AlO x insulating barriers in magnetic tunnel junctions were prepared by a masked rf plasma oxidation process to reduce direct ion-bombardment effect on the barrier. In our method, the root-mean-square value of 2.1 Å in the barrier and the magnetic resistance ratio up to 32% were observed. In addition, the surface plasmon resonance spectroscopy (SPRS) measurement was performed to efficiently determine optimum oxidation time, dielectric properties, and oxidation states inside thin barrier. The SPRS results revealed that the dielectric value and thickness of the optimum barrier were found to be 1.3576+i1.4488 and 16.3 Å, respectively, with a thickness confirmation by a high resolving transmission electron microscope measurement.
We present transmission electron microscopy (TED) and transport measurements on thin films of cobalt on (100) and (111) silicon substrates which show that first phase nucleation proceeds upon deposition past a critical thickness and is preceded by a semiconductor/metallic transition in the glassy, as-deposited phase. We have also performed electron diffraction measurements on thin cobalt films deposited on highly doped Si substrates. It is found that compound nucleation begins upon metal deposition for any thickness down to practical minimum depositions for our sputtering system on the order of 10 Å. We interpret these results to indicate that in these systems thin film nucleation is driven by an electronic two-dimensional instability of the interphase region.
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