Inorganic chemistry Z 0100Magnetic and Structural Properties of Isolated and Assembled Clusters -[227 refs.]. -(BANSMANN, J.; BAKER, S. H.; BINNS, C.; BLACKMAN, J. A.; BUCHER, J.-P.; DORANTES-DAVILA, J.; DUPUIS, V.; FAVRE, L.; KECHRAKOS, D.; KLEIBERT, A.; et al.; Surf. Sci. Rep. 56 (2005) 6-7, 189-275; Inst. Phys., Univ. Rostock, D-18051 Rostock, Germany; Eng.) -Schramke 52-215

The design and operation of a gas aggregation source is described. The source combines the attributes of high-temperature operation (enabling preparation of transition metal clusters), mass selection, ultrahigh vacuum compatibility, and transportability. This makes it ideally suited to in situ studies such as scanning tunneling microscope or synchrotron radiation experiments. Data are presented to illustrate the performance of the source; recent results obtained in synchrotron radiation studies are highlighted.

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Abstract-The mineralogy of comet 81P/Wild 2 particles, collected in aerogel by the Stardust mission, has been determined using synchrotron Fe-K X-ray absorption spectroscopy with in situ transmission XRD and X-ray fluorescence, plus complementary microRaman analyses. Our investigation focuses on the terminal grains of eight Stardust tracks:

Aurivillius phases are compounds with the general formula (Am−1BmO3m+1)2− (Bi2O2)2+ that consist of (m − 1) perovskite‐like units interrupted by bismuth oxide layers. Compounds with A = {Ba2+; Sr2+}, B = {Nb5+}, and m = 2 are studied by EXAFS spectroscopy and X‐ray diffraction. The lattice parameters a and c of the tetragonal phase, studied by X‐ray diffraction, increase with increasing Ba content. The short‐range order environment of Ba, Sr, and Bi ions are analyzed for several Ba:Sr ratios using EXAFS spectroscopy. It is found that the Ba and Sr ions substitute each other in a solid solution. Their different ionic radii cause a tilting and distortion of the surrounding NbO6 octahedra. The first BiO interatomic distances are not influenced by the composition. Thus, the (Bi2O2)2+ layers possess a very high stability and determine the structure of the unit cell.

A range of amorphous hydrogenated silicon-carbide films have been produced using the plasma-enhanced chemical-vapour deposition technique with silane and methane diluted in hydrogen as the parent molecules. The air-exposed and sputtercleaned surfaces of these films have been investigated by means of X-ray photoelectron spectroscopy. Auger electron spectroscopy, secondary-ion mass spectrometry, Raman spectroscopy and reflection-electron diffraction. The structural and chemical nature of the films has been determined as a function of the methane: silane ratio by a combination of the above techniques. X-ray photoelectron spectroscopy and Auger electron spectroscopy have been used to determine the carbon content of the films also as a function of the methane : silane ratio. § 1. INTRODUCTION Hydrogenated amorphous binary alloys, such as amorphous hydrogenated silicon carbide (a-Sic : H), have proved to be attractive materials with applications to solar cells, photoreceptors and graphic devices (Tarui et al. 1987, Tawada, Kondo, Okamoto andHamakawa 1982). These applications result from the fact that their optical gap can be continuously controlled by varying the alloy compositional ratio (Anderson and Spear 1977).It is has been shown that the optical and electronic properties of these films are a sensitive function of the specific bonding configurations present (Fukada et al. 1983) as well as the alloy composition. In the light of this, it is important to develop a more detailed fundamental understanding of the structure and bonding configurations of these films over the composition range.A previous investigation of a-Si, -xCx : H prepared by plasma-enhanced chemical vapour deposition (PECVD) of methane (CH,) and silane (SiH,) has been undertaken by Lee (1980). The techniques of X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and reported infrared spectroscopy were used to characterize the films. The main conclusions of the study were that the structure of PECVD a-Sic : H films containing less than 70% carbon is best described in terms of a t slightly cross-linked, carbon-and hydrogen-substituted polysilicon. Once the carbon content exceeds this value one obtains an almost fully cross-linked, silicon-and hydrogen-substituted polycarbon.As compared to a-Si : H, the a-Sic : H films produced using the conventional PECVD technique possess inferior photoelectric properties. Recently it has been demonstrated (Matsuda et al. 1986) that H, dilution of the starting SiH, : CH, mixture leads to highly photosensitive films with photoconductivities up to three orders of magnitude greater than their non-diluted counterparts (Matsuda and Tanaka 1987).These results stimulated the following detailed investigation aimed at relating structural, chemical and compositional data with the optical and electronic properties of the same range of specimens. The a-Si,-,C,:H films were deposited in a conventional glow discharge reactor over a range from x=O*1 to 0-7 with different H, dilutions. The structural, chemical ...

Synchrotron Fe-K X-ray absorption spectroscopy and transmission electron microscopy have been used to investigate the mineralogy and Fe-redox variations in the space-weathered (SW) rims of asteroidal samples. This study focuses on the FIB lift-out sections from five Itokawa grains, returned by the Hayabusa spacecraft, including samples RB-QD04-0063, RB-QD04-0080, RB-CV-0011, RB-CV-0089, and RB-CV-0148. Each of the samples featured partially amorphized SW rims, caused by irradiation damage from implanted low mass solar wind ions, and the impacting of micrometeorites. Using brightfield and HAADF-STEM imaging, vesicular blistering and nanophase Fe metal (npFe 0) particles were observed within grain rims, and solar flare tracks were observed in the substrate host grain, confirming the presence of SW zones. We use Fe-K XANES mapping to investigate Fe-redox changes between the host mineral and the SW zones. All SW zones measured show some increases in the ferric-ferrous ratio (Fe 3+ /ΣFe) relative to their respective host grains, likely the result of the implanted solar wind H + ions reacting with the segregated ferrous Fe in the surface material.