Epitaxial growth of cobalt oxide phases on Ru(0001) for spintronic device applications

Abstract

Cobalt oxide films are of technological interest as magnetic substrates that may support the direct growth of graphene, for use in various spintronic applications. In this work, we demonstrate the controlled growth of both Co 3 O 4 (111) and CoO(111) on Ru(0001) substrates. The growth is performed by Co molecular beam epitaxy, at a temperature of 500 K and in an O 2 partial pressure of 10 −4 Torr for Co 3 O 4 (111), and 7.5×10 −7 Torr for CoO(111). The films are distinguished by their dissimilar Co 2p x-ray photoemission (XPS) spectra, while XPS-derived O/Co stoichiometric ratios are 1.33 for Co 3 O 4 (111) and 1.1 for CoO(111). Electron energy loss (EELS) spectra for Co 3 O 4 (111) indicate interband transitions at ∼2.1 and 3.0 eV, while only a single interband transition near 2.0 eV is observed for CoO(111). Low energy electron diffraction (LEED) data for Co 3 O 4 (111) indicate twinning during growth, in contrast to the LEED data for CoO(111). For Co 3 O 4 (111) films of less than 20 Å average thickness, however, XPS, LEED and EELS data are similar to those of CoO(111). XPS data indicate that both Co oxide phases are hydroxylated at all thicknesses. The two phases are moreover found to be thermally stable to at least 900 K in UHV, while ex situ atomic force microscopy measurements of Co 3 O 4 (111)/Ru(0001) indicate an average surface roughness below 1 nm. Electrical measurements indicate that Co 3 O 4 (111)/Ru(0001) films exhibit dielectric breakdown at threshold voltages of ∼1 MV cm −1 . Collectively, these data show that the growth procedures yield Co 3 O 4 (111) films with topographical and electrical characteristics that are suitable for a variety of advanced device applications.

Electrocatalytic selectivity for nitrogen reduction vs. hydrogen evolution: a comparison of vanadium and cobalt oxynitrides at different pH values

“…The Co 2p XPS data acquired prior to EC polarization (Fig. 5a) show a feature near 780 eV binding energy attributable to Co( ii ) oxide 35 and a sharp feature near 778 eV attributable to Co–N bonding. 24 N 1s data (Fig.…”

Tuning the Néel temperature in an antiferromagnet: the case of NixCo1−xO microstructures

“…Nickel oxide or cobalt oxide films have previously been grown by oxygen-assisted molecular beam epitaxy on different oxide substrates such as MgO 19–25 . Less common is the growth on metallic substrates where Ir(100) 26 or PtFe 27 have been used, in addition to Ru(0001) 28,29 . Both oxides have also been grown in order to study the proximity effect at their common interface 25,30 .…”

Ultrathin Chromia on a Hexagonally-Ordered d0 Ferromagnet: Evidence of Interfacial Exchange Bias at the Cr2O3/TiO2–x Interface

“…Film deposition and characterization studies were carried out in a multichamber system with capabilities for molecular beam epitaxy (MBE), X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and electron energy loss spectroscopy (EELS), as described previously . The Al 2 O 3 (0001) substrates were cleaned by annealing in 10 –6 Torr O 2 until LEED and XPS showed an ordered, carbon-free alumina surface.…”