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  • 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.
    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.

  • 3.
    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.

  • 4. 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.

  • 5. 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.

  • 6. 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.

  • 7. 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.

  • 8. 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.

  • 9. 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.

  • 10.
    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.

  • 11. 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.

  • 12. 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.

  • 13. 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.

  • 14.
    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.

  • 15.
    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.

  • 16. 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.

  • 17. Chen, J.
    et al.
    Bergqvist, Hans
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Jädernäs, D.
    Granath, G.
    High resolution electron microscopy study on the thin oxide films formed on type 316L stainless steel exposed under simulated BWR water chemistry conditions2009In: 14th International Conference on Environmental Degradation of Materials in Nuclear Power Systems Water Reactors 2009, 2009, p. 604-613Conference paper (Refereed)
    Abstract [en]

    This paper describes the microstructures of the oxide films formed on a type 316L stainless steel material exposed under simulated BWR water chemistry conditions. High resolution electron microscopy (both FE-SEM and FE-TEM) was used. A TEM specimen was prepared by using focused ion beam technique. It is revealed that the inner thin oxide layer, unlike commonly believed, contains a large fraction of voids in some locations. There are concentration gradients of Fe, Ni and Cr elements in this layer. Furthermore, the TEM investigation revealed that the relatively large grains as commonly seen on the corroded surface sometimes consist of several small crystals of either different crystallographic orientations or different chemical compositions. The implication of the observed microstructures of the oxide films to the radioactivity build-up on BWR plant system piping surfaces is elaborated.

  • 18.
    Dai, Jin
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101).
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Chen, Yiting
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101).
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101).
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101).
    Light absorber based on nano-spheres on a substrate reflector2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 6, p. 6697-6706Article in journal (Refereed)
    Abstract [en]

    We systematically study a type of plasmonic light absorber based on a monolayer of gold nano-spheres with less than 30 nm in diameters deposited on top of a continuous gold substrate. The influences of particle size, inter-particle distance, particle-substrate spacer size etc on the resonance are studied thoroughly with a 3D finite-element method. We identified that the high-absorption resonance is mainly due to gap plasmon (coupled through particle bodies) when the separation between neighboring nano-spheres is small enough, such as close to 1 nm; at larger particle separations, the resonance is dominated by particle dipoles (coupled through the host dielectric). Experimentally, an absorber was fabricated based on chemically-synthesized gold nanoparticles coated with silica shell. The absorber shows a characteristic absorption band around 810 nm with a maximum absorbance of approximately 90%, which agrees reasonably well with our numerical calculation. The fabrication technique can be easily adapted for devising efficient light absorbers of large areas.

  • 19.
    Darab, Mahdi
    et al.
    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.
    Syvertsen, Guttorm Ernst
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Nanoengineered BSCF Cathode Materials for Intermediate-Temperature Solid-Oxide Fuel Cells2009In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 156, no 8, p. K139-K143Article in journal (Refereed)
    Abstract [en]

    A recently reported promising cathode material for solid-oxide fuel cells (SOFCs), namely, BaxSr1-xCoyFe1-yO3-delta (BSCF) is fabricated in nanocrystalline form by a chemical alloying approach. The approach is comprised of solution chemical synthesis of a precursor and its thermochemical processing toward the desired phase. All the constituent elements, Ba, Sr, Co, and Fe, were coprecipitated from an aqueous solution of their salts to produce a precursor with a well-defined composition, fine particle size, high homogeneity, and high reactivity. After calcining and sintering at 1000 degrees C, the individual oxides were alloyed into nanostructured perovskite (with x=0.5 and y=0.2) Ba0.5Sr0.5Co0.2Fe0.8O3 of high purity. Spark plasma sintering was used for compaction to preserve the material's nanostructure, and sintered compacts demonstrated a significant increase in electrical conductivity values at temperatures up to 900 degrees C, compared to the earlier reports. The measured conductivity values are sufficiently high for cathode applications with a maximum of about 63 S cm(-1) at 430 degrees C in air and 25 S cm(-1) at 375 degrees C in N-2, respectively. These values are about twice as high as conventional BSCF mainly due to the reduction in interfacial resistance, implying a high promise for nanoengineered BSCF as cathode material at low or intermediate-temperature SOFCs.

  • 20. Deligoz, H.
    et al.
    Baykal, A.
    Senel, M.
    Sozeri, H.
    Karaoglu, E.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis and characterization of poly(1-vinyltriazole)-grafted superparamagnetic iron oxide nanoparticles2012In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 162, no 7-8, p. 590-597Article in journal (Refereed)
    Abstract [en]

    We reported on the synthesis and detailed physicochemical characterization of poly(1-vinyltriazole)-grafted iron oxide nanoparticles. Superparamagnetic iron oxide nanoparticles (SPION) were fabricated by gel-to-crystalline conversion method. Telomerization of poly(1-vinyltriazole) on iron oxide nanoparticles was achieved via silanization process. XRD analysis confirmed the crystalline phase as magnetite, and FT-IR analysis confirmed the presence of PVTri on nanoparticles. Particle morphology was observed to be polygonic, due to the synthesis process, while average size estimated from TEM micrographs is 7 nm. Agreement between crystallite size estimated from XRD and particle size from TEM affirms single crystalline character of these nanoparticles. Dependence of conductivity on temperature showed a strong evidence for thermally activated polarization mechanism. Temperature and frequency dependence of dielectric permittivity revealed interfacial polarization and temperature-assisted-reorganization effects. Magnetic evaluation showed non-saturation and superparamagnetic characteristics of nanoparticles as well as magnetic particles being single domains.

