300 nm thick membranes, were obtained. The presented fabrication scheme to form large arrays of nanopores is attractive for parallel bio-molecule sensing and DNA sequencing using optical techniques. In particular the signal-to-noise ratio is improved compared to other alternatives such as nitride membranes suffering from a high-luminescence background.

  • 179.
    Schmidt, Torsten
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Zhang, Miao
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Yu, Shun
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Fabrication of ultra-high aspect ratio silicon nanopores by electrochemical etching2014Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, nr 12, s. 123111-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the formation of ultra-high aspect ratio nanopores in silicon bulk material using photo-assisted electrochemical etching. Here, n-type silicon is used as anode in contact with hydrofluoric acid. Based on the local dissolution of surface atoms in pre-defined etching pits, pore growth and pore diameter are, respectively, driven and controlled by the supply of minority charge carriers generated by backside illumination. Thus, arrays with sub-100 nm wide pores were fabricated. Similar to macropore etching, it was found that the pore diameter is proportional to the etching current, i.e., smaller etching currents result in smaller pore diameters. To find the limits under which nanopores with controllable diameter still can be obtained, etching was performed at very low current densities (several mu A cm(-2)). By local etching, straight nanopores with aspect ratios above 1000 (similar to 19 mu m deep and similar to 15 nm pore tip diameter) were achieved. However, inherent to the formation of such narrow pores is a radius of curvature of a few nanometers at the pore tip, which favors electrical breakdown resulting in rough pore wall morphologies. Lowering the applied bias is adequate to reduce spiking pores but in most cases also causes etch stop. Our findings on bulk silicon provide a realistic chance towards sub-10 nm pore arrays on silicon membranes, which are of great interest for molecular filtering and possibly DNA sequencing.

  • 180. Sharma, R.
    et al.
    Durrenfeld, P.
    Ranjbar, M.
    Dumas, R. K.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Gothenburg, Sweden.
    Muduli, P. K.
    Modulation rate study in spin torque oscillator based wireless communication system2015Inngår i: 2015 IEEE MAGNETICS CONFERENCE (INTERMAG), ISSN 2150-4598Artikkel i tidsskrift (Annet vitenskapelig)
  • 181. Sharma, Raghav
    et al.
    Durrenfeld, P.
    Iacocca, E.
    Heinonen, O. G.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Muduli, P. K.
    Mode-hopping mechanism generating colored noise in a magnetic tunnel junction based spin torque oscillator2014Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, nr 13, s. 132404-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The frequency noise spectrum of a magnetic tunnel junction based spin torque oscillator is examined where multiple modes and mode-hopping events are observed. The frequency noise spectrum is found to consist of both white noise and 1/f frequency noise. We find a systematic and similar dependence of both white noise and 1/f frequency noise on bias current and the relative angle between the reference and free layers, which changes the effective damping and hence the mode-hopping behavior in this system. The frequency at which the 1/f frequency noise changes to white noise increases as the free layer is aligned away from the anti-parallel orientation w.r.t the reference layer. These results indicate that the origin of 1/f frequency noise is related to mode-hopping, which produces both white noise as well as 1/f frequency noise similar to the case of ring lasers.

  • 182.
    Silberstein Hont, Markus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Modeling the Effects of Strain in Multiferroic Manganese Perovskites2015Student paper second term, 20 poäng / 30 hpOppgave
    Abstract [en]

    The effects of strain on the magnetic phases in perovskites are of interest in the highly active research field of multiferroics. A Monte Carlo program is written to investigate the influence of strain on the low– temperature magnetic phase diagram of the manganese perovskites, RMnO3, where R is a cation in the lanthanide series. A Metropolis simulation scheme is implemented together with parallel tempering to perform computations in a two–dimensional geometry using a conventional nearest–neighbor and next–nearest–neighbor Heisenberg Hamiltonian, extended to include spin–lattice couplings and single–ion anisotropies. The latter two are important to account for structural distortions such as octahedral tilting and the Jahn–Teller effect. It is shown that even weak single–ion anisotropies render incommensurability in the otherwise structurally commensurate E–type ordering, and that the Dzyaloshinskii–Moriya interaction, in combination with single–ion anisotropies, is crucial for the stabilization of previously experimentally observed incommensurate spin spirals. Simulations performed to account for strain in the crystallographic ab–plane show that tensile strain may improve stability of E–type ordering for R elements with small atomic radii and that compressive strain drives the magnetic ordering toward the incommensurate spiral states. 

