Highly sensitive hydrogen sensor based on graphite-InP or graphite-GaN Schottky barrier with electrophoretically deposited Pd nanoparticles

Depositions on surfaces of semiconductor wafers of InP and GaN were performed from isooctane colloid solutions of palladium (Pd) nanoparticles (NPs) in AOT reverse micelles. Pd NPs in evaporated colloid and in layers deposited electrophoretically were monitored by SEM. Diodes were prepared by making Schottky contacts with colloidal graphite on semiconductor surfaces previously deposited with Pd NPs and ohmic contacts on blank surfaces. Forward and reverse current-voltage characteristics of the diodes showed high rectification ratio and high Schottky barrier heights, giving evidence of very small Fermi level pinning. A large increase of current was observed after exposing diodes to flow of gas blend hydrogen in nitrogen. Current change ratio about 700,000 with 0.1% hydrogen blend was achieved, which is more than two orders-of-magnitude improvement over the best result reported previously. Hydrogen detection limit of the diodes was estimated at 1 ppm H2/N2. The diodes, besides this extremely high sensitivity, have been temporally stable and of inexpensive production. Relatively more expensive GaN diodes have potential for functionality at high temperatures

Surface, bulk, and interface electronic states of epitaxial BiFeO 3 films

The authors report on the depth-resolved cathodoluminescence spectroscopy studies of the surface, bulk, and interface-localized electronic states in the band gap of epitaxial BiFeO3 thin films. The BiFeO3 films show a near band edge emission at 2.7 eV and defect emissions at energies varying from 2.0 to 2.5 eV. The overall results clearly suggest that the electronic structure, especially the defect states and their spatial distributions, of BiFeO3 films are strongly dependent on the growth conditions and method, stoichiometry, and strain, so that understanding and controlling them are crucial to optimize BiFeO3 film properties. © 2009 American Vacuum Society

Surface, bulk, and interface electronic states of epitaxial BiFeO 3 films

The authors report on the depth-resolved cathodoluminescence spectroscopy studies of the surface, bulk, and interface-localized electronic states in the band gap of epitaxial BiFeO3 thin films. The BiFeO3 films show a near band edge emission at 2.7 eV and defect emissions at energies varying from 2.0 to 2.5 eV. The overall results clearly suggest that the electronic structure, especially the defect states and their spatial distributions, of BiFeO3 films are strongly dependent on the growth conditions and method, stoichiometry, and strain, so that understanding and controlling them are crucial to optimize BiFeO3 film properties. © 2009 American Vacuum Society