13.1 LEED, VLEED, STM/S, and PES
255
convolution of the filled and empty DOS together with the matrix of transition probabilities. This is the case in UPS and gives rise to the strong dependence of valence
spectra on photon energy. In the case of XPS, the KE of the valence photoelectrons
is such that the final states are quite devoid of structure; thus, the observed DOS
closely reflects the initially filled density of states. The complete spectrum at high
resolution shows the band structure and the sharp cut-off in electron density at E F .
The invention of STM/S has led to enormous progress in revealing direct and
qualitative information on an atomic scale about the surface but the images challenge proper physical interpretation [36]. VLEED, PES and STM/S can be used as
complementary tools to get such information that integrates both real-space and kspace, on an atomic scale, and over macroscopic areas of the surface. A combination
of VLEED with STM/S reduces certainly the limitations inherent in each of these
techniques used separately. STM/S observation provides one with a direct vision of
the surface topography; decoding VLEED spectra rewards the quantitative details,
while a logic thinking of models in real and energy domain will link the morphology
and spectroscopy. STM imaging aids establishment the models of chemical bond
formation and electronic states evolution, which is able to discriminate individual
atomic states and the non-uniformity of the SPB. Derivations of these models from
STM images can be used as input to be justified in simulating VLEED spectra.
The VLEED simulation results, in turn, improve the understanding of the STM/S
and PES observations. Thus one can extract comprehensive information from such
a combination about the behavior of atoms and electrons at surfaces, and hence, we
can obtain the common senses about the nature and dynamics of the chemisorption
bonding and band forming dynamics, which can generalize other chemisorbed surfaces [19, 20]. Under the basic principles, one may be able to specify the individual
atomic states and thereby to derive the reaction formula for surface reaction from the
profiles of VLEED, STM/S and PES. If one could specify first the STM signatures
coming from whether ionic, polarized, or vacancy of missed atoms, then elucidation
of identities due to chemisorption becomes much easier [37].
13.2 O–Cu(001) Surface Reaction
As one of the prototypes of oxygen chemisorption, O-Cu(001) surface has been
intensively investigated both experimentally and theoretically. Since 1956, when
Young et al. [38] found that the Cu(001) surface is easier to be oxidized than other
planes of copper single crystal, numerous scientists have been devoted their efforts
to the understanding of oxygen chemisorption. There have been many conflicting
opinions regarding the oxygen-induced reconstruction of Cu(001) surface. Different
atomic superstructures have been derived with various experimental techniques [39]
and theoretical approaches [40, 41]. However, the observed structures vary from
researcher to researcher even though they used the same approach.
255
convolution of the filled and empty DOS together with the matrix of transition probabilities. This is the case in UPS and gives rise to the strong dependence of valence
spectra on photon energy. In the case of XPS, the KE of the valence photoelectrons
is such that the final states are quite devoid of structure; thus, the observed DOS
closely reflects the initially filled density of states. The complete spectrum at high
resolution shows the band structure and the sharp cut-off in electron density at E F .
The invention of STM/S has led to enormous progress in revealing direct and
qualitative information on an atomic scale about the surface but the images challenge proper physical interpretation [36]. VLEED, PES and STM/S can be used as
complementary tools to get such information that integrates both real-space and kspace, on an atomic scale, and over macroscopic areas of the surface. A combination
of VLEED with STM/S reduces certainly the limitations inherent in each of these
techniques used separately. STM/S observation provides one with a direct vision of
the surface topography; decoding VLEED spectra rewards the quantitative details,
while a logic thinking of models in real and energy domain will link the morphology
and spectroscopy. STM imaging aids establishment the models of chemical bond
formation and electronic states evolution, which is able to discriminate individual
atomic states and the non-uniformity of the SPB. Derivations of these models from
STM images can be used as input to be justified in simulating VLEED spectra.
The VLEED simulation results, in turn, improve the understanding of the STM/S
and PES observations. Thus one can extract comprehensive information from such
a combination about the behavior of atoms and electrons at surfaces, and hence, we
can obtain the common senses about the nature and dynamics of the chemisorption
bonding and band forming dynamics, which can generalize other chemisorbed surfaces [19, 20]. Under the basic principles, one may be able to specify the individual
atomic states and thereby to derive the reaction formula for surface reaction from the
profiles of VLEED, STM/S and PES. If one could specify first the STM signatures
coming from whether ionic, polarized, or vacancy of missed atoms, then elucidation
of identities due to chemisorption becomes much easier [37].
13.2 O–Cu(001) Surface Reaction
As one of the prototypes of oxygen chemisorption, O-Cu(001) surface has been
intensively investigated both experimentally and theoretically. Since 1956, when
Young et al. [38] found that the Cu(001) surface is easier to be oxidized than other
planes of copper single crystal, numerous scientists have been devoted their efforts
to the understanding of oxygen chemisorption. There have been many conflicting
opinions regarding the oxygen-induced reconstruction of Cu(001) surface. Different
atomic superstructures have been derived with various experimental techniques [39]
and theoretical approaches [40, 41]. However, the observed structures vary from
researcher to researcher even though they used the same approach.