  • 183.
    Smith, Anderson D.
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Elgammal, Karim
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Fan, Xuge
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Lemme, Max
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre. Uppsala Univ, Sweden.
    Niklaus, Frank
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Östling, Mikael
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Toward Effective Passivation of Graphene to Humidity Sensing Effects2016Inngår i: 2016 46TH EUROPEAN SOLID-STATE DEVICE RESEARCH CONFERENCE (ESSDERC), IEEE, 2016, s. 299-302Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Graphene has a number of remarkable properties which make it well suited for both transistor devices as well as for sensor devices such as humidity sensors. Previously, the humidity sensing properties of monolayer graphene on SiO2 substrates were examined - showing rapid response and recovery over a large humidity range. Further, the devices were fabricated in a CMOS compatible process which can be incorporated back end of the line (BEOL). We now present a way to selectively passivate graphene to suppress this humidity sensing effect. In this work, we experimentally and theoretically demonstrate effective passivation of graphene to humidity sensing - allowing for future integration with other passivated graphene devices on the same chip.

  • 184.
    Smith, Anderson D.
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Elgammal, Karim
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Niklaus, Frank
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Fischer, Andreas C.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Vaziri, Sam
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Forsberg, Fredrik
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Råsander, Mikael
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ London Imperial Coll Sci Technol & Med, Dept Mat, England.
    Hugosson, Håkan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Bergqvist, Lars
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Schröder, Stephan
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Kataria, Satender
    Östling, Mikael
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Lemme, Max C.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar. Univ Siegen, D-57076 Siegen, Germany.
    Resistive graphene humidity sensors with rapid and direct electrical readout2015Inngår i: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 7, nr 45, s. 19099-19109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate humidity sensing using a change of the electrical resistance of single-layer chemical vapor deposited (CVD) graphene that is placed on top of a SiO2 layer on a Si wafer. To investigate the selectivity of the sensor towards the most common constituents in air, its signal response was characterized individually for water vapor (H2O), nitrogen (N-2), oxygen (O-2), and argon (Ar). In order to assess the humidity sensing effect for a range from 1% relative humidity (RH) to 96% RH, the devices were characterized both in a vacuum chamber and in a humidity chamber at atmospheric pressure. The measured response and recovery times of the graphene humidity sensors are on the order of several hundred milliseconds. Density functional theory simulations are employed to further investigate the sensitivity of the graphene devices towards water vapor. The interaction between the electrostatic dipole moment of the water and the impurity bands in the SiO(2)d substrate leads to electrostatic doping of the graphene layer. The proposed graphene sensor provides rapid response direct electrical readout and is compatible with back end of the line (BEOL) integration on top of CMOS-based integrated circuits.

