G. Holzhüter

University of Rostock, Rostock, Mecklenburg-Vorpommern, Germany

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Publications (20)38.5 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 01/2010; 28(5).
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    ABSTRACT: Photovoltaic properties of n-In1−xGaxN/p-Si, Ge (IGN) heterostructures, covering the compositional range 0<x<0.6, have been evaluated by 1d device simulation, and are compared with the performance of c-Si homojunction thin film cells. Film morphology and physical properties were characterized by high-resolution transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS) and photoluminescence (PL). Best achievable cell performances under AM1.5 illumination conditions were 18% for p-Ge, and up to 27% for n-IGN/p-Si contacts, achievable under optimum cell design, materials and operation parameters. Pure InN bottom layers, exhibiting an intrinsic band gap of 0.7 eV, reveal a reduced efficiency of 2.5%. The cell efficiency is strongly affected by film quality, accounted for by variation of electron affinity, majority carrier mobility, minority carrier lifetime, film thickness and doping levels. The morphology of thin IGN and InN films deposited onto silicon and sapphire substrate material revealed granular growth, along with a high density of grain boundaries. TEM resolved the formation of a very thin homogeneous silicon nitride interlayer on silicon substrates. The electrically isolating layer almost completely suppresses the photovoltaic effect. Depth profiling of InN films deposited onto sapphire substrates by SIMS analysis indicated oxygen as the dominant material contamination. It accounts, among other effects, for a gradually increasing band gap throughout the film structure. Observed large photoluminescence broadening effects, and related short minority carrier lifetimes are most likely related to high levels of oxygen contamination and concentration of grain boundaries. Possible routes to overcome these problems are discussed.
    Solar Energy Materials and Solar Cells 05/2006; 90(s 7–8):982–997. · 5.03 Impact Factor
  • H. Neff, W. Zong, A.M.N. Lima, M. Borre, G. Holzhüter
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    ABSTRACT: The optical properties of very thin gold films have been evaluated by Fresnel analysis, with optical boundary conditions pertaining to the surface plasmon resonance (SPR) at the gold–water interface. The experimental SPR characteristic was evaluated in the angular interrogation mode. Film morphology was characterized by high resolution transmission electron microscopy. The magnitude of the resonance, i.e., the SPR signal, sensitively depends on, and is affected by film thickness and morphology. A sharply defined thickness of 55 ± 5 nm is required, to achieve optimum SPR excitation conditions, and instrumental sensitivity. With decreasing film thickness, below 40 nm, the resonance angle starts to shift to larger values. A substantial increase of the intrinsic resonance broadening parameter is observed below 70 nm, associated with an increasingly asymmetric SPR line shape. A similar effect occurs in the presence of a very thin chromium adhesion layer. Surface roughness and film thickness modulations determine the experimentally observed line broadening parameter. Instrumental noise levels largely depend on accuracy and quality at which the resonance angle can be determined. Substantial improvement and instrumental sub-pixel resolution is achievable by optimum fitting routines, accounting for drastic noise reduction and improved instrumental sensitivity, up to two orders of magnitude over the inherent geometric sensor pixel resolution.
    Thin Solid Films 01/2006; · 1.87 Impact Factor
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    ABSTRACT: Design, technological features, and performance of polymeric diffractive optical coupling elements (DOCEs), developed for surface plasmon resonance (SPR) sensors are reported. The concept is based on input and output coupling of collimated and perpendicularly incident light beams to exchangeable SPR sensor chips. In the SPR sensor chips, one DOCE couples the input light beam to a (bio-)chemical sensor surface and another DOCE images the output light beam onto a detector array. The manufacturing technique is based on an injection moulding process similarly to the manufacturing process of compact discs allowing precision manufacturing and reproduction of the grating topography of the DOCEs. The DOCE-based SPR sensor chip is specifically suitable for miniaturisation and large scale production, while maintaining high optical quality and performance.
