Recent Studies of Near-Edge Structure

Abstract

Abstract. 2014 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 e-nm-2 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.Microsc. Microanal. Microstruct. 6 (1995) Figure 1. A benzene ring is attached to every other carbon atom of the carbon backbone. Each carbon atom has two different bonds to which the benzene ring can be attached. In isotactic polystyrene the rings are all attached to the same side of the carbon backbone. This isomer can be produced in both amorphous and crystalline forms. In atactic polystyrene the benzene rings are distributed at random on both sides of the carbon chain, which precludes the possibility of crystallization. Polystyrene was chosen because, by comparison to many polymers, it is less sensitive to irradiation damage by an electron beam. Spectra were acquired from amorphous atactic polystyrene, amorphous isotactic polystyrene and crystalline isotactic polystyrene. The amorphous films were produced by dissolving the polystyrene in toluene and drawing out a film on a glass slide. The crystals were produced as described by Tanzawa [1] and deposited from solution directly onto commercially produced SiO films on Cu

Probing the local structure and bonding at interfaces and defects using EELS in the TEM

“…The segregation of small amounts of iron (lOOOp.p.m. overall) to a-a grain boundaries in Zr-25(wt)%Nb alloys has been studied using EELS (Brown et al, 1995). The ratio of the Lj and L2 peaks at the Fe L2,3-edge as well as the Pearson ratio (the total white-line intensity normalized to the continuum) (Okamoto et al.…”