Reconstruction and modeling of pure and Cd-doped In (111) surface: Ab Initio study of structural, electronic, and hyperfine properties at and near the surface.

G. N. DARRIBA; M. RENTERÍA; R.J. FACCIO

Goa

Conferencia; HYPERFINE 2019 - International Conference on Hyperfine Interactions and their Applications; 2019

Tata Institute of Fundamental Research and Goa University

The reconstruction of pure surfaces has great importance since its most stable configuration is the structural starting point for the study of the material surface doped with impurities. We present here a complete ab initio/DFT study of structural, electronic, and hyperfine properties of pure and Cd-doped  (111) In metallic surface, with Cd at different depths from the surface. For the pure system we performed a complete optimization of all atomic positions in the supercell used to simulate this surface. For the doped systems, a Cd atom replaced an In atom at the differentin equivalent In sites of the pure surface, followed by a new optimization of all the atomic positions. In this way, we studied the structural and electronic changes produced by the generation of the surface itself and by the inclusion of the Cd impurity. The magnitude, symmetry, and orientation of theelectric-field gradient (EFG) tensor was studied as a function of the In´s  depth in the pure system, and as a functionof the Cd´s depth in the doped ones. For the doped systems, we obtainedbasically 2 EFG tensors: one when Cd is localized at the surface or inmediatelybelow it, and another one for all the other Cd positions at different depthsfrom the surface. These two predicted EFG tensors are in perfect agreement (in magnitude, asymmetry, and direction) with the ones observed in PAC experiments on layer-by-layer  111In-doped(111) In surface, assigned to  111Cd probes localized at the surface (HFIS) and at the bulk (HFIB) of these In samples [1]. Our combined approach enabled to confirm that HFIS is related with probes localized at the surface, with a V33 magnitude four times larger that the bulk value. The precision of the EFG ab initio calculation could have resolved among the 3 different Cd positions existing at the surface: the adatom, and two surface sites at different depths but both with only vacumm above the impurity. But the combination of these predicted EFGs and the EFG distribution observed in the experiments would indicate that the Cd atom islocalized at these 3 positions in the real samples.   [1] W. Körner, W. Keppner, B.Lehndorff-Junges, and G. Schatz, 1982, Phys. Rev. Lett., 49, 1735.