Near Edge Fine Structures on Electron Energy Loss Spectroscopy Core Loss Edges

Core edges recorded in Electron Energy Loss Spectroscopy (EELS) display a large variety of profiles. We have investigated several specific aspects concerning Energy Loss Near Edge Structures (ELNES) and emphasize the interest in a careful edge shape analysis to obtain refined microanalytical information, such as local symmetry. After indicating the general impact of EELS fine structures as compared to EDX and Auger spectroscopies we discuss the instrumental conditions required for recording satisfactory spectra and consider the theoretical problems which are involved in data interpretation. The major portion of this paper presents results for selected K, L23, M45 and N45 core excitations in compounds (mainly oxides). In each case the phenomena governing the ELNES distribution are pointed out. In conclusion, we summarize the potential of a careful analysis of ELNES for studying the chemical state of the absorbing atom and the symmetry of it s first coordination shell (molecular description) or longer range effects (projections of solid state density of states as seen by the ejected atom)

Structural effect of heavy ion irradiation on GdBaCuO ceramics

The influence of twin boundaries as sinks on defects induced by 480 keV Kr ion irradiation in GdBaCuO crystals was observed in situ at 40 and 300 K. The interaction of the dislocations with the twin boundaries followed on a video recording. A crystalline to amorphous transition was observed above a total fluence of ∼ 4 - 5 x 10^12 Kr/cm2. A comparison between orthorhombic (Os) crystals and a monoclinic structure (Ms) (close to Os and whose parameters were calculated) shows that the behaviour of irradiation-induced extended defects does not depend on a small initial deformation of the orthorhombic cell. In both case, an occasional orthorhombic (or monoclinic) to tetragonal phase transition only occurs when the amorphization process has begun

Caractérisation par diffraction X, microscopie électronique et fluorescence X, des couches minces obtenues par évaporation de SmS. Structures cristallographiques après recuits par le faisceau électronique

Thin films are obtained from divalent SmS evaporation under a vacuum of 10-6 torr. The layers with a thickness of less than 1 500 Å are always amorphous. Those with a thickness of more than 2 000 Å present some properties varying according to the substrate temperature. The samples deposited at 85 K and slowly heated up to 293 K are black-grey and cristallized (f.c.c. structure, a = 5.91 Å) which may be characteristic of the 2 + valence state for Sm. At 293 K, samples are yellow and poorly cristallized (f.c.c. structure, a = 5.58 Å) which may be characteristic of the 3 + valence state for Sm. Crystallographic results are obtained by X-ray diffraction and electron diffraction. Analysis have been made by the X-ray fluorescence method. The electron beam permits to anneal the films and the following compounds appear : Sm2O2S, C and B-Sm2O3. At high temperature there is formation of new structures with large lattice parameters probably belonging to the Sm-O-S ternary system as X-ray fluorescence analysis shows it.Des films minces sont obtenus par évaporation sous 10-6 torr du sulfure SmS de samarium divalent. Les dépôts d'épaisseur inférieure à 1 500 Å environ sont toujours amorphes. Ceux d'épaisseur supérieure à 2 000 Å ont des propriétés différentes en fonction de la température du support. Ces échantillons déposés à 85 K et lentement réchauffés jusqu'à 293 K sont gris-noir et cristallisés (structure c.f.c., a = 5,91 Å), et correspondraient à un état de valence + 2 de Sm. A 293 K les dépôts sont jaunes et mal cristallisés (structure c.f.c., a = 5,58 Å) et correspondraient à un état de valence + 3 de Sm. Les résultats sont obtenus par diffraction X et diffraction électronique, quelques analyses sont faites par fluorescence X. Au sein du microscope, après recuits à l'aide du faisceau d'électrons, il apparaît les composés : Sm2O2S, B-Sm2O 3 et C-Sm2O3. A haute température il y a formation de nouvelles structures ayant de grandes mailles et appartenant probablement à un système ternaire Sm-O-S, comme le révèle la fluorescence X

Transitions de phases et modes d'épitaxie complexes dans les couches minces d'oxydes de terres rares irradiées par un faisceau d'électrons

Rare earth oxide thin films are peculiar materials, especially in the case of the intermediate oxide series for cerium, praseodymium and terbium. Treatment by water-vapor and irradiation by means of an electron beam induce intricate transition phases and unexpected epitaxial modes. These phenomena are tentatively linked to shock-wave processus throughout the material.Les couches minces d'oxyde de terres rares sont des matériaux très particuliers. La série des oxydes intermédiaires de cérium, praséodyme et terbium en est une parfaite illustration. Les films traités à la vapeur d'eau, puis irradiés par un faisceau d'électrons sont le siège de transition de phases et de modes d'épitaxie complexes inattendus. Un processus d'ondes de chocs, induit par l'impact du faisceau au travers du matériau pourrait expliquer ces phénomènes