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Temperature effects on the contact electrification (CE) is of great interest. Here, different kinds of substoichiometric oxide films, such as TiO2-x, Al2O3-x, Ta2O5-x, and Cr2O3-x, are deposited and annealed at different temperatures, and the CE between the films and a Pt-coated tip is performed by using Kelvin probe force microscopy (KPFM). An intriguing finding is that the polarity on the TiO2-x surface changes from negative to positive with the increase of the sample annealing temperature in air atmosphere. Such a result is attributed to the fact that annealing under an oxidative atmosphere repairs oxygen vacancies and helps upgrade the low valency of Ti3+ to a stable high valency of Ti4+. On the contrary, after annealing occurs in an Ar/H2 atmosphere, the polarity on the TiO2-x surface reverses from positive to negative. This is mainly due to the increase of oxygen vacancies after annealing in reducing atmosphere. Through the KPFM results of Al2O3-x, Ta2O5-x, and Cr2O3-x films, the effect of oxygen vacancies is further confirmed, that is, the decrease of oxygen vacancies eases the films at capturing positive charges. Based on this, TiO2-x-based identical material triboelectric nanogenerators (IM-TENGs) are designed and prepared for the first time to control the current direction. Moreover, a surface state model for explaining the CE mechanism between the metal and annealed dielectric is proposed. This study is conducive to the development of the IM-TENGs which regulate the current direction or voltage output accurately in the future and also provides a further understanding of the dominant mechanism of electron transfer in the CE.

Description, The contact-electrification induced interface photon emission spectroscopy is revealed by electrons transfer at the interface., Contact electrification (CE) (or triboelectrification) is the phenomena where charges are produced through physical contact between two materials. Here we report the atomic featured photon emission spectra during CE between two solid materials. Photon emission provides the evidence that electron transfer takes place at the interface from an atom in one material to another atom in the other material during CE. This process is the contact electrification induced interface photon emission spectroscopy (CEIIPES). It naturally paves a way to a spectroscopy corresponding to the CE at an interface, which might impact our understanding of the interaction between solids, liquids, and gases. The physics presented here could be expanded to Auger electron excitation, x-ray emission, and electron emission in CE for general cases, which remain to be explored. This could lead to a general field that may be termed as contact electrification induced interface spectroscopy (CEIIS).

In this study, three different types of ZrO

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.

In this study, different sol-gel Nb2O5 films were prepared by using NbCl5 as precursor, and acetylacetone (ACAC), diethanolamine (DEA) and citric acid (CA) as additive, respectively. The results showed that the film with ACAC as additive presented the highest absorption and stability, corresponding to the lowest laser-induced damage threshold (LIDT) of 18.9 J/cm2, while that with CA as additive had the lowest absorption, corresponding to the highest LIDT of 24.9 J/cm2. The film prepared with DEA as additive had the smallest surface roughness, and the LIDT was 21.1 J/cm2. Moreover, although the films prepared with three different additives were all subjected to typically defect-induced damages, different types of damage features were observed. Finally, three structural evolution models of the films were proposed, accompanied by establishment of the relationship between the additives and the LIDT, which was of great significance to further understand the laser damage mechanism.

Using TaCl5 as the precursor, two types of Ta2O5 sols were synthesized with employment of different dual additives, namely, diethanolamine (DEA) with acetylacetone and DEA with polyethylene glycol (PEG). The prepared sol-gel Ta2O5 films were featured by the low surface roughness, high transmittance, low absorption and high laser-induced damage threshold (LIDT). The highest LIDT of 29.1 J/cm2 was obtained in the film prepared with the DEA and PEG additives. This should be attributed to the chelation effect of DEA and the steric hindrance imposed by PEG, which synergistically resulted in a more regular three-dimensional network structure and consequently lower film internal defects. In the case of temperature increase to 150 °C, the LIDT levels of both the films decreased. The damage morphologies indicated the defect-induced mechanism for the films irradiated either at the room temperature, or at the high temperature of 150 °C. Moreover, an evolution model was proposed to reveal the effect of dual additives on the structure of Ta2O5 films. This study was conducive to a better understanding of the fundamental laser damage mechanism and exploring the potential application of sol-gel films in high temperature environment.

In this study, three different types of ZrO2 films were prepared with different precursors and additives using the sol-gel method. High-temperature annealing was implemented to investigate the impact of temperature on optical properties, microstructure, surface morphologies and absorption of these films. According to the laser-induced damage threshold (LIDT) tests on films having experienced annealing and those implemented with in-situ high temperature, the ZrO2 film with ZrOCl2·8H2O as the precursor and copolymer of silicone and polyaldoxyl ether as the additive had the highest resistance to laser-induced damage. After annealing at 623 K, its LIDT was 21.4 J/cm2, while that at an in-situ high temperature of 523 K was 23.9 J/cm2. The strong high temperature resistance was likely attributed to the usage of carbon-free precursor and high temperature-resistant additive, which contributed to low carbon contents and less structural damage caused by organic matter evaporation. In this context, there were less high temperature-induced impurity and structural defects, leading to higher LIDT values. This study provided a novel method for preparing high temperature-resistant sol-gel films, which shed light upon wider potential application of sol-gel films at high-temperature conditions.