282
14 Principles: Bond-Band-Barrier Correlation
surface, which is not simply a superimposition of (a) and (b) but a resultant of the
DOS features:
• The resultant band shows an extra DOS feature as indicated as O-p states charge
transportation from metal to the O
−1 .
• The O
−1 polarizes its nearest neighbors to produce dipoles that form sub-band
above the E F , which lowers the local work function from original φ 0 to φ 1 .
• The processes of bond and dipole formation create electronic holes right below
the E F , which creates a band gap E G to the metal or widens the band gap of
semiconductor from E g0 to E g1 .
14.3.2 O −2 Derived Four DOS Features
Upon sp-orbital hybridization, the band configuration of the host metal evolves from
Fig. 14.8c, d. Besides the holes and the antibonding dipoles appeared in the O
−1
precursor, the O-p sub-band divided into nonbonding (lone pair) and sp-bonding
sub-bands. The antibonding states sustained now by the lone-pair induced dipoles
instead of that induced by O
−1 . [23] The sp-hybrid nonbonding (lone pair) states
of oxygen locate somewhere (normally ~1.5 eV) below E F and above the sp-hybrid
bonding states that shift slightly towards energy lower than the 2p-level of the oxygen
because hybridization lowers system energy. For the Cu example, the 4s electrons
(in conduction band, CB) either contribute to the sp-bonding or jump to its own
outer empty-shell (for 4p orbital example) with energy even higher than the E F .
Such a process empties the states below the E F , which yields the Cu-oxide to be
a semiconductor. However, the lone pair states may overlap the electronic holes in
energy domain so some time observation cannot recognize their presence.
14.3.3 Anomalous H-Bond like
Upon overdosing of oxygen, H-bond like forms. The dipoles contribute the polarized
electrons to the bonding orbitals of an additional oxygen adsorbate. The arrow in
Fig. 14.8d from the antibonding states to the sp-bonding subband of oxygen represents the process of the H-bond like formation. STS and VLEED revealed that the
antibonding states of the O-Cu system range over 1.3 ± 0.5 eV and the nonbonding
states −2.1 ± 0.7 eV around E F . The photoemission electron microscopy (PEEM)
studies of O–Pt surfaces, [43–45] detected the conversion of the dark islands, in the
scale of 10
2
μm, into very bright ones with work functions ~1.2 eV lower than that
of the clean surface, which evidence the localization nature of polarization.
14 Principles: Bond-Band-Barrier Correlation
surface, which is not simply a superimposition of (a) and (b) but a resultant of the
DOS features:
• The resultant band shows an extra DOS feature as indicated as O-p states charge
transportation from metal to the O
−1 .
• The O
−1 polarizes its nearest neighbors to produce dipoles that form sub-band
above the E F , which lowers the local work function from original φ 0 to φ 1 .
• The processes of bond and dipole formation create electronic holes right below
the E F , which creates a band gap E G to the metal or widens the band gap of
semiconductor from E g0 to E g1 .
14.3.2 O −2 Derived Four DOS Features
Upon sp-orbital hybridization, the band configuration of the host metal evolves from
Fig. 14.8c, d. Besides the holes and the antibonding dipoles appeared in the O
−1
precursor, the O-p sub-band divided into nonbonding (lone pair) and sp-bonding
sub-bands. The antibonding states sustained now by the lone-pair induced dipoles
instead of that induced by O
−1 . [23] The sp-hybrid nonbonding (lone pair) states
of oxygen locate somewhere (normally ~1.5 eV) below E F and above the sp-hybrid
bonding states that shift slightly towards energy lower than the 2p-level of the oxygen
because hybridization lowers system energy. For the Cu example, the 4s electrons
(in conduction band, CB) either contribute to the sp-bonding or jump to its own
outer empty-shell (for 4p orbital example) with energy even higher than the E F .
Such a process empties the states below the E F , which yields the Cu-oxide to be
a semiconductor. However, the lone pair states may overlap the electronic holes in
energy domain so some time observation cannot recognize their presence.
14.3.3 Anomalous H-Bond like
Upon overdosing of oxygen, H-bond like forms. The dipoles contribute the polarized
electrons to the bonding orbitals of an additional oxygen adsorbate. The arrow in
Fig. 14.8d from the antibonding states to the sp-bonding subband of oxygen represents the process of the H-bond like formation. STS and VLEED revealed that the
antibonding states of the O-Cu system range over 1.3 ± 0.5 eV and the nonbonding
states −2.1 ± 0.7 eV around E F . The photoemission electron microscopy (PEEM)
studies of O–Pt surfaces, [43–45] detected the conversion of the dark islands, in the
scale of 10
2
μm, into very bright ones with work functions ~1.2 eV lower than that
of the clean surface, which evidence the localization nature of polarization.