Kenji Hirose

Electr onic Band Structure of Various TiN/MgO Superlattices

Various TiN(001)/MgO(001) superlattices have been investigated by using the total energy pseudopotential method. They are (TiN)n/(MgO)m as (TiN)1/(MgO)7, (TiN)2/(MgO)6, (TiN)3/(MgO)5, and (TiN)2/(MgO)14. “n”, “m”, and “n+m” are TiN, MgO, and TiN/MgO layer numbers of superlattices in a supercell, respectively. Their relaxed superlattice structures and electronic properties were obtained. All the calculated electronic states of TiN/MgO superlattices correspond to metallicity. Values of an electrical conductance of the TiN/MgO superlattice along the c-axis around the Fermi level are quite small although its electronic structure is metallic. A Ti (N) atom at the TiN layer in (TiN)1/(MgO)7 is replaced with Sc, V, and Nb (B, C, and O) as (ScN)1/(MgO)7, (VN)1/(MgO)7, and (NbN)1/(MgO)7 ((TiB)1/(MgO)7, (TiC)1/(MgO)7, and (TiO)1/(MgO)7). Their detailed electronic properties were investigated systematically.

A First-Principles Calculation of Surface Electronic Structure under Strong Current and Field

We developed the local density functional theory for a non-equilibrium system under strong electric field and current. This method is applicable for various fields such as atom control by STM, field evaporation and desorption, microscopic theory of field emission and others. In our method the ratio of the transfer matrices between the two succesive mesh points is treated in a recursive way and two different chemical potentials are assigned to the linearly independent scattering waves in the left or right electrodes. We have applied this method to the Na planar junction system. The calculated results of the effective potential and the induced charge density are presented.

The electronic structures of a GaAs/AlAs Fibonacci superlattice

We study the electronic structures of a GaAs/AlAs Fibonacci superlattice in which GaAs and AlAs monolayers are arranged in the Fibonacci sequence by the semi-emperical tight-binding method, based on the sp 3 s . model. We find that the features of the Fibonacci system such as a self-similar energy spectrum appear in the electronic structures of the present system. In addition, we find that the band hybridization between the s and p bands produces a strikingly spiky density of states and a localization-like effect of the wavefunctions.