Change search
Refine search result
1234567 1 - 50 of 485
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Abdel-Karim, R.
    et al.
    Department of Metallurgy, Faculty of Engineering, Cairo University.
    Reda, Y.
    Department of Metallurgy, Faculty of Engineering, Cairo University.
    Muhammed, Mamoun A.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    El-Raghy, S.
    Department of Metallurgy, Faculty of Engineering, Cairo University.
    Shoeib, M.
    Metals Technology Department Central Metallurgical Research and Development Institute.
    Ahmed, H.
    Department of Metallurgy, Faculty of Engineering, Cairo University.
    Electrodeposition and Characterization of Nanocrystalline Ni-Fe Alloys2011In: Journal of Nanomaterials, ISSN 1687-4110, E-ISSN 1687-4129, p. 519274-Article in journal (Refereed)
    Abstract [en]

    Nanocrystalline Ni-Fe deposits with different composition and grain sizes were fabricated by electrodeposition. Deposits with iron contents in the range from 7 to 31% were obtained by changing the Ni(2+)/Fe(2+) mass ratio in the electrolyte. The deposits were found to be nanocrystalline with average grain size in the range 20-30 nm. The surface morphology was found to be dependent on Ni(2+)/Fe(2+) mass ratio as well as electroplating time. The grains size decreased with increasing the iron content, especially in case of short time electroplating. Increasing the electroplating time had no significant effect on grain size. The microhardness of the materials followed the regular Hall-Petch relationship with amaximum value (762 Hv) when applying Ni(2+)/Fe(2+) mass ratio equal to 9.8.

  • 2. Achanta, S.
    et al.
    Feuerbacher, M.
    Grishin, Alexander
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Ye, X.
    Celis, J. -P
    On the mechanical and tribological behavior of Al3Mg2 complex metallic alloys as bulk material and as coating2010In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 18, no 11, p. 2096-2104Article in journal (Refereed)
    Abstract [en]

    New materials with tunable physical, mechanical, chemical, and thermal properties are attractive for many applications and stand as prospective substitutes for the existing engineering materials. In that respect, complex metallic alloys (CMA) have recently demonstrated promising traits where a myriad of physical, mechanical, chemical properties can be obtained by altering the structure. CMA's have a large crystal size with thousands of atoms per unit cell. In this work, some mechanical properties and tribological behavior of Al3Mg2 based CMA are discussed. The surface characterization, deformation mode, mechanical and tribological properties of bulk and thin film Al3Mg2 materials are investigated, and compared with existing engineering materials. The results revealed a contrasting tribological behavior of Al3Mg2 when used as either bulk material or as coating. Al3Mg2 coatings act as a low friction solid lubricant under certain conditions, with a coefficient of friction comparable to that of diamond-like carbon coatings. It is suggested that the quasi-crystalline nature of Al3Mg2-coatings renders the surface stiff and that the characteristics of the wear debris generated are responsible for the low friction behavior.

  • 3.
    Adamopoulos, Othon
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Björkman, Eva
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Zhang, Yu
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Bog, Tassilo
    Mussmann, Lothar
    Lox, Egbert
    A nanophase oxygen storage material: Alumina-coated metal-based ceria2009In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 29, no 4, p. 677-689Article in journal (Refereed)
    Abstract [en]

    Nanoparticles of Ce1-xMxO2-delta (M = Ca or Zr) coated with Al2O3 with average crystallite size of 10 nm have been synthesised via solution chemistry approach under controlled chemical and hydrodynamic conditions. Their synthesis has been accomplished in three major steps: (1) simultaneous co-precipitation of cations, (2) sequential precipitation of Al(OH)(3) over the former particles and (3) calcination of the precipitated precursors to the corresponding oxides. Several compositions have been synthesised and their physicochemical properties are compared with commercial state-of-the-art material. The Al2O3-coating hinders the particles growth at high temperatures, resulting in materials with a large specific surface area and a restrain in the decrease of their oxygen storage capacity.

  • 4.
    Afrasiabi, Roodabeh
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sugunan, Abhilash
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Shahid, Robina
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Microwave mediated synthesis of semiconductor quantum dots2012In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 9, no 7, p. 1551-1556Article in journal (Refereed)
    Abstract [en]

    Colloidal quantum dots (QD) have tuneable optoelectronic properties and can be easily handled by simple solution processing techniques, making them very attractive for a wide range of applications. Over the past decade synthesis of morphology controlled high quality (crystalline, monodisperse) colloidal QDs by thermal decomposition of organometallic precursors has matured and is well studied. Recently, synthesis of colloidal QDs by microwave irradiation as heating source is being studied due to the inherently different mechanisms of heat transfer, when compared to solvent convection based heating. Under microwave irradiation, polar precursor molecules directly absorb the microwave energy and heat up more efficiently. Here we report synthesis of colloidal II-VI semiconductor QDs (CdS, CdSe, CdTe) by microwave irradiation and compare it with conventional synthesis based on convection heating. Our findings show that QD synthesis by microwave heating is more efficient and the chalcogenide precursor strongly absorbs the microwave radiation shortening the reaction time and giving a high reaction yield.

  • 5.
    Agnarsson, Björn
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Olafsson, S.
    Gislason, H. P.
    Karlsson, Ulf O.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Influence of initial surface reconstruction on nitridation of Al2O3 (0001) using low pressure ammonia2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 1, p. 013519-Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to investigate the effect of initial surface reconstruction on the nitridation process of Al2O3 (0001). This was done by exposing differently reconstructed sapphire substrates at different temperatures to low pressure ammonia (NH3). Structural and chemical analysis were carried out using low-electron energy diffraction and x-ray photoelectron spectroscopy. The experiments revealed that using low pressure ammonia (P-NH3 < 1 X 10(-5) Torr), no nitridation takes place on (1x1) unreconstructed surfaces. However, when the unreconstructed surface starts to change to a (root 31 x root 31) R +/- 9 degrees reconstructed surface, with increasing substrate temperature, the nitridation becomes successful. When using the initially reconstructed surface, the nitridation is successful even from the lowest temperature used. These results suggest that the initial surface reconstruction has a major effect on the nitridation process. This kinetic behavior has not been reported before, with most nitridation studies mainly focusing on the effect of surface temperature on the resulting surface morphology, rather than the actual kinetics of the process itself.

