Microsc. Microanal. Microstruct. 6, 121-125 (1995)
DOI: 10.1051/mmm:1995112

Recent Studies of Near-Edge Structure

Lawrence Michael Brown, Caroline A. Walsh, Ann Dray et Andrew L. Bleloch

Cavendish Laboratory, Madingley Rd., Cambridge CB3 0HE, UK

Abstract
The extent to which near-edge structure depends upon long-range order is explored using polymeric systems, where one can vary the disposition of side-groups and the degree of crystallinity and compare the resulting spectra. Carbon K-edges for polystyrene in atactic and isotactic forms are compared; the former is amorphous and the latter crystalline. Differences between the spectra are very slight but observable, and are attributed to bond orientation effects and to interaction between closely-spaced hydrogens bonded to neighbouring benzene rings and to the backbone. The quality of the spectra collected at doses of less than 300 from a few square microns compares favourably with previously published EXAFS data. Another example of near-edge structure is provided by segregated species. The case of iron segregated to boundaries in Zr-Nb alloys is of intense interest to the nuclear industry. An attempt has been made to interpret observed fine structure in terms of structure from reference intermetallic compounds. It seems that the fine structure displayed by the segregated iron is different from that displayed by pure metallic iron or by known compounds with Zr, but more akin to ZrNbFe.

PACS
6140K - Structure of polymers, elastomers, and plastics.
3520G - Molecular bond strengths, dissociation energies, hydrogen bonding.
7920K - Other electron surface impact phenomena.
6180M - Channelling, blocking and energy loss of particles.
6475 - Solubility, segregation, and mixing.
8130M - Precipitation.
6170N - Grain and twin boundaries.
2842Q - Fission reactor structural and shielding materials.
2850J - Heavy water reactors.
3520D - Interatomic distances and angles in molecules.

Key words
bond angles -- electron energy loss spectra -- fission reactor materials -- grain boundary segregation -- hydrogen bonds -- iron -- long range order -- niobium alloys -- polymer structure -- zirconium alloys -- near edge structure -- long range order -- polymeric systems -- side groups -- crystallinity -- C K edges -- polystyrene -- atactic form -- isotactic form -- amorphous state -- bond orientation effects -- closely spaced H bonds -- neighbouring benzene rings -- ELNES -- CANDU -- Fe segregation -- intermetallic compounds -- fine structure -- grain boundaries -- nuclear industry -- fission reactor materials -- EELS -- ZrNbFe -- ZrNb Fe


© EDP Sciences 1995