Narrow channel devices were fabricated using a split-gate high electron mobility transistor structure in which electrons are forced through a double-bend discontinuity. The low-temperature conductance shows a number of peaks in the lowest quantized conductance plateau which correspond qualitatively to resonance effects that are predicted for the geometrical discontinuities of the double bend.

Determination of T c , vortex creation and vortex imaging of a superconducting Nb film using low-temperature magnetic force microscopy A honeycomb array of submicrometer holes in a Nb superconducting thin film has been fabricated to investigate the flux pinning effect. It is found that the minima positions reveal two regimes characterized by the matching fields and the fractional ones. It is believed that the complex behavior may come from more than one vortex being captured per pinning site. Furthermore, the temperature dependence of the saturation number of vortices per pinning site together with vortex-vortex interaction gives the complex vortex configurations.

No abstract

Single crystalline FeMn/Co bilayers were grown epitaxially on Cu(001) and investigated by magneto-optic Kerr effect (MOKE). By doing the MOKE measurement within a rotating magnetic field, we were able to retrieve quantitatively the anisotropy constant of the ferromagnetic Co layer. We show unambiguously that as the FeMn layer changes from paramagnetic (PM) to antiferromagnetic (AFM) states, it enhances the interfacial magnetic anisotropy at the FeMn/Co interface by an order of magnitude. A thickness dependent study of the magnetic anisotropy constant revealed that this induced magnetic anisotropy may originate from the FeMn/Co interfacial spin frustration.

Thin polystyrene films irradiated by an electron beam to create trapped charge are shown to immobilize the positively-charged protein, avidin-fluorescein. Using electron-beam lithography, fluorescent patterns with a minimum feature size of 0.5 µm were formed. The electrostatic nature of the immobilization was supported by the spatial and temporal features of the immobilization process. Additional evidence for an electrostatic mechanism was obtained from experiments to screen the trapped charge density with poly-L-lysine.