In recent years, low-temperature plasma surface modification has been widely used in material modification due to its excellent characteristics such as fast, efficient, pollution-free, simple operation, and energy saving.

Plasma is not composed of a single species, it contains multiple types of substances, such as free radicals, neutral or excited molecules or atoms, and positive and negative ions. The production of these substances requires ionization of gases under special conditions. Due to the fact that the number of positive and negative charges inside the plasma system is basically equal, the entire system is electrically neutral. Plasma is a form of material existence that differs from the common solid, liquid, and gas states in nature. It is the fundamental form of existence for the vast majority of matter in the universe and is considered the fourth state of material existence, namely the plasma state. Due to factors such as high temperature, electromagnetic fields, and high-energy beams, gases in the environment can obtain energy and undergo partial dissociation and ionization, forming ions and free electrons. With the strengthening of applied conditions, the density of charged particles in ionized gas will increase, that is, the ionization degree will rise. Most plasmas are partially ionized gases, such as ionosphere, lightning, and plasmas generated through heating, external electric fields, and laser irradiation, all of which have low ionization degrees.

According to the charge density and generation temperature of plasma, plasma can be divided into two categories: high-temperature plasma and low-temperature plasma. Among them, low-temperature plasma is the most widely used method in modifying materials.

Characteristics of low-temperature plasma surface modification

The characteristics of low-temperature plasma mainly include the following two aspects: (1) the electron energy present in the system is extremely high, which can excite the molecules on the surface of the material, thereby promoting the ionization of these activated molecules; (2) During the discharge process, the temperature of the reaction system is extremely close to room temperature, overcoming the disadvantage of high temperature reaction conditions required for traditional high activation energy chemical reactions.

Compared with other methods, low-temperature plasma modification method has other advantages: (1) there is no solvent involved in the entire modification process, the utilization rate of modified samples is extremely high, almost no waste is generated, and it will not cause secondary pollution to the environment; (2) Compared to other high-energy radiation treatment methods, low-temperature plasma modification methods do not cause damage to the material itself, and the surface thickness of the material they can treat is only tens to thousands of angstroms. Therefore, new properties can be endowed to the original material without changing its excellent properties; (3) This method has no strict requirements for the substrate material, and almost all solid materials can be treated by low-temperature plasma. It has a wide range of applications, short surface treatment time, and low cost.