Estudo teórico das propriedades estruturais, eletrônicas e magnéticas de superfícies semicondutoras dopadas: (i) metais de transição sobre o InAs(110) e (001) e (ii) boro sobre o Si(111)

Abstract

Based on first principles calculations, we have studied the structural, electronic, and magnetic properties of transition metals (MTs) Co, Fe, and Mn adsorbed on the III-V semiconductor surfaces, namely, InAs (110) and InAs (001). As regards the structural properties, obtained through ionic relaxation and theoretical scanning tunneling microscopy (STM) images, we found that MTs were positioned closer to the arsenic, while the MTs-In interatomic distances are larger. Using NEB (Nudged Elastic Band), we have verified that MTs replace the topmost cation of the InAs (110) surface. We also verified the energetic preference to the formation MTs chains along the direction [110]. On the other hand, MTs induce large structural deformation on the InAs(001)-S2(2 x 4) (As-rich), and InAs(001)- Z(4 x 2) (In-rich) surfaces. By comparing adsorption energies, we verified the energetic preference of cobalt adatoms,compared with the other MTs, on the InAs(110) and InAs(001) surface, while MTs incorporation on the substrate express an exothermic process. Using Bader’s approach for charge transfer calculations, we find that the MTs act as acceptor dopants and, consequently, the reduction of the magnetic moments of spin of magnetic ions was observed. The magnetic coupling between the MTs (two, three or four magnetic ions per supercell) no InAs (110) is always antiferromagnetic (AF) via superexchange, whose interaction is mediated by the p orbitals of the substrate anions. However, the magnetic coupling between the MTs in the /32(2 x 4) and Z (4 x 2) reconstructions has been shown to be dependent on the location of the MTs on the substrate, for example, the magnetic ions have a ferromagnetic coupling in Co2/InAs(001)-S2(2 x 4). Finally, the magnetic anisotropy energy is sensitive to the concentration and position of the magnetic ions in the semiconductor substrate. Therefore, based on these results, we conclude that the structural, electronic and magnetic properties of the MTs/InAs systems are expressively anisotropic. The B/Si(111)-(\/3 x \/3)R300 surface reconstruction has recently been used as a platform for supramolecular assembly. However, our understanding of the native defects in this delta- doped system and their corresponding STM signatures is incomplete. So we have studied this system using ab initio total energy calculations and scanning tunneling microscopy. We find that although perturbations to the equilibrium geometry of the surface are in general weak, the perturbations to the electronic structure can be quite strong due to the presence of dangling bonds composed of Si-3p^ orbitals. Additionally, we propose a possible structure for a previously unidentified defect that appears in positive bias constant-current STM images as an equilateral triangular arrangement of Si adatoms with attenuated intensity.