Direct measurement of valence-charge asymmetry by x-ray standing waves.
By monitoring valence-photoelectron emission under condition of strong x-ray Bragg reflection, we have determined that a majority of GaAs valence charge resides on the anion sites of this heteropolar crystal, in quantitative agreement with the GaAs bond polarity as calculated from the Hartree-Fock term values. In contrast, the valence-charge distribution in Ge is found to be symmetric. In both cases, the valence emission is found to be closely coupled to the atomic cores.
Woicik
J C
JC
National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
Nelson
E J
EJ
Pianetta
P
P