| In recent years, a large number of fascination phenomena of low-dimensional nanomaterials have been found by intensive experimental studies. However, fundamental progress in theory is lagged far behind the experimental exploitations for the classical approaches such as continuum medium mechanics and the quantum approach encounter some difficulties. Therefore, a model to overcome the limitations encountered in both approaches and to understand their physical origin and predict general trend of material properties with size reduction is highly demanded.Nanomaterials are different from the corresponding bulk and single atom due to high fraction of atoms with low coordination number and its interaction. Recently-developed bond order-length-strength (BOLS) correlation mechanism establishes a series models from the perspective of from the perspective of bond making and bond breaking. It can explain the origin of nanomaterials various astonishing behaviours, and provide the rules of size effect. BOLS correlation mechanism is based on the bond-order-length (BOL) premise of Pauling and Goldschmidt, and extended to the energy space. The core idea of BOLS correlation mechanism is that the under-coordinated atoms have less atomic bonds connecting with adjacent atoms, which causes the remaining bonds to contract spontaneously together with bond strength enhancement. Then, local strain and quantum trapping are formed immediately at the sites surrounding the under-coordinated atoms. Consequently, Hamiltonian and cohesive energy are modified, which change the detectable properties from the physical origin, such as the expansion of Youngs modulus, bandgap blueshift, melting point decreasing and etc. BOLS correlation mechanism provides us a consistent understanding on the variation of various materials properties. It has been successfully predicted the nanomaterials properties with the shape and size.This thesis mainly discusses three issues using the method of incorporating the BOLS correlation mechanism into the high-resolution X-ray Photoelectron Spectroscopy (XPS) measurements:(â…°) the size and composition dependent band gap of semiconductor nanomaterials; (â…±) the physical mechanism of surface and nanomaterials'core level shifts; (â…²) the physical origin of apparently anomalous behavior of catalyst metal alloy in catalysis process. The detailed work and results achieved are as follows:1. We present an atomistic insight into the joint effect of size- and composition-induced band-gap change of semiconductive nanocompounds based on the BOLS correlation mechanism. An analytical solution has been developed to connect the band-gap energy with the bonding identities (bond order, bond length, bond strength and bond nature) of the nanocompounds. Agreement between the model predictions with the available experimental measurements of band-gap change of II-VI semiconductor nanocompounds showed that both the particle size and the composition can be used as factors tuning the band-gap energy, suggesting an effective way to realize the desirable properties of semiconductive nanocompounds.2. We have analyzed atomic-layer and crystal-orientation resolved binding energy shift of FCC (Rh and Pd) and HCP (Be and Ru) metal using the method of combining the BOLS correlation algorithm with the high-resolution XPS measurements. It has turned out with the following information:(â…°) the energy levels of an isolated Rh (3d5/2:302.163 eV), Pd (3d5/2:330.261 eV), Be (1s:106.40 eV) and Ru (3d:275.883 eV) atom and their respective bulk shifts (4.367,4.359,4.72 and 3.661 eV); (â…±) the layer-and orientation-resolved effective atomic coordination, local strain, quantum trap depth, binding energy density and atomic cohesive energy of the surface sublayers; (â…²) the physical origin for the surface induced positive core level shift. It has been clarified that the binding energy shift arises from the perturbation in the Hamiltonian by the shorter and stronger bonds between under-coordinated atoms and hence the fascinating behavior of surface electrons.3. The extremely-high catalytic efficiency of under-coordinated metal adatoms is indeed fascinating but its electronic origin remains yet puzzling. Incorporating the BOLS correlation theory into the high-resolution XPS measurements has affirmed the BOLS expectations that the broken bonds induce local strain and quantum trapping in addition to polarization of the otherwise conductive half-filled s-shell charge by the tightly- and densely-trapped inner electrons of the adatoms. Both the trapped and polarized states would be detectable from the density-of-states evolution of the valence and the core bands. The trapped states have been discovered at the bottom edges of Pt (5d106s0) 4f7/2 and Rh (4d85s1) 3d5/2 bands and the polarized states only present at the upper edge of Rh (4d85s1) 3d5/2. It is suggested that the quantum trapping will increase the electroaffinity and the polarization do oppositely. Therefore, the Rh adatom may serve as a donor and the Pt adatom as an acceptor in the process of catalytic reaction. 4. Analysis of the 2p3/2 core-level shift of Fe surface and nanoparticles based on the BOLS correlation has turned out that the Fe 2p3/2 energy shifts positively by 2.17 eV from the atomic value of 704.52 eV to the bulk of 706.69 eV and that a further 0.32 and 0.16 eV shift occurs, respectively, to the top and the second atomic layers. Consistency between theory and experiments clarifies the dominance of the broken-bond-induced local strain and quantum trapping in perturbing the Hamiltonian and hence the observed Fe 2p3/2 energy shifts.5. AgPd and CuPd alloys are important catalysts that perform very differently with physical origins being still undetermined. Using X-ray photoelectron spectroscopy we examined the density-of-states evolution of the valence and the Cu 2p, Ag 3d, and Pd 3d core bands during the alloying process of ultrathin Cu and Ag films deposited separately on Pd substrates. We found that the valence and the core electrons of the CuPd alloy shift positively, opposite to the occurrences in the AgPd alloy catalyst. This finding may distinguish the CuPd from the AgPd in the catalytic reactions, indicating that CuPd serves as an acceptor due to quantum trapping and the AgPd as a donor because of charge polarization.The consistency of theoretical study and experimental observations confirms that the shorter and stronger bonds between under-coordinated atoms induce local strain and the skin-depth charge and energy quantum trapping, and hence dictate globally the band gap blueshift and positive core level shift. Current progress in BOLS correlation mechanism and its combination of XPS measurements can extract some quantitative atomic information from XPS spectrum, which is beyond the scope of the conventional approaches. It provides a new way to study the band structure of low-dimensional nanomaterials and predict the trend by considering the bond identities variation, associated energetic response of corresponding atoms and electrons, and the consequences on the measurable quantities. It could pave a path to bridge the classical approach in macroscopic system and the quantum approach in atomic level.
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