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This work reports on the detection of the valence band of buried Heusler
compounds by means of hard x-ray photoemission spectroscopy. The
measurements have been performed on the so-called "half" tunnel
junctions that are thin films of Co2MnSi underneath MgO. Starting from
the substrate, the structure of the samples is
MgO(buffer)-Co2MnSi-MgO(t(MgO))-AlOx with a thickness tMgO of the upper
MgO layer of 2 and 20 nm. The valence band x-ray photoemission spectra
have been excited by hard x rays of about 6 keV energy. The valence band
spectra have been used to estimate the mean free path of the electrons
through the MgO layer to be 17 nm at kinetic energies of about 6 keV. In
particular, it is shown that the buried Co2MnSi films exhibit the same
valence density of states as in bulk samples. (c) 2008 American
Institute of Physics.