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3D reconstruction of a Nb specimen analyzed by LEAP tomography employing laser pulsing. The rectangular parallelepiped contains atoms in a volume. Niobium atoms are colored in pink and O atoms in sky blue.
Steady-state voltage vs number of ions (depth) analysis profile showing a voltage drop at the surface niobium oxide/Nb interface, which explains the mushroom shape of the atomic reconstruction displayed in Fig. 1.
(a) Atomic reconstruction of surface metal oxide layer on bulk Nb. The overall reconstruction dimensions are and the volume contains million atoms. The surface niobium oxide/Nb interface is identified with a O isoconcentration surface. (b) The surface niobium oxide/Nb interface identified with a O isoconcentration surface. The rms chemical roughness of the interface is 0.4 nm.
Proxigram showing quantitative Nb and O concentration profiles corresponding to the atomic reconstruction displayed in Fig. 3. The profiles yield a thickness of the surface niobium oxide of 15 nm, with a constant surface Nb oxide composition corresponding to .
The O/Nb ratio from the reconstruction of an oxidized Nb specimen plotted as a function of distance from the Nb oxide/Nb interface at zero. The stoichiometry of the surface Nb oxide is deduced from this profile, which indicates that it is close to .
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