Effect Of Hydrogen Plasma Sputtering On Diamond Surface Structure And Electrochemical Properties

Diamond film has many excellent properties.The study found that hydrogen-modified diamond films exhibited p-type conductivity.This makes diamond thin films have good application prospects in microelectronics and electrochemical devices.However,when the surface of the diamond film is modified by hydrogen plasma sputtering,the etching of the film surface by hydrogen plasma sputtering is inevitable.At present,the changes in the morphology and phase content of diamond films etched by hydrogen plasma are unclear,and the effect on the electrochemical performance of thin film electrodes is also unclear.This greatly limits the application of diamond films.In this paper,the microwave plasma chemical vapor deposition technology was used to perform hydrogen plasma sputtering on the diamond film.Under the same process and different sputtering time conditions,the surface morphology and phase structure of the diamond film after etching were analyzed to detect its conductivity.Performance and electrochemical performance,the mechanism of the influence of hydrogen plasma etching on the electrical conductivity and electrochemical performance of diamond film was discussed.The following research results were obtained:(1)With the extension of the etching time,the etching morphology changes significantly:in the early stage of etching,there are obvious etching pits,steps and subcrystals on the surface of the diamond film.As the etching time increases,the etching blurs the grain contours and eventually causes the grains to collapse.The roughness of the film surface decreases first and then increases gradually with the increase of etching time.Under the experimental conditions of this paper,the roughness is the lowest at the etching time of 20 min,which is 0.550μm;(2)The etching mechanism is related to the etching stage:in the early stage of etching,the grains mainly composed of sp~3 phase are preferentially etched.In the later period of etching,the etching is concentrated on the grain boundary,and the sp~2 phase is etched.The sp~3/sp~2 ratio of the original CVD film is 1.9,and the sp~3/sp~2 ratio first decreases and then increases with the etching time.It decreases to a minimum of 1.1at 15 minutes of etching,and increases to a maximum of 2.2 at 120 minutes of etching;(3)Obtained a clear solid-liquid interface structure when the diamond film is used as an electrode under different etching times.Through cyclic voltammetry curves and impedance spectroscopy,it was found that diamond films at different etching times all have low background current and a wide electrochemical window(3 V),and the stability of the film electrode before and after etching does not change much.The surface contact resistance and charge transfer resistance first increased and then decreased with the extension of the etching time,and reached a maximum of 972.2Ωand 5956.0Ωat 60 min and 20 min,respectively,and the minimum value in the etched state at 120 min.At the same time,the level of the flat band potential is affected by the content of sp3 phase on the electrode surface.The flat band potential of the original CVD film is 0.92 V.As the content of the sp~3 phase increases,the flat band potential is 0.71 V at 120 min;(4)The sheet resistance of the film rises first and then decreases with the extension of the etching time.Etching restores the crystal lattice integrity of diamond grains,and the integrity and high content of diamond phase(sp~3)crystal lattice is beneficial to improve the film conductivity;(5)The electrochemical performance of the diamond film electrode is related to the sp~3 content.When the sp~3 content is high,the electrochemical performance is better.Because the sp~3 content increases,the flat band potential shifts negatively,causing the Fermi level to rise to the acceptor level,thereby effectively exciting holes from the deep level,increasing the mobility of the holes,and thus improving the conductivity of the thin-film electrode.