  • 185.
    Smith, Anderson
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Niklaus, Frank
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Paussa, A.
    DIEGM, University of Udine, Via delle Scienze 206, 33100 Udine, Italy.
    Vaziri, Sam
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Fischer, Andreas C.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Sterner, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Forsberg, Fredrik
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Esseni, D.
    DIEGM, University of Udine, Via delle Scienze 206, 33100 Udine, Italy.
    Palestri, P.
    DIEGM, University of Udine, Via delle Scienze 206, 33100 Udine, Italy.
    Östling, Mikael
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Lemme, Max
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar. University of Siegen, Hölderlinstrasse 3, 57076 Siegen, Germany.
    Electromechanical Piezoresistive Sensing in Suspended Graphene Membranes2013Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 13, nr 7, s. 3237-3242Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Monolayer graphene exhibits exceptional electronic and mechanical properties, making it a very promising material for nanoelectromechanical devices. Here, we conclusively demonstrate the piezoresistive effect in graphene in a nanoelectromechanical membrane configuration that provides direct electrical readout of pressure to strain transduction. This makes it highly relevant for an important class of nanoelectromechanical system (NEMS) transducers. This demonstration is consistent with our simulations and previously reported gauge factors and simulation values. The membrane in our experiment acts as a strain gauge independent of crystallographic orientation and allows for aggressive size scalability. When compared with conventional pressure sensors, the sensors have orders of magnitude higher sensitivity per unit area.

  • 186.
    Soldemo, Markus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Transition metal oxide surfaces: Surface structures and molecular interaction2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Metal oxides are both corrosion products and useful materials with a wide range of applications. Two of the most used metals today are iron and copper. In this thesis, surface structures and molecular interaction with surfaces of iron oxides and copper oxides are studied using spectroscopy and microscopy methods.

     

    The surface structures of iron oxides grown on the low-index iron (Fe) surfaces (100) and (110) have been studied during the initial oxidation phase. The oxidation condition for both iron surfaces was 400 °C and 1×10−6 mbar of oxygen gas. For the Fe(100)-surface, a Fe3O4(100)-film is formed beyond the oxygen adsorbate structures. For the Fe(110)-surface, a FeO(111)-film is first formed. When the FeO(111)-film grows thicker, it transforms into a Fe3O4(111)-film.

     

    The surface structures of Cu2O(100) was studied and the main finding is that the most common surface structure that previously in literature has been described to have a periodicity of (3√2×√2)R45° actually has a periodicity described by the matrix (3,0;1,1). Furthermore, the low-binding energy component in the photoelectron spectroscopy O 1s-spectrum is determined to origin from surface oxygen atoms.

     

    Sulfur dioxide, a corrosive molecule that in the environment to large share comes from human activities such as burning of fossil fuels, was studied using photoelectron spectroscopy when interacting with surfaces of iron oxide thin films and bulk Cu2O-surfaces. On the iron oxide thin film surfaces under ultra-high vacuum conditions, sulfur dioxide adsorbs partly as SO4-species and partly dissociates and forms FeS2. On the Cu2O-surfaces under ultra-high vacuum conditions, the adsorption of sulfur dioxide is non-dissociative and forms SO3-species. When interacting with near-ambient pressures of water, it is observed in the photoelectron spectroscopy S 2p-region that the sulfur from SO3-species shifts to Cu2S.

  • 187.
    Soldemo, Markus
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Halldin Stenlid, Joakim
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Besharat, Zahra
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Ghadami Yazdi, Milad
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Önsten, Anneli
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Leygraf, Christofer
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    The Surface Structure of Cu2O(100)2016Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 8, s. 4373-4381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Despite the industrial importance of copper oxides, the nature of the (100) surface of Cu2O has remained poorly understood. The surface has previously been subject to several theoretical and experimental studies, but has until now not been investigated by atomically resolved microscopy or high-resolution photoelectron spectroscopy. Here we determine the atomic structure and electronic properties of Cu2O(100) by a combination of multiple experimental techniques and simulations within the framework of density functional theory (DFT). Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) characterized the three ordered surface structures found. From DFT calculations, the structures are found to be energetically ordered as (3,0;1,1), c(2 x 2), and (1 x 1) under ultrahigh vacuum conditions. Increased oxygen pressures induce the formation of an oxygen terminated (1 x 1) surface structure. The most common termination of Cu2O(100) has previously been described by a (3 root 2 x root 2)R45 degrees unit cell exhibiting a LEED pattern with several missing spots. Through atomically resolved STM, we show that this structure instead is described by the matrix (3,0;1,1). Both simulated STM images and calculated photoemission core level shifts compare favorably with the experimental results.