    Sensors and Actuators B: Chemical. 01/2004;
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    ABSTRACT: Carbon nanofibers of herringbone conformation were obtained by chemical vapor deposition on Pd/La2O3 catalyst, from ethylene—hydrogen mixture. After the removal of La2O3, samples with various Pd/C ratios were obtained by oxidation in air. The hydrogen sorption capacities measured gravimetrically at 10MPa in pure hydrogen, for six different batches of samples, show a good correlation with the Pd/C ratio reveling a catalytic effect of Pd, which supplies atomic H. A possible charge transfer might lead to the increasing of the H uptake with the increasing Pd/C ratio. A saturation value of 1.5% H (mass) per carbon is reached at rather high Pd/C mole ratio (∼1) for nanofibers with 425–455m2g−1 BET surface area.
    International Journal of Hydrogen Energy 01/2004; 29(1):97-102. · 3.55 Impact Factor
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    G Holzhüter, K Narayanan, T Gerber
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    ABSTRACT: Silicified regions in the stem and leaf of the horsetail Equisetum arvensewere studied by scanning and transmission electron microscopy. The silica was present as a thin layer on the outer surface with variation in the size of this layer depending on the part investigated. There was a dense arrangement of silica spheres with some density fluctuations. A loose arrangement of silica particles with variation in their size was found beneath this dense arrangement suggesting the agglomeration of silica. An electron diffraction pattern showed the presence of amorphous silica, with the short range order being comparable to that of silica from other chemical sources. The medium range order shows the presence of silica with a high inner surface. SAXS measurements correlate with the particle size observed in TEM, and provide values for surface fractals. A new method of plasma ashing to remove the organics is also described.
    Analytical and Bioanalytical Chemistry 07/2003; 376(4):512-7. · 3.66 Impact Factor
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    ABSTRACT: A chiral non-racemic Rh complex was entrapped in a number of charged polymer-surfactant complexes (PSCs) and used as micellar-enlarged catalyst for the enantioselective hydrogenation of an α-amino acid precursor in a membrane reactor. The retention behavior of different ultrafiltration membranes in dependence on the chemical nature and the molar mass of the PSCs as well as the loading behavior of the system were investigated. The chiral hydrogenation product was obtained with good enantioselectivity and space-time yield. A lowering of the activity of the multiply used catalyst was caused mainly by a blockage of the PSC and not by the decomposition and leaching of the encapsulated catalyst. TEM images before and after the solubilization of the catalytic system support the view that a PSC with a loose, gel-like structure and incorporated micelles yields the best results in the repetitive batch process.
    Advanced Synthesis & Catalysis 01/2003; 345(1‐2):202 - 210. · 5.54 Impact Factor
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    ABSTRACT: Hydrophobically modified water-soluble polymers (HMWSP's) and hydrophobically modified polyelectrolytes (HMPE's,“polysoaps”) of various compositions and different molecular weights have been prepared and used in the micellar promoted enantioselective hydrogenation of methyl (Z)-α-acetamidocinnamate with a chiral Rh(I) catalyst in aqueous medium. The efficiency of the micellar polymers in the catalytic reaction is greatly determined by their solubility (dispersibility) behavior and solubilization capacity for catalyst and substrate. The latters depends on the compactness of the polyamphiphiles as revealed by transmission electron microscopy (TEM) and light microscopy images. The highest catalytic performance was obtained with polymer-surfactant complexes prepared by micellar copolymerization with neutral or anionic tensides, regardless of the electrical charge of the hydrophobically modified polymer. In most cases a synergism between rate and enantioselectivity has been observed.
    New Journal of Chemistry 10/2002; 26(11):1675-1681. · 2.97 Impact Factor
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    ABSTRACT: Owner: Helmholtz, Added to JabRef: 2011.09.19
    Eur.Phys.J.D. 01/2001; 16(1-3):173-176.
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    ABSTRACT: We have investigated the magnetic properties of mass-selected iron clusters using the Magneto-Optical Kerr effect (MOKE) in longitudinal geometry. For the production of these clusters, a newly developed continuous arc cluster ion source (ACIS) was applied. The source is based on cathodic arc erosion in inert gas environment and subsequent expansion into high vacuum. Its intensity and stability allows mass selection within a wide size range. The source efficiency is demonstrated in deposition experiments and transmission electron microscopy. For mass-selected iron particles deposited into a silver matrix we could observe a change in the magnetic behaviour from ferromagnetism to superparamagnetism around a size of 10 nm at room temperature.
