348
18 Four-Stage Cu 3 O 2 Bonding Dynamics
[1, 2]. A combination of the H 2 O like tetrahedron and the paramerized VLEED decoding strategies and the excellent data collected by Hitchen, Thurgate, and Jennings
[3] made the quantification of the bonding kinetics possible [4].
Figure 18.1a–c shows the exposure-resolved VLEED(00) beam reflectance I 00 /I 0
versus incident beam energy measured at 70° incidence and 42° azimuth angles.
The fine-structure features are very sensitive to the oxygen-exposure. Examination
of the typical spectral peak intensities at 7.1, 9.1 and 10.3 eV revealed that the
reaction progresses in four discrete stages as a function of oxygen exposure ( O in
Langmuir= 10
−6 s torr) [4]:
(i) O ≤ 30 L: The peak at 7.1 eV decreases in magnitude until oxygen exposure
reaches 30 L, while other peaks have little change.
(ii) 30 L > O ≤ 35 L: The decreased peak intensity at 7.1 eV recovers a bit.
(iii) 35 L > O ≤ 200 L: The first peak attenuates while one new peak at 9.1 eV
emerges; and then both the peak at 9.1 eV and the peak at 10.3 eV have
increasing maximum up to 200 L.
(iv) O > 200 L: A general attenuation of the entire spectrum occurs.
Besides, the peak at 10.3 eV moves towards lower energy with increasing oxygen exposure. The spectral sensitivity examination suggested that the BA12 expansion and second O-Cu bond contraction (Q 2 ) modulate the intensities of the first
two peaks while the diopole dislocation (DCu x ) depresses the intensity of the entire
spectral features above 12.5 eV.
18.2 Geometrical Examination
Calculations used the same procedures described in previous section. The bond
parameters and the z 0 (E) curve for the 400 L oxygen exposure data are optimized first.
The optimal parameters are Q 2 = 0.04, BA12 = 102.0°, DCu x = 0.25 Å as listed in
Table 18.1. The optimal z 0 (E) curve for 400 L is indicated in Figure 18.1d–f. Regardless of the accuracy of the single-variable parameterization and the extent to which the
SPB varies with oxygen exposure, we then examined the structural sensitivity of the
400 L spectrum. Geometrical examination was conducted by adjusting one geometrical parameter at a time and maintaining the others and the z 0 (E) curve undisturbed.
Figure 18.1d–f compare the calculation results from individually varying the three
bond variables BA12, Q 2 or BL2, and the displacement DCu x . Results show the
following trends:
(1) Simulation of the entire set of the exposure-resolved VLEED data can be made
by keeping the oxygen-coverage constant at 0.5 monolayer. This implies that the
extra oxygen atoms due to increasing exposure promote the reaction. The additional oxygen does not participate directly in the reaction after the saturation of
adsorption. The promotion is treated as post-saturation effect. No quantitative
correspondence between exposure (measured in Langmuir) and coverage (measured in monolayer—ML) can be established, as justified in many earlier studies
18 Four-Stage Cu 3 O 2 Bonding Dynamics
[1, 2]. A combination of the H 2 O like tetrahedron and the paramerized VLEED decoding strategies and the excellent data collected by Hitchen, Thurgate, and Jennings
[3] made the quantification of the bonding kinetics possible [4].
Figure 18.1a–c shows the exposure-resolved VLEED(00) beam reflectance I 00 /I 0
versus incident beam energy measured at 70° incidence and 42° azimuth angles.
The fine-structure features are very sensitive to the oxygen-exposure. Examination
of the typical spectral peak intensities at 7.1, 9.1 and 10.3 eV revealed that the
reaction progresses in four discrete stages as a function of oxygen exposure ( O in
Langmuir= 10
−6 s torr) [4]:
(i) O ≤ 30 L: The peak at 7.1 eV decreases in magnitude until oxygen exposure
reaches 30 L, while other peaks have little change.
(ii) 30 L > O ≤ 35 L: The decreased peak intensity at 7.1 eV recovers a bit.
(iii) 35 L > O ≤ 200 L: The first peak attenuates while one new peak at 9.1 eV
emerges; and then both the peak at 9.1 eV and the peak at 10.3 eV have
increasing maximum up to 200 L.
(iv) O > 200 L: A general attenuation of the entire spectrum occurs.
Besides, the peak at 10.3 eV moves towards lower energy with increasing oxygen exposure. The spectral sensitivity examination suggested that the BA12 expansion and second O-Cu bond contraction (Q 2 ) modulate the intensities of the first
two peaks while the diopole dislocation (DCu x ) depresses the intensity of the entire
spectral features above 12.5 eV.
18.2 Geometrical Examination
Calculations used the same procedures described in previous section. The bond
parameters and the z 0 (E) curve for the 400 L oxygen exposure data are optimized first.
The optimal parameters are Q 2 = 0.04, BA12 = 102.0°, DCu x = 0.25 Å as listed in
Table 18.1. The optimal z 0 (E) curve for 400 L is indicated in Figure 18.1d–f. Regardless of the accuracy of the single-variable parameterization and the extent to which the
SPB varies with oxygen exposure, we then examined the structural sensitivity of the
400 L spectrum. Geometrical examination was conducted by adjusting one geometrical parameter at a time and maintaining the others and the z 0 (E) curve undisturbed.
Figure 18.1d–f compare the calculation results from individually varying the three
bond variables BA12, Q 2 or BL2, and the displacement DCu x . Results show the
following trends:
(1) Simulation of the entire set of the exposure-resolved VLEED data can be made
by keeping the oxygen-coverage constant at 0.5 monolayer. This implies that the
extra oxygen atoms due to increasing exposure promote the reaction. The additional oxygen does not participate directly in the reaction after the saturation of
adsorption. The promotion is treated as post-saturation effect. No quantitative
correspondence between exposure (measured in Langmuir) and coverage (measured in monolayer—ML) can be established, as justified in many earlier studies