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  • 201. Shafiu, S.
    et al.
    Baykal, A.
    Sozeri, H.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM. Yildirim Beyazit Univ, Dept Mat Sci & Engn, Ulus Ankara, Turkey.
    Triethanolamine Assisted Hydrothermal Synthesis of Superparamagnetic Co3O4 Nanoparticles and Their Characterizations2014In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, E-ISSN 1557-1947, Vol. 27, no 9, p. 2117-2122Article in journal (Refereed)
    Abstract [en]

    We present, for the first time, on a facile route for the fabrication of highly crystalline Co3O4 nanoparticles using trietanolamine (TEA) assisted hydrothermal synthesis route and single precursor. Synthesized material has been evaluated for its structural, morphological and magnetic properties using x-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM) techniques. The material has been identified as highly crystalline Co3O4, with superparamagnetic character due to size confinement. Estimated particle size from SEM is about 10 nm, which is close to the magnetic domain size (estimated from VSM as 8.4 +/- 1.7 nm) and the crystallite size (estimated from XRD as 11 pm 4 nm), which reveal nearly single crystalline character of Co3O4 nanoparticles. The suggested route is facile, which provides a good size control over the nanoparticles, and can be used for the fabrication of other ceramic materials.

  • 202. Shafiu, S.
    et al.
    Topkaya, R.
    Baykal, A.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Facile synthesis of PVA-MnFe2O4 nanocomposite: Its magnetic investigation2013In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 48, no 10, p. 4066-4071Article in journal (Refereed)
    Abstract [en]

    Manganese ferrite (MnFe2O4)-polyvinyl alcohol (PVA) nanocomposite was prepared by a PVA assisted sot-gel auto-combustion method. The magnetic core of the carriers was manganese ferrite (MnFe2O4), with average crystallite size of 9.1 +/- 2.1 nm. The PVA-MnFe2O4 nanocomposite exhibited superparamagnetic behavior at room temperature and ferromagnetic behavior at low temperatures. Zero-field-cooled and field-cooled measurements further confirm the superparamagnetic behavior with a blocking temperature of 160 K. The lower reduced remanent magnetization values than theoretical value of 0.5 indicate that the PVA/MnFe2O4 nanocomposite used in this study has uniaxial anisotropy rather than the expected cubic anisotropy according to the Stoner-Wohlfarth model. The calculated magnetic anisotropy constant of the sample is similar to 1.45 x 10(6) erg/cm(3) which is significantly higher than that of the bulk MnFe2O4 due to the strong magnetic coupling between magnetic core and surface spins.

  • 203.
    Shahid, Robina
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Gorlov, Mikhail
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    El-Sayed, Ramy
    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.
    Sugunan, Abhilash
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Microwave assisted synthesis of ZnS quantum dots using ionic liquids2012In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 89, p. 316-319Article in journal (Refereed)
    Abstract [en]

    In this work we report results from microwave (MW) assisted synthesis of highly crystalline ZnS quantum dots (QDs) using ionic liquid (ILs) as MW absorbing medium. Two types of ionic liquids, imidazolium and phosphonium based, were used. The QDs are less than 5 nm in size and of wurtzite ZnS type, as characterized by high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) pattern. The optical properties were investigated by UV-vis absorption and show a blue shift in absorption as compared to bulk wurtzite ZnS due to quantum confinement effects. The photoluminescence (PL) spectra of the QDs show different trap state emissions.

  • 204. Shahid, Robina
    et al.
    Muhammad, Nawshad
    Gonfa, Girma
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Synthesis, COSMO-RS analysis and optical properties of surface modified ZnS quantum dots using ionic liquids2015In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 85, p. 34-38Article in journal (Refereed)
    Abstract [en]

    Zinc sulfide (ZnS) quantum dots (QDs) were synthesized using the microwave assisted ionic liquid (MAIL) route. Three ionic liquids (ILs), namely, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), trihexyl(tetradecyl) phosphonium bis(trifluoromethanesulfonyl) amide ([P-6,P-6,P-6,P-14][TSFA]) and trihexyl (tetradecyl) phosphonium chloride ([P-6,P-6,P-6,P-14][Cl]) were used in this study. The size and structure of the QDs were characterized by high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) pattern, respectively. The synthesized QDs were of wurtzite crystalline structure with size less than 5 nm. The QDs were more uniformly distributed while using the phosponium based ILs as a reaction medium during synthesis. The optical properties were investigated by UV-vis absorption and photoluminescence (PL) emission spectroscopy. The optical properties of QDs showed the quantum confinement effect in their absorption and the effect of cation and anion structural moiety was observed on their bandedge emission. The QDs emission intensity was measured higher for [P-6,P-6,P-6,P-14][Cl] due to their better dispersion as well as high charge density of Cl anion. The capability of the ILs in stabilizing the QDs was interpreted by density functional theory (DFT) computations. The obtained results are in good agreement with the theoretical prediction.

  • 205.
    Shahid, Robina
    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.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Microwave-assisted low temperature synthesis of wurtzite ZnS quantum dots2012In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 187, p. 130-133Article in journal (Refereed)
    Abstract [en]

    In this work we report, for the first time, on microwave assisted synthesis of wurtzite ZnS quantum dots (QDs) in controlled reaction at temperature as low as 150 degrees C. The synthesis can be done in different microwave absorbing solvents with multisource or single source precursors. The QDs are less than 3 nm in size as characterized by transmission electron microscopy (TEM) using selected area electron diffraction (SAED) patterns to confirm the wurtzite phase of ZnS QDs. The optical properties were investigated by UV-Vis absorption which shows blue shift in absorption compared to bulk wurtzite ZnS due to quantum confinement effects. The photoluminescence (PL) spectra of QDs reveal point defects related emission of ZnS QDs.

  • 206.
    Shahid, Robina
    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.
    Soliman, Hesham M. A.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Low temperature synthesis of cubic phase zinc sulfide quantum dots2012In: Central European Journal of Chemistry, ISSN 1895-1066, E-ISSN 1644-3624, Vol. 10, no 1, p. 54-58Article in journal (Refereed)
    Abstract [en]

    In this study, we report on a new method for the synthesis of ZnS quantum dots (QDs). The synthesis was carried out at low temperature by a chemical reaction between zinc ions and freshly reduced sulfide ions in ethanol as reaction medium. Zinc chloride and elemental sulfur were used as zinc and sulfur sources, respectively and hydrazine hydrate was used as a strong reducing agent to convert elemental sulfur (S(8)) into highly reactive sulfide ions (S(2-)) which react spontaneously with zinc ions. This facile, less toxic, inexpensive route has a high yield for the synthesis of high quality metal sulfide QDs. Transmission electron microscopy (TEM) image analysis and selected area electron diffraction (SAED) reveal that ZnS QDs are less than 3 nm in diameter and are of cubic crystalline phase. The UV-Vis absorption spectrum shows an absorption peak at 253 nm corresponding to a band gap of 4.9 eV, which is high when compared to the bulk value of 3.68 eV revealing strong quantum confinement. PL emission transitions are observed at 314 nm and 439 nm and related to point defects in ZnS QDs.

  • 207.
    Singh, Sathya P.
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Nikkam, Nader
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Ghanbarpour, Morteza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Design and Evaluation of Carbon Nanotube Based Nanofluids for Heat Transfer Applications2013In: MRS Spring 2013 Proceedings: Symposium on Nanoscale Heat Transport—From Fundamentals to Devices, Materials Research Society, 2013Conference paper (Refereed)
    Abstract [en]

    The present work investigates the fabrication, thermal conductivity (TC) and rheological properties of water based carbon nanotubes (CNTs) nanofluids (NFs) prepared using a two-step method. As-received (AR) CNTs heated and the effect of heat treatment was studied using X-ray diffraction and thermogravimetric analysis. The AR-CNTs and heat-treated CNTs (HT-CNTs) were dispersed with varying concentration of surface modifiers Gum Arabic (GA) and TritonX-100 (TX) respectively. It was found that heat treatment of CNTs effectively improved the TC and influenced rheological properties of NFs. Scanning electron microscopy analysis revealed TX modified NFs showed better dispersion ability compared to GA. Surface modification of the CNTs was confirmed by Fourier Transformation Infrared (FTIR) analysis. Zeta potential measurement showed the stability region for GA modified NFs in the pH range of 5-11, whereas pH was between 9.5-10 for TX NFs. The concentration of surface modifier plays an extensive role on both TC and rheological behavior of NFs. A maximum TC enhancement of 10% with increases in viscosity around 2% for TX based HT-CNTs NFs was measured. Finally comparison of experimental TC results with the predicted values obtained from a model demonstrated inadequacy of the predictive model for CNT NFs system.

