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Crystal binding energy of a core electron at the 3d[sub 5/2] level of a Pd atom has been estimated to be -4.0±0.02 eV by decoding the X-ray photoelectron spectra obtained from both the Pd surfaces and the Pd nanoparticles. Findings indicate that the increase in the binding energy originates from the effect of coordination number (CN) imperfection of atoms at a flat surface or at the curved surface of a nanosolid. The CN imperfection shortens the remaining bonds of the lower-coordinated atoms spontaneously associated with bond energy increase, which perturbs the Hamiltonian of an extended solid and hence shifts the core level to higher binding energy. Therefore, the significance of atomic CN imperfection cannot be overlooked in dealing with a low-dimensional system, and the recent bond-order–length–strength (BOLS) correlation mechanism is essentially adequate, for the significance of atomic CN imperfection. [ABSTRACT FROM AUTHOR]

Further to the previous part [Surf. Rev. Lett. S(3/4), 367 (2001)], this part deals with VLEED numerical quantification of the Cu[sub 3]O[sub 2] bond-forming kinetics on the Cu(001) surface. Besides the solution-number certainty that has been ensured, the modeling exercises have enabled the full capacity of VLEED to be explored, revealing that the bond geometry and the elastic potential define the shapes of the VLEED fine-structure features while the inelastic potential contributes to the absolute intensity. VLEED, covering the valence band in energy, is found to be able to collect nondestructive information from the top atomic layer, as the inelastic damping dominates in this region. Except for the bond geometry, dislocation of a single atom in the unit cell produces no feature that can match the VLEED spectral change, indicating the essentiality of the parametrization techniques developed. It is the right premise that it has enabled the four-stage O-Cu(001) reaction kinetics, revealed by VLEED, to be quantified as the evolution of the CuO[sub 2] to the Cu[sub 3]O[sub 2]. In addition, it is revealed that annealing provides disturbance rather than driving force strengthening the bond energy. Therefore, formulation in terms of bond making and its consequence on the behavior of atoms and valence electrons, and the corresponding parametrization, are demonstrated to be able to correctly reflect the real process of reaction and the correlation of the parameters as well as their natural link to the observations using LEED, STM and PES, or equivalent approaches. [ABSTRACT FROM AUTHOR]

This work consists of two sequential parts, which review the advances in uncovering the capacity of VLEED, STM and PES in revealing the nature and kinetics of oxidation bonding and its consequences for the behavior of atoms and valence electrons at a surface; and in quantifying the O-Cu(001) bonding kinetics. The first part describes the model in terms of bond making and its effect on the valence DOS and on the surface potential barrier (SPB) for surfaces with chemisorbed oxygen. One can replace the hydrogen in a H[sub 2]O molecule with an arbitrary less electronegative element and extend the M[sub 2]O to a solid surface with Goldschmidt contraction of the bond length, which formulates a specific oxidation surface with identification of atomic valences and their correspondence to the STM and PES signatures. As consequences of bond making, oxygen derives four additional DOS features in the valence band and above, i.e. O-M bonding (∼ -5 eV), oxygen nonbonding lone pairs (∼ -2 eV), holes (≤ E[sub F]), and antibonding metal dipoles (≥ E[sub F]), in addition to the hydrogen-bond-like formation. The evolution of O[sup -1] to O[sup -2] transforms the CuO[sub 2] pairing off-centered pyramid in the c(2 × 2)-2O[sup -1] into the Cu[sub 3]O[sub 2] pairing tetrahedron in the (2 √2 × √2)R45°-2O[sup -2] phase on the Cu(001) surface. The new decoding technique has enabled the model to be justified and hence the capacity of VLEED, PES and STM to be fully uncovered in determining simultaneously the bond geometry, the SPB, the valence DOS, and their interdependence. [ABSTRACT FROM AUTHOR]

From the perspective of sp orbital hybrid bonding and its consequence on the behavior of valence electrons, new insight is presented into the nature of oxygen-derived features in the valence band and above of metals. It is suggested that the crystal geometry and the surface morphology may vary from surface to surface and from material to material but the oxygen-derived features in energy space are substantially the same in nature. The derived features can be consistently specified as oxygen-metal bonding (-5 to -8 eV), a nonbond lone pair of oxygen (-1 to -2 eV), holes of metal ions (∼ E[sub F]) and antibondng metal dipole states (> E[sub F]), other than the addition of the 2s or 2p states of the isolated oxygen additives. From the perspective of sp orbital hybrid bonding and its consequence on the behavior of valence electrons, new insight is presented into the nature of oxygen-derived features in the valence band and above of metals. It is suggested that the crystal geometry and the surface morphology may vary from surface to surface and from material to material but the oxygen-derived features in energy space are substantially the same in nature. The derived features can be consistently specified as oxygen-metal bonding (-5 to -8 eV), a nonbond lone pair of oxygen (-1 to -2 eV), holes of metal ions (∼ E[sub F]) and antibondng metal dipole states (> E[sub F]), other than the addition of the 2s or 2p states of the isolated oxygen additives. [ABSTRACT FROM AUTHOR]

