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Organisationseinheit der BAM
- 1 Analytische Chemie; Referenzmaterialien (4)
- 1.1 Anorganische Spurenanalytik (2)
- 4 Material und Umwelt (2)
- 6 Materialchemie (2)
- 6.1 Oberflächen- und Dünnschichtanalyse (2)
- 9 Komponentensicherheit (2)
- 9.4 Integrität von Schweißverbindungen (2)
- 1.4 Non-Target-Analytik (1)
- 1.8 Umweltanalytik (1)
- 4.2 Material-Mikrobiom Wechselwirkungen (1)
Inflammatory bowel diseases (IBD) comprise mainly ulcerative colitis (UC) and Crohn´s disease (CD). Both forms present with a chronic inflammation of the (gastro) intestinal tract, which induces excessive changes in the composition of the associated extracellular matrix (ECM). In UC, the inflammation is limited to the colon, whereas it can occur throughout the entire gastrointestinal tract in CD. Tools for early diagnosis of IBD are still very limited and highly invasive and measures for standardized evaluation of structural changes are scarce. To investigate an efficient non-invasive way of diagnosing intestinal inflammation and early changes of the ECM, very small superparamagnetic iron oxide nanoparticles (VSOPs) in magnetic resonance imaging (MRI) were applied in two mouse models of experimental colitis: the dextran sulfate sodium (DSS)-induced colitis and the transfer model of colitis. For further validation of ECM changes and inflammation, tissue sections were analyzed by immunohistochemistry. For in depth ex-vivo investigation of VSOPs localization within the tissue, Europium-doped VSOPs served to visualize the contrast agent by imaging mass cytometry (IMC). VSOPs accumulation in the inflamed colon wall of DSS-induced colitis mice was visualized in T2* weighted MRI scans. Components of the ECM, especially the hyaluronic acid content, were found to influence VSOPs binding. Using IMC, colocalization of VSOPs with macrophages and endothelial cells in colon tissue was shown. In contrast to the DSS model, colonic inflammation could not be visualized with VSOP-enhanced MRI in transfer colitis. VSOPs present a potential contrast agent for contrast-enhanced MRI to detect intestinal inflammation in mice at an early stage and in a less invasive manner depending on hyaluronic acid content.
The photocatalytic (PC) performance of titanium dioxide (TiO2) nanoparticles strongly depends on their specific surface, the presence of crystal defects, their crystal phase, and the exposed crystal facets. In order to understand which of these factors contributes most significantly to the PC activity of TiO2 colloids, all of them have to be individually analyzed. This study entails the synthesis of five anatase nanocrystal samples. By maintaining the same reactant ratios as well as hydrothermal sol–gel synthesis route and only varying the autoclaving time or temperature, different crystallite sizes are obtained under comparable experimental conditions. A decrease in PC performance with increase in specific surface area is found. Such an unexpected counterintuitive result establishes the basis for a better understanding of the crucial factors that ultimately determine the PC activity. These are investigated by studying nanocrystals bulk and surface structure and morphology using a selection of complementary analysis methods (X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), X-ray diffraction (XRD)…). It is found that a change in the nanocrystal morphology from an equilibrium state truncated tetragonal bipyramid to a more elongated rod-like structure accompanied by an increase in oxygen vacancies is responsible for an augmented PC activity of the TiO2 nanocrystals.
Determination of elemental mass fractions in sediments plays a major role in evaluating the environmental status of aquatic ecosystems. Herewith, the optimization of a new total digestion protocol and the subsequent analysis of 48 elements in different sediment reference materials (NIST SRM 2702, GBW 07313, GBW 07311 and JMC-2) based on ICP-MS/MS detection is presented. The developed method applies microwave acid digestion and utilizes HBF4 as fluoride source for silicate decomposition. Similar to established protocols based on HF, HBF4 ensures the dissolution of the silicate matrix, as well as other refractory oxides. As HBF4 is not acutely toxic; no special precautions have to be made and digests can be directly measured via ICP-MS without specific sample inlet systems, evaporation steps or the addition of e.g. H3BO3, in order to mask excess HF. Different acid mixtures with and without HBF4 were evaluated in terms of digestion efficiency based on the trace metal recovery. The optimized protocol (5 mL HNO3, 2 mL HCL, 1 mL HBF4) allows a complete dissolution of the analyzed reference materials, as well as quantitative recoveries for a wide variety of certified analytes. Low recoveries for e.g. Sr, Ba and rare earth elements due to fluoride precipitation of HF-based digestions protocols, can be avoided by the usage of HBF4 instead. Based on the usage of high purity HBF4 all relevant trace, as well as matrix elements can be analyzed with sufficiently low LOQs (0.002 μg L−1 for U up to 6.7 μg L−1 for Al). In total, 34 elements were within a recovery range of 80%–120% for all three analyzed reference materials GBW 07313, GBW 07311 and JMC-2. 14 elements were outside a recovery range of 80%–120% for at least one of the analyzed reference materials.
Metformin is widely used as a first-line treatment for type 2 diabetes, but central effects of metformin have received little attention. When metformin (200 mg/kg i.p.) was administered to C57Bl6 mice, metformin concentration in cerebrospinal fluid peaked at 29 μM after 30 min but dropped quickly and was low at 90 min. In mouse hypothalamus sampled by microdialysis, systemically administered metformin caused minor and transient increases of acetylcholine, glucose and lactate while choline levels decreased. When metformin (0.2−10 mM) was locally infused via retrodialysis, there was a short-lasting increase of acetylcholine in the hypothalamus. Extracellular lactate levels in hypothalamus showed a massive increase upon metformin infusion while glucose levels decreased. In isolated mitochondria of mouse brain, metformin inhibited oxygen consumption and the activity of complex I. Inhibition of mitochondrial respiration likely explains lactate formation in the brain during metformin infusion which may cause lactic acidosis during metformin intoxication. The changes of cholinergic activity in the hypothalamus may be associated with appetite suppression observed during metformin treatment.