  • 6.
    Agnarsson, Björn
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Qi, B.
    Szamota-Leandersson, Karolina
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Olafsson, S.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Investigation on the role of indium in the removal of metallic gallium from soft and hard sputtered GaN (0001) surfaces2009In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 517, no 21, p. 6023-6026Article in journal (Refereed)
    Abstract [en]

    Cleaning of GaN by argon sputtering and subsequent annealing introduces metallic gallium on the GaN surface. Once formed, this metallic gallium can be difficult to remove. it has a strong influence on the Fermi level position in the band gap and poses a problem for subsequent epitaxial growth on the surface. We present a method of removing metallic gallium from moderately damaged GaN surfaces by deposition of indium, and formation of an In-Ga alloy that can be desorbed by annealing at similar to 550 degrees C. After the In-Ga alloy has desorbed, photoemission spectra show that the Ga3d bulk component becomes narrower indicating a smoother and more homogeneous surface. This is also reflected in a sharper low energy electron diffraction pattern. On heavily damaged GaN surfaces, caused by hard sputtering, larger amount of metallic gallium forms after annealing at 600 degrees C. This gallium readily alloys with deposited indium, but the alloy does not desorb until a temperature of 840 degrees C is reached and even then, traces of both indium and metallic gallium could be found on the surface.

  • 7.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Chacinski, Marek
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Olsson, Fredrik
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Berrier, Audrey
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Experimental characterization of high-speed 1.55 mu m buried heterostructure InGaAsP/InGaAlAs quantum-well lasers2009In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 26, no 2, p. 318-327Article in journal (Refereed)
    Abstract [en]

    Detailed experimental characterization is performed for 1550 nm semi-insulating regrown buried heterostructure Fabry-Perot (FP) lasers having 20 InGaAsP/InGaAlAs strain-balanced quantum wells (QWs) in the active region. Light-current-voltage performance, electrical impedance, small-signal response below and above threshold, amplified spontaneous emission spectrum below threshold and relative intensity noise spectrum are measured. Different laser parameters such as external differential quantum efficiency eta(d), background optical loss alpha(i), K-factor, D-factor, characteristic temperature T-0, differential gain dg/dn, gain-compression factor epsilon, carrier density versus current, differential carrier lifetime tau(d), optical gain spectrum below threshold, and chirp parameter alpha are extracted from these measurements. The FP lasers exhibited a high T-0 (78-86.5 degrees C) and very high-resonance frequency (23.7 GHz). The results indicate that appropriately designed lasers having a large number of InGaAsP well/InGaAlAs barrier QWs with shallow valence-band discontinuity can be useful for un-cooled high-speed direct-modulated laser applications.

  • 8.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Silfvenius, Christofer
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Design optimization of InGaAsP-InGaAlAs 1.55 mu;m strain-compensated MQW lasers for direct modulation applications2004In: Indium Phosphide and Related Materials, 2004. 16th IPRM. 2004 International Conference on, IEEE , 2004, p. 418-421Conference paper (Refereed)
    Abstract [en]

    A comprehensive simulation study of InGaAsP (well)/InGaAlAs(barrier) 1.55 mu;m strain-compensated MQW lasers is presented. For MQWs, a uniform vertical distribution of holes is achieved due to a reduced effective hole confinement energy by optimizing the bandgap and strain of the barriers and p-doping in the active region. Some preliminary results are also presented for the manufactured lasers using these QWs indicating a good material platform.

  • 9. Alfieri, G.
    et al.
    Monakhov, E. V.
    Svensson, B. G.
    Hallén, Anders.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Defect energy levels in hydrogen-implanted and electron-irradiated n-type 4H silicon carbide2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 98, no 11Article in journal (Refereed)
    Abstract [en]

    Using deep level transient spectroscopy (DLTS), we have studied the energy position and thermal stability of deep levels in nitrogen doped 4H-SiC epitaxial layers after 1.2 MeV proton implantation and 15 MeV electron irradiation. Isochronal annealing was performed at temperatures from 100 to 1200 degrees C in steps of 50 degrees C. The DLTS measurements, which were carried out in the temperature range from 120 to 630 K after each annealing step, reveal the presence of ten electron traps located in the energy range of 0.45-1.6 eV below the conduction band edge (E-c). Of these ten levels, three traps at 0.69, 0.73, and 1.03 eV below E-c, respectively, are observed only after proton implantation. Dose dependence and depth profiling studies of these levels have been performed. Comparing the experimental data with computer simulations of the implantation and defects profiles, it is suggested that these three new levels, not previously reported in the literature, are hydrogen related. In particular, the E-c-0.73 eV level displays a very narrow depth distribution, confined within the implantation profile, and it originates most likely from a defect involving only one H atom.

  • 10. Alfieri, G
    et al.
    Monakhov, EV
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Svensson, BG
    Capacitance spectroscopy study of high energy electron irradiated and annealed 4H-SIC2005In: SILICON CARBIDE AND RELATED MATERIALS 2004 / [ed] Nipoti, R; Poggi, A; Scorzoni, A, ZURICH-UETIKON: TRANS TECH PUBLICATIONS LTD , 2005, Vol. 483, p. 365-368Conference paper (Refereed)
    Abstract [en]

    Deep level transient spectroscopy (DLTS) was employed to investigate the annealing behaviour and thermal stability of radiation induced defects in nitrogen doped 4H-SiC epitaxial layers, grown by chemical vapor deposition (CVD). The epilayers have been irradiated with 15 MeV electrons and an isochronal annealing series has been carried out. The measurements have been performed after each annealing step and six electron traps located in the energy band gap range of 0.42-1.6 eV below the conduction band edge (E-c) have been detected.

  • 11. Altincekic, T. G.
    et al.
    Boz, I.
    Baykal, A.
    Kazan, S.
    Topkaya, R.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis and characterization of CuFe2O4 nanorods synthesized by polyol route2010In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 493, no 1-2, p. 493-498Article in journal (Refereed)
    Abstract [en]

    Uniform, high quality, CuFe2O4 nanorods with high aspect ratios were synthesized by a surfactant-free single step polyol process at 220 degrees C. The structure of the product was characterized by XRD and FT-IR, and the morphology of the product was analyzed by SEM. The results showed that the as-prepared nanorods have a uniform cross-section and with average diameter of similar to 100 nm and aspect ratio in the range of 13-52. X-ray line profile fitting resulted in crystallite size of 15 nm, which reveals the polycrystalline nature of these nanorods. Magnetic characterization of product was performed by EPR and VSM techniques and the results show that the CuFe2O4 nanorods are ferromagnetic. The line width of the resonance lines in FMR is about 1.8 kOe which may originate from different resonance fields of randomly distributed nanocrystals which have different orientation of magnetic easy axes.

  • 12.
    Anand, Srinivasan
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Shahid, Naeem
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Naureen, Shagufta
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Li, Mingyu
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101). Zhejiang University, Hangzhou, China.
    Swillo, Marcin
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    InP-based photonic crystal waveguide filters2010In: 2010 Asia Communications and Photonics Conference and Exhibition, ACP 2010, 2010, p. 104-105Conference paper (Refereed)
  • 13.
    Anand, Srinivasan
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Shahid, Naeem
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Swillo, Marcin
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    InP-Based Photonic Crystal Waveguide Technology for Filtering and Sensing Applications2011In: 2011 13TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS (ICTON), NEW YORK: IEEE , 2011Conference paper (Refereed)
    Abstract [en]

    Photonic crystal (PhC) components in InP-based materials are of practical importance not only for their unique properties but also for integration with conventional optoelectronic components on InP substrate. Several PhC devices in the substrate approach such as filters, lasers, and waveguides have been demonstrated [1,2] and this has been possible due to the development of deep etching of PhCs in InP [3].