  • 188.
    Soldemo, Markus
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Johansson, Niclas
    Besharat, Zahra
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Önsten, Anneli
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Knudsen, Jan
    Schnadt, Joachim
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Cuprous oxide surfaces exposed to sulfur dioxide and near-ambient pressures of waterManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The interaction of sulfur dioxide with Cu2O(100) and Cu2O(111) at ultra-high vac-uum is studied. It is found that on both surfaces, the sulfur dioxide moleculesbind as SO3-species. Dosing water in UHV does not impact the SO3-species at thedoses used. When dosing water at near-ambient pressure conditions, however, itis observed that the sulfur in the SO3-species shifts to Cu2S when monitoring thePES S 2p-region.

  • 189.
    Soldemo, Markus
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Jonas, Weissenrieder
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Oxidation of Fe(100) in oxygen gas at 400 °CManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The oxidation of Fe(100) was studied at an oxygen gas pressure of 1×10−6mbarand a temperature of 400°C. The main findings is that the oxide film, beyond oxy-gen adsorbate structure, is formed by layer-by-layer growth and has a Fe3O4(100)termination.

  • 190.
    Soldemo, Markus
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Lundgren, E.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Oxidation of Fe(110) in oxygen gas at 400 °c2016Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 644, s. 172-179Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The initial oxidation of Fe(110) in oxygen gas at 400 °C beyond initial adsorbate structures has been studied using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy (STM). Formation of several ordered phases of surface oxides is observed at oxygen coverages between approximately 2.3 and 3.5 oxygen atoms/Fe(110) surface atom. Initially, a FeO(111)-like film is formed with a parallelogram-shaped moiré pattern. It has two mirror domains that are formed symmetrically around the growth direction of a zigzag-shaped adsorbate structure. With increased local oxygen coverage, the moiré structure transforms into a ball-shaped form. Both these moiré structures have equal atomic stacking at the surface and equal apparent height in STM, suggesting oxygen ions diffusing into the film upon oxidation and that the oxide growth takes place at the iron-iron oxide interface. The FeO(111)-like film turns into a Fe3O4(111)-like film with a triangular bistable surface termination as the oxidation proceeds further. The FeO(111)-like film growth proceeds according to the Frank-van der Merwe mechanism while the Fe3O4(111)-like film grows according to the Stranski-Krastanov mechanism.

  • 191.
    Soldemo, Markus
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Niu, Yuran
    Zakharov, Alexei
    Lundgren, Edvin
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    A well-ordered surface oxide on Fe(110)2015Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 639, s. 13-19Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A well-ordered surface oxide grown on Fe(110) has been studied using scanning tunneling microscopy (STM), low energy electron diffraction, low energy electron microscopy, and core level photoelectron spectroscopy. The iron oxide film exhibits wide terraces and is formed after exposure to 100-1000 L at 1 x 10(-6) mbar O-2 and 400 degrees C. Two domains, mirror symmetric in the Fe(110)-lattice mirror symmetry planes but otherwise equal, are observed. The surface oxide forms a relatively large coincidence surface unit cell (16.1 angstrom x 26.5 angstrom). Imaging by STM reveals a strong bias dependence in the apparent height within the surface unit cell. The oxygen terminating atomic layer has a hexagonal atomic structure, FeO(111)-like, with the atomic sparing of 3.2 angstrom, that is expanded by similar to 63% relative to bulk FeO(111).

  • 192.
    Soldemo, Markus
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sulfur dioxide interaction with oxidized low-index iron surfacesManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Sulfur dioxide was dosed on thin iron oxides grown on Fe(100) and Fe(110) (fromPaper 1 and Paper 2). It is found that the sulfur dioxide molecules adsorb as SO4-species at room temperature and that some of the adsorbed molecules dissociateupon adsorption and forming FeS2. The oxides corresponding to the lowest dosesof oxygen gas in Paper 1 and Paper 2 were annealed after the sulfur dioxide dos-ing, resulting in increased amount of dissociated molecules. The thicker oxides, onboth surfaces were exposed to another dose of sulfur dioxide, the change of sulfurcoverages show that the surfaces are almost saturated.

