<p>The spectroscopic, SEM and Raman measurements on carbon nanotubes under the exact conditions of which OES analysis were made showed that at<br /> a pressure of 400 Torr and a flow rate of 200 sccm, the quality and quantity of single-walled carbon nanotubes was the highest.</p>

One of the oldest goals across the science is to watch atoms undergo reactions in real time. However, such observations are only meaningful if the object of interest is looked at in its natural environment. For most biological and materials sciences samples, this means in solution phase or dispersed in a liquid. Unfortunately, this restriction normally prohibits either reaching atomic spatial (10-10m) or ultrafast time (10-15sec) resolution. Here, two sample preparation techniques are shown providing a natural environment for experiments with high spatial and temporal resolution: a nanofluidic cell for electron microscopy, and a chip for serial time resolved x-ray crystallography. The nanofluidic cell was implemented into different transmission electron microscopes, and in initial experiments, the key features of the sample cell are shown, namely the ability to create stable ultrathin liquid layers of tuneable thickness within the harsh electron microscope vacuum. The option to directionally flow liquid through the sample cell opens the door to high throughput electron microscopy and on-the-fly sample exchanges with the option of triggering and influencing chemical reactions with external sample control. First applications highlight the impact of the nanocell: structural disintegration of gold nanorods exemplary for materials science, and amyloid fibrils, exemplary for biomedical applications. In future applications diffractive imaging with high time resolution is planned, and will complement the range of experiments within the fields of traditional transmission electron microscopy. The second half of this thesis presents a solid target for x-ray crystallography. The chip enables the arrangement of thousands of micrometer sized protein crystals in a regular array. The ability to prepare protein crystals in such a fashion is unique and permits serial in situ crystallography. Real time crystallography requires samples to be mounted in a saturated natural environment, i.e. under ambient pressure and temperature conditions. The crystallography chip fills this need while being easily integrated into a synchrotron beam line. In a first set of experiments, the chip design was refined and could prove functionality for static in situ structure analysis of protein systems. Based on this success, future time resolved experiments are under way and will show the full capability of this device.

Organic semiconductors functionalized nanostructures are becoming as promising materials for electronic device applications including organic photovoltaics (OPVs). Perylenediimide (PDI) derivatives have also been known as one of the best n-type organic semiconductors. PDI derivatives can form bulk materials, which are both photochemically and thermally stable and have been widely used in various optoelectronic devices. Due to the formation of high electron mobility of crystalline domains, they prefer to incorporate into a silsesquioxane network. Here, we describe the potential applicability of perylenediimide functionalized silsesquioxane nanoribbons (PDI-dimethyl nanoribbons) as an acceptor for optoelectronic devices. We have developed synthetic procedures to make the PDI-dimethyl nanoribbons by the substitution reaction and the modified Stöber method. The PDI-dimethylethoxy silane precursor was produced in high yield by substituting 3-aminopropyldimethylethoxysilane on perylene-3,4,9,10-tetracarboxylicdianhydride as side chains. The optically active PDI-dimethyl nanoribbons were then formed upon hydrolysis with the certain concentration of ammonium hydroxide as a base. These nanoribbons were characterized using transmission electron microscopy (TEM), elemental analysis, and polarized optical microscopy. The photophysical properties in solution phase were also studied. The synthesis procedure developed here will have a great promise in large-scale manufacturing. Different shapes of PDI-dimethyl nanostructures, such as nanorods, nanochains, and nanoparticles, were discovered while varying the base concentrations. Also the morphologies of these PDI nanostructures were studied using TEM. Future studies will focus on optimizing procedures of PDI-dimethyl nanostructures and exploring new derivatives like perylenediimide dimer functionalized silsesquioxane polymers.

Several studies on small animals have shown that MRI enhanced with nanoparticles of iron oxide (USPIO) is able to detect the neuroinflammation. However, to our knowledge, no team had yet investigated the potential of this approach for monitoring an anti-inflammatory treatment. In this context, we have demonstrated the feasibility of this approach to monitor the effects of minocycline after cerebral ischemia in mice. MRI is a very sensitive technique for the detection of iron, but the precise location of USPIO as well as their quantification is difficult. We therefore propsed to complete the MRI approach by a new technique to our knowledge in the field of USPIO imaging in the brain : Synchrotron radiation tomography. We here present the first results showing the feasibility of this approach and a comparative study of the sensitivity of two techniques used for the detection of USPIO in the brain. In the last part of our work, we report our results on the biotransformation of USPIOs in the spleen of the mouse during the first 40 days after intravenous injection obtained by transmission electron microscopy (TEM).