  • 14.
    Andersson, Magnus
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    A possible way to use student peer review to improve report writing skills2012Conference paper (Other academic)
  • 15.
    Andersson, Magnus
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Comment on “Superconducting state of Ca-VII below a critical temperature of 29 K at a pressure of 216 GPa”2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 21Article in journal (Refereed)
    Abstract [en]

    In a recent paper, Sakata et al. [ Phys. Rev. B 83 220512 (2011)] report on superconductivity at 29 K in Ca under high pressure. Here, I argue that their method to define the onset of the superconducting transition temperature from resistivity measurements is misleading and that the correct value for the onset of the transition based on resistivity data shown in their paper should be 21 K. The discrepancy between these two temperatures is explained by superconducting fluctuations occurring at temperatures above the superconducting transition temperature.

  • 16.
    Andersson, Magnus
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Helt orimliga förhoppningar2012In: Forskning och framsteg, ISSN 0015-7937, no 2, p. 72-72Article in journal (Other (popular science, discussion, etc.))
  • 17.
    Andersson, Magnus
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    de Boissieu, M.
    Bruehne, S.
    Drescher, C.
    Assmus, W.
    Ohahshi, S.
    Tsai, A. P.
    Mihalkovic, M.
    Krajci, M.
    Rapp, Östen
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Electronic and structural properties of Laves-phase MgZn(2) of varying chemical disorder2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 2, p. 024202-Article in journal (Refereed)
    Abstract [en]

    The C14 Laves-phase MgZn(2) has been investigated from 30 to 36 at. % Mg. In this way chemical disorder can be monitored over a limited concentration range and the influence on electron properties can be investigated. Our studies include thermodynamic calculations of atomic configurations of Mg and Zn at off-stoichiometric compositions, electronic-transport measurements, and electronic band-structure calculations of MgZn(2). The disorder introduced by alloying was found to be substitutional for all C14 alloys, and to have a markedly stronger effect on resistivity and magnetoresistance, Delta rho(B)/rho(0), on the Mg-rich side due to strain introduced when Mg substitutes for Zn. rho(T) and Hall constant were characteristic for weakly disordered binary alloys. Delta rho/rho of MgZn(2) was large, reached 6 at 4.2 K and 8 T, and decreased strongly at off-stoichiometric compositions. The results are discussed in view of the band-structure results and in terms of relations between atomic order and electronic properties. Several properties were found to resemble pure Zn. An empirical correlation over more than six orders of magnitude in Delta rho/rho was found for Zn and Zn-based alloys.

  • 18.
    Andersson, Magnus
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Feuerbacher, M.
    Rapp, Östen
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Magnetoresistance and Hall effect of the complex metal alloy Mg2Al32008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 2Article in journal (Refereed)
    Abstract [en]

    Unusual electronic transport properties have been found in the rhombohedral beta'-phase of the complex metallic alloy Mg2Al3. The magnetoresistance (MR) is 2 orders of magnitude larger than in the related cubic beta-Mg2Al3-phase and Kohler's rule is strongly violated in the beta'-phase at higher temperatures. Above about 100 K the Hall coefficient R-H of the beta- and beta'-phases are similar and free-electron-like, while in the beta'-phase, R-H changes sign with decreasing temperature at low fields. We have inquired into the sources of these transport anomalies, but have not been able to clearly identify the grounds. Several conventional mechanisms for a large magnetoresistance are discussed, and found not to be applicable. The different properties in the beta- and the beta'-phases are puzzling since the magnitudes of the electrical resistivities are similar and omega(c)tau (cyclotron frequencyxscattering time) is equally small in both phases. The similar temperature range in which anomalies occur in the beta'-phase in the resistivity, the Hall effect, and the magnetoresistance indicates an electronic transition or a change of the electron structure in this phase below about 100 K.

  • 19. Aydin, M.
    et al.
    Durmus, Z.
    Kavas, H.
    Esat, B.
    Sozeri, H.
    Baykal, A.
    Yilmaz, F.
    Toprak, Muhammat S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis and characterization of poly(3-thiophene acetic acid)/Fe3O4 nanocomposite2011In: Polyhedron, ISSN 0277-5387, E-ISSN 1873-3719, Vol. 30, no 6, p. 1120-1126Article in journal (Refereed)
    Abstract [en]

    Poly(3-thiophene acetic acid)/Fe3O4 nanocomposite is synthesized by the precipitation of Fe3O4 in the presence of poly(3-thiophene acetic acid) (P3TAA). Structural, surface, morphological, thermal properties and conductivity characterization/evaluation of the nanocomposite were performed by XRD, FT-IR, TEM, TGA. and conductivity measurements, respectively. The capping of P3TAA around Fe3O4 nanoparticles was confirmed by FT-IR spectroscopy, the interaction being via bridging oxygens of the carboxylate and the nanoparticle surface through bidentate binding. The crystallite and particle size were obtained as 9 +/- 2 nm and 11 +/- 1 nm from XRD line profile fitting and TEM image analysis, respectively, which reveal nearly single crystalline nature of Fe3O4 nanoparticles. Magnetization measurements reveal that P3TAA coated magnetite particles do not saturate at higher fields. There is no coercivity and remanence revealing superparamagnetic character. Magnetic particle size calculated from the theoretical fitting as 9.1 nm which coincides the values determined from TEM micrographs and XRD line profile fitting. The comparison to the TEM particle size reveals slightly modified magnetically dead nanoparticle surface.

  • 20. Aydin, M.
    et al.
    Unal, B.
    Esat, B.
    Baykal, A.
    Karaoglu, E.
    Toprak, Muhammet Sadaka
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sozeri, H.
    Synthesis, magnetic and electrical characteristics of poly(2-thiophen-3-yl-malonic acid)/Fe(3)O(4) nanocomposite2012In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 514, p. 45-53Article in journal (Refereed)
    Abstract [en]

    Poly(2-thiophen-3-yl-malonic acid)/Fe(3)O(4) nanocomposite was synthesized by the precipitation of Fe(3)O(4) in the presence of poly(2-thiophen-3-yl-malonic acid) (PT3MA). Characterizations of the nanocomposite were performed by XRD, FT-IR, TEM, TGA, AC/DC conductivity and dielectric measurements. The capping of PT3MA around Fe(3)O(4) nanoparticles was confirmed by FTIR spectroscopy, the interaction being between bridging oxygen of the carboxylate and the nanoparticle surface through bidentate binding. The crystallite particle sizes of 6 +/- 3 nm and 7 +/- 3 nm were obtained from XRD line profile fitting and from TEM image analysis respectively, and they are in good agreement with each other. Magnetization measurements revealed that PT3MA coated magnetite particles do not saturate at higher fields. The material showed superparamagnetic character as revealed by the absence of coercivity and remnant magnetization. Magnetic particle size was calculated as 7.3 +/- 1.0 nm from the mean magnetization term in the Langevin function which is also in conformity with the values determined from TEM micrographs and XRD line profile fitting. The TEM particle size analysis of the nanoparticles revealed the presence of a slightly modified magnetically dead nanoparticle surface. AC and DC conductivity measurements were performed to elucidate the electrical conduction characteristics of the product.

