Electronic states and tunneling properties in step-barrier structures have been investigated. The results indicate that there exists quasibound states in step-barrier structure both at zero bias and under an applied bias. Size effect on negative-differential resistances is examined and the condition for obtaining larger current peak-to-valley ratios has been discussed.

The magnetic properties of X/5Fe/X (X: Hf, Ta, W, Re, Os, Ir, Pt) have been studied by means of the full-potential linearized augmented-plane-wave method, in which the core states are treated fully relativistically and the valence states are treated semirelativistically and the generalized gradient approximations' (GCA) exchange-correlation potentials are employed for 5d elements. It has been found that Hf, Ta, W, Re and Os overlayers on Fe(0 0 1) are almost nonmagnetic. Following this trend, if the spin-orbit interactions are taken into account, the magnetism of Ir and Pt overlayers is expected to be killed as for the Ag(0 0 1) and Au(0 0 1) substrate. So the nonexistence of the magnetism for 5d overlayers is furtherly verified on ferromagnetic substrate besides on nonmagnetic substrate. Moreover, due to the more extended 5d orbitals as compared to those of 3d and 4d, much stronger hybridizations between the 5d states of the overlayer and the Fe substrate exist, which greatly suppress the magnetic moment of the interface Fe layer.

The local magnetic properties of impurity Fe in small Nbn and NbnMom clusters have been studied by using a linear combination of atomic orbitals approach with the density functional formalism, and the Kohn

Resonant tunneling in step-barrier structures is investigated by using the transfer-matrix technique. The formulas for the transmission coefficient and the current density are derived when taking into account the coupling between components of the motion of an electron in directions parallel and perpendicular to the interfaces. By making a detailed comparison of resonant tunneling among single square-barrier structures, asymmetric double-barrier structures, and step-barrier structures, the tunneling properties in step-barrier structures are revealed. It is shown that the global behavior of step-barrier structures obtained resembles that of asymmetric double-barrier structures, and step-barrier structures are superior to both single- and double-barrier structures in many aspects. In comparison to asymmetric double-barrier structures, step-barrier structures have several features, such as a wider negative-differential resistance region, easier fabrication, high-speed response, and a relatively lower transmission coefficient and current peak-to-valley ratios. Moreover, higher resonant bias is required in order to obtain optimal transmission resonances in the step-barrier structure. The results shown in this work not only shed new light on the physics of resonant tunneling in electric-barrier structures but are also helpful in designing quantum devices based on step-barrier tunneling structures.

从理论和数值模拟两个方面分析了ESWL中的非线性的动力学焦点和实际焦点的位置，给出三种典型的动力学焦点的数值结果，说明非线性动力学焦点和实际焦点一般不是几何焦点,指出正确确定实际焦点在ESWL技术中的重要性。