Currently, researchers' research focus on gas sensors mainly includes the development of gas sensing materials, exploration of sensing mechanisms, design of devices for conducting electrical signals, and improvement of gas sensing performance testing techniques. In these aspects, the development of gas sensing materials, which are the core content of gas sensor research, is particularly crucial.

At the beginning of the 20th century, people began to explore the gas sensing properties of semiconductor materials. The earliest gas sensing materials were mainly metal oxides, such as zinc oxide (ZnO), tin dioxide (SnO2), etc. These materials have good chemical stability and electrical properties, and can produce sensitive responses to gases such as oxygen and carbon monoxide in air. With the increasing demand for gas sensors, researchers have begun to explore new types of gas sensing materials. In addition to metal oxides, semiconductor materials, metal organic frameworks (MOFs), carbon based materials, and other materials have been introduced into the field of gas sensors. These new materials have higher sensitivity, better selectivity, and a wider range of applications.

The characteristics of gas sensitive materials are closely related to their surface chemical composition, phase structure, microstructure, and stress state. Therefore, surface modification can be used to optimize the physical and chemical properties of materials. Plasma treatment is a method of treating material surfaces through high-energy electrons, ions, excited molecules, etc. It is widely used in surface modification, functionalization, and reinforcement of gas sensitive materials and composite materials.

Plasma processing technology

Plasma is the fourth form of matter besides solids, gases, and liquids. It is composed of atoms, molecules, ions, and positively and negatively charged free radicals. Plasma can be divided into high-temperature and low-temperature plasmas based on particle temperature. When the electron temperature and ion temperature are equal, it is called high-temperature plasma, and when they are not equal, it is called low-temperature plasma. Plasma treatment technology is a means of modifying the surface of materials by using the particles contained in them to react with the material, causing complex physical and chemical changes on the surface, quickly creating defects or introducing doping on the material surface. The advantage of this technology is that it not only avoids high temperatures and prolonged reactions, but also does not damage the nanostructure of the material itself. Therefore, plasma treatment has a wide range of applications in material synthesis and surface modification in different fields.

Through plasma treatment, the surface of gas sensitive materials can be activated or functionalized, improving their interaction with gas molecules and thereby enhancing the response performance of gas sensors. This technology not only enhances the surface activity of materials, but also precisely regulates their pore structure and key characteristics such as surface hydrophilicity or hydrophobicity, thereby further optimizing the selectivity and stability of sensors. Therefore, the application of plasma technology in gas sensors has become an important direction of current research.

In the process of oxygen plasma treatment, oxygen molecules are ionized into active substances such as oxygen ions and oxygen radicals. When these active oxygen species react with the surface of gas sensitive materials, they can partially remove the oxygen atoms on the surface and form oxygen vacancies. Oxygen vacancies are lattice defects that lack oxygen atoms and typically increase the conductivity of materials, as they increase the electron concentration in the material. For metal oxide gas sensitive materials, the number of oxygen vacancies directly affects their gas sensitivity. The more oxygen vacancies there are, the higher the sensitivity of the material to gases. In addition, oxygen plasma treatment is a low-temperature process that does not cause thermal damage to materials, making it particularly suitable for temperature sensitive gas sensitive materials such as nanomaterials, thin film materials, etc. This gentle modification method avoids material performance changes or structural damage that may be caused by high temperatures.