H. Klewe-Nebenius

Characterization of artificially produced copper and bronze patina by XPS

Miniaturized photoacoustic and photothermal sensors have been developed for non-destructive in situ control of the state of patinated copper and bronze monuments. For calibration purposes, various systematic surface and microanalytical studies have been carried out, including x-ray photoelectron spectroscopy (XPS) studies of artificially patinated copper and bronze substrates. In order to prevent patina sample damage by x-ray-induced reduction of cupric sulphates, it has been found necessary to perform XPS measurements at liquid nitrogen temperature. In this way reliable qualitative and semi-quantitative analyses of copper and bronze patina could be accomplished. The XPS analyses have been successful in detecting partial chemical transformations of patina films upon artificial weathering. The acid weathering procedure applied, which was thought to imitate a very aggressive industrial atmosphere with rapidly changing relative humidity, produced less basic cupric sulphates such as chalcanthite both in pure antlerite and brochantite films and in mixed patina films.

Tracer and surface spectroscopy studies of sensitivity mechanism of mercury ion chalcogenide glass sensors

Abstract Sensitivity mechanism of mercury ion microsensors based on AgBr–Ag 2 S–As 2 S 3 thin films has been investigated using 110 Ag tracer exchange experiments, X-ray photoelectron spectroscopy (XPS) and secondary neutral mass spectroscopy (SNMS). It was found that non-linear sensor response in Hg(NO 3 ) 2 solutions is caused by at least two principal potential-generating processes: (i) Hg 2+ to Ag + ion exchange, and (ii) chemical reactions at the membrane surface involving silver and mercury species.

Cu2+-selective thin films for chemical microsensors based on sputtered copper—arsenic—selenium glass

Abstract Copper-rich, chemically and mechanically stable Cu-As-Se ultrathin films (15−30 nm) have been prepared by r.f. co-sputtering of the host and metallic copper and characterized by XPS, AES and RBS. Cu 2+ -selective chemical sensors based on the sputtered films have been fabricated, and their sensor characteristics investigated in a static electrochemical cell and in a flow-through microcell. The developed sensors exhibit near-Nernstian response over six orders of magnitude, a low detection limit below 10 −7 M (6 ppb), high reproducibility of the sensor potentials and high selectivity in the presence of alkali, alkaline earth and heavy-metal ions. The sensors remain highly sensitive and selective during continous measurements over at least six weeks.

Production and surface analytical characterization of various chalcogenide glass thin films for analytical microdevices

Abstract For the detection of heavy metal ions in liquid media bulk chalcogenide glasses like AsSe alloys doped with suitable metals are well-established membrane materials for conventional potentiometric sensors. The development of sensitive microlayers using techniques compatible with planar silicon technology is prerequisite for an integration of respective microsensors into complete analytical microsystems. By means of RF magnetron co-sputtering thin copper sensitive layers (As x Se x Cu y with varying Cu contents on Si/SiO 2 substrates) have been successfully produced using a special geometry for the sputter targets. The stoichiometries of these layers were thoroughly controlled by means of surface analytical techniques such as X-ray photoelectron spectroscopy, Auger electron spectroscopy and Rutherford backscattering. The special behaviour of the AsSe system during surface analytical characterization is discussed together with other properties of the sensitive microlayers.

Surface analytical characterization of the hydrogen getter material ZrCo

SummarySurface analytical methods have been applied to characterize the surface and surface-near layers of the hydrogen getter material ZrCo as well as those of the alloy constituents Zr and Co at temperatures up to 500°C. At room temperature the high stability of ZrO2 and the oxygen solubility dominate the surface composition leading to a strong enrichment of oxidic Zr and adsorbed oxygen in case of ZrCo. The thermal behaviour of the alloy surface is completely different from that of the components and explains at least qualitatively the necessity of an activation procedure for the getter material. ZrCo with high hydrogen content shows a strong correlation between hydrogen and the Zr component but not between Co and hydrogen.