    The European Physical Journal D 01/2001; 16(1-3):173-176. · 1.51 Impact Factor
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    ABSTRACT: A novel porous material produced via sol gel process is disclosed which is osteoinductive and biodegradable. Due to the fact that high temperatures are avoided during the production process, the degree of crystallinity is very low and the packing of the crystallites is relatively loose. These are important parameters for the biodegradation properties.Nanoporous silica gel is contained to the support of strength. The low degree of crystallinity and the high degree of porosity (50–70%, pores in the range of few microns) make the material resorbable. A second type of pores designed in the range of few millimetres supports the bone ingrowth.An in vitro formation of bone tissue is shown when the material is exposed to tissue culture medium and inoculated with human osteoblastic cells. Animal tests show the formation of new bone tissue and first steps of biodegradation.
    Journal of Sol-Gel Science and Technology 11/2000; 19(1):441-445. · 1.66 Impact Factor
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    ABSTRACT: New sulfated and sulfonated cholesterol amphiphiles were synthesized and characterized by dynamic light scattering and electron microscopy. The surfactants form micelles with diameters up to 30 nm. Their critical micelle concentration values were determined by conductometry and photometric measurements. Use of the new amphiphiles enables the transfer of an asymmetric hydrogenation reaction into aqueous solution by keeping the activity and increasing the enantioselectivity. Interesting liquid-crystalline behaviour was observed.
    Colloid and Polymer Science 03/2000; 278(4):364-368. · 2.16 Impact Factor
  • Journal of Metastable and Nanocrystalline Materials 01/2000; 8:27-32.
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    ABSTRACT: We report on the synthesis of single phase diamond ceramics and its microstructural and physical characterization. The most relevant physical properties are listed and are compared to natural diamond. The ceramic solid has been fabricated from chemically treated micro crystalline diamond powder, where oxy-functional groups have been attached to the surface. The special surface treatment is considered essential to achieve direct atomic bonding between adjacent grains.The hot isostatic pressing method (HIP) has been applied for materials processing that pertains to the stability region of the related carbon phase diagram. No further additives have been used for preparation. Transmission and scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction and Raman spectroscopy have been used for the micro structural analysis. The achievable density is close to that of natural diamond, revealing porosity values of <3%. The micro structural analyses indicated the presence of small amounts of isolated diamond micro crystals, embedded into a matrix of polycrystalline diamond with a very small grain size. The grains are much smaller than the originally used micro crystalline source material, indicating crystal break-up and atomic rebonding during the sintering process. Also traces of sp2-hybridized carbon have been identified, located primarily at grain boundaries. Fracture of the material appears mostly transgranular. Relevant physical properties as thermal and electrical conductivity, hardness and Young's modulus approach those of natural diamond.
    Diamond and Related Materials 01/1999; 8(12):2140-2147. · 1.71 Impact Factor
  • V Petkov, G Holzhüter, U Tröge, Th Gerber, B Himmel
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    ABSTRACT: Amorphous TiO2 materials, layers and powders, have been produced by different preparation techniques. The layers have been subjected to electron diffraction and the bulk powders to X-ray diffraction experiments. Three-dimensional structure models consistent with the experimental structure functions have been constructed by reverse Monte Carlo simulations. Partial distribution functions, interatomic distances and coordination numbers have been extracted from the model atomic configurations. The atomic arrangement in all amorphous TiO2 materials investigated has been found to resemble that occurring in brookite, a crystalline modification of TiO2, and to be well described as an assembly of short, staggered chains of Ti–O octahedra. The crystallization behaviour of amorphous TiO2 materials has also been discussed.
    Journal of Non-Crystalline Solids 01/1998; · 1.72 Impact Factor
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    ABSTRACT: Diamond powder has been synthesized by spontaneous crystallization under high static pressure using a Mn-Ni catalyst at 4.5 GPa pressure and 1200 °C. A defined size distribution of the diamond particles has been established through adjustment of the growth period. Chemically modified microcrystalline diamond surfaces have been prepared by boiling in acid solutions. Investigations indicate that the diamond crystals have an octahedron habit with unbroken facets. Raman spectroscopic data show that the prepared diamond powder is pure diamond, without any traces of graphite and other impurities. Second-order Raman-spectra of both, single-crystalline natural diamond and the synthesized microcrystalline form reveal a similar phonon density of states. On the basis of model calculations and comparison with experimental data it is concluded that a polydisperse composition with a dominant size fraction of 28 μm suited best the compact diamond ceramics.