  • 21. Deligoz, H.
    et al.
    Baykal, A.
    Tanriverdi, E. E.
    Durmus, Z.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis, structural and electrical properties of triethylene glycol (TREG) stabilized Mn0.2Co0.8Fe2O4 NPs2012In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 47, no 3, p. 537-543Article in journal (Refereed)
    Abstract [en]

    Triethylene glycol (TREG) stabilized Mn0.2Co0.8Fe2O4 NPs was synthesized by a glycothermal reaction. XRD analysis identified the product as Mn0.2Co0.8Fe2O4 with a high phase purity. Nano-sized particles with an average size of about 6-8 nm were obtained with nearly single crystalline nature with TEM analysis. Superparamagnetic-like behavior of TREG stabilized Mn0.2Co0.8Fe2O4 NPs was observed by VSM. The binding between TREG and Mn0.2Co0.8Fe2O4 NPs was investigated with FT-IR and found to be via O on the TREG and NP surface. TG analysis indicated that the Mn0.2Co0.8Fe2O4 NP content was about 40%, with a TREG-shell content to be around 60%. Overall conductivity of the nanocomposite is in the range of 10(-10) to 10(-7) S cm(-1) with a strong dependence on temperature and frequency, indicating ionic conductivity. The nanocomposite exhibited lower epsilon' and epsilon '' compared to TREG stabilized Mn0.2Co0.8Fe2O4 NPs due to the doping of co-doping of manganese and cobalt.

  • 22. Deligöz, H.
    et al.
    Baykal, A.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Tanriverdi, E. E.
    Durmus, Z.
    Sözeri, H.
    Synthesis, structural, magnetic and electrical properties of Co 1-xZnxFe2O4 (x = 0.0, 0.2) nanoparticles2013In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 48, no 2, p. 646-654Article in journal (Refereed)
    Abstract [en]

    Co1-xZnxFe2O4 spinel nanoparticles with Zn concentrations of x = 0.0, 0.2 were prepared by a hydrothermal route in the presence of triethylene glycol (TEG). The structural, magnetic, electrical and dielectric properties of the prepared nanoparticles were studied. The XRD results confirmed the formation of single spinel ferrite structure with crystallite size 9 and 10 nm for x = 0.0 and 0.2 compositions respectively. The lattice parameter (a) increased with increasing Zn concentration. Temperature and frequency dependent electrical and dielectric properties of the prepared ferrites have also been investigated. Our findings show that overall conductivity of Co0.8Zn0.2Fe 2O4 nanoparticle is lower than that of CoFe 2O4 and roughly in the range of 10-11-10 -7 S cm-1 depending strongly temperature and frequency owing to the formation of stable electric bonds between the Zn2+ and Fe2+ ions, which localizes Fe2+ charge carriers. 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. dc conductivity of Co0.8Zn0.2Fe 2O4 nanoparticle are found to obey the Arrhenius plot and can be classified into two regions over with activation energy of 0.113 and 0.163 eV in the ranges of 20-40 °C and 70-120 °C, respectively when CoFe2O4 has an activation energy of 0.245 eV.

  • 23.
    Dong, Lin
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Sugunan, Abhilash
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Hu, Jun
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Zhou, Sicheng
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Li, Shanghua
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Photoluminescence from quasi-type-II spherical CdSe-CdS core-shell quantum dots2013In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 52, no 1, p. 105-109Article in journal (Refereed)
    Abstract [en]

    Spherical CdSe-CdS core-shell quantum dots (QDs) are found to be flexible in the transition between the type-I regime and the type-II regime with different core/shell dimensions. The quasi-type-II feature of the colloidal dots is confirmed with time-resolved photoluminescence (PL) measurements. Two recombination paths of the excitons with significantly different decay rates are observed and analyzed. The spherical CdSe-CdS core-shell QDs are numerically simulated to investigate the carrier separation. A relatively long radiative lifetime and high degree of spatial carrier separation provide good potential to achieve lasing under continuous-wave excitation. Amplified spontaneous emission at room temperature is detected from the QDs embedded in the polymer matrix. It is shown that a larger shell thickness results in a lower pumping threshold, while a smaller shell thickness leads to higher PL efficiency.

  • 24.
    Dong, Lin
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Chughtai, Adnan
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Liuolia, Vytautas
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Lasing From Water Solution of Rhodamine 6G/Gold Nanoparticles: Impact of SiO2-Coating on Metal Surface2012In: IEEE Journal of Quantum Electronics, ISSN 0018-9197, E-ISSN 1558-1713, Vol. 48, no 9, p. 1220-1226Article in journal (Refereed)
    Abstract [en]

    Gold nanoparticles embedded in an optical gain material, particularly in a water solution of Rhodamine 6G, used in dye lasers can both increase and damp dye flourescence, thus changing the laser output intensity. Simultaneously, such nanoparticles influence the gain material's resistance against photobleaching. In this paper, we report our study on the impact of the SiO2 coating of nanoparticles on the enhancement or quenching and photobleaching of the fluorescence. The investigation demonstrates a noticeable improvement of the gain material's photostability compared to uncoated gold nanoparticles when silicon dioxide coating is implemented.

  • 25.
    Dong, Lin
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Chughtai, Adnan
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Enhanced photostability of aqueous solution of Rhodamine 6G with gold nanoparticles in lasing process by silica coating2012In: 2012 Conference on Lasers and Electro-Optics, CLEO 2012, IEEE , 2012, p. 6325399-Conference paper (Refereed)
    Abstract [en]

    Gold nanoparticles are mixed in aqueous solution of Rhodamine 6G to modify the lasing output intensity. The photostability deterioration of the gain medium by gold nanoparticles is successfully compensated by silica coating on the nanoparticles.