  • 193. Stamps, Robert L.
    et al.
    Breitkreutz, Stephan
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Department of Physics, University of Gothenburg, Sweden.
    Chumak, Andrii V.
    Otani, YoshiChika
    Bauer, Gerrit E. W.
    Thiele, Jan-Ulrich
    Bowen, Martin
    Majetich, Sara A.
    Klaeui, Mathias
    Prejbeanu, Ioan Lucian
    Dieny, Bernard
    Dempsey, Nora M.
    Hillebrands, Burkard
    The 2014 Magnetism Roadmap2014Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 47, nr 33, s. 333001-Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Magnetism is a very fascinating and dynamic field. Especially in the last 30 years, there have been many major advances in a range of areas from novel fundamental phenomena to new products. Applications such as hard disc drives and magnetic sensors are part of our daily life and new applications, such as in non-volatile computer random access memory, are expected to surface shortly. Thus it is an opportune time for describing the current status and current and future challenges in the form of a roadmap article. The 2014 Magnetism Roadmap provides a view on several selected, presently very active innovative developments. It consists of twelve sections, each written by an expert in the field and addressing a specific subject, with a strong emphasis on future potential. This Roadmap cannot cover the entire field. Several highly relevant areas have been selected without attempting to provide a full review - a future update will aim to address further. The scope covers mostly nanomagnetic phenomena and applications, where surfaces and interfaces provide additional functionality. New developments in fundamental topics such as interacting nanoelements, novel magnon-based spintronics concepts, spin-orbit torques and spin-caloric phenomena are addressed. New materials such as organic magnetic materials and permanent magnets are covered. New applications are presented such as nanomagnetic logic, non-local and domain-wall based devices, heat-assisted magnetic recording, magnetic random access memory and applications in biotechnology. This Roadmap acts to serve as a guideline for future emerging research directions in modern magnetism.

  • 194. Sugiyama, Jun
    et al.
    Nozaki, Hiroshi
    Harada, Masashi
    Higuchi, Yuki
    Sakurai, Hiroya
    Ansaldo, Eduardo J.
    Brewer, Jess H.
    Keller, Lukas
    Pomjakushin, Vladimir
    Mansson, Martin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Magnetic ground state of novel zigzag chain compounds, NaCr2O4 and Ca1-xNaxCr2O4, determined with muons and neutrons2015Inngår i: 20TH INTERNATIONAL CONFERENCE ON MAGNETISM, ICM 2015, Elsevier, 2015, s. 868-875Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The magnetic nature of a novel one-dimensional compound NaCr2O4 with zigzag CrO2 chains has been studied by muon spin rotation and relaxation (mu+SR) and neutron diffraction (ND). It is found that NaCr2O4 undergoes an antiferromagnetic transition at T-N = 125 K, below which the Cr moments in each zigzag chain align ferromagnetically along the c-axis but antiferromagnetically along the a-axis between adjacent zigzag chains. For the solid solution system Ca1-xNaxCr2O4, mu+SR measurements reveal the evolution of a complex magnetic order with increasing Ca content (1 - x), which finally enters into an incommensurate AF ordered state below T-N = 21 for CaCr2O4.