    Carbon 01/1997; 35(5):697-702. · 6.16 Impact Factor
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    ABSTRACT: Reaction of 2-hydroxyethanesulfonic acid sodium salt, 3-hydroxypropanesulfonic acid sodium salt or 2-aminoethanesulfonic acid sodium salt with cholest-5-en-3β-ol-3-chloroformate yields the chiral amphiphilic compounds 2-(cholest-5-en-3β)oxy-carbonyloxy-ethanesulfonic acid sodium salt 1, 2-(cholest-5-en-3β)oxy-carbonyloxy-propanesulfonic acid sodium salt 2 and 2-(cholest-5-en-3β)oxy-carbonylaminoethanesulfonic acid sodium salt 3, respectively. Another chiral amphiphile 2-(cholest-5-en-3β)oxy-carbonylethanesulfonic acid sodium salt 4 was synthesized by treating cholest-5-en-3β-ol with sulfopropionic acid anhydride. The surfactants form vesicles in aqueous solutions, as shown by electron microscopy. Stepwise destruction of these vesicles by addition of ethanol or methanol was proved by Circular Dichroism (CD) measurements. Especially compound 3 shows pronounced induced CD effects with the achiral dye 3,6-diamino-acridine-sulfate (proflavine). The synthesized chiral amphiphiles were used in the asymmetric hydrogenation reaction of methyl (Z)-α-acetamidocinnamate. In the case of an achiral rhodium complex as catalyst the prepared surfactants 1, 2, and 4 are able to provide an enantiomer excess by themselves. The best ee-value reached was 8.5% methyl (R)-N-acetylphenyl-alaninate in connection with compound 4.
    Journal für praktische Chemie 01/1996; 338(1).
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    ABSTRACT: Low-density xSiO2-(1 - x)Al2O3 aerogels with x = 0, 0.3, 0.7, 1.0 (mole fractions) were prepared by CO2 supercritical drying of alkogels formed from Si(OMe)4 and Al(OBus)3 by hydrolytic polycondensation under different chemical conditions. The resulting aerogels were structurally characterized by X-ray scattering at small and large angles as well as by electron diffraction and transmission electron microscopy. By investigating the dependence of linear shrinkage on the heat treatment it was found that the sintering of the aerogel is influenced by the presence of Al2O3 in the network. Crystallization experiments were also performed up to 1200°C. The reduced height of the first sharp diffraction peak indicates less order in the SiO2 network of the aerogel in comparison with amorphous SiO2 prepared by other methods.
    Journal of Non-crystalline Solids - J NON-CRYST SOLIDS. 01/1995; 186:149-158.
  • J. Chem. Phys. 01/1994; 100:7722.
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    ABSTRACT: Twelve patients underwent an osteosynthesis with titanium to treat upper and lower jaw fractures. Six to 12 months later, the miniplates were removed. Tissue samples were analyzed by light and electron microscopy for detection of a metallosis. The analysis showed new bone formation like callus tissue around the miniplates. In some cases small, rounded deposits and accumulation of colloid-like particles located next to bigger titanium artifacts were detected in the cytoplasm of histiocytes and in the matrix of connective tissue. The titanium was identified by elemental analysis using EDX in SEM as well as by EELS and electron diffraction in TEM. Both kinds of particles contain titanium, but they seem to be different in composition and derivation. The bigger particles seem to consist of metallic titanium and sourced by working on the metallic implants during the implantation itself. On the other hand, the colloidal-like, small, rounded particles in tissue macrophages and outside the cells in the matrix of connective tissue are presumably of other origin; for example, they could be derived from biodegradation and chemical conversion of the metallic implants. The titanium miniplates were examined before and after implantation by using ESCA technique and revealed metallic titanium and different compositions with other elements. The amount of titanium load of the tissue was very low in most cases and presumably not of biomedical relevance.
    Ultrastructural Pathology 25(5):375-83. · 0.98 Impact Factor