  • 21. Babonas, G. J.
    et al.
    Reza, A.
    Simkiene, I.
    Sabataityte, J.
    Baran, M.
    Szymczak, R.
    Karlsson, Ulf O.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Suchodolski, Arturas
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Optical properties of Fe-doped silica films on Si2006In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 252, no 15, p. 5391-5394Article in journal (Refereed)
    Abstract [en]

    Optical properties of Fe-doped silica films on Si were investigated by ellipsometric technique in the region 1-5 eV. Samples were produced by sol-gel method. Precursors were prepared by mixing tetraethoxysilane (TEOS) solution in ethanol and water with aqueous solution of Fe-chloride or Fe-acetate. The coating solution was deposited on Si substrates by spin on technique. The size of Fe-containing nanometric-sized particles depended on technology and varied from 20 to 100 nm. Optical response of complex hybrid samples SiO2:Fe/Si was interpreted in a multi-layer model. In the inverse problem, the Maxwell equations were solved by transfer matrix technique. Dielectric function of Fe-doped silica layers was calculated in the model of effective media. Analysis of optical data has shown that various Fe-oxides formed. Experimental data for films obtained from precursors with Fe-acetate and annealed in hydrogen were well described by the model calculations taking into account a small contribution 1-5% of metal Fe imbedded in silica. The Fe/Fe-O contribution to optical response increased for samples grown from FeCl3-precursor. Ellipsometric data for Fe-doped silica films on Si were interpreted taking into account the structural AFM studies as well as the results of magnetic measurements.

  • 22. Baek, J. H.
    et al.
    Soares, F. M.
    Seo, S. W.
    Jiang, W.
    Fontaine, N. K.
    Broeke, R. G.
    Cao, J.
    Olsson, Fredrik
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Yoo, S. J. B.
    10-GHz and 20-GHz channel spacing high-resolution AWGs on InP2009In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 21, no 5, p. 298-300Article in journal (Refereed)
    Abstract [en]

    This letter reports on 10-GHz and 20-GHz channel-spacing arrayed waveguide gratings (AWGs) based on InP technology. The dimensions of the AWGs are 6.8 × 8.2 mm2 and 5.0 × 6.0 mm2, respectively, and the devices show crosstalk levels of 12 dB for the 10-GHz and 17 dB for the 20-GHz AWG without any compensation for the phase errors in the arrayed waveguides. The root-mean-square phase errors for the center arrayed waveguides were characterized by using an optical vector network analyzer, and are 18° for the 10-GHz AWG and 28° for the 10-GHz AWG.

  • 23. Baykal, A.
    et al.
    Bitrak, N.
    Ünal, B.
    Kavas, H.
    Durmus, Z.
    Özden, S.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Polyol synthesis of (polyvinylpyrrolidone) PVP-Mn3O4 nanocomposite2010In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 502, no 1, p. 199-205Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis of (polyvinylpyrrolidone) PVP-Mn3O4 nanocomposite via a polyol route. Crystalline phase was identified as Mn3O4 and the crystallite size was obtained as 6 +/- 1 nm from X-ray line profile fitting. Average particle size of 6.1 +/- 0.1 nm obtained from TEM analysis reveals nearly single crystalline nature of these nanoparticles in the composite. The capping of PVP around Mn3O4 nanoparticles was confirmed by FT-IR spectroscopy, the interaction being via bridging oxygens of the carbonyl (C=O) and the nanoparticle surface. T-C and T-B for PVP-Mn3O4 nanocomposite were observed at 42K and 28.5 K, respectively. The sample has hysteresis with small coercivity and remanent magnetization at 40K, resembling the superparamagnetic state. ac conductivity measurements on PVP-Mn3O4 nanocomposite revealed a conductivity in the order of 10(-7) S cm(-1) at lower frequencies. The conductivity change with respect to frequency can be explained by electronic exchange occurring between Mr(+2) and Mn+3 existing in sublattice of spinel lattice.

  • 24. Baykal, A.
    et al.
    Deligöz, H.
    Sozeri, H.
    Durmus, Z.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Triethylene Glycol Stabilized CoFe2O4 Nanoparticles2012In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 25, no 6, p. 1879-1892Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis and detailed composition, thermal, micro-structural, ac-dc conductivity performance and dielectric permittivity characterization of triethylene glycol (TREG) stabilized CoFe 2O 4 nanoparticles synthesized by polyol method. XRD analysis confirmed the inorganic phase as CoFe 2O 4 with high phase purity. Microstructure analysis with TEM revealed well separated, spherical nanoparticles in the order of 6 nm, which is also confirmed by X-ray line profile fitting. FT-IR analysis confirms that TREG is successfully coated on the surface of nanoparticles. Overall conductivity of nanocomposite is approximately two magnitudes lower than that of TREG with increase in temperature. The ac conductivity showed a temperature dependent behavior at low frequencies and temperature independent behavior at high frequencies which is an indication of ionic conductivity. The dc conductivity of the nanocomposites and pure TREG are found to obey the Ar- rhenius plot with dc activation energies of 0.258 eV and 0.132 eV, respectively. Analysis of dielectric permittivity functions suggests that ionic and polymer segmental motions are strongly coupled in the nanocomposite. TREG stabilized CoFe 2O 4 nanoparticles has lower ε and ε than that of pure TREG due to the doping of cobalt. As the temperature increases, the frequency at which (ε ) reaches a maximum shifted towards higher frequencies. On the other hand, the activation energy of TREG for relaxation process was found to be 0.952 eV which indicates the predominance of electronic conduction due to the chemical nature of TREG. Contrarily, no maximum peak of tan Ύ was observed for the nanocomposite due to the being out of temperature and frequency range applied in the study.

  • 25. Baykal, A.
    et al.
    Durmus, Z.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sozeri, H.
    Synthesis and characterization of PEG-Sr hexaferrite by sol-gel conversion2012In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 25, no 6, p. 2003-2008Article in journal (Refereed)
    Abstract [en]

    Sr-M-type hexagonal ferrites have been prepared via a sol-gel route, and the effects of addition of different molecular weight polyethylene glycol (PEG) into the sol solutions on the static magnetic properties and particle morphology have been studied. Crystalline phases of the samples were determined by XRD analysis. FT-IR and TG analyses were used to prove the presence of PEG on SrFe12O19. The results showed that adding PEG with different molecular weight into the sol solutions affected the formation mechanism of SrFe12O19. Sr-M precursors prepared by various PEG types show different magnetic behaviors after precalcination at 150 degrees C. This discrepancy is explained by the formation of a different phase during the synthesis of SrM particles.

