Research On The Contact Electrification Characteristics And Influencing Factors Of Oxide Thin Films

The widespread application of triboelectric nanogenerators also makes people gradually pay more attention to an ancient phenomenon,namely contact electrification.As one of the oldest scientific problems today,the discovery of contact electrification has been over 2,600 years ago,but there are still some specific mechanisms that need to be further explored and revealed.Among them,great attention is being paid to investigating the influence of temperature on contact-electrification.First of all,Nb₂O₅?Zr O₂?Hf O₂ and Si O₂ oxide films were prepared by the sol-gel method,and the viscosity of the colloid,the transmittance of the film,and the surface morphology characteristics were studied,which laid a solid foundation for the subsequent exploration of the contact electrification characteristics and influencing factors of the organic-inorganic composite film prepared by sol-gel method.Then Kelvin probe force microscopy was used to study the electrification characteristics of the above-mentioned Nb₂O₅,Zr O₂,Hf O₂ and Si O₂ films.The KPFM results show that positive triboelectric charges on the film surface gradually turn into negative ones,as the annealing temperature increases.This phenomenon is attributed to broken valence bonds of organics or organic-inorganic composites in the film at high temperature,which causes oxygen vacancy defects and consequently changes film surface states.Based on above experimental results,a surface states model is established to illustrate the CE after annealing at different temperatures,which further confirms electron transfer as 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 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 impacting the amount or direction of electron transfer.Results of this study are expected to help better elaborate the complex mechanism of CE,and act as a new supplement to the research on temperature effects in CE.Finally,different kinds of substoichiometric oxide films,such as Ti O_2-x,Al₂O_3-x,Ta₂O_5-x,Cr₂O_3-x et al.,were prepared by electron beam evaporation method and annealed at different temperatures,the CE between the oxide films and a Pt coated tip is performed by using Kelvin probe force microscopy(KPFM).The results turn out that the oxide films become more likely to receive positive charges by annealing in air atmosphere,while become more likely to be negatively charged by annealing in Ar/H₂atmosphere.Particularly,the polarity of the transferred charges on Ti O_2-x surface even reverses from negative to positive with the increasing of the annealing temperature in air atmosphere.The number of the oxygen vacancy will be changed by annealing in different atmospheres,which is suggested to be responsible for the change of the triboelectric properties of the oxide films.Based on the observations,an identical material triboelectric nanogenerator(IM-TENG)is designed,and the direction of the output current can be controlled by annealing the contact pairs.Moreover,a surface states model for the CE between metals and the annealed dielectric is further proposed,in which the effect of oxygen vacancy on the electron transfer is considered.The findings in this work provides a new idea for improving the output performance of the IM-TENG,and also gives a better understanding of the CE.This paper has 69 pictures,11 tables,and 95 references.