BaO/W(100) thermionic emitters and the effects of Sc, Y, La, and the density functional used in computations.

Journal Article · 01 June 2003 · Proposed for publication in Surface Science Letters.

OSTI ID:993919

Zavadil, Kevin Robert; King, Donald Bryan; Schultz, Peter Andrew; Jennison, Dwight Richard

Density functional theory is used to predict workfunctions, {psi}. For relaxed clean W(1 0 0), the local density approximation (LDA) agrees with experiment better than the newer generalized gradient approximation, probably due to the surface electron self-energy. The large Ba metallic radius indicates it covers W(1 0 0) at about 0.5 monolayer (ML). However, Ba{sup 2+}, O{sup 2-}, and metallic W all have similar radii. Thus 1 ML of BaO (one BaO unit for each two W atoms) produces minimum strain, indicating commensurate interfaces. BaO (1 ML) and Ba (1/2 ML) have the same {psi} to within 0.02 V, so at these coverages reduction or oxidation is not important. Due to greater chemical activity of ScO vs. highly ionic BaO, when mixing the latter with this suboxide of scandia, the overlayer always has BaO as the top layer and ScO as the second layer. The BaO/ScO bilayer has a rocksalt structure, suggesting high stability. In the series BaO/ScO/, BaO/YO/, and BaO/LaO/W(1 0 0), the latter has a remarkably low {psi} of 1.3 V (LDA), but 2 ML of rocksalt BaO also has {psi} at 1.3 V. We suggest BaO (1 ML) does not exist and that it is worthwhile to attempt the direct synthesis and study of BaO (2 ML) and BaO/LaO.

• Research Organization: Sandia National Laboratories
• Sponsoring Organization: USDOE
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 993919
• Report Number(s): SAND2003-2446J
• Journal Information: Proposed for publication in Surface Science Letters., Journal Name: Proposed for publication in Surface Science Letters. Journal Issue: 2 Vol. 549; ISSN SUSCAS; ISSN 0039-6028
• Country of Publication: United States
• Language: English

Related Subjects

30 DIRECT ENERGY CONVERSION
APPROXIMATIONS
ATOMS
ELECTRONS
FUNCTIONALS
OXIDATION
STABILITY
SYNTHESIS
THERMIONIC EMITTERS
THERMODYNAMIC ACTIVITY