Die außerordentlichen Steigerungen der Funktionalität und Produktivität in der Halbleiterindustrie sind zum wesentlichen Teil auf eine Verkleinerung der Strukturdetails auf einer logarithmischen Skala über die letzten Jahrzehnte zurückzuführen. Sowohl zur Kontrolle des Fertigungsergebnisses als auch zur Klärung von Fehlerursachen ist die Nutzung transmissionselektronenmikroskopischer Methoden unabdingbar. Für die Zielpräparation von Halbleiterstrukturen sind Techniken unter Nutzung der Focused Ion Beam Geräte etabliert, die je nach der konkreten Aufgabenstellung variiert werden. Die Abbildung von Strukturdetails mit Abmessungen von wenigen Nanometern erfordert die Anwendung unterschiedlicher Kontrastmechanismen. Die Ergänzung der Abbildung durch die analytischen Techniken der energiedispersiven Röntgenmikroanalyse und der Elektronenenergieverlustanalyse ist ein wertvolles Werkzeug bei der Klärung von Fehlerursachen oder bei prozesstechnischen Fragestellungen. Die Nutzung der Rastertransmissionselektronenmikroskopie erlaubt die unmittelbare Kombination von Abbildung und Elementanalyse. Die lokale Verteilung von Dotierstoffen als wesentliche Grundlage für die Funktion von Bauelementen in der Halbleiterindustrie ist nur über ihre Auswirkung auf die Phase der transmittierten Elektronenwelle nachweisbar. Mittels Elektronenholographie kann dieser Einfluss gemessen werden und das Prozessergebnis von Implantationen dargestellt werden. Für die Charakterisierung von Details, die kleiner als die Probendicken sind, die im TEM genutzt werden, ist die Anwendung der Elektronentomographie ein geeignetes Werkzeug. Dazu sind spezielle Präparations- und Abbildungsstrategien erforderlich. / The strong improvements in functionality and productivity in the semiconductor industry are mostly a result of the decrease of structural details on a logarithmic scale during the last decades. The monitoring of the production process, as well as failure analyses, utilize methods of transmission electron microscopy. For targeted preparations of semiconductor structures, techniques based on focused ion beams are established, with adaptions to the current task. The imaging of structural details with dimensions of a few nanometers requires the application of different contrast techniques, depending on the detailed request. Different opportunities of elemental analysis, such as energy dispersive X-ray analysis or electron energy loss analysis, deliver additional information about the chemical composition and binding states on a nanoscale. The use of scanning transmission electron microscopy enables a direct combination of imaging and elemental analysis. The local distribution of dopants, as one of the major basics for the function of semiconductor devices, can be observed via the phase shift of the transmitted electron wave only. This influence requires the application of electron holography, a technique which enables the visualization of the process result of implantations or diffusion processes. The characterization of details which are smaller than the thickness of a TEM-sample is enabled through the use of electron tomography. This technique requires special strategies for preparation and imaging and delivers a 3D-dataset, describing the structure.

No description available.

No description available.

