ABSTRACT
Plasma science and technology have fundamental importance in the modern electronics, aerospace, metallurgical, biomedical, and waste treatment industries. Many of the plasma processing applications were developed in recent decades in order to fulfill ever-growing demands of technology applications. A huge variability of plasma processing has led to new discoveries that can only be achieved using plasma-related methods. This fact is also attributed to the fast development of plasma science. It has, in turn, opened up new avenues of basic science, in particular the nonlinear dynamics or science of chaos. Understanding the complex behavior of confined plasmas has led researchers to formulate the fundamental equations of plasma physics that resulted lately in important advances in fields as diverse as computers, lighting, waste handling, space physics, switches, relays, and lasers. Studies of high-intensity laser interactions, new highly efficient lighting systems, and plasma-surface interactions in materials engineering have become important for various applications where the usage of traditional technologies were obviously limited. Plasma applications have also attracted an interest due to their potential in reduction of energy consumption and waste productions in major industrial processes. Most of the research work mentioned in this book is based on low-pressure plasma technology as an environmental friendly and cost-efficient technique for modification of surfaces of traditional materials on
a microscopic level. Surface modification and deposition of thin films have gained an enormous interest in the last years to enhance functional properties of traditional bulk materials. As an alternative technology to chemistry and metallurgy, it is widely used for preparation of new materials with new possibilities. In addition, plasma technologies have opened new perspectives in material production and development of completely new applications. Indeed, thin-film processing represents a highly versatile method of manufacturing new advanced materials of a highly metastable nature exhibiting exceptional properties. 2.1 Principles of Plasma DischargesA plasma is a collection of free charged particles, such as electrons, positive and negative ions, atoms or molecules, moving in random directions (see Fig. 2.1a). On the average, a plasma is electrically neutral. It is caused by electric fields that eliminate any charge imbalances in the plasma discharge by the charge rearrangement. As a result, the density of electrons together with negative ions in a plasma is equal to the density of positively charged ions. Plasma is also called a fourth state of matter. While a solid substance is in thermal equilibrium, it generally passes into a liquid state with increasing temperature, further into a gas and at a sufficiently high temperature the molecules in the gas decompose to form a gas of atoms that move freely in random directions. If the temperature is further increased, the substance enters the plasma state consisted of freely moving charged particles. It similarly happens in the plasma discharge. However, low-pressure plasma discharges are far away from thermal equilibrium since they are electrically driven and the applied power preferentially heats the mobile electrons with the mass much lower than the mass of ions. Hence, Te » Ti in plasma discharges. Consequently, the electrons promptly accumulate sufficient kinetic energy to have a high probability of producing excitation or ionization during collisions with heavy particles. On the other hand, the heavy ions exchange their energy mostly by collisions with the background gas. The degree of ionization is an important parameter of a plasma discharge, which represents the fraction of the original neutral atoms and molecules which have
become ionized. A weakly ionized plasma is that one which has only a small fraction of the gaseous species ionized with the rest being neutrals. Then, the high number of neutrals determines the behavior of this type of plasma commonly used for film deposition.
