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

Journal Article · Tue May 15 04:00:00 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), Journal Name: Physical Review, B: Condensed Matter; (USA) Vol. 41:14; ISSN PRBMD; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

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