  • 208. Sozeri, H.
    et al.
    Kurtan, U.
    Topkaya, R.
    Baykal, A.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Polyaniline (PANI)-Co0.5Mn0.5Fe2O4 nanocomposite: Synthesis, characterization and magnetic properties evaluation2013In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 39, no 5, p. 5137-5143Article in journal (Refereed)
    Abstract [en]

    Polyaniline (PANI)/Cobalt-manganese ferrite, (PANI)/Co0.5Mn0.5Fe2O4, nanocomposite was synthesized by oxidative chemical polymerization of aniline in the presence of ammonium peroxydisulfate (APS). Microwave assisted synthesis method was used for the fabrication of core CoFe2O4 nanoparticles. The structural, morphological, thermal and magnetic properties of the nanocomposite were investigated in detail by X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The average crystallite size of (PANI)/Co0.5Mn0.5Fe2O4 nanocomposite by the line profile method was 20 +/- 9 nm. The magnetization measurements revealed that (PANI)/Co0.5Mn0.5Fe2O4 nanocomposite has superparamagnetic behavior with blocking temperature higher than 300 K. The saturation magnetization of the composite is considerably low compared to that of CoFe2O4 nanoparticles due to the partial replacement of Co2+ ions and surface spin disorder. As temperature decreases, both coercivity and strength of antiferromagnetic interactions increase which results in unsaturated magnetization of the nanocomposite.

  • 209. Stiewe, C
    et al.
    Bertini, L
    Toprak, Muhammet S.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Christensen, M
    Platzek, D
    Williams, S
    Gatti, C
    Muller, E
    Iversen, BB
    Muhammed, Mamoun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Rowe, M
    Nanostructured Co1-xNix(Sb1-yTey)(3) skutterudites: Theoretical modeling, synthesis and thermoelectric properties2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 4Article in journal (Refereed)
    Abstract [en]

    The properties of Te-doped Co(Sb1-yTey)(3) and Te-Ni double-doped Co1-xNix(Sb1-yTey)(3) nanostructured skutterudites were evaluated by means of x-ray powder diffraction, and transport properties measured on the synthesized samples have been compared with ab initio theoretical modeling. Theoretical optimal dopant contents have been evaluated according to the maximum value of the power factor, calculating the electronic transport properties from the ab initio material band structure using semiclassical Boltzmann transport theory. The samples have been synthesized by chemical alloying with Te substitution for Sb up to 2.5 at. % and Ni substitution for Co up to 2.0 at. %. X-ray powder diffraction has been performed on all samples to reveal information about phase purity and Rietveld refinement was performed for the phase composition and cell parameter. The thermoelectric properties of the resulting consolidates were investigated in a temperature range from 300 to 723 K using various measurement facilities. A standardization and round robin program was started among the participating evaluation laboratories in order to ensure reliability of the data obtained. The significant reduction in thermal conductivity, when compared to highly annealed CoSb3, could be proved which is caused by the nanostructuring, resulting in a high concentration of grain boundaries. A combination of substitution levels for Ni and Te has been found resulting in the largest ZT value of 0.65 at 680 K among unfilled skutterudite materials.

  • 210. Stiewe, C.
    et al.
    He, Z.
    Platzek, D.
    Karpinski, G.
    Mueller, E.
    Li, S.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Muhammed, Mamoun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Control of thermoelectric properties in ZrO2/CoSb3 nano-dispersed composites2007In: Materialwissenschaft und Werkstofftechnik, ISSN 0933-5137, E-ISSN 1521-4052, Vol. 38, no 9, p. 773-776Article in journal (Refereed)
    Abstract [en]

    Nano-dispersed ZrO2/CoSb3 composites of various composition were prepared by uniaxial hot pressing of nano-sized powders of thermoelectric CoSb3 intermixed with ceramic nano-powders. The phase purity, the niicrostructure, and the temperature dependent transport parameters of the composites were investigated. Non-dispersed samples from nano-sized CoSb3 powders show higher electrical conductivity compared to melt-grown material which is attributed to the presence of a small excess of metallic Sb, but they exhibit lower thermal conductivity due to the fine-grained structure. Addition of 5 at.-% ZrO2 enhances the ratio of electrical to thermal conductivity, whereas hardly affects the See-beck coefficient. In this manner the nano-dispersion method provides an effective approach to improving the materials thermoelectric performance.

  • 211. Stiewe, C.
    et al.
    He, Z.
    Platzek, D.
    Müller, E.
    Li, Shen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Toprak, Muhammet
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Muhammed, Mamoun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Influence of phase composition on the thermoelectric properties of nanostructured skutterudite and ceramic composites2006Conference paper (Refereed)
    Abstract [en]

    Nanostructuring of unfilled CoSb3 Skutterudites has been successful in reducing the thermal conductivity of these materials [1]. First measurements on a mixture of the Skutterudite and an inert ceramic with particle sizes in the nanometer range have shown promising results for a further reduced thermal conductivity by decorating the grain boundaries of the thermoelectric material [2]. A strong influence of additional phases like CoSb2 and pure Sb in the samples has been encountered, too. Therefore in the present work a more detailed investigation of the effect of phase purity and grain size by an intential variation of the phase composition is presented. The impact of a variation in the amount of the ceramics addition and of the phase composition on the thermoelectric properties (κ, σ, S) of pure and doped CoSb 3, respectively, are studied and the results are discussed with respect to an enhancement of the thermoelectric figure of merit.

  • 212.
    Sugunan, Abhilash
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Guduru, Veerendra K.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Uheida, Abdusalam
    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.
    A ‘Continuous flow’ Photochemical Water Treatment System Based on Radially Oriented ZnO Nanowires on Flexible Poly-L-Lactide NanofibersManuscript (preprint) (Other academic)
    Abstract [en]

    Several oxide ceramics, notably ZnO and TiO2 are known to catalyze decomposition of organic molecules in water under ultra-violet irradiation. Here we describe fabrication of highly flexible ZnO-based hierarchical nanostructure obtained by growing radially oriented ZnO nanowires on poly-L-lactide nanofibers. Utilizing the flexibility and high surface area of polymeric nanofibers as novel ‘substrate’ for growth of the photochemically active ZnO nanowires we show a proof-of-principle demonstration of a ‘continuous flow’ water treatment set-up. We have monitored photocatalytic decomposition of known organic pollutants, such as methylene blue, monocrotophos and diphenylamine under illumination with ultraviolet light using this highly flexible hierarchical nanostructure.

  • 213.
    Sugunan, Abhilash
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Guduru, Veerendra K.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Uheida, Abdusalam
    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.
    Radially Oriented ZnO Nanowires on Flexible Poly-L-Lactide Nanofibers for Continuous-Flow Photocatalytic Water Purification2010In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 93, no 11, p. 3740-3744Article in journal (Refereed)
    Abstract [en]

    Several oxide ceramics, notably ZnO and TiO2 are known to catalyze decomposition of organic molecules in water under ultraviolet (UV) irradiation. Here we describe fabrication of highly flexible ZnO-based hierarchical nanostructure obtained by growing radially oriented ZnO nanowires on poly-L-lactide nanofibers. Utilizing the flexibility and high surface area of polymeric nanofibers as novel substrate for growth of the photochemically active ZnO nanowires we show a proof-of-principle demonstration of a continuous flow water treatment setup. We have monitored photocatalytic decomposition of known organic pollutants, such as methylene blue, monocrotophos, and diphenylamine under illumination with UV light using this highly flexible hierarchical nanostructure.