  • 26.
    Baykal, A.
    et al.
    Fatih Univ, Istanbul, Turkey.
    Toprak, M. S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Durmus, Z.
    Fatih Univ, Istanbul, Turkey.
    Senel, M.
    Fatih Univ, Istanbul, Turkey.
    Sozeri, H.
    Natl Metrol Inst, Gebze, Kocaeli, Turkey.
    Demir, A.
    Fatih Univ, Istanbul, Turkey.
    Synthesis and Characterization of Dendrimer-Encapsulated Iron and Iron-Oxide Nanoparticles2012In: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, ISSN 1557-1939, Vol. 25, no 5, p. 1541-1549Article in journal (Refereed)
    Abstract [en]

    In this paper, a series of iron (Fe) containing nanoparticles were prepared by employing PAMAM (Poly(amidoamine), dendrimers with different generations (G0-G3) as templates and sodium borohydride as a reducing agent. The products have been characterized by TEM, FT-IR, XRD, VSM, TGA, and XPS. XRD analysis reveal low crystallinity of formed particles within the dendrimers, however, crystallinity of the nanoparticles was observed to increase with increasing generation of dendrimers. Dominant phases were determined as magnetite (Fe3O4 or maghemite, gamma-Fe2O3). XPS analysis revealed the chemical composition of nanoparticles as iron oxide which indicated the oxidation of Fe species subsequent to the reduction process, in agreement with XRD analysis. The magnetization curves have superparamagnetic nonhysteretic characteristic at lower fields and with nonsaturation characteristic at high fields. Magnetic evaluation of samples with the 20:1 molar ratio of Fe:PAMAM showed decreasing superparamagnetic character and decreasing saturation magnetisation with increasing generation of dendrimers.

  • 27. Baykal, A.
    et al.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Durmus, Z.
    Sozeri, H.
    Hydrothermal synthesis of SrFe 12O 19 and its characterization2012In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 25, no 6, p. 2081-2085Article in journal (Refereed)
    Abstract [en]

    We have synthesized strontium hexaferrite particles in an alkaline medium using a hydrothermal process at 180°C. Crystalline phase of samples were determined by XRD and spectroscopic, morphological, and magnetic investigation of the sample were FT-IR, SEM, and TG analysis, respectively. XRD analysis revealed few impurity phases in the as-made powder; upon calcinations, the material is converted to desired hexaferrite phase. As synthesized powder exhibits agglomerates with rather smooth facets, in the form of thick platelets. Upon calcination, all these structures were observed to transfer to rod-like structures. The As calcined sample has high specific saturation magnetization (Ms ) values of 65 emu/g that is close to its theoretical value of 74.3 emu/g but the hydrothermally synthesized sample does not. This is in agreement with the observations from XRD analysis where few impurity phases observed in the as-made powder cause a weak magnetic response. Upon calcination, the material is converted to a desired hexaferrite phase with better magnetic properties.

  • 28. Baykal, Abdulhadi
    et al.
    Kasapoglu, Nermin
    Durmus, Zehra
    Kavas, Hueseyin
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Koeseoglu, Yueksel
    CTAB-Assisted Hydrothermal Synthesis and Magnetic Characterization of NixCo1-xFe2O4 Nanoparticles (x=0.0, 0.6, 1.0)2009In: Turkish journal of chemistry, ISSN 1300-0527, E-ISSN 1303-6130, Vol. 33, no 1, p. 33-45Article in journal (Refereed)
    Abstract [en]

    Nickel ferrite, NixCo1-xFe2O4, NPs (where x = 0.0, 0.6 and 1.0) were successfully synthesized by a rapid and reproducible CTAB-assisted hydrothermal route. The influence of different hydrolyzing agents on the particle size and magnetic behavior of NixCo1-xFe2O4 NPs was investigated. Particles showed very high phase purity and crystallinity in powder XRD analysis. Compositions of Co, Fe, and Ni in fabricated powders were also determined by AAS and results are in very good agreement with the targeted compositions. Samples hydrolyzed using NH3 showed no significant changes in the particle size and morphology. NH3 hydrolyzed samples were much smaller than their NaOH hydrolyzed counterparts, which was attributed to the strength and concentration of the hydrolyzing agents, NH3 being about 6 times more concentrated than NaOH. This in turn influenced the nucleation rate thus the size of each nucleus formed. Strong temperature and Ni concentration dependence of magnetic parameters was observed. These samples are considered as promising materials for high density magnetic recording media.

  • 29. Baykal, Abdulhadi
    et al.
    Kavas, Hueseyin
    Durmus, Zehra
    Demir, Mine
    Kazan, Sinan
    Topkaya, Ramazan
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sonochemical synthesis and chracterization of Mn3O4 nanoparticles2010In: Central European Journal of Chemistry, ISSN 1895-1066, Vol. 8, no 3, p. 633-638Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis of Mn3O4 nanoparticles (NPs) using a novel sonochemical method without requiring any pH adjustment. Synthesized material was identified as tetragonal hausmannite crystal structure model of Mn3O4 from XRD analysis. Crystallite size was estimated from x-ray line profile fitting to be 17 +/- 5 nm. FTIR analysis revealed stretching vibrations of metal ions in tetrahedral and octahedral coordination confirming the crystal structure. TEM analysis revealed a dominantly cubic morphology of NPs with an average size of similar to 20 nm. Magnetic evaluation revealed a blocking temperature, T-B of 40 K above which the material behaves paramagnetic. Asymmetric coercive field is attributed to the interaction between ferromagnetic Mn3O4 and antiferromagnetic Mn oxide at the surface of nanoparticles.

  • 30.
    Bergqvist, Hans
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Chen, J.
    Jädernäs, D.
    Bengtsson, B.
    CHaracterization of PWR CRUD phases and their variation under plant operation by transmission electron microscopy2009In: 14th International Conference on Environmental Degradation of Materials in Nuclear Power Systems Water Reactors 2009, 2009, p. 1136-1147Conference paper (Refereed)
    Abstract [en]

    The solid particles suspended and circulated in PWR primary water may consist of fuel CRUD, solid corrosion products of water-contacting materials, additives and various impurities of reactor water. This paper demonstrates a new methodology by using transmission electron microscopy to characterize the phase compositions of CRUD particles and their variation under reactor operation. Several new CRUD phases have been imaged and confirmed by energy dispersive X-ray spectroscopy and selected area electron diffraction studies. The differences in CRUD phase composition between scraped fuel CRUD, CRUD from primary water in an event of elevated Co-58 activity or shutdown or H 2O 2 injection are reported and discussed with respect to the thermodynamic stability of some phases and possible chemical reactions involved.

