title: Combined structure-factor phase measurement and theoretical calculations for mapping of chemical bonds in GaN.
abstract: For non-centrosymmetric crystals, the refinement of charge-density maps requires highly accurate measurements of structure-factor phase, which can now be obtained using the extinction-free convergent-beam electron microdiffraction method. We report here accurate low-order structure-factor phases and amplitudes for gallium nitride (GaN) in the wurtzite structure. The measurement accuracy is up to 0.1% for amplitude and 0.2 degrees for phases. By combining these with high-order structure factors from electronic structure calculation, charge-density maps were obtained. Fine bonding features suggest that the Ga-N bonds are polar and covalent, with charge transfer from Ga to N; however, the polarity effect is extremely small.
authors.affiliation: Department of Physics, Arizona State University, Tempe, Arizona 85287, USA.
authors.forename: B
authors.initials: B
authors.lastname: Jiang
authors.forename: J M
authors.initials: JM
authors.lastname: Zuo
authors.forename: D
authors.initials: D
authors.lastname: Holec
authors.forename: C J
authors.initials: CJ
authors.lastname: Humphreys
authors.forename: M
authors.initials: M
authors.lastname: Spackman
authors.forename: J C H
authors.initials: JC
authors.lastname: Spence