  • 214.
    Sugunan, Abhilash
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Jafri, S. Hassan M.
    Qin, Jian
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Blom, Tobias
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Leifer, Klaus
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Low-temperature synthesis of photoconducting CdTe nanotetrapods2010In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 20, no 6, p. 1208-1214Article in journal (Refereed)
  • 215.
    Sugunan, Abhilash
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Mitra, Somak
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Dong, Lin
    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.
    Marcinkevicius, Saulius
    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.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis of tetrahedral quasi-type-II CdSe-CdS core-shell quantum dots2011In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 22, no 42, p. 425202-Article in journal (Refereed)
    Abstract [en]

    Synthesis of colloidal nanocrystals of II-VI semiconductor materials has been refined in recent decades and their size dependent optoelectronic properties have been well established. Here we report a facile synthesis of CdSe-CdS core-shell heterostructures using a two-step hot injection process. Red-shifts in absorption and photoluminescence spectra show that the obtained quantum dots have quasi-type-II alignment of energy levels. The obtained nanocrystals have a heterostructure with a large and highly faceted tetrahedral CdS shell grown epitaxially over a spherical CdSe core. The obtained morphology as well as high resolution electron microscopy confirms that the tetrahedral shell have a zinc blende crystal structure. A phenomenological mechanism for the growth and morphology of the nanocrystals is discussed.

  • 216.
    Tafti, Mohsen Yakhshi
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Stockholm University, Sweden.
    Han, Li
    Nong, Ngo V.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    On the chemical synthesis route to bulk-scale skutterudite materials2016In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 42, no 4, p. 5312-5318Article in journal (Refereed)
    Abstract [en]

    In this article an alternative high yield route for the synthesis of CoSb3-based unfilled skutterudites is presented. Using low-melting temperature salts of the constituents, melting and mixing them homogeneously in a hydrophobic liquid with postprocessing of the powders we achieve a more intimately mixed alloy compared to the conventional melting and metallurgical processes. The proposed method consists of a fast and low-temperature processing step followed by a thermochemical post-processing step, compared to the conventional methods of fabricating skutterudites, which require high temperatures and long processing times. Several structural characterization techniques were used to assess the mechanism of synthesis, verify the purity of the material as well as the reproducibility of the process. Detailed analysis and results are presented in support of the proposed process. Additionally, compaction of the powders with SPS technique provided a safe route to maintaining the nanopowder size and achieving low thermal conductivity (3 W/mK). The proposed method can easily be scaled up and adopted by the industry.

  • 217.
    Tafti, Mohsen Yakshi
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Toprak, Muhammet S
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Johnsson, Mats
    Stockholm University.
    Jacquot, Alexandre
    Jägle, Martin
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Fabrication and characterization of nanostructured thermoelectric FexCo1-xSb32015In: Open Chemistry, E-ISSN 2391-5420, Vol. 13, no 1, p. 629-635Article in journal (Refereed)
    Abstract [en]

    A novel synthesis route for the fabrication of p-type nanostructured skutterudite, FexCo1-xSb3 in large quantity is reported. This scalable synthesis route provides nano-engineered material with less impact on the environment compared to conventional synthesis procedures. Several Fe substituted compositions have been synthesized to confirm the feasibility of the process. The process consists of a nano-sized precursor fabrication of iron and cobalt oxalate, and antimony oxides by chemical co-precipitation. Further thermochemical processes result in the formation of iron substituted skutterudites. The nanopowders are compacted by Spark Plasma Sintering (SPS) technique in order to maintain nanostructure. Detailed physicochemical as well as thermoelectric transport properties are evaluated. Results reveal strongly reduced thermal conductivity values compared to conventionally prepared counterparts, due to nanostructuring. P-type characteristic was observed from the Seebeck measurements while electrical conductivity is high and shows metallic behavior. The highest TE figure of merit of 0.25 at 800 K has been achieved, which is strongly enhanced with respect to the mother compound CoSb3. This suggests the promise of the utilized method of fabrication and processing for TE applications with improved performance.

  • 218. Topkaya, R.
    et al.
    Kurtan, U.
    Baykal, A.
    Sozeri, H.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Materials- and Nano Physics, Functional Materials, FNM.
    Polymer Assisted Co-precipitation Synthesis and Characterization of Polyethylene Glycol (PEG)/CoFe2O4 Nanocomposite2013In: Journal of Inorganic and Organometallic Polymers and Materials, ISSN 1574-1443, Vol. 23, no 3, p. 592-598Article in journal (Refereed)
    Abstract [en]

    Polyetylene glycol (PEG)/CoFe2O4 nanocomposite have been synthesized by PEG assisted co-precipitation method. The presence of PEG on the surface of CoFe2O4 nanoparticles was confirmed by Fourier transform infrared spectroscopy. Vibrating sample magnetometer measurements revealed a saturation magnetisation (M (s)) value of 90.95 emu/g, which is higher than bulk value, and coercive field (H (c)) of 862 Oe that is close to the bulk value at room temperature. The temperature dependent magnetization increases initially and then decreases with increasing temperature. This anomality is attributed to the decrease of B sublattice magnetization more rapidly than A sublattice magnetization. The M (r)/M (s) values lower than theoretical value of 0.5 suggests that the PEG/CoFe2O4 nanocomposite has effective uniaxial anisotropy according to the Stoner-Wohlfarth model. Enhanced magnetic properties (higher M (s) and bulk-like H (c) value) make the PEG/CoFe2O4 nanocomposite a promising candidate for high density magnetic recording media.

  • 219. Topkaya, R.
    et al.
    Kurtan, U.
    Baykal, A.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Polyvinylpyrrolidone (PVP)/MnFe2O4 nanocomposite: Sol-Gel autocombustion synthesis and its magnetic characterization2013In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 39, no 5, p. 5651-5658Article in journal (Refereed)
    Abstract [en]

    A polyvinylpyrrolidone (PVP)/MnFe2O4 nanocomposite was prepared by the sol-gel autocombustion method and its structural, thermal, spectroscoppic, morphological and magnetic characterizations were done by XRD, FT-IR, TGA, SEM and VSM techniques. The presence of MnFe2O4 was confirmed by XRD and the size of crystallites was estimated to be 11 +/- 3 nm. Morphology analysis by SEM revealed spherical agglomerates of 15 nm. The magnetization curves confirm a superparamagnetic behavior with a blocking temperature of 287 K. The M-r/M-s value suggests the presence of uniaxial anisotropy in MnFe2O4 nanoparticles, instead of the expected cubic anisotropy according to the Stoner-Wohlfarth model. The effective magnetic anisotropy constant K-eff has been determined to be about 1.42 x 10(6) erg/cm(3) which is significantly higher than that of the bulk MnFe2O4. This suggests a strong magnetic coupling between magnetically ordered core spins and disordered surface spins of the nanoparticles in the nanocomposite.

