Study On Non - Equilibrium Characteristics Of Interfacial Electron Transfer In Nano - Composite Photoelectric Materials

Energy and environmental issues are the bottlenecks of the development of economics. Due to the quantized structure and high range of surface, and exhibited abundant optical, electric and magnetic properties, nanomaterials is one of the potential materials to avoid the bottlenecks. For the limits of single nanomaterials,many nanocomposites have been prepared for synergistic using of their individual excellent properties. Now, nanocomposites have presented good prospects for development in some important areas like catalysis chemistry and molecular electronics.There are plentiful surface, interface and interaction between them in the nanocomposites. The interactions always contain multi-sale coupling. The order and ?uctuation of coupling are range from ?uctuation mediums to mesoscale stuctures. Also, the atomic bonds and electron distributions are discrete at quantum and atomic scales. Although there are many achievements in experiment,naonocomposites are prepared or controlled in ”try-error” manner. Therefore, the simulations of complex surface-interface interactions in nanocomosites are very important.The key points of theoretical research on nanocomposites are focus on the following two aspects. First, get the key factors for controlling its properties.Second, get the connection with experiments for the potential rational design of nanocomposites. In consideration of them, the works in this dissertation can be divided into two groups. Based on density functional theory(DFT), we have computed the electronic structure of several kinds of nanocomposites with typical applications. Through the systematical analysis, especially the interface electron transfer driven by the large work functions di?erence, we got the critical factors a?ected its properties and designed di?erent functional nanocomposites. In the other hand, based on the simulation of spectroscopies, we probed the local electronic structure using X-ray and inelastic electron tunneling spectroscopy(IETS).The local geometry information and electronic structure could be able to get and use as a maker for di?erent nanocomposites. This can contribute the correlation of various experiments. On the other way, the signal resolution of complex spectrum could provide crucial conformations.In the ?rst chapter of this dissertation, we introduced the background and applications of nanocomposites in various ?elds. The achievements have been presented at three aspects, the preparing and controlling of nanocomposites, the spectroscopy characterization of surface-interface interactions, and the properties and mechanism’s simulation. Then we pointed out the key questions in theoretical simulations. How to combine the classical model and quantum mechanics? How to describe the force ?elds and energy between ?uctuation mediums and mesoscale mater? Coupling between the move of surface atom con?gurations(align of atom, molecular structure) and the dynamical evolution of micro quantum sates(electron, photon, phonon and exciton). In one word, the key point is how to describe the interface electronic state in a more reliable way in nanocomposites.In the second chapter, the computational methods of electronic structure and related properties in nanocomposites were introduced brie?y. The backgrounds and main approximations were presented ?rstly, and then we pointed out that how to treat the electronic correlations is the key of modern electronic structure theory. At last, the methods for post-process of electron structure calculations and the computational procedure of electron transport and IETS in molecular devices were described step by step.In 3thchapter, focus on the key issue, reduced the usage of Pt metals, in hydrogen evolution reaction(HER), we designed Pt-Pd-r GO ternary nanocomposites and studied its multiple surface-interface interactions systematically. We found that surface polarization which is caused by electron transfer driven by work function di?erence is the crucial factor for HER enhancement. The HER performance of these hybrid structures turns out to have a strong correlation with the shell thickness. Combing with the experiments, the surface polarization mechanism have been demonstrated, which provided a possible manner for the designing of composite catalyst.In the 4th, to design the suitable electro-catalyst at micro-scale and control the catalysis reaction process and mechanism at molecular scale, we built a series of Pt Au alloy catalysts by deposited some Pt atoms onto Au(111) surface. Also, various reaction HCOOH oxidation pathways were studied in aqueous phase.Based on the average potential alignment and electron transfer analysis, we con-?rmed that the Pt is existed as activity center, and found that Pt non-equilateral doped Au(111) surface is the favorite catalysts.In the 5thchapter, we found that both of the Schottky barrier and charge spatial distribution are critical elements to the electron–hole separation and charge accumulation at surface, and highly dependent on semiconductor facets in a semiconductor–metal con?guration. These two e?ects can be reconciled in a singlefaceted con?guration by taking advantage of high work function of semiconductor surface. To achieve better e?ciency, the establishment of the Schottky barrier has to be prioritized by selecting an appropriate surface facet for metal deposition and charge migration sites, meanwhile the photoexcited electrons should be allowed to migrate out from this facet by virtue of the charge spatial distribution. This conclusion provided a possibility to design photocatalyst using the facet e?ect of semiconductors.In the 6thchapter, to probe the local electron structure of nanocomposites, we studied the ?exible molecular junctions and azafullerene using spectroscopy. By using IETS, we have demonstrated that the IETS of BPE MJ is sensitive to the molecular conformation and can be used to extrapolate key geometric parameters.By examining the molecular vibrational modes and selecting several of them as the reference point, we have evaluated the contributions of local vibrations to the IETS intensity. A linear dependence of IETS on the sinusoidal function of molecular angles and lengths of atomic bonds has been established. This provides the opportunity to quantitatively measure key geometric parameters with IETS,and built up a theoretical procedure to extract precise geometric information from the complicated IETS measurements. In the last work, we conformed that the azafullerene and its derivatives have various response to X-ray. It can provide the information of molecular orbitals. In particular with the help from theoretical simulations, we can gain an in-depth understanding of the individual peaks in the experimental spectra and their relationships with the electronic and geometric structures of the investigated molecules.In the 7thchapter, we have drawn an simply conclusion of this dissertation and pointed out some open questions.As a summary, starting with the interface electron transfer, we investigated the special surface electronic state formed by the carriers migration driven by work function di?erence of unequal materials in nanocomposites, and found that the surface polarization e?ect, the ensemble e?ect of surface electronic state and the synergism of Schottky barrier and charge spatial distribution play particular roles in the performance of nanocomposites. Through the resolution of complex spectrum signals, we found the intensity of IETS signals of BPE molecular junctions are linear dependent with the change of the center angle and the correlations between the X-ray, azafullerene and its derivatives. Above conclusions are provided e?ective methods for rational design, practical ways for conformations and performance controlling of nanocomposites, which brings us the possible applications in the energy and environment issues.