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Correlation between the elastic and the vibronic behavior of TiO 2 and their responses to the variation of crystal size, applied pressure, and measuring temperature has been investigated based on the bond order–length-strength correlation mechanism. Theoretical reproduction of the measurements clarified that: (i) the elastic modulus (B) and the Raman shifts (Δω) are strongly correlated and we can know either one of the B or the Δω from the other; (ii) the under-coordination induced cohesive energy loss and the energy density gain in the surface up to skin depth determines the size effect; (iii) bond expansion and bond weakening due to thermal vibration originates the thermally softened elastic modulus and the Raman shifts; and (iv) bond compression and bond strengthening results in the mechanically stiffened elastic modulus and the Raman shifts. With the developed premise, one can predict the changing trends of the concerned properties with derivatives of quantitative information of the atomic cohesive energy, binding energy density, Debye temperature, and nonlinear compressibility of the specimen.

Incorporating the bond–order–length–strength correlation mechanism [C. Q. Sun, Prog. Solid State Chem.35, 1 (2007)] and Born's criterion for melting [J. Chem. Phys.7, 591 (1939)] into the conventional Hall–Petch relationship has turned out an analytical expression for the size and temperature dependence of the mechanical strength of nanograins, known as the inverse Hall–Petch relationship (IHPR). Reproduction of the measured IHPR of Ni , NiP , and TiO 2 nanocrystals revealed that: (i) the competition between the size-induced energy–density gain and atomic cohesive energy loss in the surface skins of nanograins originate from the IHPR; (ii) the competition between the activation and inhibition of atomic dislocations motion activate the entire IHPR behavior; (iii) the bond nature involved and the T/Tm ratio between the temperature of operating and the temperature of melting dictate the measured strongest sizes of a given specimen; (iv) a quasimolten phase present before melting determines the size-induced softening and the superplasticity of nanostructures.

Nanostructural zinc oxide has been successfully fabricated by heating the mixture of ZnO and graphite powders in air. The growth of these zinc oxide nanostructures with respect to the growing time and temperature has been studied. The morphologies and the crystal structures have been characterized by scanning electronic microscopy and the X-ray diffraction. The results indicated that ZnO nanostructure formed mainly along the crystal orientation [002] on silicon substrate at moderate temperatures. The crystallization was improved by prolonging growth time and the morphologies mainly depended on the distribution of the growth temperature. The growth process was attributed to vapor-liquid-solid mechanism.

Crystal binding energy of a core electron at the 3d 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.

Grain growth dependence of microstructure in La 2/3 Ba 1/3 MnO 3+δ oxides has been studied in detail. The result shows that the crystals grew along three vertical axes with a concentric terrace pattern in the sample sintered at 1673K while the oxides sintered at 1573K grew with a lateral growth manner. However, the concentric terrace growth pattern resulted in twin microstructure in the cooling processing and the lateral growth manner produced non-twin microstrcuture in the oxides at ambient, respectively. It was found that the oxide with twin microstructure has a much higher saturation magnetization than the non-twin oxide. This may be due to the easier alignment of the domains in the twin-grained oxide through the rearrangement of dislocations in twin-boundaries.

The interfacial characteristics of the TiSi 2/ Si structure were investigated in detail. It was found that the semi-coherent formed with a certain disregistry which was periodically taken up by the misfit dislocations between every three (030)C49 planes. The semi-coherent interface dominated the interfacial structure in the material and was responsible to the wavy surface of TiSi 2/ Si structure. However, the interface accommodated higher energy was a favorable nucleation sites for the C54 phase. Its existence may enhance the C54 phase formation in the further thermal treatments.

It has been elegantly accepted that oxygen adsorption onto the Cu (110) surface induces an expansion of the first layer-spacing and a contraction of the second in addition to the alternative Cu [001] row that is either missing or forming the O-Cu-O row of high protrusions. However, it needs yet to clarify the vertical position of the oxygen and the hard-sphere models of added-, missing- and buckled-row. Here we justify that all the structures determined and all the models developed so far are correct in the sense of numerical solutions and phenomenological descriptions. A tetrahedral bond configuration of sp-orbital hybridization developed recently, however, may serve as a criterion to identify the physical solution that could account consistently for the observations using scanning tunneling microscopy/spectroscopy (STM/S), X-ray diffraction (XRD), and ultraviolet photoelectron spectroscopy (UPS).