  • 26.
    Dong, Lin
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Chughtai, Adnan
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Photostability of lasing process from water solution of Rhodamine 6G with gold nanoparticles2012In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 37, no 1, p. 34-36Article in journal (Refereed)
    Abstract [en]

    We report the lasing performance and photobleaching of gain material containing a water solution of Rhodamine 6G dye and gold nanoparticles (NPs). In comparison to a pure dye solution, the investigated material demonstrated both enhancement and quenching of the lasing output, depending on the relative concentration of the gold NPs. Although the presence of NPs with an optimized concentration looks preferable in terms of the lasing output enhancement, such additives deteriorate the operational resource of the gain material; i.e., the photobleaching rate speeds up.

  • 27.
    Dong, Lin
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Hu, Jun
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Fluorescence quenching and photobleaching in Au/Rh6G nanoassemblies: impact of competition between radiative and non-radiative decay2011In: JOURNAL OF THE EUROPEAN OPTICAL SOCIETY-RAPID PUBLICATIONS, ISSN 1990-2573, Vol. 6, p. 11019-Article in journal (Refereed)
    Abstract [en]

    We report the study of fluorescence quenching from nanoassemblies formed by Rhodamine 6G and gold nanoparticles (Au NPs) of 2.6 nm radius. The presence of Au NPs induces long-term degradation of the photostability (photobleaching) of Rhodamine 6G used as a gain medium in a Fabry-Perot laser cavity. We found that the degradation gets profound when the Au NPs concentration is significantly increased. Calculation of the radiative rate and direct time-resolved measurement of the fluorescence decay indicates that both the decrease of radiative decay rate and increase of non-radiative decay rate are responsible for the fluorescence quenching and photostability degradation. An energy transfer from the dye molecules to gold nanoparticles is dominating within small distance between them and suppresses the quantum efficiency of Rhodamine 6G drastically. In a long time scale, the photobleaching rate was slowing down, and the laser output intensity reached a stabilized level which depends on the gold nanoparticles concentration.

  • 28. Durmus, Z.
    et al.
    Baykal, A.
    Sozeri, H.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Preparation of PVP (Polyvinyl Pyrrolidone)/Ba-Sr hexaferrites via gel to crystalline method2012In: Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, ISSN 1553-3174, Vol. 42, no 10, p. 1390-1397Article in journal (Refereed)
    Abstract [en]

    Ba-M- and Sr-M-type hexagonal ferrites have been prepared via a sol-gel route, and the effects of adding different amounts of polyvinyl pyrrolidone (PVP) into the sol solutions. The average crystallite, size, D and σ, was obtained as for Z13 = 22 ± 2 nm and Z13-2 = 16 ± 3 nm and for Z16 = 18 ± 7 nm and Z16-2 = 17 ± 5 nm by XRD. FT-IR and TG analysis were used to prove the presence of PVP on BaFe12O19 and SrFe12O19. Based on the TGA curves the mass losses of the samples are assessed as follows: Z13 ̃15%, Z13-2 ̃25%, Z16 ̃5%, and Z16-2 ̃10%.

  • 29. Durmus, Z.
    et al.
    Erdemi, H.
    Aslan, A.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sozeri, H.
    Baykal, A.
    Synthesis and characterization of poly(vinyl phosphonic acid) (PVPA)-Fe3O4 nanocomposite2011In: Polyhedron, ISSN 0277-5387, E-ISSN 1873-3719, Vol. 30, no 2, p. 419-426Article in journal (Refereed)
    Abstract [en]

    Poly(vinyl phosphonic acid) (PVPA)-Fe3O4 nanocomposite is synthesized by the precipitation of Fe3O4 in the presence of PVPA. 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 PVPA around the Fe3O4 nanoparticles was confirmed by FT-IR spectroscopy, the interaction being via bridging oxygens of the phosphate and the nanoparticle surface. The crystallite and particle size were obtained as 6 +/- 2 and 8.7 +/- 0.1 nm from XRD line profile fitting and TEM image analysis respectively, which reveal nearly single crystalline nature of the Fe3O4 nanoparticles. Magnetic characterization of the bulk magnetite and (PVPA)-Fe3O4 nanocomposite reveals that both are in the superparamagnetic state at room temperature. The average magnetic domain size of the nanoparticles has been calculated using the Langevin function, which was fitted to the measured M-H hysteresis curves as 7.6 nm for the nanocomposite. In the nanocomposite, the reduction is due to the adsorption of PVPA onto the magnetite surface, which cancels some of the free spins at the surface causing a magnetically dead layer. Analysis of the conductivity and permittivity measurements revealed the coupling of ionic and polymer segmental motions and strong temperature dependency in the nanocomposite.

  • 30. Durmus, Z.
    et al.
    Kavas, H.
    Baykal, A.
    Sozeri, H.
    Alpsoy, L.
    Celik, S. U.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis and characterization of L-carnosine coated iron oxide nanoparticles2011In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 509, no 5, p. 2555-2561Article in journal (Refereed)
    Abstract [en]

    L-Carnosine coated iron oxide nanoparticles (CCIO NPs) have been prepared via co-precipitation of iron oxide in the presence of L-carnosine. Crystalline phase was identified as magnetite with an average crystallite size of 8 nm as estimated from X-ray line profile fitting. Particle size estimated from TEM by log-normal fitting was similar to 11 nm. FTIR analysis showed that the binding of carnosine onto the surface of iron oxide is through unidentate linkage of carboxyl group. CCIO NPs showed superparamagnetic charactersitic at room temperature. The magnetic core size of superparamagnetic CCIO NPs was found slightly smaller than the size obtained from TEM, due to the presence of magnetically dead layer. Magnetization measurements revealed that L-carnosine iron oxide composite has immeasurable coercivity and remanence with absence of hysteritic behavior, which implies superparamagnetic behavior at room temperature. The low value of saturation magnetization compared to the bulk magnetite has been explained by spin canting. LDH activity tests showed slight cytotoxicity of high dose of CCIO NPs. The ac conductivity of CCIO NPs was found to be greater than that of carnosine and the effective conduction mechanism was found as correlated barrier hopping (CBH). dc activation energy of the product at around room temperature was measured as 0.312 eV which was in good agreement with the earlier reports.