  • 195. Sugiyama, Jun
    et al.
    Nozaki, Hiroshi
    Harada, Masashi
    Umegaki, Izumi
    Higuchi, Yuki
    Miwa, Kazutoshi
    Imai, Masaki
    Michioka, Chishiro
    Yoshimura, Kazuyoshi
    Ansaldo, Eduardo J.
    Brewer, Jess H.
    Andreica, Daniel
    Baines, Christopher
    Mansson, Martin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Magnetic phases in Sr1-xCaxCo2P2 studied by mu+SR2015Inngår i: 20TH INTERNATIONAL CONFERENCE ON MAGNETISM, ICM 2015, Elsevier, 2015, s. 426-434Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In order to elucidate the dependence of the magnetic ground state on the Ca content (x) in Sr1-xCaxCo2P2 (0 <= x <= 1, ThCr2Si2-type structure), we have performed muon spin rotation and relaxation (mu+SR) experiments on Sr1-xCaxCo2P2 powder samples mainly in a zero applied field. The end member compound, SrCo2P2, is found to be paramagnetic down to 19 mK. As x increases, such a paramagnetic ground state is observed down to 1.8 K until x = 0.45. Then, as x increases further, a short-range antiferromagnetic (AF) ordered phase appears at low temperatures for 0.48 <= x <= 0.75, and finally, a long-range AF ordered phase is stabilized for x > 0.75. The internal magnetic field of the other end member compound, CaCo2P2, is well consistent with that of the A-type AF order state, which was proposed from neutron scattering experiments. The phase diagram determined with mu+SR is different from that proposed by macroscopic measurements. For an isostructural compound, LaCo2P2, static magnetic order is found to be formed below similar to 130 K.

  • 196. Sugiyama, Jun
    et al.
    Nozaki, Hiroshi
    Umegaki, Izumi
    Harada, Masashi
    Higuchi, Yuki
    Miwa, Kazutoshi
    Ansaldo, Eduardo J.
    Brewer, Jess H.
    Imai, Masaki
    Michioka, Chishiro
    Yoshimura, Kazuyoshi
    Månsson, Martin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Variation of magnetic ground state of Sr1-xCaxCo2P2 determined with mu(+) SR2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, nr 14, artikkel-id 144423Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to study the variation of a microscopic internal magnetic field with the Ca content (x), we have systematically measured muon-spin rotation and relaxation (mu+SR) spectra for Sr1-xCaxCo2P2 (0 <= x <= 1) powder samples mainly in a zero external field. As x increases from 0, a Pauli-paramagnetic phase is observed even at the lowest T measured (1.8 K) until x = 0.45; then, a short-range antiferromagnetic (AF) ordered phase appears for 0.48 <= x <= 0.75, and finally a long-range AF ordered phase is stabilized for x >= 0.75. The evolution of the magnetic order is connected to the shrinking of the c-axis length as a function of x, which naturally enhances the AF interaction between the two adjacent Co planes.

  • 197. Sugiyama, Jun
    et al.
    Nozaki, Hiroshi
    Umegaki, Izumi
    Mukai, Kazuhiko
    Miwa, Kazutoshi
    Shiraki, Susumu
    Hitosugi, Taro
    Suter, Andreas
    Prokscha, Thomas
    Salman, Zaher
    Lord, James S.
    Månsson, Martin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Li-ion diffusion in Li4Ti5O12 and LiTi2O4 battery materials detected by muon spin spectroscopy2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, nr 1, artikkel-id 014417Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lithium diffusion in spinel Li4Ti5O12 and LiTi2O4 compounds for future battery applications has been studied with muon spin relaxation (mu+SR). Measurements were performed on both thin-film and powder samples in the temperature range between 25 and 500 K. For Li4Ti5O12 and above about similar to 200 K, the field distribution width (Delta) is found to decrease gradually, while the field fluctuation rate (nu) increases exponentially with temperature. For LiTi2O4, on the contrary, the Delta(T) curve shows a steplike decrease at similar to 350 K, around which the nu(T) curve exhibits a local maximum. These behaviors suggest that Li+ starts to diffuse above around 200 K for both spinels. Assuming a jump diffusion of Li+ at the tetrahedral 8a site to the vacant octahedral 16c site, diffusion coefficients of Li+ at 300 K in the film samples are estimated as (3.2 +/- 0.8) x 10(-11) cm(2)/s for Li4Ti5O12 and (3.6 +/- 1.1) x 10(-11) cm(2)/s for LiTi2O4. Further, some small differences are found in both thermal activation energies and Li-ion diffusion coefficients between the powder and thin-film samples.