  • 220.
    Toprak, Muhammet
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Li, Shanghua
    KTH.
    Muhammed, Mamoun
    KTH.
    Fabrication routes for nanostructured TE material architectures2017In: Materials, Preparation, and Characterization in Thermoelectrics, CRC Press , 2017, p. 17-1-17-18Chapter in book (Other academic)
    Abstract [en]

    Nanomaterials have been an emerging œeld of research due to the novel properties exhibited when the size of building blocks is reduced below 100 nm. Several size-dependent phenomena make nanomaterials attractive in terms of potential applicability compared to their larger-sized counterparts, justifying the importance and attention of this research.1-3 For thermoelectric research, nanomaterials are of great interest due to the possibility of decoupling electrical and thermal transport properties which may help attain higher ZT values for the currently available materials.4,5 še commonly accepted nomenclature of nanomaterials is based on the number of degrees of freedom of charge carriers for the description of their dimensionalities. šus, a thin œlm or superlattice is conœned in one dimension, but is a 2D nanomaterial. Similarly, a nanowire is conœned in two dimensions, hence is a 1D nanomaterial, and œnally a nanoparticle is conœned in three dimensions and is therefore a 0D nanomaterial. In the case of larger nanocrystals (not quantum conœned), the size and shape of the nanocrystals also affect their properties due to differences in surface-to-volume ratio. Bulk nanostructured (NS) TE materials are fabricated using a bulk process rather than a nanofabrication process, which has the important advantage of being produced in large quantities and in a form that is compatible with commercially available devices.6 šey are different from the advanced low-dimensional TE materials as they are consolidated under high T and P, resulting in larger-sized (40-200 nm) grains. še advanced low-dimensional TE materials are usually in quantum size and have well-deœned shapes such as rod-like or tube-like structures. še nanoeffects of bulk NS TE materials will not be as strong as in the case of advanced low-dimensional TE materials, but since the material is closer to bulk material, it can be easily handled the same way as bulk TE materials using conventional TE module/device technology for further steps toward direct applications. So far, of all the NS materials, only bulk NS materials have been produced in enough quantity to be used in this manner. 

  • 221. Toprak, Muhammet
    et al.
    McKenna, Brandon J.
    Waite, Herb
    Stucky, Galen D.
    Tailoring magnetic microspheres with controlled porosity2007In: Heterogeneous Integration of Materials for Passive Components and Smart Systems: MATERIALS RESEARCH SOCIETY SYMPOSIUM PROCEEDINGS / [ed] Nino, JC; Roozeboom, F; Muralt, P; TrolierMcKinstry, S; LaVan, D, Materials Research Society, 2007, Vol. 969, p. 93-98Conference paper (Refereed)
    Abstract [en]

    The synthesis of organic and inorganic nano- and microspheres has attracted much interest for a variety of applications ranging from drug delivery to chemical storage and catalysis. We recently demonstrated the assembly of magnetic nanoparticles and polycations into hybrid microspheres in a single-step synthesis via complex coacervation. These microspheres showed viability for bio-applications as indicated by toxicity tests, and are therefore potential targeted drug delivery devices, as they can be directed magnetically. This work reports the recent progress on the potential use of these assemblies in drug release by controlling their porosity. Fluorescein tagged dextran molecules with different MW have been infiltrated into these entities to determine critical pore size by confocal fluorescence microscopy. Different physicochemical characterization results are also presented.

  • 222.
    Toprak, Muhammet S.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Darab, Mahdi
    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.
    Synthesis of nanostructured BSCF by oxalate co-precipitation - As potential cathode material for solid oxide fuels cells2010In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 35, no 17, p. 9448-9454Article in journal (Refereed)
    Abstract [en]

    BaxSr1-xCoyFe1-yO3 (BSCF) cathode material for solid oxide fuel cells (SOFC) was synthesized in nanocrystalline form by a novel chemical alloying approach. Thermodynamic modeling has been performed using Medusa software for obtaining the optimum conditions for the fabrication of a precursor with the desired composition. Precursor powder was then calcined and annealed to produce the final mixed oxide BSCF composition. The thermal properties, phase constituents, microstructure and elemental analysis of the samples were characterized by TGA, XRD, SEM and EDS techniques respectively. Spark Plasma Sintering (SPS) has been used at 1080 degrees C and under 50 MPa pressure to obtain the pellets of BSCF with preserved nanostructure and rather high compaction density for electrical conductivity measurements. The results show that the powders have cubic perovskite-type structure with a high homogeneity. Finer resultant powder, compared to earlier reports, and SPS sintered BSCF with nanosized grains exhibited a significantly higher electrical conductivity up to 900 degrees C. Specific conductivity values have been measured in air and N-2 and the maximum of 63 5 cm(-1) at 430 degrees C in air and 25 S cm(-1) at 375 degrees C in N-2 correspondingly show twice as much as conventional BSCF implying a high pledge for nano-BSCF as cathode material in intermediate-temperature SOFC. This is due to the lower interfacial resistance of preserved nanograins by the use of SPS sintering. Presented co-precipitation method is easy to handle and has a high promise to synthesize BSCF at large-scale for IT-SOFCs.

  • 223.
    Toprak, Muhammet S
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Karlsson, Hanna L
    Fadeel, Bengt
    Handbook on the Toxicology of Metals2014In: Handbook on the Toxicology of Metals: Toxicity of Metal and Metal Oxide Nanoparticles / [ed] Nordberg,G.F., Fowler, B.A., Nordberg, M., Elsevier, 2014, 4, p. 75-112Chapter in book (Other academic)
    Abstract [en]

    Engineered nanomaterials hold great potential in many sectors of society, not least in medicine. However, the increasing production and use of engineered nanomaterials also raises concerns about inadvertent exposure and the potential for adverse effects on human health and the environment. This chapter provides an overview of metal and metal oxide nanoparticles, their applications, and the potential for human exposure. This is followed by a discussion of general principles of nanoparticle-induced toxicity and methods for toxicity testing of nanomaterials. Careful assessment of the material properties is required for a full understanding of nanomaterial toxicity; a section of the chapter is therefore devoted to physicochemical characterization. This is followed by a detailed description of the current knowledge concerning 12 of the most important metal and metal oxide nanoparticles, with a systematic evaluation of in vitro (cell culture) and in vivo (animal) toxicity studies. Ecotoxicological effects are not discussed because the chapter is focused on implications for human health.

  • 224.
    Toprak, Muhammet S.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Kim, Do-Kyung
    KTH, Superseded Departments, Materials Science and Engineering.
    Mikhaylova, Maria
    KTH, Superseded Departments, Materials Science and Engineering.
    Jo, Yunsuk
    KTH, Superseded Departments, Materials Science and Engineering.
    Muhammed, Mamoun
    KTH, Superseded Departments, Materials Science and Engineering.
    Fabrication of 3D TE structures2004In: Functional Nanomaterials For Optoelectronics And Other Applications / [ed] Lojkowski, W; Blizzard, JR, 2004, Vol. 99-100, p. 73-76Conference paper (Refereed)
    Abstract [en]

    Templating methods provide an alternative approach for fabricating macroporous solids with three-dimensionally ordered arrays of pores with diameters from tens to hundreds of nanometers. The main goal of this work is the fabrication of thermoelectric-opal composite and inverse opals made of thermoelectric material in order to obtain enhanced performance by reducing the thermal conduction. Chemical bath deposition (CBD) has been employed and thermodynamic modelling was used to obtain optimum conditions for the desired phase of particle formation within the channels of the opal-like structures. The wetting behaviours of opals were considered in the choice of the appropriate solvents. When loading is finished, the precursor is decomposed and reduced when appropriate. The opal template is then removed by pyrolysis to obtain the macroporous structures. The structural properties of materials produced were investigated.

  • 225. Toprak, Muhammet S.
    et al.
    McKenna, B.J.
    University of California at Santa Barbara.
    Waite, J.H.
    Stucky, G.D.
    Control of size and permeability of nanocomposite microspheres2007In: Chemistry of Materials, ISSN 0897-4756, Vol. 19, no 17, p. 4263-4269Article in journal (Refereed)
    Abstract [en]

    This work reports on progress in controlling the size and porosity of spontaneously assembled composite polyelectrolyte microspheres for their potential use in targeted drug delivery applications. In this study, the composite polyelectrolyte microsphere is exemplified by PLK/TSC containing magnetic nanoparticles. The stability of these microspheres against environmental alterations such as pH, ionic strength, and dilution is a critical issue for practical considerations. The effects of ionic strength and dilution on the size of these hybrid spheres were investigated by the addition of salts with different cationic charges and deionized water. Increasing both ionic strength and dilution caused a decrease in the average size of microspheres from similar to 700 to similar to 200 nm. Ions of +2 charge were observed to screen interactions between the assembling components via a substitution effect. The composite polyelectrolyte microspheres could be mechanically stabilized by cross-linking with glutaraldehyde (GA). The microsphere permeabilities were analyzed using fluorescein-tagged dextran molecules of different MW with confocal laser scanning microscopy and fluorescence recovery after photobleaching. Microsphere permeabilities and critical pore sizes could be controllably decreased by altering the extent of cross-linking, which was monitored by UV-vis spectroscopy. Quantitative analysis revealed that cross-linking can be used to control the diffusion coefficient of dextran and can reduce it by 4 orders of magnitude.

