Measuring the hole-state anisotropy in (formula presented) by electron energy-loss spectroscopy

Abstract

We have examined polycrystalline (formula presented) by electron energy-loss spectroscopy (EELS) and density of states calculations. In particular, we have studied two different crystal orientations, [110] and [001], with respect to the incident electron beam direction, and found significant changes in the near-edge fine structure of the B K-edge. Density-functional theory suggests that the pre-peak of the B K-edge core loss is composed of a mixture of (formula presented)- and (formula presented)-hole states and we will show that these contributions can be distinguished only with an experimental energy resolution better than 0.5 eV. For conventional transmission electron microscope/scanning transmission electron microscope instruments with an energy resolution of ∼1.0 eV the pre-peak still contains valuable information about the local charge-carrier concentration that can be probed by core-loss EELS. By considering the scattering momentum transfer for different crystal orientations, it is possible to analytically separate (formula presented) and (formula presented) components from the experimental spectra. With careful experiments and analysis, EELS can be a unique tool measuring the superconducting properties of (formula presented) doped with various elements for improved transport properties on a subnanometer scale. © 2003 The American Physical Society.