  • 198. Sugiyama, Jun
    et al.
    Umegaki, Izumi
    Andreica, Daniel
    Baines, Christopher
    Amato, Alex
    Guignard, Marie
    Delmas, Claude
    Månsson, Martin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Unveiled magnetic transition in Na battery material: mu+SR study of P2-Na0.5VO22015Inngår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 5, nr 24, s. 18531-18537Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated the microscopic magnetic nature of a novel Na battery material, P2-Na0.5VO2, in which V ions form a two-dimensional triangular lattice, by means of muon-spin rotation and relaxation (mu+SR) measurements down to 50 mK. Although magnetization measurements indicated the presence of an antiferromagnetic transition at 13 K, the internal magnetic field due to the formation of magnetic order appears not at 13 K but at 2 K. Furthermore, the magnetic order is found to have a wide field distribution even at 50 mK. Such wide field distribution is reasonably explained by a combination of multiple muon sites and the formation of a long-range magnetic order, while the reliable spin structure is still unknown.

  • 199.
    Suvanam, Sethu Saveda
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Gulbinas, K.
    Usman, M.
    Linnarsson, Margareta
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Martin, David M.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Grivickas, V.
    Hallén, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    4H-silicon carbide-dielectric interface recombination analysis using free carrier absorption2015Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, nr 10, artikkel-id 105309Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, an alternative method to characterize the interface between 4H polytype of Silicon Carbide (4H-SiC) and passivating dielectric layers is established. The studies are made on dielectric-semiconductor test structures using Al2O3 as dielectric on 4H-SiC n-type epitaxial layers. Samples with different pre-and post-dielectric deposition preparations have been fabricated on epilayers of varying thicknesses. Effective lifetimes (tau(eff)) of all the samples were measured by an optical pump-probe method utilizing free carrier absorption (FCA) to analyse the influence of the 4H-SiC/dielectric interface on charge carrier recombination. The relative contribution to tau(eff) from the surfaces increases with decreasing epilayer thickness, and by analysing the data in combination with numerical modelling, it is possible to extract values of the surface recombination velocities (SRVs) for interfaces prepared in different ways. For instance, it is found that SRV for a standard cleaning procedure is 2 x 10(6) cm/s compared to a more elaborate RCA process, yielding a more than 50 times lower value of 3.5 x 10(4) cm/s. Furthermore, the density of interface traps (D-it) is extracted from capacitance-voltage (CV) measurements using the Terman method and a comparison is made between the SRV extracted from FCA measurements and D(it)s extracted from CV measurements on the same structures fabricated with metal contacts. It is observed that the SRV increase scales linearly with the increase in Dit. The strong qualitative correlation between FCA and CV data shows that FCA is a useful characterization technique, which can also yield more quantitative information about the charge carrier dynamics at the interface.

  • 200.
    Sychugov, Ilya
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Pevere, Federico
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Luo, Jun-Wei
    Zunger, Alex
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Single-dot absorption spectroscopy and theory of silicon nanocrystals2016Inngår i: Physical Review B, ISSN 2469-9950, Vol. 93, nr 16, artikkel-id 161413Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Photoluminescence excitation measurements have been performed on single, unstrained oxide-embedded Si nanocrystals. Having overcome the challenge of detecting weak emission, we observe four broad peaks in the absorption curve above the optically emitting state. Atomistic calculations of the Si nanocrystal energy levels agree well with the experimental results and allow identification of some of the observed transitions. An analysis of their physical nature reveals that they largely retain the indirect band-gap structure of the bulk material with some intermixing of direct band- gap character at higher energies.

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