  • 226.
    Toprak, Muhammet S
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Seisenbaeva, Gulaim A.
    Kessler, Vadim G.
    ANNEX: Synthesis of Nanomaterials2012In: Adverse Effects of Engineered Nanoparticles / [ed] Bengt Fadeel, Antonio Pietroiusti, and Anna Shvedova, Academic Press, 2012Chapter in book (Other academic)
  • 227.
    Toprak, Muhammet S.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Stiewe, C
    Platzek, D
    Williams, S
    Bertini, L
    Muller, Eckhard
    Gatti, C
    Zhang, Yu
    KTH, Superseded Departments, Materials Science and Engineering.
    Rowe, M
    Muhammed, Mamoun
    KTH, Superseded Departments, Materials Science and Engineering.
    The impact of nanostructuring on the thermal conductivity of thermoelectric CoSb32004In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 14, no 12, p. 1189-1196Article in journal (Refereed)
    Abstract [en]

    The high concentration of grain boundaries provided by nanostructuring is expected to lower the thermal conductivity of thermoelectric materials, which favors an increase in their thermoelectric figure-of-merit, ZT. A novel chemical alloying method has been used for the synthesis of nanoengineered-skutterudite CoSb3. The CoSb3 powders were annealed for different durations to obtain a set of samples with different particle sizes. The samples were then compacted into pellets by uniaxial pressing under various conditions and used for the thermoelectric characterization. The transport properties were investigated by measuring the Seebeck coefficient and the electrical and thermal conductivities in the temperature range 300 K to 650 K. A substantial reduction in the thermal conductivity of CoSb3 was observed with decreasing grain size in the nanometer region. For an average grain size of 140 nm, the thermal conductivity was reduced by almost an order of magnitude compared to that of a single crystalline or highly annealed polycrystalline material. The highest ZT value obtained was 0.17 at 611 K for a sample with an average grain size of 220 nm. The observed decrease in the thermal conductivity with decreasing grain size is quantified using a model that combines the macroscopic effective medium approaches with the concept of the Kapitza resistance. The compacted samples exhibit Kapitza resistances typical of semiconductors and comparable to those of Si-Ge alloys.

  • 228.
    Toprak, Muhammet S.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Vogt, Carmen
    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.
    Active Cooperative Assemblies Towards Nanocomposites2009In: ADVANCES IN MATERIAL DESIGN FOR REGENERATIVE MEDICINE, DRUG DELIVERY AND TARGETING/IMAGING    / [ed] Shastri VP; Lendlein A; Liu L; Mikos A; Mitragotri S, 2009, Vol. 1140, p. 197-202Conference paper (Refereed)
    Abstract [en]

    This work reports on the fabrication of novel type of assemblies bearing magnetic nanoparticles and inorganic shells prepared via a biomimetic route of complex coacervation. Magnetic nanoparticles fabricated under controlled conditions were surface modified with polyacrylic acid (PAA). Subsequently, PAA spontaneously formed spherical assemblies in contact with certain ions, such as Ca2+. The stability of these microspheres against environmental alterations such as pH, ionic strength, and dilution was increased through cross-linking. Ethylene diammine (EDA) was used as a cross-linker, which resulted in mechanically stabilized system that does not show sensitivity towards the external pH values. Important parameters for the formation of these coacervates as well as mechanism of formation and cross-linking have been evaluated by FTIR analysis. The cooperative assemblies are still active for further reaction and were used for the growth of an inorganic aluminum oxide shell. SEM analysis of these spheres showed that the structures are hollow with a large interior volume. A biocompatible outer surface combined with the magnetic functionality is very important for the targeted drug delivery devices for biomedical applications.

  • 229.
    Toprak, Muhammet S.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Zhang, Y
    Muhammed, Mamoun
    KTH, Superseded Departments, Materials Science and Engineering.
    Chemical alloying and characterization of nanocrystalline bismuth telluride2003In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 57, no 24-25, p. 3976-3982Article in journal (Refereed)
    Abstract [en]

    A novel chemical alloying method has been developed for the fabrication of nanocrystalline thermoelectric alloy Bismuth telluride, Bi2Te3. The method consists of a combination of solution chemical method and thermal processing under controlled heating conditions. The components have been coprecipitated from a solution and the precursor consists of a solid solution of the different intermediate compounds and exhibits high reactivity. Calcination and hydrogen reduction of the precursor at moderate temperature, 350 degreesC, for 2 h resulted in the alloying of these elements to obtain the pure phase of the thermoelectric material in fine powder. The method is simpler than conventional melt processing and produced a 95-98% yield in laboratory scale. High concentration of grain boundaries provided by nanostructuring is expected to lower the thermal conductivity of thermoelectric material and further increase the performance.

  • 230.
    Toprak, Muhammet
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zhang, Yu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jo, Yunsuk
    Kim, Do-Kyung
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Muhammed, Mamoun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Nanocrystalline thermoelectric alloys: Processing, chemistry and characterization2005In: BULK AND GRADED NANOMETALS / [ed] Kurzydlowski, KJ; Pakiela, Z, 2005, Vol. 101-102, p. 197-204Conference paper (Refereed)
    Abstract [en]

    A novel chemical alloying method has been developed for the fabrication of nanocrystalline thermoelectric alloys cobalt antimonide, CoSb3, and bismuth telluride, Bi2Te3. The method combines a solution chemical method and thermal processing under controlled heating conditions. The components have been co-precipitated from a solution and the precursor consisted of a solid solution of the different intermediate compounds with different crystallinity. Calcination and hydrogen reduction of the precursor at moderate temperature, 350degreesC, resulted in the alloying of these elements to obtain the nanocrystalline thermoelectric material. Crystallization of the amorphous precursor as well as the processing route have been investigated by following the changes in the chemistry of the material from the precursor to the final alloy. Detailed microstructure investigation by electron microscopy has also been presented.

  • 231. Unal, B.
    et al.
    Durmus, Z.
    Baykal, A.
    Sozeri, H.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Alpsoy, L.
    L-Histidine coated iron oxide nanoparticles: Synthesis, structural and conductivity characterization2010In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 505, no 1, p. 172-178Article in journal (Refereed)
    Abstract [en]

    L-Histidine capped iron oxide nanoparticles (HCIO) have been synthesized in one pot in the presence of L-histidine. The final product was analyzed for composition, microstructure, ac-dc conductivity performance as well as dielectric permittivity. Results revealed that magnetic nanoparticles are maghemite (or magnetite) and L-histidine is covalently bonded to the nanoparticle surface via carboxyl groups. Thermal analysis revealed that magnetic nanoparticles showed catalytic effect that caused an early degradation/decomposition of the L-histidine capping. Near spherical morphology was assessed by TEM and particle size calculated from TEM analysis and crystallite size calculated from XRD analysis reveal single crystalline nature of iron oxide NPs. Magnetic measurements reveal the superparamagnetic character of the nanoparticles, hence the nanocomposite. 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 is found to obey the Arrhenius plot with activation energy of 0.934 eV. Analysis of electrical modulus and dielectric permittivity functions suggest that ionic and polymer segmental motions are strongly coupled in the nanocomposite. (C) 2010 Elsevier B.V. All rights reserved.

