Journal of Electron Spectroscopy and Related Phenomena 101–103 (1999) 277–280 Evolution of Cu–L fluorescence lineshape during aging of Cu–Al a studied with direct excitation by undulator radiation a, b a c * L. Braicovich , C. Dallera , B. De Michelis , N.B. Brookes a INFM, Dipartimento di Fisica del Politecnico, Piazza Leonardo da Vinci 32, 20133 Milan, Italy b INFM, Istituto Nazionale di Fisica della Materia, Milan, Italy c ESRF, European Synchrotron Radiation Facility, BP 220, 38043 Grenoble, France Abstract The high sensitivity obtained by direct excitation by undulator radiation allows the shape of the Cu–L fluorescence ab spectrum to be measured accurately also at low Cu concentrations. We study the evolution of the L lineshape of 0.5 and a 1.5% Cu in Al following the thermal history of the sample. The Cu spectra in the precipitates are given and the formation of Guinier–Preston (GP1) zone of type 1 is studied for the first time with this approach. The results point out the importance of GP1 arrangement with platelets rich in Cu. The effect of selfabsorption on the L spectra is also investigated.  1999 ab Elsevier Science B.V. All rights reserved. Keywords: Fluorescence; Alloys; Cu; Cu–Al alloys; Cu–Al 1. Introduction advantages inherent the high brilliance (typically good counting rate, small spot, background reduc- In soft X-Ray fluorescence spectroscopy [1] the tion). We have already shown [2] the usefulness of direct excitation with undulator radiation from high this approach in the physical metallurgy of Cu–Al brilliance third generation synchrotrons is an interest- alloys with low Cu content (0.5%). In fact the L a ing option in material science although it does not linewidth has been correlated to the structure of the exploit the high selectivity typical of monochromatic precipitates which are formed during the aging of the excitation. In fact one can still have distinct advan- system [3] and are important in the determining the tages with respect to conventional fluorescence. One mechanical properties of these alloys having well can get rid completely of the surface contribution known technological interest. In Ref. [2] we have typical of electron excitation so that one can easily studied the CuAl precipitates obtained after anneal- 2 study ‘as grown’ samples, a fact which can hardly be ing at 2208C (phase u 9 ) which are a kind of underevaluated in physical metallurgy. On the other asymptotic limit in the alloy aging. These precipi- hand in some conventional fluorescence experiments tates have a structure different from bulk CuAl 2 one uses X-Ray tubes to obtain bulk sensitivity; (C16- u phase) although they have the same stoi- however, with undulator excitation, there are the chiometry. We could correlate the change in the Cu–Cu distance with the bandwidth (and thus with the L linewidth) through a tight binding calculation. a *Corresponding author. Tel.: 139-02-23996180; fax: 139-02- This was due to the high sensitivity of the bandwidth 23996126. E-mail address: lucio.braicovich@polimi.it (L. Braicovich) to the interatomic distance since the overlap integrals 0368-2048 / 99 / $ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0368-2048(98)00459-9