The Studies Of The Physical And Chemical Properties Of The Surface And Interface Of Metal Oxides

The studies of the physical and chemical properties of the surface and interface of solid are a active and multi-disciplinary field and become more and more important with the development of the science and technique nowadays. In the most active field, nanoscience, the proportion of surface atoms increases observably with the materials in nanoscale and the properties of the surface may decide the real properties of the nanomaterials and nano-devices. With the continuous miniaturization of the operational scale of semi-conductor devices, the semiconductor heterojunctions are at the heart of most novel nanometric devices and modern optoelectronic devices. In the field of material science the utilizations of the surface properties are often the ground-work of the diverse applications of the materials, such as sensors, coating materials and catalyst. At the same time the electron exchange, energy exchange, matter exchange and phase transition between the surface and the interface are often the key problems of many physics and chemistry process, material syntheses and biological function. The last tens of years, many powerful characterization methods are created with the development of science and technique and it is possible to obtain all kinds of information of the surface and the interface precisely and directly and get the knowledge of the surface and the interface at the atom level. The first chapter reviews the development history of surface science and diverse surface and interface characterization methods and introduces briefly the properties of the interface and the surface. Some growth methods of surface and interface and new progresses are also recommended. In chapter II surface photovoltage(SPV) technique and the principles are briefly illuminated. Based on the giving equivalent circuit of steady-state SPV measurement, the principle and analysis of MIS mode and analogous MS mode are explained. Combined with the equivalent circuit diagram and principle sketch map of steady-state SPV measurement, the SPV values of c-axis TiO2 single crystal are estimated and compared with the value estimated from photocurrent measurement. The SPV values are obtained by the analogous MS measurement model of SPV and the MIS measurement model of SPV. And the experiment shows that the analogous MS SPV measurement model is similar with MIS SPV measurement model and has higher sensitivity. Furthermore, the analogous MS model can provide sub-gap transition SPV information when biasing a weak dc field. And the weak dc field is of no effect on MIS model SPV and photocurrent signal. The weak dc field works in localized state transition and can not affect delocalized transition. On the other hand the sub-gap transition SPV has different carrier separating mechanism with super-gap transition SPV. Moreover, the R, X, Y and phase values from the lock-in can be collected synchronously and this extends the information of SPV measurement. In chapter III the application of SPV technique in the analysis of the interface is introduced and some films were characterized by SPV technique. TiO2, SnO2 thin films and the composition films of them of different thickness were formed on p-type Si substrates by sol-gel methods. Their SPV properties are varied much with different thickness. When the film is very thin, the Si and TiO2 represent their own SPV properties respectively. This means that the interaction between the upper films and the interface states is weak. While increasing the thickness of the films, the interface states may become adominant factor in SPV properties. It is due to the interaction between the upper films and the interface states is strong. Further experiment the interaction between the upper films and the interface states is dominated by the charge densities of the upper films. The experiment also shows that SPV technique is sensitive to buried interface as to the external surface. Though the components of the composition films are the same, the SPV responses are very different. This shows that the difference in the interface, the thickness of the film, the surface state and the composition way all can influence the SPV charaterization. In chapter IV vanadium oxide sol solutions are prepared through pouring melten vanadium pentoxide into deionized water while being stirred. The gelation behaviors on fused silica, sodium silicate glass and mica substrates are studied and it can be seen that the acid-base capacity of the substrates can influence the water content and the distance of the plane of the xerogel. And the syntheses and properties of V2O5 films on different substrates are studied. The obtained nanoparticles films on the ITO and Pt sheet show good electronic conduction for the mixed valence of the nanoparticles and the I-V curves of the films measured by AFM of current measurement model are like that of the metal. The conduction of the film is determined by the surface and crystal boundary properties of particles. However, particles in the micrometer scale are formed on Si and fused silica substrates and the film on Si substrate shows a rectified characterization and the conduction of the film is determined by the bulk properties of particles. At the same time, fine VO2 films are produced on fused silica substrate by heat treated the xerogel films in a low vacuum and low pressure H2 condition at 570oC. The films show good thermalchromatic properties in near IR scale and take a semiconductor to metal phase transition at 68oC. One-dimensional (1D) nanostructured materials including nanorods, nanotubes,...