  • 31.
    Bergsåker, Henric
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Litnovsky, A.
    Ogata, Douglas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Sahle, Wubeshet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Studies of mobile dust in scrape-off layer plasmas using silica aerogel collectors2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 415, no 1, p. S1089-S1093Article in journal (Refereed)
    Abstract [en]

    Dust capture with ultralow density silica aerogel collectors is a new method, which allows time resolved in situ capture of dust particles in the scrape-off layers of fusion devices, without substantially damaging the particles. Particle composition and morphology, particle flux densities and particle velocity distributions can be determined through appropriate analysis of the aerogel surfaces after exposure. The method has been applied in comparative studies of intrinsic dust in the TEXTOR tokamak and in the Extrap T2R reversed field pinch. The analysis methods have been mainly optical microscopy and SEM. The method is shown to be applicable in both devices and the results are tentatively compared between the two plasma devices, which are very different in terms of edge plasma conditions, time scale, geometry and wall materials.

  • 32.
    Berntsen, Magnus H.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Götberg, Olof
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    An experimental setup for high resolution 10.5 eV laser-based angle-resolved photoelectron spectroscopy using a time-of-flight electron analyzer2011In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 82, no 9, p. 095113-Article in journal (Refereed)
    Abstract [en]

    We present an experimental setup for laser-based angle-resolved time-of-flight photoemission. Using a picosecond pulsed laser, photons of energy 10.5 eV are generated through higher harmonic generation in xenon. The high repetition rate of the light source, variable between 0.2 and 8 MHz, enables high photoelectron count rates and short acquisition times. By using a time-of-flight analyzer with angle-resolving capabilities, electrons emitted from the sample within a circular cone of up to +/- 15 degrees can be collected. Hence, simultaneous acquisition of photoemission data for a complete area of the Brillouin zone is possible. The current photon energy enables bulk sensitive measurements, high angular resolution, and the resulting covered momentum space is large enough to enclose the entire Brillouin zone in cuprate high-T(c) superconductors. Fermi edge measurements on polycrystalline Au shows an energy resolution better than 5 meV. Data from a test measurement of the Au(111) surface state are presented along with measurements of the Fermi surface of the high-T(c) superconductor Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212).

  • 33.
    Berntsen, Magnus H.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Palmgren, P.
    Leandersson, M.
    Hahlin, A.
    Åhlund, J.
    Wannberg, B.
    Mansson, M.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    A spin- and angle-resolving photoelectron spectrometer2010In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 81, no 3Article in journal (Refereed)
    Abstract [en]

    A new type of hemispherical electron energy analyzer that permits angle and spin resolved photoelectron spectroscopy has been developed. The analyzer permits standard angle resolved spectra to be recorded with a two-dimensional detector in parallel with spin detection using a mini-Mott polarimeter. General design considerations as well as technical solutions are discussed and test results from the Au(111) surface state are presented.

  • 34.
    Berrier, Audrey
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Shi, Yaocheng
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Siegert, Jörg
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Marcinkevicius, Saulius
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    He, Sailing
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Accumulated sidewall damage in dry etched photonic crystals2009In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 27, no 4, p. 1969-1975Article in journal (Refereed)
    Abstract [en]

    Evidence for accumulated damage is provided by investigating the effect of etch duration on the carrier lifetime of an InGaAsP quantum well (QW) inside the InP-based photonic crystal (PhC) structures. It is found that once the quantum well is etched through, additional etching reduces the carrier lifetimes from 800 to 70 ps. The surface recombination velocity (SRV) at the exposed hole sidewalls is determined from the measured carrier lifetimes of the PhC fields with different lattice parameters. The observed variation in the SRV with etch duration also confirms the presence of accumulated sidewall damage. It increases from 6x10(3) to 1.2x10(5) cm s(-1) as the etching time increases from 3 to 50 min. A geometric model based on sputtering theory and on the evolution of the hole shape is developed to explain the accumulation of sidewall damage. The model is used to estimate the number of impact events from sputtered species reaching the QW sidewalls, and the variation in the accumulated impact events with etch duration is shown to be qualitatively consistent with the experimental observations. Finally, the results suggest a new method for tailoring the carrier lifetimes in PhC membrane structures.

  • 35.
    Berrier, Audrey
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Shi, Yaocheng
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Siegert, Jörg
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Marcinkevicius, Saulius
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Srinivasan, Anand
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Impact of dry-etching induced damage in InP-based photonic crystals2008In: PHOTONIC CRYSTAL MATERIALS AND DEVICES VIII, 2008, Vol. 6989, p. U9890-U9890Conference paper (Refereed)
    Abstract [en]

    In this work variations of the carrier lifetime in a GaInAsP/InP quantum well in two-dimensional PhC structures etched by Ar/Cl-2 chemically assisted ion beam etching as a function of the processing parameters is investigated. It is shown that the deposition conditions of the SiO2 mask material and its coverage as well as other process steps such as annealing affect the carrier lifetimes. However the impact of patterning the semiconductor on the carrier lifetime is dominant, showing over an order of magnitude reduction. For given PhC lattice parameters, the sidewall damage is shown to be directly related to the measured carrier lifetimes. A simple qualitative model based on sputtering theory and assuming a conical hole-shape development during etching is used to explain the experimental results.

  • 36. Birsoz, B.
    et al.
    Baykal, A.
    Sozeri, H.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis and characterization of polypyrrole-BaFe12O19 nanocomposite2010In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 493, no 1-2, p. 481-485Article in journal (Refereed)
    Abstract [en]

    Polypyrrole-BaFe12O19 nanocomposite was successfully synthesized by an in situ polymerization of pyyrole in the presence of synthesized BaFe12O19 nanoparticles. Structural, morphological, electrical and magnetic properties of the nanocomposite were performed by XRD, FT-IR, TEM, TGA, VSM and ac conductivity measurements respectively. XRD analysis reveals the inorganic phase as bariumhexaferrite and TGA shows about 22 wt% loading of hexaferrite in the nanocomposite. FT-IR analysis indicates a successful conjugation of hexaferrite particles with polypyrrole. Magnetization measurements show that polypyrrole coating decreases the saturation magnetization of BaFe12O19 significantly. This reduction has been explained by the pinning of the surface spins by the possible adsorption of non-magnetic ions during the polymerization process. Interactions between the hard and impurity phases, determined using the Stoner-Wohlfarth theory, reveal that particles' single domain character and the coating destabilizes the remanence state of the polypyrrole-BaFe12O19 nanocomposite.

