DFT Study of Electric-Field Gradients and Magnetic Fields at Dilute Cd Atoms Doping near the (001) alpha-Al2O3 surface

G. N. DARRIBA; R. FACCIO; M. RENTERÍA

Canberra

Conferencia; 5th Joint International Conference on Hyperfine Interactions and Symposium on Nuclear Quadrupole Interactions (HFI/NQI 2014); 2014

In this work we present an electronic structure calculation study from first principles of Cd atoms located at and near the (001) alpha-Al2O3 semiconductor surface. In particular, we focus at the origin of the magnetic interaction that appears at Cd impurities located at this surface. For this, we studied the total and partial density of states projected at Cd and their nearest oxygen neighbors, as a function of the Cd atom depth from the (001) alpha-Al2O3 surface. Two methods with different basis set were used: the Full-Potential Augmented Plane Wave plus local orbitals (FP-APW+lo), using the WIEN2k code,  and a linear combination of numerical localized atomic orbital basis sets, using the SIESTA code. The Cd impurity is located at Al substitutional sites in the reconstructed alpha-Al2O3 surface and at different depth positions from the surface. Besides the appearance of the magnetic interaction, the electric-field gradient (EFG) at the topmost Cd atom at the equilibrium positions in the reconstructed surface is 4 times larger than the EFG at dilute Cd atoms located in bulk, in agreement with the experimental EFG ratio for 111Cd atoms located at the surface and at bulk of metallic indium. Through these comparisons we demonstrate the large sensitivity of 111Cd probe atoms for evaluating surface and bulk properties on Al2O3.