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Effects of thin cerium overlayers on the oxidation of tantalum and aluminium
A557 Surface Science 222 (1989) 499-516 North-Holland, Amsterdam
499
EFFECTS OF THIN CERIUM OVERLAYERS OF TANTALUM AND ALUMINIUM N.A. BRAATEN,
J.K. GREPSTAD
ON THE
OXIDATION
a n d S. R A A E N
University of Trondheim, NTH, N-7034, Trondheim, Norway Received 17 April 1989; accepted for publication 3 July 1989 Oxidation of aluminium and tantalum with thin (4-15 ,~) overlayers of cerium has been studied with X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS) using synchrotron radiation. The cerium layer is found to induce a large enhancement in the oxidation of the Ta and A1 substrates at room temperature. The catalytic oxidation of Ta exhibits growth characteristics identical with those previously reported for Nb. This enhanced growth was attributed to a mechanism in which a conversion from tetra- to trivalent Ce-oxide plays an important role. In contrast, the enhanced oxidation of AI is caused by formation of an intermetallic surface layer which enables increased oxygen uptake. The growth of bulk Ta- and Al-oxide follows logarithmic growth laws at room temperature. The absence of bulk oxide formation at liquid nitrogen temperature shows that the enhanced surface oxidation is limited by a thermally activated process and not by electron tunneling across the oxide barrier. Field assisted diffusion is assumed to be the rate determining mechanism for both systems investigated.
Surface Science 222 (1989) 517-529 North-Holland, Amsterdam
517
PLASMON INTERACTIONS IN METALLIC GRATINGS: to- A N D k - M I N I G A P S A N D T H E I R C O N N E C T I O N WITH
POLES
AND ZEROS
E. P O P O V
Institute of Solid State Physics, Bulgarian Academy of Sciences, blvd. Lenin 72, Sofia 1784, Bulgaria Received 17 April 1989; accepted for publication 6 July 1989 A numerical analysis is presented of two types of minigaps: co- and k-gap that are formed in the reflectivity dips when two oppositely propagating plasmon surface waves (PSW's) are excited simultaneously. Their connection with complex trajectories of poles and zeros is revealed: an co-gap is formed when splitting of poles is observed and a k-gap only exists when a splitting of zeros occurs.
499
EFFECTS OF THIN CERIUM OVERLAYERS OF TANTALUM AND ALUMINIUM N.A. BRAATEN,
J.K. GREPSTAD
ON THE
OXIDATION
a n d S. R A A E N
University of Trondheim, NTH, N-7034, Trondheim, Norway Received 17 April 1989; accepted for publication 3 July 1989 Oxidation of aluminium and tantalum with thin (4-15 ,~) overlayers of cerium has been studied with X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS) using synchrotron radiation. The cerium layer is found to induce a large enhancement in the oxidation of the Ta and A1 substrates at room temperature. The catalytic oxidation of Ta exhibits growth characteristics identical with those previously reported for Nb. This enhanced growth was attributed to a mechanism in which a conversion from tetra- to trivalent Ce-oxide plays an important role. In contrast, the enhanced oxidation of AI is caused by formation of an intermetallic surface layer which enables increased oxygen uptake. The growth of bulk Ta- and Al-oxide follows logarithmic growth laws at room temperature. The absence of bulk oxide formation at liquid nitrogen temperature shows that the enhanced surface oxidation is limited by a thermally activated process and not by electron tunneling across the oxide barrier. Field assisted diffusion is assumed to be the rate determining mechanism for both systems investigated.
Surface Science 222 (1989) 517-529 North-Holland, Amsterdam
517
PLASMON INTERACTIONS IN METALLIC GRATINGS: to- A N D k - M I N I G A P S A N D T H E I R C O N N E C T I O N WITH
POLES
AND ZEROS
E. P O P O V
Institute of Solid State Physics, Bulgarian Academy of Sciences, blvd. Lenin 72, Sofia 1784, Bulgaria Received 17 April 1989; accepted for publication 6 July 1989 A numerical analysis is presented of two types of minigaps: co- and k-gap that are formed in the reflectivity dips when two oppositely propagating plasmon surface waves (PSW's) are excited simultaneously. Their connection with complex trajectories of poles and zeros is revealed: an co-gap is formed when splitting of poles is observed and a k-gap only exists when a splitting of zeros occurs.