Further to the previous part [Surf. Rev. Lett.8(3/4), 367 (2001)], this part deals with VLEED numerical quantification of the Cu3O2bond-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 Cu2to the Cu3O2. 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.

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 2 O molecule with an arbitrary less electronegative element and extend the M 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 correpondence to the STM and PES signatures. As consequences of bond making, oxygen derives foou additional DOS features in the valence band and above, i.e. O–M bonding (~ -5 eV), oxygen nonbounding lone pairs (~ - 2 eV), holes (≤ EF ), and antibonding metal dipoles (≥ EF ), in addition to the hydrogen-bond-like formation. The evolution of O -1 to O -2 transforms the CuO 2 pairing off-centered pyramid in the c(2× 2)-2 O -1 into the CU 3 O 2 pairing tetrahedron in the [Formula: see text] 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.

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 (~EF) and antibonding metal dipole states (>EF), other than the addition of the 2s or 2p states of the isolated oxygen additives.

A new description of bonding and band-forming is presented for the nature and dynamics of O–Rh(111) and O–Ru(0001) surface bonding and its consequences on the behavior of atoms and electrons at the surfaces. The sp-orbital hybridization and electron transportation define that oxygen retains inside the hcp hollow site throughout the course of reaction in which O -1 forms and then O -2-hybrid follows with production of nonbonding lone pairs and the lone-pair induced antibonding dipoles. Consequently, the valence band and surface morphology are modified with the corresponding features, and the radial and pairing-row reconstruction arises in the corresponding phases.

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 (Eg) of nanoclusters are independent concepts, because the ϕ depends on the surface electron density while the Eg is a function of the crystal field of the solid. The ϕ and Eg 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 Eg. Reaction with electronegative elements, such as oxygen and nitrogen, widens extrinsically the Eg 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.

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 -1 polarizes and pushes its surface neighbors radially away from the site center, and hence a Ni 5 C cluster forms. Then, sp hybridization of the C happens, leading to a Ni 4 C tetrahedron. Besides the Ni + 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 + ions and the other half to be Ni 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.

It is shown that the model for oxygen chemisorption improves our understanding of the [Formula: see text] surface reaction. The disordered p (2×1)-O precursor is identified as molecule adsorption in which the paired O -1 rests on top of the surface along the close-packed direction. Meanwhile, O -1 polarizes its rest neighbors, leading to the protruding domain boundaries. At higher coverage, c (2×4)-4O and then p (2×1)-2O develop due to O -2 hybridization. O -2 is located at a threefold hollow site and forms a tetrahedron with two Co atoms at the surface and one atom in the second layer. The lack of one atom of bonding is compensated for by an electron cloud of dipoles; namely, a virtual bond forms. The virtual bonding lowers the STM protrusions and narrows the antibonding band.

From the perspective of bond forming, origin of phase-formation on the O-Cu(001) and the O-Cu(110)is analyzed. It is suggested that the formation of the O -1 and the hybridized- O -2 gives in nature the c (2 × 2)-O and subsequently, the [Formula: see text]phase, on the Cu(001). The re-ordering of the primary Cu2O units transforms the Cu(110)-(2×1)-O into the c (6 × 2)-O. As consequences of the O-2 -hybridization, the Cu(001)-[Formula: see text] differs from the Cu(110)-(2×1)-O in origin by nothing more than that the -O-Cu-chain rotates 45° to fit itself to the coordination-surrounding. It proposed that one metal atom may donate more than one-electron to different oxygen atoms. However, one oxygen, with two directional bonding orbitals and two nonbonding orbitals, can never get more than one-electron from a specific metal atom. The sp-hybridization of oxygen cannot occur before its two bonding orbitals are fully occupied. Besides the ionization of oxygen and metal atoms, the polarization of the metal and the hybridization of O -2 dominate the processes of oxidation and the behavior of the oxides. Further considerations are required regarding how the O-coverage reversibly varies the valence-state of oxygen, and how the coverage and temperature reassemble the Cu2O on the Cu(110).

