X‐ray photoelectron spectroscopic studies of thin film oxides of cobalt and molybdenum

Abstract

Surface oxidation reactions of cobalt, molybdenum and mixed cobalt-molybdenum metals have been investigated using x-ray pbchelectron spectroscopy (XPS). Tbe oxide stoicbiometries have been determined from XPS intensity measurements Sucb quantification has been important in identifying oxide compositions with cbaracteristic XPS spectra. A number of discrete binary molybdenum oxides have been characterized after reactions at 2OOOC and pressures ranging from 1 atm to Pa. At the lowest pressure, the Mo 3d spectra and O/Mo ratias suggest the formation of a molybdenum-oxygen structure with a stoicbiometry oear unity. By contrast, at bigber presa~ures, oxides that are predominantly MOO, and MOO, appear, but other intermediate oxide structures are also identified. Wellde6ned binary oxides of cobalt can be prepared from cobalt metal after beating in oxygen at merent pressures. New binary oxides of cobalt and molybdenum have been generated by the reaction on MOO, or c0#4 substrates. Oxidation of a tbin film of molybdenum on a Co,O, substrate bas been shown to produce a nearly stoichiometric rrurface layer of CoMd), . The procedure could be wieful for the production of other ternary oxides of possible interest for use as XPS reference materials.

Application of zero-valent iron nanoparticles for the removal of aqueous Co2+ ions under various experimental conditions

“…According to this analysis, the recorded Co 2p 3/2 peaks were located at 781.2 ± 0.1 eV and were asymmetric to the high binding energy side. This value occurs in between the values reported earlier to correspond to Co 2+ in CoO (780.0 ± 0.2 eV for the 2p 3/2 line) [20,21], and to Co 2+ in Co(OH) 2 (782.0 ± 0.1 eV for the 2p 3/2 line) [22]. Both lines are readily discerned from that corresponding to metallic cobalt, Co 0 (778.0 ± 0.2 eV for the Co2p 3/2 line) [20,23].…”

Synthesis and characterization of kaolinite-supported zero-valent iron nanoparticles and their application for the removal of aqueous Cu2+ and Co2+ ions

“…This value, which is identical to the one we reported earlier for Co-loaded nZVI (Üzüm et al, in press), occurs well above that reported in the literature for metallic cobalt, Co 0 , i.e. 778.0 ± 0.2 eV (Wagner et al, 1979;McIntyre and Cook, 1975), and is close to those reported earlier for Co 2+ in cobalt oxide (780.0 ± 0.2 eV) (McIntyre and Cook, 1975;McIntyre et al, 1990), and cobalt hydroxide (782.0 ± 0.1 eV) (Tan et al, 1991). Although Co 2+ possesses a standard reduction potential ( = −0.28 V at 298 K) that is somewhat larger than that of Fe 2+ (= −0.44 V at 298 K), the reduction of Co 2+ by Fe 0 might not take place.…”

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

“…31,32 The calculated concentration ratio of oxygen to cobalt (C O /C Co ), CoO 2 ϩ cations are high spin d 8 in octahedral lattice sites and the intense satellite structure has been proposed to result from the charge-transfer band structure found in late 3d transition metal monoxides with partially filled e g character. 15,16,25,[33][34][35] The unpaired nature of the half-filled e g band of the Co 2ϩ cation in CoO results in strong electron correlation and substantial broadening of the cobalt 2p main peaks due to many closely lying 3d final states in photoemission. In contrast, the low-spin, diamagnetic nature of the Co 3ϩ octahedral cation and the weaker crystal field effect of tetrahedral coordination for the There is a second peak at higher binding energy, 531.1 eV at 10%-15% intensity of the main peak.…”