Liu Hong

By Hong Liu

This chapter mainly introduces five basic stages of the film deposition process (vapor adsorption, surface diffusion, reaction between adsorbed species, reaction of film materials to form bonding surface, and nucleation and microstructure formation), analyzes the influence of deposition process parameters on the three basic growth modes of the film, focuses on the relationship between the control parameters of homoepitaxy and heteroepitaxy and the film structure, gives the dynamic characteristics of each growth stage, and examines the factors determining epitaxy film structure, topography, interfacial properties, and stress. It is shown that two-dimensional nucleation is a key to obtain high-quality epitaxial films.

Part of the book: 21st Century Surface Science

By Hong Liu and Chunlan Ma

The research in the field of laser-induced materials processing is evolving continuously with new inventions in laser technology. This chapter mainly discusses the relevant physical mechanisms of laser ablation based on laser-matter interaction. Femtosecond laser excitation provides suitable conditions for studying the basic processes in irradiated materials, as compared to the duration of these processes, femtosecond laser pulses are sufficiently short. In the process of laser action on the matter, the thermal mechanism, charge carrier removal, thermal and structural effects, and other processes are extremely complex. The ultrashort laser pulse instantly puts the material in a strong nonequilibrium state characterized by hot electrons and cold ions. After the pulse ends, the electron transfers its energy to the ion through electron phonon coupling in sub-picoseconds. This heats up the phonon bath before the slow thermal effect can reconstruct the material. The electron effect plays an important and possibly dominant role in the laser ablation of nonmetallic solid surfaces. This review first describes the mechanism of laser-matter interaction from the perspective of energy, summarizes the electronic excitation and energy relaxation paths of light on semiconductors and dielectric materials, focuses on the electronic excitation and relaxation mechanisms in laser-induced ionization, desorption, and ablation, and finally analyzes the above-mentioned related processes from the perspective of material structure relaxation.

Part of the book: Laser Ablation

By Hong Liu and Xinli Cheng

Thermoelectric materials can directly convert thermal energy into electrical energy. Although the low efficiency of thermoelectric devices limits their use in the professional market, the development and improvement of condensed matter physics theory, as well as the emergence of various new material synthesis processes, have brought new research and development momentum to the utilization of thermoelectric materials. This chapter first starts from the basic theory of thermoelectricity, introduces the thermoelectric transport equation and the Boltzmann transport equation that controls phonon and electron transport, and then reviews the strategies to further improve the thermoelectric properties of materials in the past two decades. and evaluated the effectiveness and universality of existing strategies, pointing out their limitations. Subsequently, based on the superconducting Bardeen-Cooper-Schrieffer (BCS) theory and phonon drag effect, this chapter proposes a new physical paradigm different from the phonon-glass-electron-crystal method. The core of the new paradigm is to shift from decoupling the electron-phonon transport process to optimizing the electron-phonon coupling mechanism and provides a theoretical mechanism for improving the performance of thermoelectric materials by optimizing the electron-phonon coupling. Identified the material design concepts and challenges for implementing the new paradigm.

Part of the book: Advanced Thermoelectric Materials