Pulse Enhanced Graphite Cathodic Arc And Its Induced Glow Discharge And Preparation Of Carbon Based Films

Diamond like carbon(DLC)film,one kind of carbon-based film,has the characteristics of low friction coefficient,high hardness and stable chemical properties,which is widely used.Cathodic arc technology is often utilized to prepare H-free diamond-like carbon films(ta-C),but the deposition rate is low.Cathode arc induced glow discharge is one of the most suitable methods to deposit hydrogenated diamond-like carbon films.However,the existing arc-enhanced glow discharge method often causes the problem of"element contamination",which leads to degrade in the structure and performance of the film.In order to solve the above problems,this paper proposes the use of pulse-enhanced graphite cathode arc technology,imposing high pulse current in traditional direct current,to increase deposition rate of ta-C film.Meanwhile,a method for preparing C-DLC films by using pulse-enhanced graphite cathode arc to induce glow discharge is also proposed to solve the problem of the"element contamination".The discharge characteristics and the composition of the particles in the plasma during the pulse-enhanced graphite cathode arc and its induced glow discharge were studied.The ta-C film and C-DLC film were prepared,respectively.The structure and properties of the both films were systematically analyzed and studied based on the results of the discharge characteristics and the composition of plasma particles.Firstly,the substrate current and the composition of the particles in the plasma during pulse enhanced graphite cathode arc discharge was measured in Ar atmosphere.The results show that compared with DC discharge mode,pulse enhanced discharge mode significantly improves the substrate current and the yield of the carbon plasma.With the increase of pulse current,the substrate current increases gradually.In addition,the yield of C plasma and the proportion of C ions in C plasma increase gradually.Then,pulse enhanced graphite cathode arc is used as electron emission source to enhance the glow discharge.The substrate current and the particle composition in the plasma are studied in Ar atmosphere and mixed atmosphere of Ar and C₂H₂.Similar to the pulse enhanced graphite cathode arc discharge,the pulse discharge mode significantly improves the substrate current and the spectral intensity of each particle compared with the DC discharge mode.With the increase of discharge current,the substrate current andthe emission intensity increases gradually.The intensity ratio of C⁺to(CH+C₂)changes slightly.The intensity ratio of(H+Ar⁺)to(CH+C₂+C⁺)gradually increases with the increase of the pulse current.When the average current and peak current are fixed in the pulse discharge mode,large substrate current and high spectral intensity can be obtained at low pulse frequency with large pulse width or high pulse frequency with small pulse width.Compared with the substrate current measured in Aratmosphere,the substrate current measured in Ar-acetylene mixture is smaller but the discharge voltage is higher.Based on the above results of substrate current and particle composition in plasma,ta-C thin films were prepared by pulse enhanced graphite cathode arc technique under different pulse currents.The microstructure and properties of the ta-C films were systematically studied.The results show that the deposition rate increased from 3.4nm/min to 7.81 nm/min with the increase of pulse current.This is owing to that the pulse enhanced discharge increases the substrate current,improves the carbon plasma yield and promotes the carbon plasma transport to the substrate,thus increasing the deposition rate of the film.The content of sp³ bond increases first and then decreases with the increase of pulse current.The maximum value(about 64.3%)is obtained when the pulse current is 800 A.This is related to the increase of C ion ratio with the increase of pulse current.With the increase of the ratio of C ions,the bombardment of C ions on the films is enhanced,which is favorable for the formation of sp³ bond.The highest hardness,elastic modulus,H/E^*and H³/E^*2 of the films are obtained by pulsed current of 800 A,and the films show excellent tribological properties and corrosion resistance.In view of the influence of pulse current on substrate current and the composition of the particles in the plasma,C-DLC thin films are prepared under different discharge modes and pulse currents.The results show that the surface roughness of DLC films prepared by pulse enhanced discharge is smaller than that by DC discharge.With the increase of pulse current,the surface roughness of C-DLC film decreases gradually.Additionally,the content of sp³ bond in the film increases first and then decreases.The maximum value(42.9%)is obtained at the pulse current of 700 A.With the increase of pulse current to 700 A,the deposition rate decreases,but the film density increases gradually.This is due to that the increase of pulse current leads to the increase of the ratio of(H+Ar⁺)to(CH+C₂+C⁺)in the plasma,which makes more loose groups easy to be etched.The decrease of surface roughness and deposition rate and the increase of sp³bond content are observed.With the increase of pulse current,the hardness and elastic modulus of the films increase first and then decrease.The hardness of the films reaches the maximum value when the pulse current is 700 A.At the same time,there exit the best tribological properties and corrosion resistance of the films.By using the graphite as the cathodic material,the pure DLC is produced,avoiding the“element pollution” problem.