Joachim Urban

Fritz Haber Institute of the Max Planck Society, Berlín, Berlin, Germany

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Publications (69)188.77 Total impact

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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 09/2010; 33(36). DOI:10.1002/chin.200236010
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    ABSTRACT: Organic dye namely Coumarin 7 has been entrapped in silica particles using a single silica precursor viz. tetraethylorthosilicate. Both bare Coumarin 7 dye and dye incorporated core–shell particles were studied. Investigations of these core–shell composites were carried out using different characterization techniques such as energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and transmission electron microscopy. It has been shown that the photostability of dye molecules is improved along with an increase in photoluminescence.
    Materials Letters 10/2007; 61(25):4738–4742. DOI:10.1016/j.matlet.2007.03.030 · 2.27 Impact Factor
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    ABSTRACT: Nanoshells, which are thin coatings deposited on core particles of different material have gained considerable attention. These materials show novel properties which are different from their single-component counterpart. By simply tuning the core to shell ratio, the properties can be altered. With emerging new techniques it is now possible to synthesize these nanostructures in desired shape, size and morphology. Various synthesis routes have been developed over the past few years to prepare these nanostructures. They can be prepared with customized properties such as increased stability, surface area, magnetic, optical and catalytic properties. A review of their synthesis techniques, properties and applications is given here.
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    ABSTRACT: We report on the synthesis of TbMnO3 nanoparticles by chemical co-precipitation route and their structural, chemical bonding, magnetic and dielectric properties. It is shown that the interesting multiferroic properties of this system as reflected by the concurrent occurrence of magnetic and dielectric transitions are retained in the nanoparticles (size∼40 nm). However, the nanoparticle constitution and properties are seen to depend significantly on the calcination temperature. While the nanoparticles obtained by calcination at 800 °C correspond very well with the reported properties of single phase TbMnO3 (all the key magnetic and dielectric features near 7, 27 and 41 K, albeit with reduced dielectric constant) the nanoparticles obtained by calcination at 900 °C develop a Tb deficient skin which softens the transitions, reducing the dielectric constant further.
    Solid State Communications 05/2006; 138(8):395-398. DOI:10.1016/j.ssc.2006.03.034 · 1.70 Impact Factor
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    ABSTRACT: We studied unsupported VxOy nanoparticles prepared by a novel nonaqueous route in the selective oxidation of n-butane to maleic anhydride. The evolution of the electronic and geometric structure of the material was characterized by X-ray photoemission spectroscopy, electron energy-loss spectroscopy, transmission electron microscopy, and electron diffraction before and after the reaction at different temperatures. A change from a water-mediated CC bond cracking functionality of the catalyst forming acetic acid to an oxidizing functionality resulting in maleic anhydride was observed. It was found that the particles underwent a radical modification of the geometric and electronic structure that finally resulted in V2O5 crystals. Experimentally derived conclusions are related to some conceptual claims from the literature.
    Journal of Catalysis 12/2005; 236(2-236):221-232. DOI:10.1016/j.jcat.2005.10.005 · 6.07 Impact Factor
  • L Motte · J Urban
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    ABSTRACT: Nanocomposite crystals, (Ag)(x)(Ag(2)S)(y) with x < y, are synthesized in micellar media. The generation of Ag clusters on Ag(2)S nanocrystals is attributed to the reduction of mobile Ag(+) ions in the Ag(2)S nanocrystals by sulfur derivatives. The proportions in the composite material can be modulated by electron beam irradiation. Using dodecanethiol as surface passivating agent, 2D self-organizations of these nanocomposite crystals are produced.
    The Journal of Physical Chemistry B 11/2005; 109(46):21499-501. DOI:10.1021/jp0542322 · 3.30 Impact Factor
