Using photoemission and inverse photoemission, we have been able to characterize the Cr2O3 oxide surface of CrO2 thin films. The Cr2O3 surface oxide exhibits a band gap of about 3 eV, although the bulk CrO2 is conducting. The thickness of this insulating Cr2O3 layer is twice the photoelectron escape depth which is about 2 nm thick. The effective Cr2O3 surface layer Debye temperature, describing motion normal to the surface, is about 370 K. From a comparison of CrO2 films grown by different techniques, with different Cr2O3 content, evidence is provided that the CrO2 may polarize the Cr2O3.

No abstract

We investigated the valence band structure of graphite oxide by photoelectron spectroscopy at the Pohang Accelerator Laboratory, Korea. The typical sp 2 hybridization states found in graphite were also seen in graphite oxide. However, the π state disappeared near the Fermi level because of bonding between the π and oxygen-related states originating from graphite oxide, indicating electron transfer from graphite to oxygen and resulting in a downward shift of the highest occupied molecular orbital (HOMO) state to higher binding energies. The band gap opening increased to about 1.8 eV, and additional oxygen-related peaks were observed at 8.5 and 27 eV. The electronic states of graphite were also found in graphite oxide. Thus, graphite oxide has an electronic structure similar to that of pristine graphite except for the states near the Fermi level and oxygen-related states.

No abstract

Magnetoresistance properties of Ni nanocontacts in the ballistic quantum regime are investigated in situ during closure and opening of electrochemically grown planar electrodes. The magnitude of conductance change when sweeping the magnetic field is of the order of the quantum conductance e2/h for conductance values spanning 1–100 quanta. The relative orientation of electric current and applied magnetic field changes the magnetoresistance sign, with symmetry properties reminiscent of bulk anisotropy magnetoresistance. Ex situ investigations of samples of higher conductance values, of the order of 1000 quanta, unambiguously show the analogy with bulk anisotropy magnetoresistance.