Resonant photoemission study of the electronic structure of3 keVnitrogen-implanted tantalum

Abstract

The electronic properties of tantalum nitride thin films grown by $3\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ nitrogen implantation have been studied with resonant photoemission using synchrotron radiation. Resonant photoemission from the valence band was observed when the photon energy was in the neighborhood of the $\mathrm{Ta}\phantom{\rule{0.2em}{0ex}}5p\ensuremath{\rightarrow}5d$, $5p\ensuremath{\rightarrow}6sp$ and $4f\ensuremath{\rightarrow}5d$ transition energies. The constant initial state curves show multiple resonance maxima that are explained in terms of the $\mathrm{Ta}\phantom{\rule{0.2em}{0ex}}5p\ensuremath{\rightarrow}5d$, $5p\ensuremath{\rightarrow}6sp$ and $4f\ensuremath{\rightarrow}5d$ photoabsorption mechanisms, the spin-orbit splitting of the $\mathrm{Ta}\phantom{\rule{0.2em}{0ex}}5p$ and $\mathrm{Ta}\phantom{\rule{0.2em}{0ex}}4f$ core levels, and the splitting of the $\mathrm{N}--\mathrm{Ta}$ hybridized unoccupied states by crystal-field interactions. A strong resonance has been observed at the $\mathrm{Ta}4f\ensuremath{\rightarrow}5d$ transition. Resonant photoemission results suggest a strong hybridization of the $\mathrm{Ta}\phantom{\rule{0.2em}{0ex}}5d$ and $\mathrm{N}\phantom{\rule{0.2em}{0ex}}2p$ atomic orbitals along the main feature of the VB (between $\ensuremath{\sim}3--9\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$) due to the extended nature of Ta orbitals. Occupied vacancy states at $\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ show a resonance enhancement that supports the Ta character recently predicted for such states by Stampfl and Freeman. Stronger resonances are found for the hybridized $\mathrm{Ta}\phantom{\rule{0.2em}{0ex}}5d\text{\ensuremath{-}}\mathrm{N}\phantom{\rule{0.2em}{0ex}}2p$ valence band features lying in the $\ensuremath{\sim}3--9\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ range, than for the essentially Ta-like ones just below the Fermi level. This suggests that an interatomic recombination mechanism in which $\mathrm{N}\phantom{\rule{0.2em}{0ex}}2p$ states resonate themselves could also take place.