Nitrogen valence electronic structure in the strong chemisorption limit: Molecular adsorption on Cr(110) and O/Cr(110)

Journal Article · Tue May 15 00:00:00 EDT 1990 · Physical Review, B: Condensed Matter; (USA)

DOI:https://doi.org/10.1103/PhysRevB.41.9771· OSTI ID:7061305

Shinn, N D ^[1]

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1. Division 1114, Sandia National Laboratories, Albuquerque, New Mexico 87185 (USA) Surface Science Division, National Institute of Standards and Technology, Gaithersburg, MD (USA)

Nitrogen adsorption and dissociation on clean and oxygen-dosed Cr(110) surfaces have been studied with angle-integrated synchrotron-radiation ultraviolet photoelectron spectroscopy (UPS) and work-function measurements. At 90 K, nitrogen adsorbs molecularly {ital via} a mobile precursor state and exhibits UPS valence-orbital peaks at binding energies of 12.7 (weak), 8.4, and 7.1 eV with respect to the Fermi level; these positions and separations suggest an unusual N{sub 2}(ads) valence electronic structure similar to that of {pi}-bonded'' N{sub 2} on Fe(111). Thermal dissociation of N{sub 2}(ads) commences at 100 K but remains incomplete until {similar to}265 K. Chemisorbed N{sub 2} increases the work function {Phi} by 0.1{plus minus}0.1 eV, whereas annealing the adlayer to 300 K subsequently reduces {Phi} by 0.7 eV due to dissociation. At 300 K, only dissociative chemisorption is observed but with a reduced sticking probability and a lower saturation coverage compared with thermally dissociating a molecular adlayer. A surface-sensitive Cr valence-band feature is identified which (i) shifts to increasing binding energy with N{sub 2} adsorption, but (ii) exhibits different coverage-dependent behavior for isoelectronic N{sub 2}(ads) and CO(ads). Low coverages of chemisorbed oxygen do not inhibit N{sub 2} adsorption but co-adsorption effects are observed when a N{sub 2}(ads) saturated surface is exposed to large oxygen doses. Consideration of these results in comparison with other nitrogen chemisorption studies shows that the bonding of nitrogen to Cr(110) is not well described by the usual {sigma}-donation and {pi}-backbonding concepts. A bonding geometry with both nitrogen atoms coordinated to chromium atoms is proposed in spite of the absence of surface hollow sites usually invoked to account for such a species.

• DOE Contract Number: AC04-76DP00789
• OSTI ID: 7061305
• Journal Information: Physical Review, B: Condensed Matter; (USA), Vol. 41:14; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CHROMIUM
SORPTIVE PROPERTIES
CHROMIUM OXIDES
NITROGEN
ADSORPTION
ELECTRONIC STRUCTURE
VALENCE
OXYGEN
CHEMISORPTION
LOW TEMPERATURE
MEDIUM TEMPERATURE
PHOTOELECTRON SPECTROSCOPY
TEMPERATURE DEPENDENCE
WORK FUNCTIONS
CHALCOGENIDES
CHEMICAL REACTIONS
CHROMIUM COMPOUNDS
ELECTRON SPECTROSCOPY
ELEMENTS
FUNCTIONS
METALS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
SEPARATION PROCESSES
SORPTION
SPECTROSCOPY
SURFACE PROPERTIES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
360104* - Metals & Alloys- Physical Properties