Y. Y. Sun

Electronic structure of germanium nitride considered for gate dielectrics

First-principles calculations based on density-functional theory and the local-density approximation have been used to investigate structural, electronic, and optical properties of α, β, and γ phases of germanium nitride (Ge3N4). β-Ge3N4 was found to be the most stable among the three structures, and it has a very small lattice mismatch with Ge, which indicates that it could be grown epitaxially on Ge. The calculated band gaps of α-, β-, and γ-Ge3N4 are about 3.15, 3.07, and 2.33eV, and the corresponding static dielectric constants are 4.70, 4.74, and 6.27, respectively, within local-density approximation. Results of our calculations indicate that the band gap and static dielectric constants of Ge3N4, as well as Si3N4, could satisfy the requirements of gate dielectrics for Ge-based field effect transistors.

Smac-mediated sensitization of human B-lymphoma cells to staurosporine- and lactacystin-triggered apoptosis is apoptosome-dependent.

Second mitochondrial activator of caspase (Smac)-derived peptides have previously been shown to facilitate apoptosis of various types of cancer cells. However, it remains unclear whether the effects of such Smac agonists are dependent on apoptotic protease-activating factor-1 (Apaf-1), a key component of the apoptosome. Here, we explored the role of Apaf-1 through overexpression of this protein in the B-lymphoma cell line Raji that is defective for cytosolic Apaf-1 expression. Enforced expression of Apaf-1 rendered Raji cells sensitive to staurosporine as well as to the proteasome inhibitor, lactacystin. Importantly, co-treatment with Smac peptides resulted in a threefold higher degree of apoptosis in Apaf-1-expressing Raji cells, but not in mock-transfected cells. Smac peptides also potentiated apoptosis of the DG-75 cell line following liberation of endogenous Apaf-1 from the plasma membrane, but were ineffective when added alone. Furthermore, we observed high levels of expression in several B-lymphoma cell lines of cellular inhibitor of apoptosis protein-2 (cIAP2), and immunodepletion of cIAP2 (a target of Smac) was found to sensitize Apaf-1-overexpressing Raji cells to cytochrome c-dependent caspase activation. Collectively, these results demonstrate the importance of Apaf-1 in Smac-mediated potentiation of apoptosis of B-lymphoma-derived cells.

Cobalt Nanowire Fabrication on Activated Nitrogen-Templated Cu(210) Surface

We have investigated self-organized cobalt nanowires grown on activated nitrogen (AN)-templated Cu(210) high index surface. The morphology and magnetic properties of the grown Co nanowires were studied by scanning tunneling microscopy (STM) and magneto-optic Kerr effect (MOKE), respectively. The chemical state of the nanowires formed was characterized by in-situ X-ray photoelectron spectroscopy (XPS). It was found that Co grew preferentially along the narrow chains induced by the AN to form periodic Co nanowire arrays with diameter of 10 nm, which leads to a strong magnetic in-plane uniaxial anisotropy. Unlike the Co nanostructures formed on AN-modified low index Cu surfaces [Cu(100) and Cu(110)], these Co nanowires showed good thermal stability up to 470 °C, at which temperature the AN had desorbed from the surface.

Study of a Computational-Time-Saving Scheme for Quantitative Leed Analysis by the Matrix Inversion Method

A computational-time-saving scheme for quantitative LEED analysis by the matrix inversion method was studied. Two computational-time-critical parameters, the number of atomic layers (Nl) in the surface slab and the number of ion-core scattering phase shifts (lmax), were tested for energy dependence. Our study on a Cu(210) surface shows that no dependence of Nl on the incident energy exists in the energy range of LEED (50–400 eV), i.e. using energy-dependent Nl is not feasible. The effect of slab thickness reduction on the precision of the Pendry R-factor based best-fit structure search was then studied. This study provides a guide to the selection of surface slab thickness in quantitative LEED analysis by the matrix inversion method. Also, we show that using an energy-dependent lmax can save nearly half of the overall computational time for obtaining a set of I–V curves by the matrix inversion method.