Valence excitations and dopant distribution of Al doped ZnO nanowires analyzed by electron energy loss spectroscopy.

: Valence electron energy loss spectroscopy (VEELS) with scanning transmission electron microscopy (STEM) has been employed to probe the valence excitations and dopant distribution of Al doped ZnO nanowires. The results reveal that while the typical Al concentration is on the order of 1020 1/cm3, Al tends to segregate at the surface leading to an Al-rich sheath. In VEEL spectra, O-2p, Zn-3d, Al-3p, O-2s, interband transitions as well as bulk plasmon have been identified. The bulk plasmon peak is blue-shifted, and the projected interband transition decreases from 2.14 to 1.88 eV as the doping concentration increases from 0.83 x 10(20) to 2.18 x 10(20) 1/cm3.