  • 31.
    Durmus, Z.
    et al.
    Fatih Univ, Istanbul, Turkey .
    Kavas, H.
    Gebze Inst Technol, Izmit, Turkey .
    Sozeri, H.
    Natl Metrol Inst, Gebze, Turkey .
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Aslan, A.
    Fatih Univ, Istanbul, Turkey .
    Baykal, A.
    Fatih Univ, Istanbul, Turkey .
    Poly(vinyl phosphonic acid) (PVPA)-BaFe12O19 Nanocomposite2012In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 25, no 4, p. 1185-1193Article in journal (Refereed)
    Abstract [en]

    We present a method for the fabrication of PVPA/BaFe12O19 nanocomposite by in-situ polymerization of vinyl phosphonic acid, VPA in the presence of synthesized BaFe12O19 NPs. Nanoparticles and the nanocomposite were analyzed by XRD, FTIR, TGA, SEM, TEM, VSM, and conductivity techniques for structural and physicochemical characteristics. Nanoparticles, identified as BaFe12O19 from XRD analysis, were successfully coated with PVPA and the linkage was assessed to be via P-O bonds. Electron microscopy analysis revealed aggregation of BaFe12O19 particles and dominantly platelet morphology upon composite formation. TGA analysis revealed the composition of the nanocomposite as 65% BaFe12O19 and 35% polymer. Magnetic evaluation revealed that adsorption of PVPA anions during the preparation of the nanocomposite strongly influenced the magnetic properties resulting in much lower saturation magnetization values. DC conductivity measurements were used to calculate activation energy of PVPA/BaFe12O19 nanocomposite and it was obtained as 0.37 eV.

  • 32. Durmus, Z.
    et al.
    Sozeri, H.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Baykal, A.
    The Effect of Condensation on the Morphology and Magnetic Properties of Modified Barium Hexaferrite (BaFe12O19)2011In: Nano-Micro Letters, ISSN 2150-5551, Vol. 3, no 2, p. 108-114Article in journal (Refereed)
    Abstract [en]

    We present a comparison for the effect of condensation on the morphology and magnetic properties of oleic acid modified BaFe12O19 nanoparticles. Two different samples of BaFe12O19 nanoparticles were synthesized by dehydration (Z1) and rotary evaporation (Z2) method, respectively. Oleic acid was used as the surface modification agent to observe the morphological and magnetic changes. The nanoparticles were analyzed by XRD, FTIR, TGA, SEM, and VSM techniques for structural and physicochemical characteristics. Crystallographic analysis reveals the phase as hexaferrite and the average crystallite size of Z1 and Z2 is 21 +/- 3 nm and 17 +/- 2 nm, respectively. Rotary evaporator accelerates the condensation process in viscous gel (Z2). Due to the use of rotary evaporator, the coating with oleic acid for Z2 product has been accomplished very well, as compared with Z1. As a result, saturation magnetization of Z2 sample is much lower than that of Z1 sample.

  • 33. Durmus, Z.
    et al.
    Sozeri, H.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Baykal, A.
    Effect of Fuel on the Synthesis and Properties of Poly(methyl methacrylate) Modified SrFe12O19 Nanoparticles2012In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 25, no 6, p. 1957-1963Article in journal (Refereed)
    Abstract [en]

    Nanosized strontium hexaferrite (SrFe 12O 19) has been synthesized by citrate, urea, oxalic, and glycine precursor via a sol-gel route with poly(methyl methacrylate) (PMMA) as a templating agent. Crystal structure, morphology, and magnetic properties of as-synthesized nanoparticles were characterized by XRD, SEM, FT-IR, and VSM techniques. The formation of strontium hexaferrite and its crystallite size in presence of different fuels were compared. The influence of different fuels was reflected on the phase purity, morphology of the final powders as well as the magnetic properties. Magnetic measurements revealed that samples prepared by citric acid and glycine as fuel have high specific saturation magnetization and moderate coercivity, while urea and oxalic acid fuels resulted in low phase purity, and thus inferior magnetic properties.

  • 34. Durmus, Z.
    et al.
    Sozeri, H.
    Unal, B.
    Baykal, A.
    Topkaya, R.
    Kazan, S.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Magnetic and dielectric characterization of alginic acid-Fe3O4 nanocomposite2011In: Polyhedron, ISSN 0277-5387, E-ISSN 1873-3719, Vol. 30, no 2, p. 322-328Article in journal (Refereed)
    Abstract [en]

    We have reported the synthesis of water dispersible alginic acid (AA)-Fe3O4 nanocomposites. The crystallite size was obtained as 9 +/- 2 nm from X-ray line profile fitting. As compared to the particle size of 9.2 nm obtained from TEM analysis, these particles show dominantly single crystalline nature. Dielectric analysis show that the real and imaginary parts of the permittivity of both pure AA and AA-Fe3O4 nano-composite obey the ionic polarization mechanism comprised of ionic conductivity and interfacial or space charge polarization. Magnetization measurements show that the saturation magnetization of AA-capped magnetite is significantly lower than the theoretical bulk value, partly due to the structural distortions on the surface of the particles. Moreover, magnetite does not saturate and exhibits no coercivity above a certain temperature, revealing superparamagnetic behavior of the nanocomposite above a blocking temperature, T-B. of similar to 175 K. The magnetic core size, determined by theoretical fitting to the magnetization data at room temperature, is 9.55 nm.