  • 232. Unal, B.
    et al.
    Durmus, Z.
    Baykal, A.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sozeri, H.
    Bozkurt, A.
    Synthesis, dielectric and magnetic characteristics of poly(1-vinyl-1,2,4-triazole) (PVTri)-barium hexaferrite composite2011In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 509, no 32, p. 8199-8206Article in journal (Refereed)
    Abstract [en]

    The production of PVTri-BaFe(12)O(19) composites was carried out by in situ polymerization of PVTri in the presence of synthesized BaFe(12)O(19) particles. Crystalline phase was determined as BaFe(12)O(19) by XRD analysis and thermal analysis revealed an inorganic content of similar to 45% in the composite. SEM and TEM analyses showed strongly agglomerated particles in the range of 200 nm to several micrometers in the composite. The dielectric function of the various temperatures showed frequency dependency in a reciprocal power law. The dissipation (or loss) of energy stored within the composite was found to obey the reciprocal rule of power law of the frequency dependency. The real part of electrical modulus formalism increased exponentially with frequency for various temperatures, reaching a constant value and finally saturated. The imaginary part showed a reciprocal power law against the applied frequency and shifted to higher frequency at elevated temperatures. Magnetization measurements revealed substantially lower saturation magnetization of the composite material as compared to the bulk barium ferrite powders, possibly due to pinning of some of the surface spins by the adsorption of the PVTri molecules to the surface of the BaFe(12)O(19).

  • 233. Unal, B.
    et al.
    Durmus, Z.
    Kavas, H.
    Baykal, A.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis, conductivity and dielectric characterization of salicylic acid-Fe3O4 nanocomposite2010In: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 123, no 1, p. 184-190Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis of water dispersible salicylic acid -Fe3O4 nanocomposites via a co-precipitation route by using Fe(III) and Fe(II) chloride salts, and salicylic acid. Crystalline phase was identified as Fe3O4 and the crystallite size was obtained as 13 +/- 6 nm from X-ray line profile fitting. As compared to the particle size of 20 nm obtained from TEM analysis these particles show polycrystalline nature. The capping of salicylic acid around Fe3O4 nanoparticles was confirmed by FTIR spectroscopy, the interaction being via bridging oxygens of the carboxylate and the nanoparticle surface. ac and dc conductivity measurements performed on the nanocomposite revealed semiconductor characteristics and varying trends with temperature due to reorganization of the nanocomposite. Permittivity measurements showed increasing dielectric constant with increasing temperature as expected from semiconductors. Analysis of electrical modulus and dielectric permittivity functions suggest that ionic and polymer segmental motions are strongly coupled in the nanocomposite. (C) 2010 Elsevier B.V. All rights reserved.

  • 234. Unal, B.
    et al.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Durmus, Z.
    Sozeri, H.
    Baykal, A.
    Synthesis, structural and conductivity characterization of alginic acid-Fe3O4 nanocomposite2010In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 12, no 8, p. 3039-3048Article in journal (Refereed)
    Abstract [en]

    Alginic acid-Fe3O4 nanocomposite is synthesized by the precipitation of Fe3O4 in the presence of alginic acid (AA). Structural, surface, morphological, thermal and electrical transport properties of the nanocomposite were performed by XRD, FT-IR, TEM-SEM, TGA and conductivity measurements respectively. FT-IR analysis revealed that Fe3O4 NPs are strongly capped with AA and TGA analysis showed that nanocomposite have 80% of Fe3O4 content. TEM analysis of Fe3O4 NPs show an average particle size of 9.5 nm, and upon nanocomposite formation with AA these particles are observed to form aggregates of similar to 150 nm. The frequency-dependency of the AC conductivity show electrode polarization effect. Analysis of electrical modulus and dielectric permittivity functions suggest that ionic and polymer segmental motions are strongly coupled. DC electrical conductivity is strongly temperature dependent, and is classified into three regions over a limited temperature range of up to 100 A degrees C.

  • 235. Uzun, K.
    et al.
    Cevik, E.
    Senel, M.
    Sozeri, H.
    Baykal, A.
    Abasiyanik, M. F.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Covalent immobilization of invertase on PAMAM-dendrimer modified superparamagnetic iron oxide nanoparticles2010In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 12, no 8, p. 3057-3067Article in journal (Refereed)
    Abstract [en]

    In this study, polyamidoamine (PAMAM) dendrimer was synthesized on the surface of superparamagnetite nanoparticles to enhance invertase immobilization. The amount of immobilized enzyme on the surface-hyperbranched magnetite nanoparticle was up to 2.5 times (i.e., 250%) as much as that of magnetite nanoparticle modified with only amino silane. Maximum reaction rate (V (max)) and Michaelis-Menten constant (K (m)) were determined for the free and immobilized enzymes. Various characteristics of immobilized invertase such as; the temperature activity, thermal stability, operational stability, and storage stability were evaluated and results revealed that stability of the enzyme is improved upon immobilization.

  • 236.
    Vasileva, Elena
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Fei, Ye
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Marinins, Aleksandrs
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Etcheverry, Sebastián
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Popov, Sergei Yu
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Optimization of optical gain in composite materials containing Rh6G dye and gold nanoparticles2015In: Asia Communications and Photonics Conference, ACPC 2015, 2015Conference paper (Refereed)
    Abstract [en]

    The existence of metal nanoparticles in a dye material can lead not only to quenching or enhancement of dye luminescence, or random lasing action, but also to the change of the fundamental material characteristic as optical gain. © 2015 OSA.

  • 237.
    Vogt, Carmen M.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Kunzmann, Andrea
    Division of Molecular Toxicology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
    Torres, Neus Feliu
    Institute of Environmental Medicine, Karolinska Insitutet.
    Thurnherr, Tina
    Laboratory for Materials-Biology Interactoins, Swiss Federal Laboratories for Materials Testing and Research (EMPA), Gallen, Switzerland.
    Laurent, Sophie
    University of Mons-Hainaut, Belgium.
    Bridot, Jean-Luc
    University of Mons-Hainaut, Belgium.
    Müller, Robert N.
    University of Mons-Hainaut, Belgium.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Krug, Harald F.
    Laboratory for Materials-Biology.
    Fadeel, Bengt
    Institute of Environmental Medicine, Karolinska Institutet.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Biocompatibility of tuneable silica shell-magnetic core nanoparticles evaluated in vitro using primary human monocute-derived macrophagesManuscript (preprint) (Other (popular science, discussion, etc.))
  • 238.
    Vogt, Carmen M.
    et al.
    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.
    Laurent, Sophie
    University of Mons-Hainaut, Belgium.
    Bridot, Jean-Luc
    University of Mons-Hainaut, Belgium.
    Müller, Robert N.
    University of Mons-Hainaut.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    High quality and tuneable silica shell-magnetic core nanoparticles2010In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 12, no 4, p. 1137-1147Article in journal (Refereed)
    Abstract [en]

    Obtaining small (<50 nm), monodispersed, well-separated, single iron oxide core-silica SiO2) shell nanoparticles for biomedical applications is still a challenge. Preferably, they are synthesized by inverse microemulsion method. However, substantial amount of aggregated and multicore core- shell nanoparticles is the undesired outcome of the method. In this study, we report on the production of less than 50 nm overall size, monodispersed, free of necking, single core iron oxide-SiO2 shell nanoparticles with tuneable shell thickness by a carefully optimized inverse microemulsion method. The high degree of control over the process is achieved by understanding the mechanism of core-shell nanoparticles formation. By varying the reaction time and recursor concentration, the thickness of silica layer an the core nanoparticles can be finely adjusted from to 13 nm. Residual reactions during the workup were inhibited by a combination of pH control with hock freezing and ultracentrifuging. These highquality tuneable core-shell nanocomposite particles exhibit superparamagnetic character and sufficiently high magnetization with great potential for biomedical applications (e.g. MRI, cell separation and magnetically driven drug delivery systems) either as-prepared or by additional surface modification for improved biocompatibility.