Surface analytical investigation of the tritium getter ZrCO after exposure to various gases

ZrCo is a hydride forming material frequently investigated and proposed for storage and handling of hydrogen isotopes. It is of special interest for deuterium and tritium storage needed for the operation of a nuclear fusion reactor. An interaction of ZrCo powder with contaminant gases particularly during the thermal release of the hydrogen isotopes from the hydride at temperatures above 300 °C was found to cause a reduction of the reactivity of the powder. Consequently, a serious decrease of the hydrogen storage capacity occurs. From surface analytical investigations of ZrCo after exposure to the contaminant gases CO, CO2, O2, N2, CH4, and C2H4 it was concluded that CH4, C2H4, O2, or N2 react predominantly with Zr, the principal hydride forming alloy component, to carbide, nitride, and/or oxide. The resulting decrease of the storage capacity is possibly due to either a reduction in the amount of unreacted Zr available for the formation of Zr hydrides or to a formation of a thick protective overlayer. CO or CO2, which react mainly with the Co component but with Zr in surface near layers only, cause a less pronounced decrease in storage capacity.

Copper(II)-ion response of CuAsSe thin-film sensors in a flow-through microcell

Abstract Chemical microsensors combined with flow-through and flow-injection analysis microsystems are promising analytical instruments for reliable, high performance environmental monitoring, medical applications and process control. In this report we discuss the sensitivity, selectivity, response time, and potential stability of CuAsSe ultrathin films (obtained by r.f. co-sputtering of the host glass and metallic copper) in a flow-through microcell with a volume of ≈ 10 μ1. As expected, the Cu2+-ion response at micromolar concentrations is much better in comparison with static measurements, i.e., measurements done without stirring or moving the solution. Thin-film sensors exhibit near-Nernstian response over six orders of magnitude with a detection limit between 10−8 and 10−7 M. The better detection limit of the sensors in the flow-through cell causes improved apparent selectivity at low Cu2+ concentrations in the presence of high alkali and alkali-earth cation concentrations. It was quite unexpected that we could observe a better selectivity (by a factor of 100) in the presence of Cd2+ ions as well as Ni2+, H+ and Fe3+ cations. Possible reasons for such behaviour are discussed.

Untersuchungen zur Wechselwirkung von gasförmigem molekularem Iod mit Silberoberflächen mittels XPS und AES

SummaryThe adsorption of gaseous molecular iodine on clean silver surfaces proceeds in the first stage by dissociative chemisorption. After the formation of half a monolayer of chemisorbed iodine atoms the formation of silver iodide begins, which forms a very regular overlayer on top of the substrate. Both iodine species can be distinguished due to a difference in chemical shift of the M4N4, 5N4, 5-Auger transitions. After completion of this overlayer further iodine uptake is slowed down significantly. Above an overlayer thickness of about 10 nm a further progress of the reaction cannot be followed anymore due to the limited information depth of XPS.

XPS and AES investigations of the reaction behaviour of iodine with Zircaloy-4 surfaces

SummaryThe reaction behaviour of gaseous iodine on Zircaloy-4 surfaces is of interest with regard to the corrosion of fuel cladding tubes in light water reactors. XPS and AES have been employed for its investigation as these methods are most suitable because of their small information depth and their sensitivity to chemical states. It has been shown that the formation of zirconium iodide overlayers reduces further iodine uptake indicating a diffusion-controlled reaction. Further results are discussed in detail.

Development of Na+-sensitive membranes based on sputtered Na-Al-Si glasses

Na+-sensitive microdevices are of increasing interest for integration in microanalytical systems e.g. for biomedical applications or for industrial process control. In order to produce ultra thin Na+-sensitive layers with fixed and reproducible composition and, in particular, defined Na concentration by means of RF sputtering, an off-axis geometry of a magnetron with cylindrical target was chosen for minimizing back-sputtering effects from the already deposited material. With this inverted cylindrical magnetron (ICM) it was possible to obtain reproducible and controllable sodium aluminosilicate glass layers on semiconductor substrates. Several surface and thin layer analytical techniques were applied for characterization of the membranes and for stoichiometry control. Especially by the non-destructive nuclear reaction analysis method a constant Na profile throughout the glass layer and — together with AES depth profiles — the diffusion barrier effect of an Si3N4 interface layer could be verified. Electrochemical measurements proved Nernstian sensitivity down to 10−4M Na+ in solutions of pH 7, supporting sufficient stability and reproducibility of the sputtered Na+-sensitive layers.