XAS spectra measured on GaAs wafer through the As Kα and Ga Kα channels at the As K-edge. All compared with the standard (black line). (a) Lower: XANES from As Kα at α = 5°, 45°, and 80°. Upper: XANES from 1/Ga Kα and As Kα/Ga Kα, α = 5° and 45°. (b) The FT moduli of the corresponding EXAFS spectra (k = 3–12.4 Å−1, Hanning window).