|
Autor/a:
|
Rodríguez, J. A.; Liu, P.; Gomes, J.; Nakamura, K.; Viñes Solana, Francesc; Sousa Romero, Carmen; Illas i Riera, Francesc
|
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Abstract:
|
High-resolution photoemission and first-principles density-functional calculations were used to study the interaction of oxygen with ZrC(001) and VC(001) surfaces. Atomic oxygen is present on the carbide substrates after small doses of
O
2
at room temperature. At
500
K
, the oxidation of the surfaces is fast and clear features for
Zr
O
x
or
V
O
x
are seen in the
O
(
1
s
)
,
Zr
(
3
d
)
, and
V
(
2
p
3
∕
2
)
core levels spectra, with an increase in the metal/carbon ratio of the samples. A big positive shift
(
1.3
–
1.6
eV
)
was detected for the C
1
s
core level in
O
∕
Zr
C
(
001
)
, indicating the existence of strong
O
↔
C
or
C
↔
C
interactions. A phenomenon corroborated by the results of first-principles calculations, which show a CZrZr hollow as the most stable site for the adsorption of O. Furthermore, the calculations also show that a
C
↔
O
exchange is exothermic on ZrC(001), and the displaced C atoms bond to CZrZr sites. In the
O
∕
Zr
C
(
001
)
interface, the surface C atoms play a major role in determining the behavior of the system. In contrast, the adsorption of oxygen induces very minor changes in the
C
(
1
s
)
spectrum of VC(001). The
O
↔
V
interactions are stronger than the
O
↔
Zr
interactions, and
O
↔
C
interactions do not play a dominant role in the
O
∕
V
C
(
001
)
interface. In this system,
C
↔
O
exchange is endothermic. VC(001) has a larger density of metal
d
states near the Fermi level than ZrC(001), but the rate of oxidation of VC(001) is slower. Therefore the
O
∕
Zr
C
(
001
)
and
O
∕
V
C
(
001
)
systems illustrate two different types of pathways for the oxidation of carbide surfaces. |