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    ABSTRACT: Nearly monodispersed particles of silica were prepared and coated with uniform layers of titanium dioxide in anatase phase by hydrolysis and condensation of titanium butoxide. The coating thickness could be altered by adjusting the concentration of reactants (titanium butoxide and water) and the amount of added silica particles. Different coating thicknesses were deposited and studied using optical absorption spectroscopy, electron microscopy and Fourier transform infra-red spectroscopy. It was found that silica particles of size 170 ±5 nm were coated with 23±5 nm thick layer of titanium dioxide. Alternatively titania particles of size 340±5 nm were synthesized by controlled hydrolysis of titanium ethoxide in the presence of sodium chloride. These particles were further coated with 135±5 nm thick layer of silica to investigate changes in properties after changing the shell material
    Pramana 11/2005; 65(5):787-791. DOI:10.1007/BF02704076 · 0.72 Impact Factor
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    ABSTRACT: Zinc oxide and cadmium selenide particles in the nanometer size regime have been synthesized using chemical routes. The particles were capped using thioglycerol in case of ZnO and 2-mercaptoethanol in case of CdSe to achieve the stability and avoid the coalescence. Zinc oxide nanoparticles were doped with europium to study their optical properties. A variety of techniques like UV-Vis absorption spectroscopy, X-ray diffraction (XRD), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) were used to carry out structural and spectroscopic characterizations of the nanoparticles.
    Pramana 10/2005; 65(4):615-620. DOI:10.1007/BF03010449 · 0.72 Impact Factor
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    ABSTRACT: Copper nanocrystals with plate-like morphologies and face-centered cubic (fcc) structures have been synthesized in mixed reverse micelles with a large excess of reducing agent. High-resolution transmission electron microscopy images and image simulations show the presence of multiple twin defects parallel to the (111) surface responsible for the forbidden reflections 1/3{422} of the fcc structure. A growth process related to the formation of twin defects is proposed to explain the existence of these morphologies.
    Advanced Functional Materials 08/2005; 15(8):1277 - 1284. DOI:10.1002/adfm.200400594 · 11.81 Impact Factor
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    ABSTRACT: Using a single silica precursor, Rhodamine 6G organic dye molecules have been entrapped in silica particles resulting into core-shell particles of ∼500nm diameter. Energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and transmission electron microscopy analysis reveals that dye molecules are trapped inside the silica particles. Photoluminescence investigations show that highly luminescent and photostable core-shell particles are formed. Such core-shell particles can be easily suspended in water and would be useful for a variety of applications. However, there is a blue shift in the photoluminescence wavelength in case of core-shell particles compared to bare dye powder sample.
    Journal of Luminescence 07/2005; 114(1):15-23. DOI:10.1016/j.jlumin.2004.11.005 · 2.37 Impact Factor
  • C. Salzemann · J. Lermé · J. Urban · I. Lisiecki
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    ABSTRACT: Copper nanocrystals characterized by various sizes and shapes are synthesized in reverse micelles. The average size of the metallic nanocrystals increases from 3 to 8.4 nm. Experimental (UV spectroscopy) and theoretical (TDLDA formalism) optical studies permit to correlate the optical response to size and shape effects of the nanocrystals.
    Chemistry of Materials 03/2005; 17(6):1279. DOI:10.1021/cm048970z · 8.54 Impact Factor
  • C Salzemann · I Lisiecki · J Urban · M-P Pileni
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    ABSTRACT: In the chemical reduction of copper ions in mixed reverse micelles it is found that a large excess of reducing agent favors the production of a new generation of copper nanocrystals. At low reducing agent concentration, nanocrystals are mostly spherical, while in the supersaturated regime, they have various shapes such as pentagons, squares, triangles, and elongated forms. The nanocrystal structures, characterized by high-resolution transmission electron microscopy, are based on the face-centered cubic structure. A tentative explanation for the growth mechanism of copper nanocrystals having various shapes is proposed.
    Langmuir 01/2005; 20(26):11772-7. DOI:10.1021/la0492862 · 4.46 Impact Factor
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    ABSTRACT: Semiconductor nanoparticles exhibit size dependent properties, when their size is comparable to the size of Bohr diameter for exciton. This can be exploited to increase fluorescence efficiency or increase the internal magnetic field strength in doped semiconductors. Nanoparticles are usually unstable and can aggregate. It is therefore necessary to protect them. Surface passivation using capping molecules or by making core–shell particles are some useful ways. Here synthesis and results on doped and un-doped nanoparticles of ZnS, CdS and ZnO will be discussed. We shall present results on core–shell particles using some of these nanoparticles and also discuss briefly the effect of Mn doping on hyperfine interactions in case of CdS nanoparticles.