  • 239.
    Vogt, Carmen M.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Shi, J.
    Torres, N. F.
    Fadeel, B.
    Laurent, S.
    Bridot, J. -L
    Müller, R. N.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Optimised synthetic route for tuneable shell Si02@Fe304 core-shell nanoparticles2009In: Advances in material design for regenerative medicine, drug delivery, and targeting/imaging, Materials Research Society, 2009, p. 209-214Conference paper (Refereed)
    Abstract [en]

    Multifunctional nanoparticles (that have in their structure different components that can perform various functions) are subject of intensive research activities as they find a large variety of applications in numerous biomedical fields from enhancement of image contrast in MRI to different magnetically controllable drug delivery systems. In this study we report on the synthesis of well-separated, monodisperse single core-shell Si02@Fe304 nanoparticles with an overall diameter of ̃30 nm. The influence of stirring rate and reaction time on synthesis of tuneable shell thickness core-shell nanoparticles is reported. Particles' cell toxicity and performance as MRI contrast agents were also studied due to their promising biological applications (as contrast agents, cell labelling and separation, drug delivery systems, etc.) and results are promising in terms of MRI performance as well as having no significant cytotoxicity.

  • 240.
    Vogt, Carmen M.
    et al.
    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.
    Shi, Jingwen
    Institute of Environmental Medicine, Karolinska Institutet.
    Torres, Neus Feliu
    Institute of Environmental Medicine, Karolinska Institutet.
    Fadeel, Bengt
    Institute of Environmental Medicine, Karolinska Institutet.
    Laurent, Sophie
    University of Mons-Hainaut, Belgium.
    Bridot, Jean-Luc
    University of Mons-Hainaut, Belgium.
    Müller, Robert N.
    University of Mons-Hainaut.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Optimised Synthetic Route for Tuneable Shell SiO2@Fe3O4 Core-Shell Nanoparticles2009In: Materials Research Society Symposium Proceedings, 2009, Vol. 1140, p. 209-214Conference paper (Other academic)
    Abstract [en]

    Multifunctional nanoparticles (that have in their structure different components that can perform various functions) are subject of intensive research activities as they find a large variety of applications in numerous biomedical fields from enhancement of image contrast in MRI to different magnetically controllable drug delivery systems. In this study we report on the synthesis of well-separated, monodisperse single coreshell SiO2@Fe3O4 nanoparticles with an overall diameter of ~30 nm. The influence of stirring rate and reaction time on synthesis of tuneable shell thickness core-shell nanoparticles is reported. Particles’ cell toxicity and performance as MRI contrast agents were also studied due to their promising biological applications (as contrast agents, cell labelling and separation, drug delivery systems, etc.) and results are promising in terms of MRI performance as well as having no significant cytotoxicity.

     

  • 241. Vogt, Carmen
    et al.
    Pernemalm, Maria
    Kohonen, Pekka
    Laurent, Sophie
    Hultenby, Kjell
    Vahter, Marie
    Lehtio, Janne
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Fadeel, Bengt
    Proteomics Analysis Reveals Distinct Corona Composition on Magnetic Nanoparticles with Different Surface Coatings: Implications for Interactions with Primary Human Macrophages2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 10, article id e0129008Article in journal (Refereed)
    Abstract [en]

    Superparamagnetic iron oxide nanoparticles (SPIONs) have emerged as promising contrast agents for magnetic resonance imaging. The influence of different surface coatings on the biocompatibility of SPIONs has been addressed, but the potential impact of the so-called corona of adsorbed proteins on the surface of SPIONs on their biological behavior is less well studied. Here, we determined the composition of the plasma protein corona on silica- coated versus dextran-coated SPIONs using mass spectrometry-based proteomics approaches. Notably, gene ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed distinct protein corona compositions for the two different SPIONs. Relaxivity of silica-coated SPIONs was modulated by the presence of a protein corona. Moreover, the viability of primary human monocyte-derived macrophages was influenced by the protein corona on silica-coated, but not dextran-coated SPIONs, and the protein corona promoted cellular uptake of silica-coated SPIONs, but did not affect internalization of dextran-coated SPIONs.

  • 242. Wang, Q.
    et al.
    Rihtnesberg, D. B.
    Bergström, A.
    Almqvist, S.
    Zhang, A. Z. Z.
    Kaplan, W.
    Andersson, J. Y.
    Sugunan, Abhilash
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Yang, Xuran
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Compacted nanoscale sensors by merging ZnO nanorods with interdigitated electrodes2011In: Proc SPIE Int Soc Opt Eng, 2011Conference paper (Refereed)
    Abstract [en]

    ZnO nanorods (NRs) sensors utilizing hybrid or monolithic integration of the NRs on nanoscale or microscale interdigitated electrodes (IDEs) were fabricated and characterized. The IDEs with their finger electrode width ranging from 50 nm to 3 μm were formed on SiO2/Si substrates by nanoimprint lithography or conventional photolithography and metallization techniques, whereas the ZnO NRs were grown by chemical synthesis method. The average diameter of the ZnO NRs is about 100 nm, and their length can be varied from 2 to 5 μm by controlling growth time. When sensing targets, such as molecules or nanoparticles, bind onto the ZnO NRs, the conductance between IDEs will change. As probing test, II-VI quantum dots (QDs) were attached on the ZnO NRs, and clear responses were obtained by measuring and comparing current-voltage (I-V) characteristic of the sensor before and after binding the QDs.

  • 243.
    Wang, Xiaodi
    et al.
    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.
    Sugunan, Abhilash
    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.
    Zhu, Bin
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis of uniform quasi-octahedral CeO2 mesocrystals via a surfactant-free route2011In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 13, no 11, p. 5879-5885Article in journal (Refereed)
    Abstract [en]

    A facile surfactant-free nonaqueous method is presented to prepare uniform quasi-octahedral ceria, CeO 2 , mesocrystals, in which only Ce(NO 3 ) 3 and octanol were used as the reactants at a reaction temperature of 150 °C. CeO 2 sample synthesized using this technique consists of well-dispersed quasi-octahedrons and exhibits an uniform size and morphology. Based on structural characterization, it is proposed that the CeO 2 mesostructure was formed by self-assembly of primary nanocrystals based on unique 3D oriented-attachment mechanism. Optical characterization exhibited a strong quantum confinement, revealing small size of primary nanocrystals. The thermal stability and UV–Vis study reveal CeO 2 mesocrystal has various potential for high temperature applications and optical apparatus applications.

  • 244.
    Wärnheim, Alexander
    et al.
    KTH. RISE Biosci & Mat, Stockholm, Sweden..
    Toprak, Muhammet
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ahniyaz, Anwar
    RISE Biosci & Mat, Stockholm, Sweden..
    Swerin, Agne
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. RISE Biosci & Mat, Stockholm, Sweden..
    Abitbol, Tiffany
    RISE Bioecon, Stockholm, Sweden..
    Nanocellulose-based hybrid materials for optical applications2019In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 257Article in journal (Other academic)
  • 245.
    Yakhshi Tafti, Mohsen
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Ballikaya, Sedat
    Khachatourian, Adrine Malek
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Noroozi, Mohammad
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Han, Li
    Nong, Ngo V.
    Bailey, Trevor
    Uher, Ctirad
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Promising bulk nanostructured Cu2Se thermoelectrics via high throughput and rapid chemical synthesis2016In: RSC ADVANCES, ISSN 2046-2069, Vol. 6, no 112, p. 111457-111464Article in journal (Refereed)
    Abstract [en]

    A facile and high yield synthesis route was developed for the fabrication of bulk nanostructured copper selenide (Cu2Se) with high thermoelectric efficiency. Starting from readily available precursor materials and by means of rapid and energy-efficient microwave-assisted thermolysis, nanopowders of Cu2Se were synthesized. Powder samples and compacted pellets have been characterized in detail for their structural, microstructural and transport properties. alpha to beta phase transition of Cu2Se was confirmed using temperature dependent X-ray powder diffraction and differential scanning calorimetry analyses. Scanning electron microscopy analysis reveals the presence of secondary globular nanostructures in the order of 200 nm consisting of <50 nm primary particles. High resolution transmission electron microscopy analysis confirmed the highly crystalline nature of the primary particles with irregular truncated morphology. Through a detailed investigation of different parameters in the compaction process, such as applied load, heating rate, and cooling profiles, pellets with preserved nanostructured grains were obtained. An applied load during the controlled cooling profile was demonstrated to have a big impact on the final thermoelectric efficiency of the consolidated pellets. A very high thermoelectric figure of merit (ZT) above 2 was obtained at 900 K for SPS-compacted Cu2Se nanopowders in the absence of the applied load during the controlled cooling step. The obtained ZT exceeds the state of the art in the temperature ranges above phase transition, approaching up to 25% improvement at 900 K. The results demonstrate the prominent improvement in ZT attributed both to the low thermal conductivity, as low as 0.38 W m(-1) K-1 at 900 K, and the enhancement in the power factor of nanostructured Cu2Se. The proposed synthesis scheme as well as the consolidation could lead to reliable production of large scale thermoelectric nanopowders for niche applications.

