In-situ X-ray photoelectron spectroscopic study of the reversible phase transition between CoO and Co3O4 in oxygen of 10−3 Pa

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

“…Changes that occur in the cobalt 2p region are considerably more subtile and are most obvious in the region of x = 0.6-0.7 (Figure 8), where there is a decrease in the 2p satellite structure and an appearance of a lower binding energy species, found as a shoulder at 779.6 eV for the 2p 3/2 transition. The changes are similar to those reported for Co 3 O 4 epitaxies formed upon oxidation of CoO(100) single crystal surfaces [13] and are comparable to the Co 2p XP spectra of Co 3 O 4 powdered samples [25,26].…”

“…Comparable O 1s XPS structure has been observed before upon polycrystalline Co 3 O 4 samples, and although the identity of the higher binding energy O 1s species has not been unequivocally identifi ed, it is most likely due to some sort of surface oxide defect [29]. Similar changes in the O 1s peak structure have also been observed for cobalt monoxide as it is oxidized to Co 3 O 4 [25] and for Co 3 O 4 -like epitaxies that have formed on CoO(100) [13]. In these cases, the 531.2 eV peak has been observed to rival the lattice oxygen peak in intensity, even for cases in which large amounts of surface hydroxyls can be eliminated as a source of surface contamination [13].…”

Surface composition and structure of Co3O4(110) and the effect of impurity segregation

“…However, the extensive sputtering and extended high temperature anneals for the Co 3 O 4 (110) single crystal substrate make detectible levels of surface hydroxyls unlikely. A similar structure attributed to defects and/or adsorbed oxygen has been observed in Co 3 O 4 thin films that did not show hydroxylation by high resolution electron energy loss spectroscopy ͑HREELS͒, [17][18][19] Co 3 O 4 powder surfaces that were thermally treated to remove hydroxyls, 23 and UHV-cleaved Co 3 O 4 single crystal surfaces. 31 Not only did the intensity of the peak not diminish after prolonged sputtering and high temperature anneals to 1000 K, but attempts to observe water or other hydroxylated desorption products with a quadrupole mass spectrometer by thermal desorption methods detected no such desorbing species.…”

“…16 The surface chemical composition of the stoichiometric spinel has been previously studied using x-ray photoelectron spectroscopy ͑XPS͒. Characteristic of the Co 3 O 4 spinel surface is a set of sharp Co 2p peaks at 779.8 and 795.7 eV with a broad satellite structure located about 9 eV higher in binding energy 10,15,[17][18][19][20][21][22][23] 27 with increasing complexity at higher incident energies as fractional-ordered spots come into and out of focus. The Cu-segregated, reduced surface LEED pattern shows a different surface structure than that of the clean, stoichiometric Co 3 O 4 (110) surface.…”

Exchange bias and interface electronic structure inNi/Co3O4(011)

“…22 After the Co 3 O 4 growth and in situ characterization, the sample was cleaved ex situ; one half was then annealed at atmospheric pressure in flowing O 2 (900 scc/min) at 820 K for 12 h; this temperature and oxygen pressure favor the formation of Co 3 O 4 over CoO. [33][34][35] Both asgrown and annealed samples were then returned to the growth system for Ni deposition. The Co 3 O 4 films were first cleaned in an O plasma at 770 K for 30 min, and in one instance cooled to below 370 K under the O plasma.…”