    Hyperfine Interactions 01/2005; 160(1):81-94. DOI:10.1007/s10751-005-9151-y · 0.21 Impact Factor
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    ABSTRACT: Cadmium sulfide nanoparticles (approximately 5 nm), chemically capped using thioglycerol molecules, have been anchored onto silica particles (approximately 80 nm) functionalized with 3-aminopropyltrimethoxysilane. Transmission electron microscopy clearly showed that at a low concentration of cadmium sulfide, nanoparticles were discretely and more or less uniformly attached onto the silica particles. At a high concentration of cadmium sulfide nanoparticles, an approximately 6-nm-thick compact shell of cadmium sulfide was formed on the silica particles. In both cases the nanocrystalline nature of cadmium sulfide particles was preserved, as is evident from X-ray diffraction and optical absorption spectra.
    Journal of Colloid and Interface Science 11/2004; 278(1):107-14. DOI:10.1016/j.jcis.2004.05.037 · 3.55 Impact Factor
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    ABSTRACT: The synthesis of monodispersed ZnS nanoparticles (~1.2 nm) stabilised with thioglycerol molecules which have been attached to functionalised silica particles is reported. The coupling agent used was 3-aminopropyltrimethoxysilane. The chemical bonding was studied by Fourier transform infrared spectroscopy. TEM of these particles clearly shows a uniform coating of ZnS on silica particles. These SiO2@ZnS core shell particles were also studied using characterisation techniques such as optical absorption spectroscopy, X-ray diffraction and EDAX.
    Surface Engineering 09/2004; 20(5):367-372. DOI:10.1179/026708404225016391 · 1.51 Impact Factor
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    ABSTRACT: The use of reverse micelles makes it possible to produce copper nanocrystals characterized by various sizes and shapes. By increasing the water content, the average size of the metallic nanocrystals increases from 3 to 13 nm. Structural investigations clearly indicate the formation of pure copper with various crystallographic structures. The absorption spectra of the corresponding colloidal solutions exhibit two plasmon modes in the UV−visible range, around 560 and 640 nm. The progressive emergence of the first mode (Mie's resonance of a perfect sphere) with the increase in the mean particle size is attributed to a mere finite-size effect. The second resonance is explained in terms of nanocrystal shape.
    The Journal of Physical Chemistry B 08/2004; 108(35). DOI:10.1021/jp048491n · 3.30 Impact Factor
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    ABSTRACT: The orientation relations m(100) || t(001), m[001] || t[110]; m(011) || t(100), m[001] || t[110]; m(100) || t(110), m[001] || t[001]; m(013) || t(116), m[001] || t[001]; (indices for the primitive tetragonal cell) have been found between the tetragonal (t) and monoclinic (m) domains during the electron irradiation-induced m-t phase transition observed in-situ with HREM within isolated zirconia nanoparticles. Geometric models of the m-t interfaces are proposed. Keywords High-resolution transmission electron microscopy, nanoparticles, orientation relations, polymorphism, zirconia, catalyst
    Journal of Materials Science 01/2004; 39(6). DOI:10.1023/B:JMSC.0000017778.29744.98 · 2.37 Impact Factor
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    ABSTRACT: Silver nanoparticles in the size range of 2-5 nm were synthesized extracellularly by a silver-tolerant yeast strain MKY3, when challenged with 1 mM soluble silver in the log phase of growth. The nanoparticles were separated from dilute suspension by devising a new method based on differential thawing of the sample. Optical absorption, transmission electron microscopy, x-ray diffraction and x-ray photoelectron spectroscopy investigations confirmed that metallic (elemental) silver nanoparticles were formed. Extracellular synthesis of nanoparticles could be highly advantageous from the point of view of synthesis in large quantities and easy downstream processing.
    Nanotechnology 11/2003; 14:95-100. · 3.67 Impact Factor
  • Microscopy and Microanalysis 09/2003; 9(S03). · 1.76 Impact Factor
  • Angewandte Chemie 08/2003; 115(32). DOI:10.1002/ange.200250709

Publication Stats

2k Citations
188.77 Total Impact Points

Institutions

  • 1997–2007
    • Fritz Haber Institute of the Max Planck Society
      • Department of Inorganic Chemistry
      Berlín, Berlin, Germany
  • 1993–2006
    • Max Planck Society
      München, Bavaria, Germany
  • 1989–2005
    • MPG Ranch
      Lolo, Montana, United States
  • 2004
    • Pierre and Marie Curie University - Paris 6
      • Laboratoire des Matériaux Mésoscopiques et Nanométriques (LM2N -UMR 7070)
      Lutetia Parisorum, Île-de-France, France
    • University of Pune
      • Department of Physics
      Poona, Maharashtra, India