  • 35. Durmus, Z.
    et al.
    Tomas, M.
    Baykal, A.
    Kavas, H.
    Altincekic, T. Gurkaynak
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    The effect of neutralizing agent on the synthesis and characterization of Mn3O4 nanoparticles2010In: Russian Journal of Inorganic Chemistry, ISSN 0036-0236, E-ISSN 1531-8613, Vol. 55, no 12, p. 1947-1952Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis of Mn3O4 nanoparticles via a two-step hydrothermal route by using Mn(CH3COO)(2) as the only starting material and TMAOH and NaOH as hydrolysing agents. XRD and FT-IR analyses confirmed the composition and structure of Mn3O4. TEM images showed that spheroid Mn3O4 nanostructures obtained by this method have average particle size of 6 and 14 nm for NaOH and TMAOH hydrolyzed samples respectively. Particle size analysis indicated a strong aggregation of nanoparticles and exhibited bi-modal distribution with average size of aggregates as similar to 250 nm and 1.1 mu m for both samples. Zeta potential analysis revealed adsorbed TMAOH species on the surface of Mn3O4 nanoparticles hydrolyzed using TMAOH. ESR analyses resulted in broader lines and smaller g values than bulk Mn3O4 nanoparticles, probably due to the exchange-coupled system with unlike spins such as canted spin at surface of high-surface-disordered nanoparticles.

  • 36. Durmus, Z.
    et al.
    Unal, B.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Aslan, A.
    Baykal, A.
    Synthesis and characterization of poly(1-vinyl-1,2,4-triazole) (PVTri)-barium hexaferrite nanocomposite2011In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 406, no 11, p. 2298-2302Article in journal (Refereed)
    Abstract [en]

    We present a method for the fabrication of PVTri-BaFe12O19 nanocomposites by in-situ polymerization of PVTri in the presence of synthesized BaFe12O19 nanoparticles. Nanoparticles, polymer and nanocomposite were analyzed by XRD, FTIR, TGA, TEM, NMR, GPC and conductivity techniques for structural and physicochemical characteristics. Crystallographic analysis revealed the phase as hexaferrite and X-ray line profile fitting yielded a crystallite size of 17 +/- 5 nm. Conjugation of PVTri to nanoparticle surface was assessed to be via carbonyl groups on the polymer. TG analysis revealed that 45 wt% of nanocomposite is inorganic phase (BaFe12O19). It was found out that the ac conductivity of nanocomposite under a certain frequency increases with temperature.

  • 37. Durmus, Z.
    et al.
    Unal, B.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sozeri, H.
    Baykal, A.
    Synthesis and characterization of poly(3-thiophenyl acetic acid) (P3TAA)-BaFe12O19 nanocomposite2011In: Polyhedron, ISSN 0277-5387, E-ISSN 1873-3719, Vol. 30, no 7, p. 1349-1359Article in journal (Refereed)
    Abstract [en]

    We have presented a method for the fabrication of poly(3-thiophenyl acetic acid) (P3TAA)-BaFe12O19 nanocomposites by the in situ polymerization of P3TAA in the presence of synthesized BaFe12O19 nanoparticles. The nanoparticles and the nanocomposite were analyzed by XRD, FTIR, TGA, TEM, VSM and conductivity techniques for structural and physicochemical characteristics. Crystallographic analysis revealed the phase as hexaferrite and X-ray line profile fitting yielded a crystallite size of 32 nm. The particles, observed by TEM, exhibit irregular shapes and sizes between 100 and 500 nm, revealing polycrystalline character when compared with the crystallite size from XRD. FTIR and TGA analysis results show that P3TAA is conjugated to the particle surface via a carboxylate group and that the composite has a polymer content of similar to 10%. Magnetic hysteresis curves do not saturate at high fields, which is a characteristic feature of fine particle systems with grain sizes smaller than 1 mu m. Conductivity measurements showed a semiconductor character of the nanocomposite.

  • 38. Durmus, Zehra
    et al.
    Baykal, Abdulhadi
    Kavas, Hueseyin
    Direkci, Mikail
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Ovalbumin mediated synthesis of Mn3O42009In: Polyhedron, ISSN 0277-5387, E-ISSN 1873-3719, Vol. 28, no 11, p. 2119-2122Article in journal (Refereed)
    Abstract [en]

    By using Mn2+ and Mn3+ salts, and freshly extracted ovalbumin. Mn3O4 nanocrystals have been synthesized successfully. The X-ray diffraction results indicated that the synthesized nanoparticles have only the spinel structure without the presence of any other phase impurities. As the ovalbumin-water mixture was highly basic, the process did not require any use of base to increase the pH where hydrolysis took place. A gel formed where water soluble ovalbumin proteins served as a perfect matrix for entrapment of metal ions (Mn2+ and Mn3+). Upon heat treatment, the dried gel precursor decomposed into nanocrystalline Mn3O4. The discrepancy between the crystallite size from XRD and particle size SEM analysis reveals polycrystalline nature of the synthesized particles with this route. EPR analysis of Mn3O4 shows a narrow and symmetric line indicating the absence of hyperfine splitting.

