Study On Preparation Of Carbon Nitrides

In this thesis,we concentrate on the development in theoretical and experimental study of CN compounds in the recent 20 years.The prosperities and characterization methods of CN compounds have also been reviewed. The analysis shows that:finding a method or a condition to obtain high concentration of sp³C-N single bond is the key of synthesis crystalline carbon nitride.By means of pulsed arc discharge from methanol and methanol/ammonia water under nitrogen gas,pulsed arc discharge combined with microwave nitrogen plasma treatment of dicyandiamide and microwave plasma CVD assisted by pulsed nitrogen ion beam sputtering,we explore the routes to synthesize crystalline carbon nitrides.The chemical compositions, crystal structures and bonding states of the CN films and powders obtained from the experiment are studied by the means of FTIR,EDX,XRD,XPS, Micro-Raman,SEM and HRTEM.The experimental results show that the films containing crystalline carbon nitride may be prepared at low substrate temperature(220℃) using pulsed arc discharge from methanol solution with nitrogen atmosphere.At same time,the substrate temperature has a significantly effect on the nitrogen content and the structure of the films.Increasing substrate temperature(300℃) would decrease the content of nitrogen in the films and result in a formation of carbon films.However,the films containing crystalline carbon nitride may still be prepared at substrate temperature 450℃using pulsed arc discharge from methanol/ammonia water.While the deposits would be carbon film demonstrated fiom Raman analysis when the substrate temperature was increased to 550℃.Carbon nitride precursor is prepared from dicyandiamide using pulsed arc discharge under nitrogen atmospheric pressure and then the formation conditions of high concentration C atoms,N atoms and sp³C-N bonds needed to synthesis of crystalline carbon nitride are investigated by microwave nitrogen plasma treating the precursor.The results show that the C-N bonds on the surface of the nitride micro-dicyandiamide obtained by the pulsed nitrogen arc plasma with high nitrogen ions and energy density restricted the transformation of organic crystals directly into carbon structures and reconstructed under the effect of the microwave nitrogen plasma.At the same time,the amorphous carbon nitride compound which is result from the pulsed arc plasma is transited into the crystalline carbon nitride phase.A modified chemical vapor deposition system,microwave nitrogen plasma combined with pulsed nitrogen ions sputtering dicyandiamide target, has been applied to deposit carbon nitride films on quartz glass substrate.The effects of deposition temperature on the morphology,composition and structure of the samples are investigated.It is found that the surface morphologies of the deposits are from well crystallized hexagonal crystals (800℃) turn into semi-developed poly-sheet crystals(700℃) and last turn to amorphous small grains(550℃).XRD measurements suggest that the intensity of the diffraction peaks is diminished and the values of the cell parameter a and c are lessened with decreased the deposition temperature. XPS analysis reveal that the prepared crystalline films are silicon carbon nitride with a crystalline structure of Si₃N₄ modified with the carbon atoms instead of some Si atoms.The N atoms are mainly bonded to Si and C atoms are in the form of sp³C-N,sp²C=N and sp²C=C bonds.Decreasing deposition temperature is helpful for increased the content of C atoms and sp³C-N bond.