Versatile vacuum chamber for in situ surface X‐ray scattering studies

A compact portable vacuum‐compatible chamber designed for surface X‐ray scattering measurements on beamline ID01 of the European Synchrotron Radiation Facility, Grenoble, is described. The chamber is versatile and can be used for in situ investigation of various systems, such as surfaces, nanostructures, thin films etc., using a variety of X‐ray‐based techniques such as reflectivity, grazing‐incidence small‐angle scattering and diffraction. It has been conceived for the study of morphology and structure of semiconductor surfaces during ion beam erosion, but it is also used for the study of surface oxidation or thin film growth under ultra‐high‐vacuum conditions. Coherent X‐ray beam experiments are also possible. The chamber is described in detail, and examples of its use are given.     

Long-lived contaminants in cyclotron-produced radiopharmaceuticals: measurement and dosimetry

Oxygenated target waters of cyclotron targets contain long-lived contaminants due to (p,n) reactions in the HAVAR target window that are spalled into the target water. These contaminants are largely removed during the synthesis of the final imaging agent. Currently the USP requires that the final drug product be 99.5% pure, so the total activity of the long-lived contaminants can be no more than 0.5% of the final radiopharmaceutical product. A method has been developed to identify and quantify the primary contaminants using high resolution gamma spectroscopy and VRF, a new spectrum analysis tool. Uptake, retention, and excretion functions for each of the contaminating isotopes in a soluble, injected chemical form have also been calculated using International Commission on Radiological Protection (ICRP) Publication 123 models and are presented in the Appendices A and B of Electronic Supplementary Material. In addition, specific organ and effective dose coefficients were also calculated using ICRP Publication 103 tissue weighting factors and are also presented in the Appendices A and B of Electronic Supplementary Material. Typical imaging agents have contaminant loads far below the USP limit and contribute negligible doses to the patients receiving the drugs.     

X-ray structure analysis of free-standing lipid membranes facilitated by micromachined apertures

Silicon and Teflon substrates have been structured by wet etching and a focused ion beam (FIB) to obtain very defined, clean apertures. Planar, free-standing lipid membranes (black lipid membranes (BLM)) with enhanced long-term stability have been prepared on these apertures by the methods of Montal and Müller(1,2) as well as Müller and Rudin.(3) The stability and geometric control enables the use of X-ray analysis of free-standing single bilayers. With the presented setup, simultaneous structural and electrophysiological measurements will become feasible.     

Elastic and inelastic electron tunneling spectroscopy of a new rectifying monolayer

Rectification of electrical current was observed in a Langmuir-Schaefer monolayer of fullerene-bis[ethylthio-tetrakis(3,4-dibutyl-2-thiophene-5-ethenyl)-5-bromo-3,4-dibutyl-2-thiophene] malonate, Au electrodes at room temperature (there are two regimes of asymmetry, at lower bias, i.e., between 0 and +/-2 V, and at higher bias), and also between Pb and Al electrodes at 4.2 K. The latter experiment was coupled with second harmonic detection of the second derivative of the current with respect to voltage (d2I/dV2). The d2I/dV2 spectrum shows intramolecular vibrations, and also two antisymmetric broad bands, centered at +/-0.65 V, due to resonant electron tunneling between the Fermi level(s) of the electrodes and the lowest unoccupied molecular orbital of the molecule.     

Direct equilibration of soil water for delta(18)O analysis and its application to tracer studies

Current methods for stable oxygen isotopic (delta (18)O) analysis of soil water rely on separation of water from the soil matrix before analysis. These separation procedures are not only time consuming and require relatively large samples of soil, but also have been shown to introduce a large potential source of error. Current research at Queen's University Belfast is focused on using direct equilibration of CO(2) with the pore water to eliminate this extraction step using the automated Multiprep system and a Micromass Prism III isotope ratio mass spectrometer (IRMS). The findings of this research indicate the method is less time consuming, more reliable, and reproducible to within accepted limits (+/-0.1% per thousand delta (18)O). In this study the direct equilibration method is used to analyse delta (18)O tracer profiles in the unsaturated zone of field soils, concurrently with chloride tracer profiles, which can be used to assess infiltration rates and mechanisms through the unsaturated zone. Copyright 1999 John Wiley & Sons, Ltd.     

Secondary ion yields produced by keV atomic and polyatomic ion impacts on a self-assembled monolayer surface

A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd.     

Umweltchemie 1998

Nachdem im Trendbericht des letzten Jahres ausgewählte Beispiele aus Bereichen der Umweltchemie besprochen wurden,¹⁾ sollen in diesem Jahr Ergebnisse aus Ökotoxikologie and Humantoxikologie behandelt werden. Zunächst werden einige Arbeiten aus den Bereichen der Entsorgungsverfahren und neue Entwicklungen bei Spurenstoffen vorgestellt. Da das Gebiet der nachhaltigen Chemie immer mehr in den Brennpunkt des Interesses rückt, werden auch neue umweltfreundliche Synthesen und Produkte ausführlich diskutiert.