  • 39. Durmus, Zehra
    et al.
    Kavas, Hueseyin
    Baykal, Abdulhadi
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    A green chemical route for the synthesis of Mn3O4 nanoparticles2009Article in journal (Refereed)
    Abstract [en]

    A novel environmental friendly, room temperature route using an ionic liquid 1-n-butyl-3-methylimidazolium hydroxide ([BMIM]OH) for the synthesis of Mn3O4 nanoparticles is presented. The product was characterized using Fourier transform infrared spectroscopy, X-ray powder diffraction, and transmission electron microscopy. Phase purity was confirmed by XRD, and X-ray line profile fitting determined a crystallite size of 42 +/- 11 nm. TEM analysis revealed various morphologies. EPR measurements have indicated the existence of long-range interactions, due to the wide range of particle sizes and morphologies observed

  • 40. Durmus, Zehra
    et al.
    Kavas, Hueseyin
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Baykal, Abduelhadi
    Altincekic, Tuba Guerkaynak
    Aslan, Ayse
    Bozkurt, Ayhan
    Cosgun, Sedat
    L-lysine coated iron oxide nanoparticles: Synthesis, structural and conductivity characterization2009In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 484, no 1-2, p. 371-376Article in journal (Refereed)
    Abstract [en]

    L-lysine coated iron oxide (LCIO) nanoparticles were synthesized by a co-precipitation method in the presence of amino acid. XRD analysis confirmed the presence of cubic magnetite phase with an average crystallite size of 8 +/- 4 nm. Particle size estimated from TEM, by log-normal fitting, is similar to 114 nm. The difference between the crystallite size from XRD and particle size from TEM indicates polycrystalline nature of synthesized particles. FT-IR show that the binding Of L-lysine on the surface of iron oxide through carboxyl groups is via unidentate linkage. The presence of L-lysine on iron oxide is also confirmed by zeta potential measurements on LCIO nanoparticles, revealing a partial coverage of iron oxide with L-lysine. In order to obtain chemically stable, well-dispersed and uniform sized nanoparticles, amino acids are suitable because they play a very important role in the body. Conductivity measurements were performed to investigate the influence of the coating on the conduction characteristics of iron oxide and results show the existence of a hopping conduction mechanism. Magnetic transition is observed at similar to 70 degrees C for uncoated iron oxide and LCIO samples. Frequency (1 Hz to 3 MHz) and temperature (290-420 K) dependant AC conductivity measurements have resulted in AC activation energies between 0.048 and 0.041 eV for uncoated and 0.050-0.044 eV for LCIO nanoparticles. Temperature-dependant DC resistivity measurements of iron oxide and LCIO at high temperatures resulted in the DC activation energies of 0.22 and 0.43 eV respectively. The higher activation energy value for LCIO is the result of coating by insulating L-lysine layer.

  • 41. Durmus, Zehra
    et al.
    Tomas, Merve
    Baykal, Abdulhadi
    Kavas, Huseyin
    Toprak, Muhammed S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    PEG-Assisted Synthesis of Mn(3)O(4) Nanoparticles: A Structural and Magnetic Study2011In: SYNTH REACT INORG M, ISSN 1553-3174, Vol. 41, no 7, p. 768-773Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis of Mn(3)O(4) nanoparticles via a polyethyleneglycol (PEG)-assisted hydrothermal route. Crystalline phase was identified as Mn(3)O(4). The crystallite size from X-ray Diffraction (XRD) pattern and particle size from transmission electron microscopy (TEM) micrographs were calculated as 23 +/- 1 nm and 24.5 +/- 0.5 nm, respectively. Nanoparticles (NPs) exhibit mainly tetragonal and spherical morphologies. Magnetic characteristics of Mn(3)O(4) NPs were evaluated by electron spin resonance (ESR) in the temperature range of 24-294 K and the Curie temperature was observed as 43 K. Also the magnetic phases that occur in nanosize Mn(3)O(4) are detected below Tc by this method. The room-temperature paramagnetic characteristic are verified by vibrating sample magnetometry (VSM).

  • 42.
    Eita, Mohamed
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    El Sayed, Ramy
    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.
    Optical properties of thin films of zinc oxide quantum dots and polydimethylsiloxane: UV-blocking and the effect of cross-linking2012In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 387, p. 135-140Article in journal (Refereed)
    Abstract [en]

    Thin films of polydimethylsiloxane (PDMS) and ZnO quantum dots (QDs) were built up as multilayers by spin-coating. The films are characterized by a UV-blocking ability that increases with increasing number of bilayers. Photoluminescence (PL) emission spectra of the thin films occur at 522 nm, which is the PL wavelength of the ZnO QDs dispersion, but with a lower intensity and a quantum yield (QY) less than 1% that of the dispersion. Cross-linking has introduced new features to the absorption spectra in that the absorption peak was absent. These changes were attributed to the morphological and structural changes revealed by transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR), respectively. TEM showed that the ZnO particle size in the film increased from 7 (+/- 2.7) nm to 16 (+/- 7.8) upon cross-linking. The FTIR spectra suggest that ZnO QDs are involved in the cross-linking of PDMS and that the surface of the ZnO QDs has been chemically modified.

  • 43.
    Eita, Mohamed
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Wagberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Spin-Assisted Multilayers of Poly(methyl methacrylate) and Zinc Oxide Quantum Dots for Ultraviolet-Blocking Applications2012In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 4, no 6, p. 2920-2925Article in journal (Refereed)
    Abstract [en]

    Thin UV-blocking films of poly(methyl methacrylate) (PMMA) and ZnO quantum dots (QDs) were built-up by spin-coating. Ellipsometry reveals average thicknesses of 9.5 and 8.6 nm per bilayer before and after heating at 100 degrees C for one hour, respectively. The surface roughness measured by Atomic force microscopy (AFM) was 3.6 and 8.4 nm for the one and ten bilayer films, respectively. The linear increase in thickness as well as the low surface roughness increment per bilayer indicates a stratified multilayer structure and a smooth interface without: aggregation. The absorption of UV radiation increased with increasing number of bilayers. At the same time, transmission was damped at wavelengths shorter than 375 nm. The thin films had a high and constant transparency in the visible region. Green-light emitting QDs could be detected by confocal microscopy at a concentration of 20% in a single layer of PMMA/ZnO. PMMA/ZnO QDs thin films are hydrophobic, as indicated by contact angle measurements.

