Preparation And Electrochemical Performances Of Nitrogen-doped Ultrananocrystalline Diamond Films With Different Structure

Nitrogen-doped ultrananocrystalline diamond(N-UNCD)film has a promising application because it not only possesses the excellent physicochemical properties of traditional diamond,but also shows some special effects of nano-materials and N-type semiconductors.The structure of N-UNCD has great influence on its macroscopic performances,so further research on the preparation technology and performance characteristics of different structural films are the basis and precondition for further development of its application.In this thesis,the nitrogen-doped ultrananocrystalline diamond(N-UNCD)films were deposited on Si substrates via 2kW microwave plasma chemical vapor deposition(MPCVD)technique,in which diethylamine was utilized as the sole reaction sources and H2 as auxiliary gas.Surface morphological,microstructural and composition characteristics of as-deposited N-UNCD films were investigated using scanning electron microscopy(SEM),Raman spectrum and X-ray diffraction(XRD).On the basis,the electrochemical activity properties,electric double layer capacitance and impedance properties of the films were investigated by electrochemical analysis.Furthermore using N-UNCD films as working electrodes,the effect of electrochemical detection dopamine,ascorbic acid and copper ion on the films had also been investigated.The results indicate that:(1)A typical N-UNCD film was fabricated by diethylamine as the reaction source.With the increase of diethylamine intake,the surface morphology of N-UNCD films evolved from the typical isometric grain agglomeration to the ultrananocrystalline diamond/vertical nano-graphene wall composite structure.The crystalline graphite phase content of the film increased markedly,and the conductivity also increased remarkably.(2)The N-UNCD films have better electrochemical properties than most carbon materials,and the electrochemical properties of N-UNCD with different structural properties are also different.When the N-UNCD film exhibits the grain agglomeration and the graphite phase content is low,the electrochemical activity is investigated by [Fe(CN)6]3-/4-redox probe,the oxidation peak and the reduction peak-peak difference ?EP value is 119 mV.With the increase of graphite phase content in the film,the surface gradually becomes ultrananocrystalline diamond/vertical nano-graphene wall composite structure,?EP decreases to 75 mv,and oxidation peak current intensity increases gradually.The electric double layer capacitance of the film increases from 42.1 ?F/cm2 to 337.6 ?F/cm2.The capacitance value only decreases 10.3% after 10,000 cycles charge and discharge test of the N-UNCD film with high content of graphite phase.The impedance fitting results show that the charge transfer resistor decreases from 2486 ? to 10.17,and the capacitance value of the double layer also increases.(3)N-UNCD films have good electrochemical detection ability in detecting organic molecules and metal ions.When the film with lower graphite phase content was used to detect DA,the detection limit was 8.8 ?M.With the graphite phase of films increased,the DA detection limit reached to 0.4 ?M,and the reduction peak potential moved from +0.35 V to +0.175 V.The linearity correlation was more than 0.99%.When detecting AA,the detection limit was decreased from 12.95 ?M to 4.4?M and the linearity correlation was also above 0.99.For detecting Cu2+,the N-UNCD film with less graphite phase had a lower detection limit only 0.12 ppb.With the increase of graphite phase in the film,the detection limit increased to 3.08 ppb,and the linear correlation 0.99 decreased to 0.98.(4)The electrochemical performance of N-UNCD thin films with specific compositions is a very promising electrochemical energy storage and detection material.