Mean Adsorption Lifetimes and Activation Energies of Silver and Gold on Clean, Oxygenated, and Carburized Tungsten Surfaces
作者:
A. Y. Cho,
C. D. Hendricks,
期刊:
Journal of Applied Physics
(AIP Available online 1969)
卷期:
Volume 40,
issue 8
页码: 3339-3345
ISSN:0021-8979
年代: 1969
DOI:10.1063/1.1658185
出版商: AIP
数据来源: AIP
摘要:
Direct measurements of the mean adsorption lifetimes and the activation energies of silver and gold have been made on a polycrystalline tungsten substrate. The lifetime was determined by the time constant of the exponential increase of the surface concentration when an atomic beam impinged on the substrate. The activation energy was determined by the slope of the logarithm of the lifetime as a function of the inverse substrate temperature. The adsorption lifetime of atoms on a metal surface is &tgr;=(1/&ngr;0) exp (E/kT), where &ngr;0is the vibrational frequency andEis the activation energy. The experiments were conducted in an ultrahigh‐vacuum system free of hydrocarbon contamination. A clean substrate surface was obtained by heating in a partial pressure of oxygen for a long period of time and flashing to 2500°K before each data point was taken. The well‐defined surface condition and the precisely known temperature allow reliable interpretation of the experimental results. The experimental results for silver and gold on clean, oxygenated, and carburized tungsten substrates when &tgr; is in seconds andEis in electron volts are the following: Ag on W, &tgr;=(1/3.6×1012) exp (2.9/kT); Ag on O&sngbnd;W, &tgr;=(1/1.43×1012) exp (2.06/kT); Ag on C&sngbnd;W, &tgr;=(1/8.2×1012) exp (3.18/kT); Au on W, &tgr;=(1/8.2×1013) exp (4.54/kT); Au on O&sngbnd;W, &tgr;=(1/4.7×1011) exp (1.99/kT); Au on C&sngbnd;W, &tgr;=(1/1.73×1014) exp (4.725/kT).
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