  • 44.
    Eita, Mohamed
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Wagberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Thin Films of Zinc Oxide Nanoparticles and Poly(acrylic acid) Fabricated by the Layer-by-Layer Technique: a Facile Platform for Outstanding Properties2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 7, p. 4621-4627Article in journal (Refereed)
    Abstract [en]

    The incorporation of nanoparticles into polyelectrolytes thin films opens the way to a broad range of applications depending on the functionality of the nanoparticles. In this work, thin films of ZnO nanoparticles and poly(acrylic acid) (PAA) were built up using the layer-by-layer technique. The thickness of a 20-bilayer film is about 120 nm with a surface roughness of 22.9 nm as measured by atomic force microscopy (AFM). Thin ZnO/PAA films block UV radiation starting at a wavelength of 361 nm due to absorption by ZnO although the films are highly transparent. Due to their high porosity, these thin films show a broadband antireflection in the visible region, and thus they provide selective opacity in the UV region and enhanced transmittance in the visible region up to the near-infrared region. They are also superhydrophilic due to their high porosity and surface roughness.

  • 45. El-Sayed, Ramy
    et al.
    Eita, Mohamed
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Barrefelt, Åsa
    Ye, Fei
    Jain, Himanshu
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Fares, Mona
    Lundin, Arne
    Crona, Mikael
    Abu-Salah, Khalid
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Hassan, Moustapha
    Thermostable Luciferase from Luciola cruciate for Imaging of Carbon Nanotubes and Carbon Nanotubes Carrying Doxorubicin Using in Vivo Imaging System2013In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 13, no 4, p. 1393-1398Article in journal (Refereed)
    Abstract [en]

    In the present study, we introduce a novel method for in vivo imaging of the biodistribution of single wall carbon nanotubes (SWNTs) labeled with recombinant thermo-stable Luciola cruciata luciferase (LcL). In addition, we highlight a new application for green fluorescent proteins in which they are utilized as imaging moieties for SWNTs. Carbon nanotubes show great positive potential compared to other drug nanocarriers with respect to loading capacity, cell internalization, and biodegradability. We have also studied the effect of binding mode (chemical conjugation and physical adsorption) on the chemiluminescence activity, decay rate, and half-life. We have shown that through proper chemical conjugation of LcL to CNTs, LcL remained biologically active for the catalysis of D-luciferin in the presence of ATP to release detectable amounts of photons for in vivo imaging. Chemiluminescence of LcL allows imaging of CNTs and their cargo in nonsuperficial locations at an organ resolution with no need of an excitation source. Loading LcL-CNTs with the antitumor antibiotic doxorubicin did not alter their biological activity for imaging. In vivo imaging of LcL-CNTs has been carried out using "IVIS spectrum" showing the uptake of LcL-CNTs by different organs in mice. We believe that the LcL-CNT system is an advanced powerful tool for in vivo imaging and therefore a step toward the advancement of the nanomellicine field.

  • 46. Erdemi, H.
    et al.
    Baykal, A.
    Karaoglu, E.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis and conductivity studies of piperidine-4-carboxylic acid functionalized Fe 3O 4 nanoparticles2012In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 47, no 9, p. 2193-2199Article in journal (Refereed)
    Abstract [en]

    Piperidine-4-carboxylic acid (PPCA) functionalized Fe 3O 4 nanoparticles as a novel organic-inorganic hybrid was fabricated and characterized by XRD, FT-IR, VSM, and TEM techniques. Its detailed electrical properties are also presented. Composition was determined as Fe 3O 4, while particles were observed to have spherical morphology. VSM measurement proved the super-paramagnetic property of the as synthesized nanocomposite. ac and dc conductivity measurements indicated semiconductor characteristics and changing trends with temperature because of reorganization of the nanocomposite. dc conductivity is strongly temperature dependent and is classified into three regions. Analysis of the real and imaginary parts of the permittivity of nanocomposite showed the ionic polarization mechanism consisting of ionic conductivity and interfacial polarization.

  • 47.
    Fan, Liangdong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Zhu, Bin
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Chen, Mingming
    Chemical engineering and technology.
    Wang, Chengyang
    Chemical engineering and technology.
    Raza, Rizwan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Qin, Haiying
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Wang, Xuetao
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Wang, Xiaodi
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Ma, Ying
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    High performance transition metal oxide composite cathode for low temperature solid oxide fuel cells2012In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 203, no 1, p. 65-71Article in journal (Refereed)
    Abstract [en]

    Low temperature solid oxide fuel cells (SOFCs) with metal oxide composite cathode on the ceria–carbonate composite electrolyte have shown promising performance. However, the role of individual elements or compound is seldom investigated. We report here the effect of the ZnO on the physico-chemical and electrochemical properties of lithiated NiO cathode. The materials and single cells are characterized by X-ray diffraction, scanning electron microscopy, DC polarization electrical conductivity, electrochemical impedance spectroscopy and fuel cell performance. The ZnO modified lithiated NiO composite materials exhibit smaller particle size and lower electrical conductivity than lithiated NiO. However, improved electro-catalytic oxygen reduction activity and power output are achieved after the ZnO modification. A maximum power density of 808 mW cm−2 and the corresponding interfacial polarization resistance of 0.22 Ω cm2 are obtained at 550 °C using ZnO modified cathode and 300 μm thick composite electrolyte. The single cell keeps reasonable stability over 300 min at 500 °C. Thus, ZnO modified lithiated NiO is a promising cathode candidate for low temperature SOFCs.

