Epitaxial growth of Co3O4 on CoO(100)

Abstract

Under mildly oxidizing ultrahigh vacuum conditions, it is possible to form on top of CoO(100) single crystal substrates, thin films that have higher oxygen content but that preserve the overall symmetry of the CoO(100) low-energy electron diffraction pattern. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy (HREELS) data indicate that the epitaxial film grown on CoO(100) at 625 K and 5×10−7 Torr is Co3O4-like in both oxygen content and XP/HREEL spectroscopic characteristics. Both materials are closest packed in lattice oxygen, with the mismatch of bulk O2−–O2− distances of approximately 5%. However, the Co3O4 is only able to grow to a thickness of approximately 5 Å before the oxidation process halts. It is proposed that the orientation of Co3O4 that forms most readily on the CoO(100) surface does not present a thermodynamically stable orientation of the bulk Co3O4 substrate but is that which grows under the constraint of the best CoO(100)/Co3O4 epitaxial arrangement. While the mismatch in lattice parameters may in part be to blame for the limitation of higher oxide thickness, thicker oxide films have been grown under conditions with significantly larger mismatch.

Structural and magnetic properties of insulating Zn1−xCoxO thin films

“…The very intense satellite structure results from the charge-transfer band structure characteristic of the late 3d transition metal monoxides. 14 The differences between the main peaks and the corresponding satellites are close to that of CoO in the literature. 15 These results may further prove that Co ions are surrounded by oxygen atoms and have a chemical valence of 2ϩ.…”

Surface properties of LiCoO2, LiNiO2 and LiNi1−xCoxO2

“…X-ray photoemission (XPS) from C 1s and O 1s spectral regions showed carbonate to be detectable by XPS for some, although not all, of the samples studied, as will be described in detail below. poses and have been obtained on well-defi ned single crystal substrates [45], [46] and [47]. The Co 2p spectra of the lithium-containing oxides are characteristic of Co 3+ in an octahedral or near-octahedral environment, as is also observed for the spinel Co 3 O 4 structure.…”

“…[53], [54], [55] and [56]), and slightly lower than that for CoO (529.4-529.6 eV; refs. [53], [55], [56], [57] and [58]). Furthermore, doping cobalt oxide powders with lithium for up to 50% of the total metal concentration does not appear to change the O 1s binding energy signifi cantly [54].…”

Surface composition of CoxNi1−xO solid solutions by X-ray photoelectron and Auger spectroscopies

“…Of particular interest in this phenomenon is the differences in oxidation properties of the two rocksalt monoxides. CoO readily forms layers of the spinel Co 3 O 4 [13], even under relatively low partial pressures of oxygen. The Ni 3+ -containing oxides are thermodynamically less accessible, particularly for the binary oxide compounds, and the spinel Ni 3 O 4 is considerably more diffi cult to obtain.…”