Epitaxial V0.6W0.4N/MgO(001): Evidence for ordering on the cation sublattice

• V0.6W0.4N alloys are grown on MgO(001) by ultrahigh vacuum reactive magnetron sputtering from V and W targets in 10 mTorr pure-N-2 atmospheres at temperatures T-s ranging from 600 to 900 degrees C. Based on x-ray diffraction and transmission electron microscopy results, all films have the B1-NaCl crystal structure and grow with a cube-on-cube epitaxial relationship to the substrate, (001)(VWN)parallel to(001)(MgO) and [100](VWN parallel to)[100](MgO). Rutherford backscattering spectrometry analyses show that the N content in V0.6W0.4Nx alloys decreases with increasing T-s from overstoichiometric with x = 1.13 at 600 degrees C, to approximately stoichiometric with x = 1.08 at 700 degrees C, to understoichiometric at 800 degrees C (x = 0.80) and 900 degrees C (x = 0.75). High-resolution scanning transmission electron microscopy, Z-contrast, and selected-area electron diffraction investigations of V0.6W0.4N(001) alloys grown at 600 and 700 degrees C reveal the onset of W ordering on adjacent 111 planes of the metal sublattice; no ordering is observed for understoichiometric films grown at higher temperatures.

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