Epitaxial growth of cobalt oxide phases on Ru(0001) for spintronic device applications. (17th August 2017)

• Record Type: Journal Article
• Authors: Olanipekun, Opeyemi; Ladewig, Chad; Kelber, Jeffry A; Randle, Michael D; Nathawat, Jubin; Kwan, Chun-Pui; Bird, Jonathan P; Chakraborti, Priyanka; Dowben, Peter A; Cheng, Tao; Goddard, W A
• Is Part Of: Semiconductor science and technology. Volume 32:Number 9(2017:Sep.)
• Publication Date: 2017-08-17
• Subjects: cobalt oxide -- graphene -- spintronics -- magnetic oxides -- molecular beam epitaxy; Semiconductors -- Periodicals; 621.38152
• DOI: 10.1088/1361-6641/aa7c58
• Languages: English
• ISSNs: 0268-1242

Abstract

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 Co3 O4 (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 O2 partial pressure of 10 −4 Torr for Co3 O4 (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 Co3 O4 (111) and 1.1 for CoO(111). Electron energy loss (EELS) spectra for Co3 O4 (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 Co3 O4 (111) indicate twinning during growth, in contrast to the LEED data for CoO(111). For Co3 O4 (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 Co3 O4 (111)/Ru(0001) indicate an average surface roughness below 1 nm. Electrical measurements indicate that Co3 O4 (111)/Ru(0001) films exhibit dielectric breakdown at threshold voltages of ∼1 MV cm −1 . Collectively, these data show that the growth procedures yield Co3 O4 (111) films with topographical and electrical characteristics that are suitable for a variety of advanced device applications.