Novel electrical transport properties of native Fe-Nb oxide layers leading to unilateral conductivity of a refractory metallic glass

Fe-based metallic glasses (also called amorphous alloys) are known to have high hardness and high wear resistance. Here we study and present a Fe-Nb amorphous material with an unusual type of electrical conductivity behavior. The electrical transport properties of Fe-Nb oxide layers were studied by measuring local current-voltage characteristics by the atomic-force microscopy technique. At certain voltage levels the samples containing native oxides showed clearly asymmetrical conductivity relative to polarity of the applied potential. Fe-Nb metallic glassy surface oxide film growth process was monitored at ambient conditions. The growth rate keeps constant during the initial 2.5 hours. After that the growth rate drastically decreases and becomes almost zero while the final oxide thickness is 1.0–1.5 nm. The Fe-Nb film sample annealed for 15 minutes at 300 °C demonstrates several times larger oxide thickness and becomes an insulator. X-ray photoelectron spectroscopy was used to characterize the oxidation states in the surface amorphous oxides. This material can be readily applied as inexpensive nanoscale tunnel diode operating at the commonly utilized voltage of ±5 V.