Evidence for an Ultrafast Breakdown of the BeO Band Structure Due to Swift Argon and Xenon Ions

Auger-electron spectra associated with Be atoms in the pure metal lattice and in the stoichiometric oxide have been investigated for different incident charged particles. For fast incident electrons, for ${\mathrm{Ar}}^{7+}$ and ${\mathrm{Ar}}^{15+}$ ions as well as ${\mathrm{Xe}}^{15+}$ and ${\mathrm{Xe}}^{31+}$ ions at velocities of 6% to 10% the speed of light, there are strong differences in the corresponding spectral distributions of Be-K Auger lines. These differences are related to changes in the local electronic band structure of BeO on a femtosecond time scale after the passage of highly charged heavy ions.

Figure 1

Differentiated Auger-electron spectra. The black symbols and smoothed (red) curve were obtained in this work (averaged over 18 spectra induced by 2.7 keV electrons during the heavy-ion beam time). Other curves are taken from the literature and correspond also to $a$-BeO [17, 18] as well as to a BeO bulk single crystal ($c$-BeO) [19].

Figure 2

Projectile dependence of the Be $K$-Auger electron spectrum for $a$-BeO due to fast Ar and Xe ions of different incident charge states (averaged over many raw spectra) and 2.7 keV electrons. Secondary-electron backgrounds have been subtracted and intensity offsets have been applied, as indicated by the base lines on the right side.

Figure 3

Comparison of the Be $K$ Auger-electron spectra (after background subtraction) for $a$-BeO with clean metallic Be, both excited by 230 MeV ${}^{129}\mathrm{Xe}^{31+}$ ions. A reference spectrum for metallic Be ionized by incident electrons and averaged over the two primary energies of 1.0 and 2.7 keV (without any significant difference) is also shown.