Electronic states of the θ′ phase in Cu-Al alloys as compared to C16-${\mathrm{CuAl}}_2$: Cu Lα emission excited directly by undulator radiation

The electronic states of the θ′ phase formed by thermal aging in the Al-Cu (0.5 at. %) alloy are compared with those in C16-${\mathrm{CuAl}}_2$, which is the final phase separated at equilibrium. This is done by means of Cu ${\mathit{L}}_{\mathrm{\alpha }}$ fluorescence spectroscopy. The high brilliance of undulator radiation used as an excitation source is exploited. The spectra are taken using the first harmonic of the undulator at 1.7 keV, with a full width half maximum of ∼250 eV. A narrowing of around 0.5 eV of the Cu ${\mathit{L}}_{\mathrm{\alpha }}$ spectra in the θ′ phase is found. This is explained in terms of the differences in the Cu 3d–Cu 3d interaction in the two phases and of the hybridization between Cu 3d and the nearly free-electron-like electrons. The results demonstrate the future possibilities of fluorescence spectroscopy of minority species in inhomogeneous systems. © 1996 The American Physical Society.