9.1 STS and IPES: Antibonding and Nonbonding States
183
Fig. 9.1 Oxygen chemisorption derived a STS LDOS for the Nb(110) surface [11] and b the IPES
(9.7 eV incident beam sources) for Cu(110) surface [12]. Inset a shows the STM image of O–
Nb(110) surface with O–Nb chains and triangle-shaped atomic vacancies. Oxygen chemisorption
attenuates the IPES S peak intensity at 2.0 eV as the occupancy of the empty surface states by
antibonding dipoles. Features A and D are the O-induced and the direct transition in the bulk band
structure. Reprinted with permission from [11, 12]
Room temperature oxygen chemisorption reduces the work function of Nb by φ
= −0.45 eV at less-than-one monolayer coverage and then is followed by an increase
of φ = +0.8 eV at higher oxygen coverages, which is even higher than that of the
clean surface [16]. The shift of the second peak at 5.6 eV is consistent with the work
function increase and the rest two peaks correspond to satellites of resonance. The
occupied DOS features of the O–Nb bond are at −5.8 and at −6.2 eV, which is in the
STM triangular vacancy positions. The clean Nb(110) surface DOS is at −5.0 eV.
The energy shift of the occupied states was ever attributed to the overlap of the O 2p
and the Nb 4d states of the reconstructed O–Nb(110) surface [11].
The obviously symmetric dispersion of this state with respect to the occupied
oxygen 2 p y − states agrees with a two-level approximation for the O–Cu σ-bond.
The band above E F is an empty surface state, which means that the agreement of
its dispersion with that of the O 2 p y − state below E F is accidental [17]. No definite
interpretation to this phenomenon has been available up to now. Nevertheless, it
should be noted that the feature at +2 eV is in accordance with those probed using
STS on the same O–Cu(110) surface. This empty feature decreases with increasing
oxygen exposure.
Figure 9.1b shows the exposure dependence of the IPES unoccupied bands of
the O–Cu(110) surface [12] exhibiting the resonant features similar to that observed
183
Fig. 9.1 Oxygen chemisorption derived a STS LDOS for the Nb(110) surface [11] and b the IPES
(9.7 eV incident beam sources) for Cu(110) surface [12]. Inset a shows the STM image of O–
Nb(110) surface with O–Nb chains and triangle-shaped atomic vacancies. Oxygen chemisorption
attenuates the IPES S peak intensity at 2.0 eV as the occupancy of the empty surface states by
antibonding dipoles. Features A and D are the O-induced and the direct transition in the bulk band
structure. Reprinted with permission from [11, 12]
Room temperature oxygen chemisorption reduces the work function of Nb by φ
= −0.45 eV at less-than-one monolayer coverage and then is followed by an increase
of φ = +0.8 eV at higher oxygen coverages, which is even higher than that of the
clean surface [16]. The shift of the second peak at 5.6 eV is consistent with the work
function increase and the rest two peaks correspond to satellites of resonance. The
occupied DOS features of the O–Nb bond are at −5.8 and at −6.2 eV, which is in the
STM triangular vacancy positions. The clean Nb(110) surface DOS is at −5.0 eV.
The energy shift of the occupied states was ever attributed to the overlap of the O 2p
and the Nb 4d states of the reconstructed O–Nb(110) surface [11].
The obviously symmetric dispersion of this state with respect to the occupied
oxygen 2 p y − states agrees with a two-level approximation for the O–Cu σ-bond.
The band above E F is an empty surface state, which means that the agreement of
its dispersion with that of the O 2 p y − state below E F is accidental [17]. No definite
interpretation to this phenomenon has been available up to now. Nevertheless, it
should be noted that the feature at +2 eV is in accordance with those probed using
STS on the same O–Cu(110) surface. This empty feature decreases with increasing
oxygen exposure.
Figure 9.1b shows the exposure dependence of the IPES unoccupied bands of
the O–Cu(110) surface [12] exhibiting the resonant features similar to that observed