Nondestructive characterization of nanoscale layered samples.

Multilayered samples consisting of Al, Co and Ni nanolayers were produced by MBE and characterized nondestructively by means of SRXRF, mu-XRF, WDXRF, RBS, XRR, and destructively with SIMS. The main aims were to identify the elements, to determine their purity and their sequence, and also to examine the roughness, density, homogeneity and thickness of each layer. Most of these important properties could be determined by XRF methods, e.g., on commercial devices. For the thickness, it was found that all of the results obtained via XRR, RBS, SIMS and various XRF methods (SRXRF, mu-XRF, WDXRF) agreed with each other within the limits of uncertainty, and a constant deviation from the presets used in the MBE production method was observed. Some serious preliminary discrepancies in the results from the XRF methods were examined, but all deviations could be explained by introducing various corrections into the evaluation methods and/or redetermining some fundamental parameters.

Characterization of individual aerosol particles in workroom air of aluminium smelter potrooms.

Aerosol particles with aerodynamic diameters between 0.18 and 10 microm were collected in the workroom air of two aluminium smelter potrooms with different production processes (Soderberg and Prebake processes). Size, morphology and chemical composition of more than 2000 individual particles were determined by high resolution scanning electron microscopy and energy-dispersive X-ray microanalysis. Based on chemical composition and morphology, particles were classified into different groups. Particle groups with a relative abundance above 1%(by number) include aluminium oxides, cryolite, aluminium oxides-cryolite mixtures, soot, silicates and sea salt. In both production halls, mixtures of aluminium oxides and cryolite are the dominant particle group. Many particles have fluoride-containing surface coatings or show agglomerations of nanometer-sized fluoride-containing particles on their surface. The phase composition of approximately 100 particles was studied by transmission electron microscopy. According to selected area electron diffraction, sodium beta-alumina (NaAl(11)O(17)) is the dominant aluminium oxide and cryolite (Na(3)AlF(6)) the only sodium aluminium fluoride present. Implications of our findings for assessment of adverse health effects are discussed.

Topochemical speciation of intercalated palladium in graphite by valence band X-ray spectrometry in the electron microprobe.

The binding state of palladium was studied within the frame of an investigation on the mechanism of analyte fixation during the pyrolysis step in graphite furnace atomic spectrometry. One approach was the determination of the palladium intercalated in the pyrolytic coating of the graphite tube. Due to the low concentrations of intercalated palladium in the pyrolytic coating, precise determination of the shift of certain X-ray lines was chosen. From several investigated valence state sensitive X-ray transitions, the Pd Lbeta2/15 (L3-N4,5) line shift was the one best determinable. The measured line shifts are in the range of -0.14 to 0.71 eV at line widths of 13 eV (fwhm) and a line energy of 3.1729 keV. These very small line shifts were determined by electron probe microanalysis. The detection of the small line shifts was performed with a new method-by evaluation of the change of the intensity in the flanks of the X-ray line. The measurements yielded the following results: inside the pyrolytic graphite, the palladium is distributed inhomogeneously in the form of clusters or islands and in the form of particles on the surface of the pyrolytic graphite. The differentiation between particles and clusters is a very practical one: as long as a particle can be seen in the SEM we talk of particles. Often, however, Pd is detected in an area on the tube or platform surface without detection of a particle. Hence, it can be assumed that the Pd is present in the form of clusters which might even be intercalated in the uppermost graphite layers. The valence state inside these clusters does not appear to be uniform. It can be interpreted as a mixture of Pd with PdO in the center of the clusters or particles (positive peak shift) and of Pd bound to the graphite (strong negative peak shift). On the basis of these observations, a way is proposed to determine how activated Pd atoms in intercalated Pd domains are forming strong covalent bonds to analytes. These bonds are responsible for the analyte fixation of even very volatile analytes.