Incorporating the bond-to-band and the potential barrier model [J. Phys. Chem. Solids58, 903 (1997); J. Phys.: Cond. Matt.27, 5823 (1997)] into the existing database reveals that the O-Ru(0001) triphase results from the formation of O -1, hybridized O -2 and the addition of a virtual bond, respectively. Oxygen is located at the center of a tetrahedron, forming a Ru 4 O cluster. Initially (4 O ( O -1+ Ru ++ 3Ru dipole) forms, retaining C 3v symmetry. Then (1/2 ML), the Ru 4 O develops into a Ru 2 O ( O -2+ 2Ru + + 2Ru dipoles) by forming another bond with a surface Ru atom; as a result, a dipole-ion pairing row forms. Finally (1.0 ML), a virtual bond [2Ru(dipoles)+] forms by redistributing the dipole electrons; this process not only reduces the dipole moment but also narrows the antibond subband. The first layer spacing depends upon bond geometry and the second layer spacing contracts due to charge redistribution.

New insight into the nature and formation of the multiphase ordering of oxygen onto threefold sites of fcc(110) (Rh, Pd and [Formula: see text] analogue) is presented. By including bond-to-band model and the potential-barrier for oxygen-metal chemisorption with theoretical and experimental observations, it is shown that the multiphase ordering, composed of (2×1)pmg, (2×1)p2mg and (2×2)p2mg structures, originates from the hybridized- O -2 forming at different oxygen coverages with a specific bonding environment. Unlike the long-bridge sited O -2 ions on the Cu(Ni, Ag)(110) which give the missing-row type reconstruction, the threefold-coordinated O -2 ions on the Rh(Pd)(110) form a tetrahedron through one bond to the metal atom underneath and two nonbonding lone pairs acting on its two neighbors in the first layer. In the (2×1)p2mg structure, the lack of one metal atom for the tetrahedron is compensated by a virtual bond pulling the electron-cloud of the dipoles that are induced by the lone pairs of other O -2 ions. The tetrahedron in the (2×2)pg structure requires an electron from a metal atom in the next nearest row at the surface. Therefore, the bond network interlocks all the surface atoms; and thereby, no atoms are missing. The zigzag protrusions in the STM images are recognized as metal dipoles deformed by the lone pairs of O -2 ions. The depressions correspond to rows of M + metal ions other than missing-row vacancies as had been expected previously.

A bond-and-band model is developed to incorporate the chemical bond and the energy band of nitrides. It is suggested that the symmetrical difference of the tetrahedral bond-structure and the similarity in the energy-band determine the performance of these compounds. The presence of bonding, nonbonding lone-pair and the lone-pair-induced antibonding features are of key importance to these materials. Well acclaimed by existing evidence, this model provided preliminary understanding of the physical properties of some nitrides and oxides and particularly, some insight into the origins of the N-enhanced magnetization, the blue-shift in nitride and oxide light emitting as well as the ultrahard and super elastic materials.

It is shown that the VLEED, furnished with appropriate modelling approaches, is able to reveal comprehensive information about the details of a surface. Constructing Brillouin zones from the critical positions on the angular-resolved VLEED spectra yields information about valence bands and in-plane reconstruction of the O-Cu(001) surface. Decoding the fine-structure features with new models [J. Phys. Chem. Solids58 903 (1997) and J. Phys.: Condens. Matt., C9, 5823 (1997)] rewards us with consistent understanding of the bond formation and its consequences. It is interpreted that the bond forming results in the dislocation of surface atoms, the variation of energy states, the nonuniformity and anisotropy of the potential barrier, and the reduction in both work function and inner potential of the surface.

In order to quantify the behaviour of surface electrons on O-chemisorbed metal surface, as observed wtith STM and STS, we developed a model on nonuniform electrical potential barrier. The new modelling approach contains: (1) the elastic potential, the spatial variation and the energy dependence of the inelastic damping are unified by the electronic distribution; (2) the O-induced spatial-localisation and the nonuniformity in energy-state are taken into effect; (3) the single-variable parameterised functions simplify the numerical optimisation and ensure the uniqueness in solutions. Therefore, crystal structure models can be judged by comparing the shapes of the crystal-dependent-z0(E) profiles that exhibit joint features of topography and spectroscopy.

The modelling analysis herein and corresponding VLEED calculations suggest that the formation of the O -1 and the hybridised- O -1 effects in nature the c(2×2)-O and subsequently the [Formula: see text] phase on the O-Cu(001) surface.