Study On Humidity Sensitivity Properties Of Carbon Nitride Polymer Films Based On Asymmetric Structures

Humidity is intimately related to our life.Humidity sensor as detection device play an important role in our life and production.The current improvement in the performance of humidity sensors is mainly through sensitive materials.Graphitic carbon nitride,as a new high molecular polymer,has attracted considerable attention owing to its appealing electronic structure and excellent performance since its inception.In this paper,carbon nitride humidity sensitive films were prepared by thermal decomposition of guanidinium carbonate as precursor onto glass substrate.The humidity mechanism of the proposed film was analyzed by scanning electron microscope,X-ray diffraction,X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.The results showed that the carbon nitride film obtained is non-symmetric along thickness direction with larger sheet distance and more nitrogen defective as active site toward its growth side rather than substrate side.In this case,more water molecules were absorbed on the growth side possessed by growth side were beneficial for water molecule adsorption and desorption.Thus,the carbon nitride with anisotropic structure exhibited deformation characteristic as the humidity changes.In addition,the effects of calcining temperature,heating rate and heating time on the humidity sensitivity of carbon nitride films were discussed.Through the characterization and analysis of the morphology and composition of the carbon nitride films under different preparation conditions,it was proved that increasing the calcination temperature,prolonging the heating time and decreasing the heating rate were beneficial to the growth of the carbon nitride film,at the same time,the content of nitrogen defective in the film would be reduced.The humidity sensor was fabricated by combining the thin film with characteristics of moisture absorption deformation and the strain gauge,and the humidity sensor was tested.The results showed that the humiditysensor has the advantages of good repeatability,high sensitivity and little humidity hysteresis.By investigating the properties of carbon nitride films under different preparation conditions comprehensively,the optimum process parameters for the preparation of the carbon nitride humidity sensitive films in this experiment range were determined: the calcination temperature,heating rate,and heating time were 570?C,2.5?C/min and 120 min,respectively.