Photoemission study of Ce/Ta(110) and Ce/W(110) interfaces and the catalytic oxidation effect

Technical Report · Tue Aug 06 04:00:00 EDT 1991

OSTI ID:5373905

Gu, Chun

Photoemission spectroscopy was used to study Ce/Ta(110) and Ce/W(110) interfaces, and the catalytic oxidation effect on both surfaces. A weak Ce/Ta interface reaction is illustrated by the reduced Ta 4f surface core-level shift (SCS) upon Ce adsorption. No Ce/Ta interdiffusion was found. The Ce layer may greatly enhance the oxidation of Ta(110). Oxidation of Ce/Ta(110) at 300 K yields on monolayer (ML) of Ta suboxide ({approximately}TaO), followed by the rapid formations of Ta{sub 2}O{sub 5}. Ce/W(110) adsorption patterns were determined by low-energy electron diffraction. For {Theta} {le} 0.5 ML, the adsorption structure is characterized by one-dimensional commensuration along the (110) direction. It changes abruptly to a hexagonal pattern after 0.5 ML. The interatomic spacing shrinks continuously from 9% larger than that for {gamma}-Ce to 3% smaller than that for {alpha}Ce. Correspondingly the Ce 4f photoelectron spectrum evolves to resemble that of {alpha}-Ce. W 4f core levels are also correlated to the adsorption. A significantly widened W SCS is found at low Ce coverages. After the formation of the hexagonal patterns, the Ce-W registration is lost, and the interaction within the Ce layer increases. The SCS for the top layer of W is partially restored. Electronic charge polarization from Ce toward the W (or Ta) substrate is believed to be the key mechanism for the Ce-induced SCS.

• Research Organization: Ames Lab., IA (United States)
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 5373905
• Report Number(s): IS-T-1494; ON: DE91018167
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
400500 -- Photochemistry
656002* -- Condensed Matter Physics-- General Techniques in Condensed Matter-- (1987-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CATALYTIC EFFECTS
CERIUM
CHEMICAL REACTIONS
ELECTRON SPECTROSCOPY
ELEMENTS
EMISSION
INTERFACES
METALS
OXIDATION
PHOTOELECTRON SPECTROSCOPY
PHOTOEMISSION
RARE EARTHS
SECONDARY EMISSION
SPECTROSCOPY
TANTALUM
TRANSITION ELEMENTS
TUNGSTEN