Electronic Properties and Stability of Silicon Nanoclusters Passivated by Hydrogen

The total energy, geometry and electronic spectra of nanoclusters \shm{} ($m=0\ldots11$) are calculated using the evolutionary algorithm and density functional theory (DFT). It is shown, that the features of electron spectrum, namely HOMO-LUMO gap and valence band width, correlate with cluster geometry and stability. The HOMO-LUMO gap becomes wider as the number of hydrogen atoms increases whereas the width of valence band gets lower. The widening of the band gap indicates the increasing of cluster stability which is consistent with existing data on reaction energy.

Electronic Structure Analyses of BN in Cubic and Hexagonal Phases

First principle calculations are performed on the structure, energy band gap, and dielectric properties of wurtzite and hexagonal BN by using a plane-wave pseudopotential method. It is found thath-BN has much narrower VB (valence band ) width and much sharper band edge than those ofw-BN. And the N 2sstates of the two phases of BN are dominant below 30.03 eV and the N 2pstates are dominant in the range between −20.62 and 20.32 eV.

Core Level Shifts and Grain Boundary Cohesion

The role of core level shifts at metallic interfaces has often been ignored in electron energy loss spectroscopy (EELS) even though very small changes in bond length can lead to large core level shifts. However, the popular interpretation of core level shifts as measures of charge transfer is highly problematic. For instance, in binary alloys systems, the core level shifts can be the same sign for both atomic constituents[l]. The simple interpretation would require that both atomic species had lost or gained charge. Further, the signs of the core level shifts can be opposite to those expected from electronegativity arguments[2]. A core level shift (CLS) is still possible, even when no charge transfer occurs. As illustrated in Fig. 1, if the valence band width is increased, the position of the center of the valence band with respect to the Fermi energy will change (as the number of electrons remains unchanged).