This brief review focuses on the nature, kinetics, dynamics and consequences of the sp-orbital hybrid bonding of C, N and O to the Ni/Rh(001) surfaces which give rise to the same kind of "radial and then the p4g clock" reconstruction. It is identified that the "radial" and the subsequent "clock" reconstruction result from the adsorbate-substrate bond formation with sp-orbital hybridization, and that the driving force behind the reconstruction originates from the electrostatic interaction along the 〈11〉 direction. At the initial stage, A[sup -1] (A = C, N or O adsorbate) sinks into the fourfold hollow site and forms one bond with a B (B = Ni or Rh host atom) underneath, giving rise to an AB[sub 5] cluster with four dipoles at the surface. As A[sup -1] evolves into the hybridized-A[sup -n] (n = 4, 3, 2), the AB[sub 5] cluster evolves into an AB[sub 4] tetrahedron. Meanwhile, the AB[sub 4] tetrahedron redefines three of the four surface dipoles as B[sup +], B[sup 2+], B[sup +/dipole] or B[sup dipole], depending on the valence value of the adsorbate. The electrostatic force arises upon repopulating the valence electrons, which creates rhombus strings along the 〈11〉 direction. With the presence of nonbonding lone pairs, the clock rotation on Ni(001)-(2 × 2)p4g-2N[sup -3] and Rh(001)(2 × 2)p4g-20[sup -2] surfaces is initiated by the alternate attraction and repulsion in the 〈11〉 direction and the rotation is stabilized by bond tension; whereas the clock rotation on the Ni(001)-(2 × 2)p4g-2C[sup -4] surface is driven by the nonequivalent electrostatic repulsion in the 〈11〉 direction and the rotation is balanced by strong bond compression. The findings so far have led to technical innovation for the adhesion between diamond and metals by designing a gradient TiCN transition layer to neutralize the bond stress. [ABSTRACT FROM AUTHOR]

A new model is presented to describe the quantum confinement and surface passivation effects of nanoclusters. The quantum well depth (φ) and the band gap width (E[sub g]) of nanoclusters are independent concepts, because the $\phi$ depends on the surface electron density while the E[sub g] is a function of the crystal field of the solid. The φ and E[sub g] can be correlated with the joint physical and chemical effects, which are quite simple but have rarely been noticed. It is suggested that the bond contraction at the surface and the rise in the surface-to-volume ratio (γ), as well as the cluster interaction, enhance intrinsically the crystal field and hence the band gap E[sub g]. Reaction with electronegative elements, such as oxygen and nitrogen, widens extrinsically the E[sub g] by producing holes below the Fermi level [Appl. Phys. Lett.72, 1706 (1998)]. The formulation agrees well with experimental observations on the band gap enlargement by reducing particle size. [ABSTRACT FROM AUTHOR]

It is shown that the atomic states, bonding dynamics, driving force and bond strain for the C–Ni(100) surface reaction can be consistently understood by considering the sp orbital hybridization of carbon. It is proposed that, at the initial stage, C sinks into the hollow site and bonds to one Ni atom underneath. The C[sup -1] polarizes and pushes its surface neighbors radially away from the site center, and hence a Ni[sub 5]C cluster forms. Then, sp hybridization of the C happens, leading to a Ni[sub 4]C tetrahedron. Besides the Ni[sup +] underneath the C adsorbate, three of the four surface Ni neighbors donate electrons to the adsorbate. The half-monolayer coverage of C defines therefore half of the surface Ni atoms to be Ni[sup +] ions and the other half to be Ni[sup 2+] ions. As a result, one-dimensional nonuniform “- (+) - (2+) – (2+) - (+) – (+) -” chains form along the < 11> direction. It is suggested that the forces arising from charge redistribution drive the reconstruction. Calculation reveals that an increase of ∼ 90 dyne electrostatic repulsion along the < 11> direction and a responding ∼ 130 dyne bond compression stabilize the network of (2× 2)p4g clock rotation. [ABSTRACT FROM AUTHOR]