  • 48.
    Fornara, Andrea
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Magnetic nanostructured materials for advanced bio-applications2008Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In the recent years, nanostructured magnetic materials and their use in biomedical and biotechnological applications have received a lot of attention. In this thesis, we developed tailored magnetic nanoparticles for advanced bio-applications, such as direct detection of antibodies in biological samples and stimuli responsive drug delivery system.

    For sensitive and selective detection of biomolecules, thermally blocked iron oxide nanoparticles with specific magnetic properties are synthesized by thermal hydrolysis to achieve a narrow size distribution just above the superparamagnetic limit.  The prepared nanoparticles were characterized and functionalized with biomolecules for use in a successful biosensor system. We have demonstrated the applicability of this type of nanoparticles for the detection of Brucella antibodies as model compound in serum samples and very low detection limits were achieved (0.05 mg/mL).

    The second part is concerning an in-depth investigation of the evolution of the thermally blocked magnetic nanoparticles. In this study, the formation of the nanoparticles at different stages during the synthesis was investigated by high resolution electron microscopy and correlated to their magnetic properties.  At early stage of the high temperature synthesis, small nuclei of 3.5 nm are formed and the particles size increases successively until they reach a size of 17-20 nm. The small particles first exhibit superparamagnetic behavior at the early stage of synthesis and then transform to thermally blocked behavior as their size increases and passes the superparamagnetic limit.

    The last section of the Thesis is related to the development of novel drug delivery system based on magnetically controlled release rate. The system consists of hydrogel of Pluronic FP127 incorporating superparamagnetic iron oxide nanoparticles to form a ferrogel. The sol to gel formation of the hydrogel could be tailored to be solid at body temperature and thus have the ability to be injected inside living biological tissues.

    In order to evaluate the drug loading and release, the hydrophobic drug indomethacin was selected as a model compound. The drug could be loaded in the ferrogel owning to the oil in water micellar structure. We have studied the release rate from the ferrogel in the absence and presence of magnetic field. We have demonstrated that the drug release rate can be significantly enhanced by use of external magnetic field decreasing the half time of the release to more than 50% (from 3200 to 1500 min) upon the application of the external magnetic field.

    This makes the developed ferrogel a very promising drug delivery system that does not require surgical implant procedure for medical treatment and gives the possibility of enhancing the rate of release by external magnetic field.

  • 49.
    Fornara, Andrea
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Multifunctional nanomaterials for diagnostic and therapeutic applications2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the past few years, the use of nanostructured materials in medical applications hasdramatically increased, both in the research phase and for clinical purposes, due to thepeculiar properties and the ability of such materials to interact at a similar scale withbiological entities. In this thesis, we developed tailored magnetic multifunctionalnanoparticles for diagnostic and therapeutic applications, such as detection ofbiomolecules, simultaneous enhanced magnetic resonance imaging (MRI), fluorescentvisualization and controlled drug release.For sensitive and selective detection of specific biomolecules, thermally blocked ironoxide nanoparticles with tailored magnetic properties were developed. The formation ofsuch nanoparticles has been studied both in terms of size and magnetic behavior in liquidsuspension or in polymer matrixes. These particles with narrow size distribution (averagediameter of 19 nm) were surface functionalized by antigen molecules and were used forthe detection of Brucella antibodies in biological samples. The binding of biomoleculesresults in an increase in the particle’s hydrodynamic diameter, affecting the relaxationbehavior that was monitored by magnetic measurements. This sensing system is a fastand sensitive biosensor with very low detection limits (0.05 μg/mL).Superparamagnetic iron oxide nanoparticles (SPION) have been synthesized withaverage diameter of 10-12 nm, narrow size distribution, high crystallinity and superiormagnetic properties as liquid suspensions or embedded in a bulk transparent magneticnanocomposite. These nanoparticles were synthesized in organic solvents and, after phasetransfer with Pluronic F127 amphiphilic copolymer, show excellent relaxivity properties(high r2/r1 ratio) and great contrast enhancement in T2 weighted MRI, confirmed by invivostudies of rat inner ear.SPION have been used as a component for different multifunctional nanostructures. Thefirst system based on poly (L,L lactide)-methoxy polyethylene glycol (PLLA-mPEG)copolymer has been prepared by an emulsion/evaporation process that lead to polymericnanoparticles containing several imaging agents, such as SPION, quantum dots (QDs)and gold nanorods as well as indomethacin (IMC) as therapeutic payload. With a similarprocedure, but using poly (lactide-co-glycolide) (PLGA-PEG-NH2) copolymer, a secondtype of multifunctional nanoparticles has been obtained. Their size can be tailored from70 to 150 nm varying synthesis parameters, such as the surfactant concentration or waterto oil ratio. Both these polymer-based multifunctional nanoparticles can be visualized byfluorescence microscopy (QDs photoemission) and MRI (SPION magnetization) and theycan be used for photothermal therapy (gold nanorods) and drug delivery. The last systemconsists of SPION nanoparticles coated with PLLA directly on the surface by an in-situpolymerization process. A hydrophobic drug was loaded before the phase transfer withPluronic F127 and these nanoparticles show simultaneous MRI T2 contrast enhancementas well as high drug loading and sustained delivery.Controlling the drug release rate is also a critical parameter for tailored therapeutictreatments, and for this reason we developed a novel drug delivery system based on theintegration of SPION and Pluronic F127 gels. IMC was loaded in the ferrogel (with atailored gelation temperature) and its release rate was triggered by applying an externalmagnetic field owing to the SPION magnetic properties.

  • 50.
    Fornara, Andrea
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Chiavarino, Annalisa
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Qin, Jian
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Toprak, Muhammet
    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.
    PLGA-PEG multifunctional nanoparticles for simultaneous drug delivery and visualizationIn: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896XArticle in journal (Other academic)
1234 1 - 50 of 178
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