  • 37.
    Blomqvist, Mats
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Khartsev, Sergiy
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Grishin, Alexander M.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Electro-optic effect in ferroelectric Na0.5K0.5NbO3 thin films on oxide substrates2006In: Integrated Ferroelectrics, ISSN 1058-4587, E-ISSN 1607-8489, Vol. 80, no 1, p. 97-106Article in journal (Refereed)
    Abstract [en]

    We have deposited Na0.5NbO3 (NKN) films oil single crystal Al2O3(1 (1) under bar 02) and SrTiO3(001) substrates using rf-magnetron sputtering of a stoichiometric, high-density ceramic target. Using x-ray diffraction it was confirmed that NKN grows preferentially c-axis oriented on sapphire substrate and epitaxially oil the perovskite SrTiO3(001) substrate. Electro-optical (EO) properties were measured in visible light through a transverse method. With an applied dc field up to 20 kV/cm, the effective linear EO response was determined to r(eff) = 28 pm/V for NKN/Al2O3 and r(eff) = I I pm/V for NKN/SrTiO3, where a superlinear dependence was observed.

  • 38.
    Blomqvist, Mats
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Khartsev, Sergiy
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Grishin, Alexander M.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Electrooptic ferroelectric Na0.5K0.5NbO3 films2005In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 17, no 8, p. 1638-1640Article in journal (Refereed)
    Abstract [en]

    We report on waveguiding and electrooptic properties of epitaxial Na0.5K0.5NbO3 films grown by radio-frequency magnetron sputtering on Al2O3 (1102) single crystal substrates. High optical waveguiding performance has been demonstrated in infrared and visible light. The in-plane electrooptic effect has been recorded in transmission using a transverse geometry. At dc fields, the effective linear electrooptic coefficient was determined to 28 pm/V, which is promising for modulator applications.

  • 39.
    Blomqvist, Mats
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Khartsev, Sergiy
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Grishin, Alexander M.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Visible and IR light waveguiding in ferroelectric Na0.5K0.5NbO3 thin films2005In: Integrated Ferroelectrics, ISSN 1058-4587, E-ISSN 1607-8489, Vol. 69, p. 277-286Article in journal (Refereed)
    Abstract [en]

    High-quality ferroelectric thin films are attractive materials for integrated optics applications including electro-optic waveguide modulators and frequency doubling secondharmonic generators. Several fefroelectric thin film materials, such as BaTiO3, KNbO3, LiNbO3, and (Pb,La)(ZrTi)O-3, have been investigated regarding their optical and waveguiding properties. Recently the first results on waveguiding in ferroelectric Na0.5K0.5NbO3 (NKN) thin films were presented. Perovskite NKN films have previously been investigated as electrically tunable material for low loss rf and microwave applications. Na0.5K0.5NbO3 thin films of thickness 0.5-1.0 mum have been deposited on Nd:YAlO3(001) and Al2O3(0112) substrates using rf-magnetron sputtering of a stoichiometric, high-density ceramic target. X-ray diffraction measurements confirmed films grown highly (00l) oriented on the perovskite Nd:YAlO3 substrate and preferentially c-axis oriented on the single crystal r-cut sapphire substrate. Optical and waveguiding properties were characterized using a Metricon 2010 prism-coupling apparatus with a rutile prism. Dark-line spectra were obtained at visible light (lambda = 632.8 nm) as well as at infrared optical communication wavelengths, lambda = 1319 nm and lambda = 1549 nm, in both transverse electric (TE) and transverse magnetic (TM) polarizations. Sharp dips corresponding to waveguide propagation modes in the thin film layers where observed for both substrates. The calculated refractive index values and corresponding birefringence (Deltan = n(TM) - n(TE) = n(e) - n(o)) as a function of wavelength has been compared. Generally a larger birefringence is observed for the NKN film on Nd:YAlO3, which is in agreement with the larger degree of preferential c-axis orientation measured by XRD.

  • 40.
    Bonanni, Valentina
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Bonetti, Stefano
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Pakizeh, Tavakol
    Pirzadeh, Zhaleh
    Chen, Jianing
    Nogues, Josef
    Vavassori, Paolo
    Hillenbrand, Rainer
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Dmitriev, Alexandre
    Designer Magnetoplasmonics with Nickel Nanoferromagnets2011In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 12, p. 5333-5338Article in journal (Refereed)
    Abstract [en]

    We introduce a new perspective on magnetoplasmonics in nickel nanoferromagnets by exploiting the phase tunability of the optical polarizability due to localized surface plasmons and simultaneous magneto-optical activity. We demonstrate how the concerted action of nanoplasmonics and magnetization can manipulate the sign of rotation of the reflected light's polarization (i.e., to produce Kerr rotation reversal) in ferromagnetic nanomaterials and, further, how this effect can be dynamically controlled and employed to devise conceptually new schemes for biochemosensing.

  • 41.
    Bonetti, Stefano
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Magnetization Dynamics in Nano-Contact Spin Torque Oscillators: Solitonic bullets and propagating spin waves2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Magnetization dynamics in nano-contact spin torque oscillators (STOs) is investigated from an experimental and theoretical point of view. The fundamentals of magnetization dynamics due to spin transfer torque are given.

    A custom-made high frequency (up to 46 GHz) in large magnetic fields (up to 2.2 T) microwave characterization setup has been built for the purpose and described in this thesis. A unique feature of this setup is the capability of applying magnetic fields at any direction θe out of the sample plane, and with high precision.

    This is particularly important, because the (average) out-of-plane angle of the STO free magnetic layer has fundamental impact on spin wave generation and STO operation.

    By observing the spin wave spectral emission as a function of θe, we find that at angles θe below a certain critical angle θcr, two distinct spin wave modes can be excited: a propagating mode, and a localized mode of solitonic character (so called spin wave bullet). The experimental frequency, current threshold and frequency tuneability with current of the two modes can be described qualitatively by analytical models and quantitatively by numerical simulations. We are also able to understand the importance, so far underestimated, of the Oersted field in the dynamics of nano-contact STOs. In particular, we show that the Oersted field strongly affects the current tuneability of the propagating mode at subcritical angles, and it is also the fundamental cause of the mode hopping observed in the time-domain. This mode hopping has been observed both experimentally using a state-of-the-art real-time oscilloscope and corroborated by micromagnetic simulations. Micromagnetic simulations also reveal details of the spatial distribution of the spin wave excitations.

    By investigating the emitted power as a function of θe, we observed two characteristic behaviors for the two spin wave modes: a monotonic increase of the power for increasing out-of-plane angles in the case of the propagating mode; an increase towards a maximum power followed by a drop of it at the critical angle for the localized mode. Both behaviors are reproduced by micromagnetic simulations. The agreement with the simulations offers also a way to better understand the precession dynamics, since the emitted power is strongly connected to the angular variation of the giant magnetoresistance signal.

    We also find that the injection locking of spin wave modes with a microwave source has a strong dependence on θe, and reaches a maximum locking strength at perpendicular angles. We are able to describe these results in the theoretical framework of non-linear spin wave dynamics.

