354
18 Four-Stage Cu 3 O 2 Bonding Dynamics
the STM observations [1] that confirmed the co-existence of clean Cu(001), c(2 × 2)2O
−1 and the (
√
2 × 2
√
2)R45°-2O
−2 phases at low oxygen exposures (<25 L). The
extremely low damping of the clean Cu(001) surface [ImV(E = 6.0 eV, 16.0 eV) ∼ =
(0.78, 0.81 eV)], and the c(2 × 2)-2O
−1 (1.0, 3.0 eV) [4] indicates that information
from these two phases has been filtered out by the high damping of the (
√
2 ×
2
√
2)R45°-2O
−2 phase (1.3, 6.5 eV).
The high damping for the Cu 3 O 2 phase can be gained by substituting
γ = −0.9703, δ = 6.4478 and φ L ∼ = 4.0 eV into the ImV(z, E). In fact, the relative number and the saturation degree of the dipoles dominate the intensity of the
damping. O
−1 induced dipoles composing the c(2 × 2)-2O
−1 domain boundaries
should be less saturated than those induced by the lone pairs of O
−2 in the (
√
2 ×
2
√
2)R45°-2O
−2 phase. Fig. 18.3 illustrates the VLEED resolved four-stage Cu 3 O 2
bonding dynamics. O 2 dissociates and bonds to a surface Cu atom to form the CuO 2
pairing-pyramid and then the second O-Cu bond follows with a Cu atom underneath associated with sp
3 orbital hybridization and lone pair production. The lone
pair polarizes the neighboring Cu atom into dipoles. During the process of reaction,
bond length and angle relaxatiom continues with production of the missing-row
vacancy by isolating the vacanted atom from other neighbors.
18.4 Aging and Annealing Effects on VLEED Profiles
VLEED I-E scans after aging and annealing of the specimen provide useful information about the bond formation, relaxation, and dissociation under such conditions.
Figure 18.4a shows the effect of annealing and aging on the VLEED I-E curves of
a 300 L oxygen-exposed Cu(001) surface. The time-resolved spectra to be decoded
were collected at 72.0° incidence and 42.0° azimuth [3]. The experimental conditions
and the fine-structure features of these spectra are summarized as follows:
(1) Scan A was taken immediately after the clean Cu(001) surface exposed to 300
L oxygen. There are two broad peaks at 9.0, 11.0 eV due to Rydberg resonance
and two sharp peaks at 10.5 and 12.0 eV due to Bragg diffraction.
(2) Scan B was taken after 25 min aging and produced the same result, apart from
a change in slope (goes up) below 9.5 eV.
(3) Scan C was taken after 5 min of mild heating (~550 K), to a dull red color,
and showed a change in structure. Besides the slope below 9.5 eV, the whole
spectrum increases in intensity.
(4) Scan D was taken after a further three hours aging. No change in structure from
scan C is noted apart from a general attenuation in intensity of the spectrum and
a significant intensity decrease below 9.5 eV. The changes between scan C and
D are similar in effect to the result of oxygen exposure greater than 200 L.
In general, the spectral shape and intensity below 9.5 eV are more sensitive to the
aging and annealing, which indicates that reaction modifies energy states of the lone
pairs—orbital hybridization and dehybridization.
18 Four-Stage Cu 3 O 2 Bonding Dynamics
the STM observations [1] that confirmed the co-existence of clean Cu(001), c(2 × 2)2O
−1 and the (
√
2 × 2
√
2)R45°-2O
−2 phases at low oxygen exposures (<25 L). The
extremely low damping of the clean Cu(001) surface [ImV(E = 6.0 eV, 16.0 eV) ∼ =
(0.78, 0.81 eV)], and the c(2 × 2)-2O
−1 (1.0, 3.0 eV) [4] indicates that information
from these two phases has been filtered out by the high damping of the (
√
2 ×
2
√
2)R45°-2O
−2 phase (1.3, 6.5 eV).
The high damping for the Cu 3 O 2 phase can be gained by substituting
γ = −0.9703, δ = 6.4478 and φ L ∼ = 4.0 eV into the ImV(z, E). In fact, the relative number and the saturation degree of the dipoles dominate the intensity of the
damping. O
−1 induced dipoles composing the c(2 × 2)-2O
−1 domain boundaries
should be less saturated than those induced by the lone pairs of O
−2 in the (
√
2 ×
2
√
2)R45°-2O
−2 phase. Fig. 18.3 illustrates the VLEED resolved four-stage Cu 3 O 2
bonding dynamics. O 2 dissociates and bonds to a surface Cu atom to form the CuO 2
pairing-pyramid and then the second O-Cu bond follows with a Cu atom underneath associated with sp
3 orbital hybridization and lone pair production. The lone
pair polarizes the neighboring Cu atom into dipoles. During the process of reaction,
bond length and angle relaxatiom continues with production of the missing-row
vacancy by isolating the vacanted atom from other neighbors.
18.4 Aging and Annealing Effects on VLEED Profiles
VLEED I-E scans after aging and annealing of the specimen provide useful information about the bond formation, relaxation, and dissociation under such conditions.
Figure 18.4a shows the effect of annealing and aging on the VLEED I-E curves of
a 300 L oxygen-exposed Cu(001) surface. The time-resolved spectra to be decoded
were collected at 72.0° incidence and 42.0° azimuth [3]. The experimental conditions
and the fine-structure features of these spectra are summarized as follows:
(1) Scan A was taken immediately after the clean Cu(001) surface exposed to 300
L oxygen. There are two broad peaks at 9.0, 11.0 eV due to Rydberg resonance
and two sharp peaks at 10.5 and 12.0 eV due to Bragg diffraction.
(2) Scan B was taken after 25 min aging and produced the same result, apart from
a change in slope (goes up) below 9.5 eV.
(3) Scan C was taken after 5 min of mild heating (~550 K), to a dull red color,
and showed a change in structure. Besides the slope below 9.5 eV, the whole
spectrum increases in intensity.
(4) Scan D was taken after a further three hours aging. No change in structure from
scan C is noted apart from a general attenuation in intensity of the spectrum and
a significant intensity decrease below 9.5 eV. The changes between scan C and
D are similar in effect to the result of oxygen exposure greater than 200 L.
In general, the spectral shape and intensity below 9.5 eV are more sensitive to the
aging and annealing, which indicates that reaction modifies energy states of the lone
pairs—orbital hybridization and dehybridization.