María Guadalupe Moreno-Armenta

Adsorption and diffusion of 3d transition metal atoms on the GaN(0001) surface

We carried out first-principles spin-polarized calculations in order to study the adsorption and diffusion of 3d transition metal (TM = Ti, V, Cr, Mn, Fe, Co, and Ni) atoms on a GaN(0001)- 2×2 surface using density functional theory within a plane-wave ultrasoft pseudopotential scheme. The results show that, for Ti, V, Cr, and Mn atoms, the most stable adsorption sites are all at the T4 site (the top site of the N-surface atom), whereas Fe, Co, and Ni slightly prefer the H3 hollow site. The adsorption energies can vary significantly with different TM atoms. A comparative study suggests that the TM–N bond formation is energetically more favorable for Ti, V, and Cr atoms, while the formation of a TM–Ga surface alloy is more favorable for elements such as Fe, Co, and Ni, as experimental results have shown. We found that the 3d TM adatom diffusion energy barrier between the H3 and T4 sites is around 0.40 eV, which is an indication of a significant TM adatom diffusion on the GaN(0001) surface. Furthermore, the...

Incorporation of iron on the clean and gallium-bilayer GaN(0001) surface

First-principles calculations of the energetic and magnetic properties of Fe incorporation in various sites on clean and Ga-bilayer GaN(0001) surfaces are presented. Employing a thermodynamic approach, the calculated formation energies demonstrate characteristic features in the structural stability and magnetism of Fe incorporated surfaces depending on the growth condition. It is found that the N-rich conditions produce greater magnetization compared to the Ga-rich condition. N-rich magnetization is attributed to the interface formation of FeN layers on the GaN(0001) surface. In addition, calculations for Fe incorporation in Ga-bilayer terminated surface suggest that it is possible to form a FeGax ferromagnetic alloy by performing the growth under extreme Ga-rich conditions.

First-principles study of the (0001)-MgB2 surface finished in Mg and B

We present a study based on Density Functional Theory (DFT) of the volume and two surfaces (0001) of MgB2, one of them terminated in Mg and the other one terminated in B. Each one of the surface was relaxed and their electronic properties were determined. From calculation of the enthalpy of formation we found that the Mg-terminated surface is energetically favored. The bands seem to present a formation similar to the Diracs cone as that are presented in graphene, but in MgB2 is above of the Fermi level. In the three cases, volume and the two surfaces, the behaviour is boron-metallic, because there are strong presence of B orbitals in the neighborhood of the Ferm level.