14.2 Oxide Tetrahedron Bond Formation
281
This physical picture agrees with that probed with STS from the O–Cu(110) system showing the energy levels of the occupied DOS increases relative to the pure Cu
system. These results evidence for the polarization of metal electrons. On another
hand, the strong localization of the electron density resulting from the polarization of metals, formation of the missing rows and ionization of metals cause the
nonuniformity of the contact-potential difference from one site to another on the
surface.
14.2.6.4 The Force Driving Reconstruction
Unlike bonding and anti-bonding states, the energy levels of the non-bonding electron
pairs change little relative to an unpaired electrons in its isolated atomic orbital.
However, the lone pair is capable of polarizing the neighboring metal atoms, raising
their electronic energy above E F [28]. The centers of the negative and positive charges
of the dipoles shift oppositely along the resultant direction at which the two lone pairs
are acting. The strength of interaction for a “O
−2 : Cu
p : O
−2 ” system is twice that of
a nonbonding interaction, which is in the order of ~0.1 eV [29].
Transformation from the metallic bond of ~1.0 eV to the contracting ionic bonds
gains ~3.0 eV energy. Part of the amount of energy contributes to the hybridization
of the sp-orbitals of oxygen. The hybridization of the sp-orbitals further lowers the
system energy. These energies due to ionic bond formation provides forces driving
the reconstruction and missing-row formation.
14.3 Valence Density-of-States
14.3.1 O −1 Derived Three DOS Features
Because of oxide bond formation, the valence band of the host metal exhibits additional features. Figure 14.8 illustrates the evolution of the DOS in the valence band,
or above the vacuum level E 0 , of the host. Arrows represent the dynamic processes
of electron transportation between (a) the energy bands of an arbitrary metal and (b)
the energy levels of oxygen adsorbate. Initially, the energy states below Fermi level
of metals are fully occupied. The work function φ 0 , the Fermi energy E F , and the
E 0 follows the relationship: E 0 = φ 0 + E F . For Cu example, E 0 = 12.04 eV, φ 0 =
5.0 eV and E F = 7.04 eV. The Cu-3d band is located at energies from −2.0 to −
5.0 eV below the E F . For oxygen, the O-2p level is at −5.5 eV with respect to the
E F of Cu.
At the initial stage of reaction, one electron transports from the outmost shell
of a metal atom to the unfilled O-2p states of oxygen. The O
−1 polarizes its rest
neighbors. Figure 14.8c represents the resultant effect of O
−1 formation on metal
281
This physical picture agrees with that probed with STS from the O–Cu(110) system showing the energy levels of the occupied DOS increases relative to the pure Cu
system. These results evidence for the polarization of metal electrons. On another
hand, the strong localization of the electron density resulting from the polarization of metals, formation of the missing rows and ionization of metals cause the
nonuniformity of the contact-potential difference from one site to another on the
surface.
14.2.6.4 The Force Driving Reconstruction
Unlike bonding and anti-bonding states, the energy levels of the non-bonding electron
pairs change little relative to an unpaired electrons in its isolated atomic orbital.
However, the lone pair is capable of polarizing the neighboring metal atoms, raising
their electronic energy above E F [28]. The centers of the negative and positive charges
of the dipoles shift oppositely along the resultant direction at which the two lone pairs
are acting. The strength of interaction for a “O
−2 : Cu
p : O
−2 ” system is twice that of
a nonbonding interaction, which is in the order of ~0.1 eV [29].
Transformation from the metallic bond of ~1.0 eV to the contracting ionic bonds
gains ~3.0 eV energy. Part of the amount of energy contributes to the hybridization
of the sp-orbitals of oxygen. The hybridization of the sp-orbitals further lowers the
system energy. These energies due to ionic bond formation provides forces driving
the reconstruction and missing-row formation.
14.3 Valence Density-of-States
14.3.1 O −1 Derived Three DOS Features
Because of oxide bond formation, the valence band of the host metal exhibits additional features. Figure 14.8 illustrates the evolution of the DOS in the valence band,
or above the vacuum level E 0 , of the host. Arrows represent the dynamic processes
of electron transportation between (a) the energy bands of an arbitrary metal and (b)
the energy levels of oxygen adsorbate. Initially, the energy states below Fermi level
of metals are fully occupied. The work function φ 0 , the Fermi energy E F , and the
E 0 follows the relationship: E 0 = φ 0 + E F . For Cu example, E 0 = 12.04 eV, φ 0 =
5.0 eV and E F = 7.04 eV. The Cu-3d band is located at energies from −2.0 to −
5.0 eV below the E F . For oxygen, the O-2p level is at −5.5 eV with respect to the
E F of Cu.
At the initial stage of reaction, one electron transports from the outmost shell
of a metal atom to the unfilled O-2p states of oxygen. The O
−1 polarizes its rest
neighbors. Figure 14.8c represents the resultant effect of O
−1 formation on metal