  • 246.
    Yakhshi Tafti, Mohsen
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Jacquot, A.
    Jagle, M.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Fabrication and characterization of nanostructured bulk skutterudites2013In: 2013 MRS Spring Meeting - Symposium H/I/V – Nanoscale Thermoelectric Materials, Thermal and Electrical Transport, and Applications to Solid-State Cooling and Power Generation, Materials Research Society, 2013, p. 105-110Conference paper (Refereed)
    Abstract [en]

    Latest nanotechnology concepts applied in thermoelectric (TE) research have opened many new avenues to improve the ZT value. Low dimensional structures can improve the ZT value as compared to bulk materials by substantial reduction in the lattice thermal conductivity, κL. However, the materials were not feasible for the industrial scale production of macroscopic devices because of complicated and costly manufacturing processes involved. Bulk nanostructured (NS) TEs are normally fabricated using a bulk process rather than a nano- fabrication process, which has the important advantage of producing in large quantities and in a form that is compatible with commercially available TE devices. We developed fabrication strategies for bulk nanostructured skutterudite materials based on FexCo1-xSb3. The process is based on precipitation of a precursor material with the desired metal atom composition, which is then exposed to thermochemical processing of calcination followed by reduction. The resultant material thus formed maintains nanostructured particles which are then compacted using Spark Plasma Sintering (SPS) by utilizing previously optimized process parameters. Microstructure, crystallinity, phase composition, thermal stability and temperature dependent transport property evaluation has been performed for compacted NS Fe xCo1-xSb3. Evaluation results are presented in detail, suggesting the feasibility of devised strategy for bulk quantities of doped TE nanopowder fabrication.

  • 247.
    Yakhshi Tafti, Mohsen
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Jacquot, Alexandre
    Johnsson, Mats
    Toprak, Muhammet S
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Temperature Dependent Structure Stability Studies on Thermoelectric Yb0.025Fe0.3Co0.7Sb32015In: Materials Research Society Proceeding / [ed] S.R. Bishop , D. Cahen , R. Chen , E. Fabbri , F.C. Fonseca and D. Ginley, Materials Research Society , 2015, Vol. 1735Conference paper (Refereed)
    Abstract [en]

    Depending on their application temperature thermoelectric (TE) materials are classified in three main categories; as low (up to 250°C), intermediate (up to 550°C) and high (above 600°C) temperature. Currently, Skutterudites (CoSb3) based materials have shown promising results in the intermediate temperature range (300-500°C). This family of material is highly suitable for automotive, marine transportation and industrial power generation applications to recover the waste heat from the exhaust and generate electricity. Conventional TE modules need p- and n-type semiconductor materials and for the skutterudite family, iron (Fe) has proven to be among the best candidates for the substitution of cobalt sites. Additionally, rare earths are introduced as rattlers in the crystal cages of the skutterudite to decrease the thermal conductivity, thus improving the figure of merit ZT of the TE material. For practical application for device fabrication, stability of these materials is of great importance. Compositional stability is being addressed as the material decomposes above certain temperature. Temperature dependent x-ray diffraction study was performed on Fe substituted, Yb-filled skutterudites, using Beam Line I711 at MAX LAB, to observe the crystal structure as a function of temperature. Diffraction patterns were collected from room temperature up to 500°C by utilizing Huber furnace. The results show success in filling process showing almost 80% reduction of the thermal conductivity from bulk. Additionally the thermal expansion coefficient value was within the average value for skutterudites which proves practical application of this powder for industrial applications.

  • 248.
    Ye, Fei
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Brismar, Torkel
    Shi, Jingwen
    Lin, Dong
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Sayed, Ramy El
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    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.
    Gold nanorod/mesoporoussilica/gadolinium oxide carbonate hydrate core/shell nanoparticles: A multimodalcontrast agent for MRI, CT and fluorescence imaging2012Manuscript (preprint) (Other academic)
  • 249.
    Ye, Fei
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Laurent, Sophie
    Fornara, Andrea
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Astolfi, Laura
    Qin, Jian
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Roch, Alain
    Martini, Alessandro
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Muller, Robert N.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Uniform mesoporous silica coated iron oxide nanoparticles as a highly efficient, nontoxic MRI T2 contrast agent with tunable proton relaxivities2012In: Contrast Media & Molecular Imaging, ISSN 1555-4309, E-ISSN 1555-4317, Vol. 7, no 5, p. 460-468Article in journal (Refereed)
    Abstract [en]

    Monodisperse mesoporous silica (mSiO2) coated superparamagnetic iron oxide (Fe3O4@mSiO2) nanoparticles (NPs) have been developed as a potential magnetic resonance imaging (MRI) T2 contrast agent. To evaluate the effect of surface coating on MRI contrast efficiency, we examined the proton relaxivities of Fe3O4@mSiO2 NPs with different coating thicknesses. It was found that the mSiO2 coating has a significant impact on the efficiency of Fe3O4 NPs for MRI contrast enhancement. The efficiency increases with the thickness of mSiO2 coating and is much higher than that of the commercial contrast agents. Nuclear magnetic resonance (NMR) relaxometry of Fe3O4@mSiO2 further revealed that mSiO2 coating is partially permeable to water molecules and therefore induces the decrease of longitudinal relaxivity, r1. Biocompatibility evaluation of various sized (ca. 3595 nm) Fe3O4@mSiO2 NPs was tested on OC-k3 cells and the result showed that these particles have no negative impact on cell viability. The enhanced MRI efficiency of Fe3O4@mSiO2 highlights these coreshell particles as highly efficient T2 contrast agents with high biocompatibility.

  • 250.
    Ye, Fei
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Qin, Jian
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Muhammed, Mamoun
    KTH, School of Engineering Sciences (SCI), Applied Physics, Functional Materials, FNM.
    Multifunctional core-shell nanoparticles: superparamagnetic, mesoporous, and thermosensitive2011In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 13, no 11, p. 6157-6167Article in journal (Refereed)
    Abstract [en]

    Multifunctional core-shell composite nanoparticles (NPs) have been developed by the combination of three functionalities into one entity, which is composed of a single Fe3O4 NP as the magnetic core, mesoporous silica (mSiO2) with cavities as the sandwiched layer, and thermosensitive poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAAm-co-AAm)) copolymer as the outer shell. The mSiO2-coated Fe3O4 NPs (Fe3O4@mSiO2) are monodisperse and the particle sizes were varied from 25 to 95 nm by precisely controlling the thickness of mSiO2-coating layer. The P(NIPAAm-co-AAm) were then grown onto surface-initiator-modified Fe3O4@mSiO2 NPs through free radical polymerization. These core-shell composite NPs (designated as Fe3O4@mSiO2@P(NIPAAm-co-AAm)) were found to be superparamagnetic with high r2 relaxivity. To manipulate the phase transition behavior of these thermosensitive polymer-coated NPs for future in vivo applications, the characteristic lower critical solution temperature (LCST) was subtly tuned by adjusting the composition of the monomers to be around the human body temperature (i.e. 37 °C), from ca. 34 to ca. 42 °C. The thermal response of the core-shell composite NPs to the external magnetic field was also demonstrated. Owing to their multiple functionality characteristics, these porous superparamagnetic and thermosensitive NPs may prove valuable for simultaneous magnetic resonance imaging (MRI), temperature-controlled drug release, and temperature-programed magnetic targeting and separation applications.

23456 201 - 250 of 259
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