Transmission electron microscopy study of rapid thermally annealed Pd/Ge contacts on In0.53Ga0.47As
(1996)
Phase formation in rapid thermally annealed Pd/Ge contacts on In0.53Ga0.47As has been investigated by means of cross-sectional transmission electron microscopy, convergent-beam electron diffraction, and energy-dispersive x-ray analysis. Solid-phase regrowth is observed to occur similarly as in Pd/Ge contacts on GaAs or InP. The reaction starts at low temperatures with the formation of an amorphous Pd–In–Ga–As layer, which crystallizes at elevated temperatures yielding hexagonal Pd4In0.53Ga0.47As being first described in this work. At temperatures .250 °C, this phase decomposes due to epitaxial solid-phase regrowth of In0.53Ga0.47As and formation of Pd–Ge phases. The stable composition is reached at temperatures .350 °C with excess Ge diffused through top Pd–Ge to the contact interface and growing epitaxially on the semiconductor.
Platinum does not form any adherent oxides and can be easily wetted by tin-based solders. Platinum is also an available metallization in semiconductor laboratories. Therefore we investigated the diffusion of platinum thin-film metallizations into eutectic tin–lead solder by using a high-resolution secondary ion mass spectroscopy (SIMS) profiling from the back side. It is shown that an intermetallic phase (PtSn4) is formed during soldering, which controls the consumption of platinum during soldering and in operation. The consumption of platinum follows the well-known parabolic diffusion law. The activation energy of this process is 0.63 eV. Even at extended heating cycles of 2 min at 250°C, 190 nm from the original 300 nm of the platinum film remain undissolved. This high stability makes platinum a very attractive thin-film metallization for flip-chip (FC) bonding of new microsystems.
XTEM and TFXRD investigations of ohmic Ti/Al/Ti/Au/WSiN contacts on AlGaN/GaN HFET layer systems
(2002)
The microstructural features of the high-temperature-stable ohmic contact system Ti/Al/Ti/Au/WSiN on AlGaN/GaN were investigated using analytical transmission electron microscopy and thin film x-ray diffraction.
For two typical rapid thermal annealing steps at 750 ◦C (non-ohmic behaviour) and 850 ◦C (ohmic behaviour) the intermetallic phases at the metal–semiconductor interface are presented. Increased annealing leads to the transformation of an Al2Au-AlAuTi phase mixture to a mixture of Al2Au-Al3Au8 phases and the formation of Ti-Al-nitride layers at the interfaces. In light of these results the electrical contact properties are discussed.
Spin transition in heptanuclear star-shaped iron(III)-antimony(V) NCS- and CN-bridged compounds
(2009)
The precursor [FeIII(L)Cl] (LH2 = N,N'-bis(2'-hydroxy-benzyliden)-1,6-diamino-3-azahexane) has been prepared and Mössbauer spectroscopy assigned a high-spin (S = 5/2) state at room temperature. The precursor is combined with the bridging units [SbV(X)6]- (X = CN-, NCS-) to yield star-shaped heptanuclear clusters [(LFeIII-X)6SbV]Cl5. The star-shaped compounds are in general high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers switch to the low-spin state as indicated by Mössbauer spectroscopy, i.e. multiple electronic transitions. While the cyano-bridged complex performs a multiple spin transition the thiocyanate-compound shows no significant population at both temperatures.
Parkhaus "Am Gericht" in Frankfurt am Main - Eine Sanierung mit kathodischem Korrosionsschutz
(2007)
Parkhäuser haben nach mehreren Jahrzehnten der Nutzung häufig Sanierungsbedarf in Bezug auf die tragende Stahlbetonkonstruktion, die durch eingedrungene Chloride aus eingeschlepptem Tausalz und die hierdurch hervorgerufene Korrosion der Bewehrung in der Tragfähigkeit erheblich beeinträchtigt sein kann. Das Verfahren des kathodischen Korrosionsschutzes kann hier als elektrochemisches Instandsetzungsverfahren eine wirtschaftliche und zuverlässige Alternative zu herkömmlichen Sanierungsverfahren bieten. Voraussetzungen sind intensive Voruntersuchungen, die Kenntnis der sinnvollen Anwendungsgrenzen des Systems, eine qualitativ hochwertige bauliche Umsetzung des Systems und die Nutzung der Möglichkeiten der Überwachung des Instandsetzungserfolges durch Monitoring, was am Beispiel des Parkhauses Am Gericht in Frankfurt am Main erläutert wird.
Parking garage Am Gericht in Frankfurt am Main - a refurbishment with cathodic corrosion protection.
After several decades in use a refurbishment is often necessary for the bearing structure of reinforced concrete parking garages due to chlorides, which have been brought into concrete by road salt, and the resulting corrosion of the reinforcement, which may lead to a serious decrease of the bearing capacity. With the system of the cathodic protection of the reinforcement exists a cost-effective and reliable technique as an alternative to common solutions. An intensive investigation of the structure, the knowledge of the reasonable limits of the system, excellent design and execution of the construction work and the monitoring of the working system are nevertheless required, which is illustrated by the example of the parking garage Am Gericht in Frankfurt am Main.