Sodium borohydride is stable in alkaline solution, however, it hydrolyses and generates hydrogen gas in the presence of suitable catalyst. By this way hydrogen can be generated safely for the fuel cells. All of the catalyst having been used in the hydrolysis of sodium borohydride, with one exception, are heterogeneous. The limited surface area of the heterogeneous and therefore, have limited activity because of the surface area. Thus, the use of metal nanoclusters as catalyst with large surface area is expected to provide a potential route to increase the catalytic activity. In this dissertation we report for the first time the use of ruthenium(0) nanoparticles as catalyst in the hydrolysis of sodium borohydride. The water dispersible ruthenium(0) nanoparticles were prepared by the reduction of RuCl3.xH2O with sodium borohydride and were stabilized by three different ligands dodecanethiol, ethylenediamine and acetate. Among these three colloidal materials the acetate stabilized ruthenium(0) nanoparticles were found to have the highest catalytic activity in catalyzing the hydrolysis of sodium borohydride. The acetate stabilized ruthenium(0) nanoparticles were characterized by tranmission electron microscopy (TEM), X-ray photoelectron spectroscopy and FT-IR spectroscopy. The particle size of the acetate stabilized ruthenium(0) nanoparticles was determined to be 2.62&plusmn / 1.18 nm from the TEM analysis. The kinetic of the ruthenium(0) nanoparticles catalyzed hydrolysis of sodium borohydride was studied depending on the catalyst concentration, substrate concentration and temperature. The activation parameters of this reaction were also determined from the evaluation of the kinetic data. This catalyst provides the lowest activation energy ever found for the hydrolysis of sodium borohydride.

ABSTRACT CARBON SUPPORTED AND SURFACTANT STABILIZED METAL NANOPARTICLE CATALYSTS FOR DIRECT METHANOL FUEL CELLS &Ccedil / elik, &Ccedil / aglar M.S., Department of Chemistry Supervisor: Assoc. Prof. Dr. G&uuml / ls&uuml / n G&ouml / kaga&ccedil / August 2005, 72 pages Carbon supported surfactant, such as 1-decanethiol and octadecanethiol, stabilized platinum and platinum/ruthenium species have been prepared recently. In this thesis, for the first time, 1-hexanethiol has been used as an organic stabilizer for the preparation of carbon supported platinum and platinum/ruthenium nanoparticle catalysts. These new catalysts were employed for methanol oxidation reaction, which were used for direct methanol fuel cells. Cyclic voltammetry, X-ray photoelectron spectroscopy and transmission electron microscopy have been used in order to determine the nature of the catalysts. The effect of temperature and time on catalytic activity of catalysts were examined and the maximum catalytic activity was observed for carbon supported 1-hexanethiol stabilized platinum nanoparticle catalyst (with 1:1 thiol/platinum molar ratio) which was heated up at 200oC for 5 hours. The particle size of platinum nanoparticles was determined to be ~ 10 nm in diameter. The size and distribution of metal nanoparticles on carbon support, the Pt/Ru surface composition, the relative amount of Pt(0), Pt(II) and Pt(IV) and the removal of organic surfactant molecules around the metal nanoparticles were found to be important in determining the catalytic activity of electrodes towards methanol oxidation reaction. A significant decrease in catalytic activity was observed for carbon supported 1-hexanethiol stabilized Pt75Ru25 and Pt97Ru3 (with 1:1 thiol/PtRu molar ratio) with respect to carbon supported 1-hexanethiol stabilized Pt (with 1:1 thiol/platinum molar ratio). This result might be due to unremoved stabilizer shell around platinum/ruthenium nanoparticles and increase in amount of Pt(II) and Pt(IV) compared to Pt(0) where the methanol oxidation occured.

Gegenstand der Arbeit ist die Analyse der bei hohen Verformungsgraden in Werkstoffen durch kollektive Bewegung der Versetzungen entstandenen neuen Defektkonfigurationen, die auf der mesoskopischen Skala agieren. Diese so genannte Disklinationen rufen neben starken Gitterdehnungen auch erhebliche lokale Gitterrotationen hervor. Es wurde der Nachweis der Existenz der Disklinationen in plastisch verformten Kristallen geliefert sowie die qualitative und quantitative Analyse der Disklinationskonfigurationen und der Disklinationsstärke durchgeführt. Die Untersuchungen an stark verformten Ein- und Vielkristallen wurden mittels sowohl lokalen Methoden der Transmissions- (TEM, CBED) und Rasterelektronenmikroskopie (REM, EBSD) als auch der integralen Methoden der Röntgenstrukturanalyse (XRD) durchgeführt. Die Ergebnisse haben gezeigt, dass die Entwicklung der Zellblockstruktur mit erheblichem Anstieg der Desorientierungen und Versetzungsdichten in Versetzungswänden verbunden ist und durch die Bildung der Netzwerke von Disklinationen gefördert wird.