  • 42.
    Bonetti, Stefano
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Consolo, G.
    Finocchio, G.
    Eklund, A.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Mancoff, F.
    Azzerboni, B.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Time-space analysis of spin wave  dynamics in nano-contact spin torque oscillatorsManuscript (preprint) (Other academic)
  • 43.
    Bonetti, Stefano
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    de Vreede, Niels
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Conte, Gianluca
    Finocchio, Giovanni
    Mancoff, Fred
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Phase locking of nanocontact spin torque osillators as a function of applied field angleManuscript (preprint) (Other academic)
  • 44.
    Bonetti, Stefano
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Kim, Jang-Yong
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Khartsev, Sergiy
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Grishin, Alexander
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Buried tantalate-niobate microwave varactors2007In: 2006 15TH IEEE INTERNATIONAL SYMPOSIUM ON APPLICATIONS OF FERROELECTRICS, 2007, p. 347-350Conference paper (Refereed)
    Abstract [en]

    We present characteristics of microwave variable capacitors (varactors) buried in 2.5 mu m thick AgTa0.5Nb0.5O3 (ATN) film pulsed laser deposited on sapphire single crystal. 2 gm gap interdigital capacitors (IDC) were fabricated by photolithographic, dry etching and lift-off processes. For comparison, similar IDCs were also defined on top of ATN film. Capacitance and loss tangent have been determined using a modified de-embedding technique in the microwave range 25 MHz - 40 GHz. Buried structures show higher values of capacitance and tunability, keeping the same level of losses compared to standard topped devices and resulting in an increased K-factor = tunability/tan delta. Experimental results are explained within equivalent circuit model. Besides the increased performance, the new design avoids the need of a successive planarization step, which could be required in an integration process.

  • 45.
    Bonetti, Stefano
    et al.
    Stanford University.
    Pulisgiyo, Vito
    Consolo, Giancarlo
    Mancoff, Fred
    Tiberkevich, Vasyl S.
    Slavin, Andrei N.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Power and linewidth of propagating and localized modes in nanocontact spin-torque oscillators2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 17, p. 174427-Article in journal (Refereed)
    Abstract [en]

    The integrated power and linewidth of a propagating and a self-localized spin-wave mode excited by spin-polarized current in an obliquely magnetized magnetic nanocontact are studied experimentally as functions of the angle theta(e) between the external bias magnetic field and the nanocontact plane. It is found that the power of the propagating mode increases monotonically with theta(e), while the power of the self-localized mode has a broad maximum near theta(e) = 40 degrees and exponentially vanishes near the critical angle theta(e) = 58 degrees, at which the localized mode disappears. The linewidth of the propagating mode in the interval of angles 58 degrees < theta(e) < 90 degrees, where only this mode is excited, is adequately described by the existing theory, while in the angular interval where both modes can exist the observed linewidth of both modes is substantially broadened due to the telegraph switching between the modes. Numerical simulations and an approximate analytical model give a good semiquantitative description of the observed results.

  • 46.
    Bonetti, Stefano
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Tiberkevich, Vasil
    Consolo, Giancarlo
    Finocchio, Giovanni
    Muduli, Pranaba
    Mancoff, Fred
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Experimental evidence of self-localized and propagating spin wave modes in obliquely magnetized current-driven magnetic nanocontacts2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, no 21, p. 217204-Article in journal (Refereed)
    Abstract [en]

    Through detailed experimental studies of the angular dependence of spin wave excitations in nanocontact-based spin-torque oscillators, we demonstrate that two distinct spin wave modes can be excited, with different frequency, threshold currents, and frequency tunability. Using analytical theory and micromagnetic simulations we identify one mode as an exchange-dominated propagating spin wave, and the other as a self-localized nonlinear spin wave bullet. Wavelet-based analysis of the simulations indicates that the apparent simultaneous excitation of both modes results from rapid mode hopping induced by the Oersted field.

  • 47.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Sangghaleh, Fatemeh
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Fabricating single silicon quantum rods for repeatable single dot photoluminescence measurements2011In: Physica Status Solidi A-applications and materials science, ISSN 1862-6319, Vol. 208, no 3, p. 631-634Article in journal (Refereed)
    Abstract [en]

    A fabrication method for a matrix pattern of laterally separated silicon quantum rods was developed, consisting of a three-step recipe utilizing electron beam lithography (EBL), reactive ion etching (RIE), and oxidation. Photoluminescence (PL) measurements -images, spectra, and blinking-verified that the presented method results in a high number of luminescing single silicon quantum rods in well defined positions on the sample. These are suitable for single dot spectroscopy and repeatable measurements, even using different measurement methods and instruments. [GRAPHICS] Colorized scanning electron microscope images of undulating silicon nanowalls for controlled single quantum rod fabrication.

  • 48.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Valenta, Jan
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Controlled fabrication of individual silicon quantum rods yielding high intensity, polarized light emission2009In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 20, no 50, p. 1-5Article in journal (Refereed)
    Abstract [en]

    Elongated silicon quantum dots (also referred to as rods) were fabricated using a lithographic process which reliably yields sufficient numbers of emitters. These quantum rods are perfectly aligned and the vast majority are spatially separated well enough to enable single-dot spectroscopy. Not only do they exhibit extraordinarily high linear polarization with respect to both absorption and emission, but the silicon rods also appear to luminesce much more brightly than their spherical counterparts. Significantly increased quantum efficiency and almost unity degree of linear polarization render these quantum rods perfect candidates for numerous applications.

  • 49.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Valenta, Jan
    Sangghaleh, Fatemeh
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Blinking Statistics of Silicon Quantum Dots2011In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 12, p. 5574-5580Article in journal (Refereed)
    Abstract [en]

    The blinking statistics of numerous single silicon quantum dots fabricated by electron-beam lithography, plasma etching, and oxidation have been analyzed. Purely exponential on- and off-time distributions were found consistent with the absence of statistical aging. This is in contrast to blinking reports in the literature where power-law distributions prevail as well as observations of statistical aging in nanocrystal ensembles. A linear increase of the switching frequency with excitation power density indicates a domination of single-photon absorption processes, possibly through a direct transfer of charges to trap states without the need for a bimolecular Auger mechanism. Photoluminescence saturation with increasing excitation is not observed; however, there is a threshold in excitation (coinciding with a mean occupation of one exciton per nanocrystal) where a change from linear to square-root increase occurs. Finally, the statistics of blinking of single quantum dots in terms of average on-time, blinking frequency and blinking amplitude reveal large variations (several orders) without any significant correlation demonstrating the individual microscopic character of each quantum dot.

  • 50.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Valenta, Jan
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Mitsushi, Kazutaka
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Transition fromsilicon nanowires to isolated quantum dots: Optical and structural evolution2009Manuscript (preprint) (Other (popular science, discussion, etc.))
1234567 1 - 50 of 485
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf