The term plasma was originally defined by Irving Langmuir in 1928. In a special gas state, at least one electron breaks free from the confinement of an atom and forms a charged particle, namely an ion. The degree of ionization in this gas can vary greatly, from complete ionization to only partial particle ionization. Plasma not only contains various charged particles such as positive and negative ions, but also many non ionized neutral components such as atoms, molecules, free radicals, and particles in excited states. These excited state particles are capable of emitting light, which is the source of plasma luminescence characteristics. The interactions between these components endow the plasma with high reactivity, making it a dynamic and complex chemical environment. Due to its high activity, plasma has shown extensive potential for applications in various fields. In the field of materials science, plasma is used to deposit thin films, alter material surface properties, and manufacture nanomaterials. In the microelectronics industry, plasma technology is applied to the manufacturing process of microchips. In addition, the luminescent properties of plasma make it applicable in light sources, lasers, and display technologies. The multifunctionality of plasma has also extended to environmental and medical fields, such as disinfection, wound treatment, and even demonstrated its potential application value in cancer treatment. With further research on the physical and chemical properties of plasma, it is expected that more innovative applications will be discovered.

Plasma is often referred to as the "fourth state of matter", as shown in the figure. It is a special form of ionized gas composed of electrons and cations, which originate from the transformation of neutral atoms or molecules. In plasma, significant heat is generated due to the internal resistivity of the system, leading to further dissociation of gas molecules into atomic states. As the temperature increases, electrons are more easily detached from atoms, a process called ionization, which produces a large amount of high-energy and highly reactive substances in the plasma. In plasma, the density of electrons and positive ions is roughly equal, thus forming a quasi neutral state. Electrons, due to their light weight and high mobility, will first acquire energy under the action of an electric field, becoming the key source of energy supply in plasma chemistry processes. Electrons are fundamental particles with a negative charge, and their mass is much smaller than ions and neutral particles, about three to four orders of magnitude lighter. Electrons, due to their large number and sufficient energy, can maintain the chemical activity of plasma. After obtaining energy, electrons will transfer it to other components in the plasma, providing necessary energy for ionization, excitation, dissociation, and other plasma chemical processes. This energy transfer process can be described by the Electronic Energy Distribution Function (EEDF). The ionization process is mainly divided into five types: ionization directly caused by electron shock, gradual ionization caused by electron shock, ionization caused by collision of large mass particles, ionization caused by light, and ionization caused by surface. These processes collectively constitute the complex chemical and physical properties of plasma, making it of significant value in scientific research and industrial applications.

Plasma state of matter

The principle of plasma technology

The ionization reaction in plasma technology is shown in the figure, which was proposed by Fridman and Kennedy and mainly involves the chemical reaction kinetics in plasma, especially the ionization mechanism in plasma processing and material synthesis processes. It focuses on the ionization process caused by the collision of electrons with molecules or atoms in the plasma, as well as the impact of these processes on the chemical and physical properties of the plasma. In plasma chemistry, ionization process usually refers to the collision of electrons with molecules or atoms, resulting in the detachment of electrons from atoms or molecules, forming positive ions and free electrons.

Ionization reaction

Glow discharge plasma is a plasma state generated through the phenomenon of glow discharge. Glow discharge usually occurs in low-pressure environments. When a voltage is applied between two electrodes, electrons and ions are generated. These charged particles interact with gas atoms or molecules, causing gas ionization and forming plasma.

Application of plasma treatment technology

Plasma treatment technology is an advanced dry treatment method that utilizes active particles (including high-energy electrons, ions, and photons) in the plasma to react with the material surface, thereby altering the chemical composition and morphology of the material surface. Plasma is composed of partially ionized gases, where the number of free electrons and positive ions is roughly equal, making it a conductor and responsive to magnetic fields. The application of plasma technology mainly includes the following aspects: firstly, plasma treatment can cause four main surface effects, including surface cleaning, surface etching, molecular cross-linking near the surface, and changes in surface chemical structure. 2、 Electron collisions and photochemical reactions can lead to molecular separation, producing a plasma containing high-density free radicals that can cause the breaking of chemical bonds on the surface of materials, forming new chemical substances. 3、 Plasma treatment can introduce new functional groups on the surface of materials, such as hydroxyl (- OH), aldehyde (- COOH), and carboxyl (- COOH), which can alter the wettability of materials and facilitate molecular processing. 4、 In addition to changes in chemical structure, plasma treatment can also lead to changes in the physical properties of the material surface, such as changes in surface morphology. 5、 Plasma technology is a low-temperature, dry, and environmentally friendly treatment method suitable for the development of new materials and fields, which can achieve effects that traditional treatment methods cannot achieve. Plasma technology has become an effective tool for material surface treatment due to its unique physical and chemical properties, and is widely used in fields such as surface cleaning, etching, activation, coating, and modification.