Fig. 6: Local structure around Fe atoms.
a X-ray absorption fine structure (XAFS) spectrum at the Fe K-edge, measured in sample A4 (tInAs = 5 MLs). Inset shows the extended X-ray absorption fine structure (EXAFS) oscillation component extracted from the XAFS spectrum. Here, the EXAFS oscillation is weighted by wavenumber k2. b The red curve with white circles shows the Fourier transformed (FT) spectrum of the experimental k2-weighted EXAFS oscillation shown in (a) as a function of atomic distance. Black curve is the spectrum simulated from the nearest As atoms in the FeAs monolayer, whose lattice in the z direction shrinks as mentioned in (c). Green and purple dotted curves are the spectra simulated from the two Fe disorder positions, As-antisite Fe (FeAs) and octahedral interstitial Fe (Fei), respectively, using the atomic distances obtained by our first principles calculation. The peak position of each curve is pointed by an arrow and provided in the legend. c First principles calculation with the VASP code shows that the thickness in the z direction of the FeAs layer shrinks to 0.165 nm, which is only 54% of that (0.307 nm in our calculations) in the InAs layers. Atomic distances from an Fe atom in the lattice site (Feδ) to the nearest As, FeAs, and Fei atoms are also shown in the table.
