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Using Kelvin probe force microscopy, we studied the contact-electrification (CE) induced charge density on the surfaces of organic–inorganic composite oxide films, such as Nb2O5, ZrO2, and HfO2 films, prepared by a sol–gel method and annealed at different temperatures. The results show that positive triboelectric charges on the film surface gradually turn into negative ones with the increase in the annealing temperature. This phenomenon is attributed to the broken valence bonds between organics and organic–inorganic composites in the film at high temperature, which causes oxygen vacancy defects and consequently changes the surface states of the film. A surface states model is established to understand the process of CE, which further confirms that electron transfer is the dominant mechanism of CE. Moreover, it indicates that in addition to oxygen vacancies, there are also many other factors that can influence CE, including but not limited to non-stoichiometric ratios, impurities, and other types of defects. These factors will modify the surface states through changing the potential barrier energy of the bound electrons on the surface and thus impact the amount and even the direction of electron transfer. [ABSTRACT FROM AUTHOR]

Contact electrification (CE) is one of the oldest topics in physics, which has been discussed for more than 2600 years. Recently, an overlapped electron‐cloud (OEC) model was proposed by Wang to explain all types of CE phenomena for general materials in which a deep overlapping of electron clouds belonging to two atoms results in a lowered potential barrier for electron transfer from one to the other by applying a compressive force, which is simply referred to as Wang transition for CE. Here, the degree of electron‐cloud overlap between two atoms is controlled by using tapping mode atomic force microscopy. A temperature difference and electric field are applied between atoms of two surfaces. It is found that electron transfer only occurs when the contact tip and sample interact in the repulsive‐force region, which corresponds to a strong overlap of the electron clouds. Such a fact even preserves if the tip is at a higher temperature than the sample for 120 K. Alternatively, by applying a bias, electron tunneling would occur when the tip is in the attractive‐force region within which normal electron transfer would not occur. These studies solidify the overlapped electron‐cloud model first proposed by Wang. Further, the temperature and bias effects on the CE are explained based on a modified OEC model. [ABSTRACT FROM AUTHOR]