High Power DC Arc Plasma Research Articles

Fabrication and characterizations of large homoepitaxial single crystal diamond grown by DC arc plasma jet CVD

Homoepitaxial diamond layers have been grown on HPHT synthetic type Ib (100) single crystal diamond plates brazed on a Φ65mm Mo holder using a commercial type 30kW dc arc plasma jet CVD with rotating arc root and operating at gas recycling mode with gas mixture of Ar/H2/CH4. The effects of substrate temperature and CH4/H2 ratio on the surface morphology, the growth rate and the quality of the synthesized diamond have been studied using optical microscopy and Raman spectroscopy. The growth rate up to 17.4μm/h has been obtained in the single crystal diamond sample deposited at 1000°C with CH4/H2=0.813%, exhibiting relatively smooth surface morphology with the typical feature of step-flow growth, without any non-epitaxial diamond crystallites. Under the optimum synthesis conditions, large size (7.5mm×7.5mm) polished freestanding single crystal diamond plate up to 1.03mm thickness has been produced and characterized by UV–vis–IR absorption, photoluminescence and Raman spectroscopy, as well as high-resolution X-ray diffraction. It was demonstrated that the quality of the as-grown CVD single crystal diamond was close to that of the natural type IIa single crystal diamond. It was shown that the epitaxial growth of high quality CVD single crystal diamonds could be achieved over the entire Φ65mm Mo holder on which a large quantity of CVD single crystal diamonds could be grown simultaneously. This is of economical importance in the development of high power DC arc plasma jet CVD systems for fabricating large size, high quality CVD single crystal diamond.

A Review on Mechanical Properties of Freestanding Diamond Films

As an emerging brand new type of engineering material for a variety of important high technology applications, the deep understanding of the mechanical behavior of freestanding diamond films has become an emergent task of vital importance. Of the many deposition methods dc arc plasma jet has been regarded as the most promising technique for large area high quality and low cost production of freestanding diamond films. In the present paper, recent progress in mechanical properties of freestanding diamond films mainly by high power dc arc plasma jet with rotating arc root and gas recycling is reviewed. Testing methods for fracture strength and fracture toughness are discussed. Experimental data are presented and compared to that by MWCVD. Dc arcjet diamond films start to oxidize at about 700°C, however, oxidation up to 800°C for 10 min does not affect the fracture strength. Fracture mechanism is discussed. The strange mechanical behavior of freestanding diamond films is explained. It is surprising that CVD diamond film is such a kind of material which is strong, but full of different size of defects. It is hoped that the present paper will be helpful for those who wish to understand and use this brand new type of engineering material.

Diamond Films Synthesis with a DC Arc Plasma Jet: Effect of Substrate Temperature on Quality of Diamond Films

. High quality diamond film wafers with different thickness are prepared by high power DC arc plasma jet CVD (DCPJ CVD) method using a CH4/Ar/H2 gas mixture. The effect of substrate temperature on the quality of diamond film was studied with theoretical analysis and experimental investigation. The results indicate that different structures in diamond film may grow with different substrate temperatures. The temperatures of 800°C, 900°C and 1000°C were tested in the experiments. The quality of diamond film showed the best at the temperature of 900°C. Characterization by X-ray diffraction, Raman spectroscopy and SEM analysis are also carried out.

Application of High Power DC Arc Plasma for Mass Production of High Quality Freestanding Diamond Films and Diamond Film Coated Cutting Tools

As quasi-thermodynamic equilibrium plasma, DC Arc Plasma has the advantage of very high gas temperature and thus the very high degree of activation of the precursors for diamond film deposition. The present paper reviews the progresses in the R&D of the novel high power dc arc plasma jet CVD system with rotating arc and operated at gas recycling mode for large area high quality diamond film deposition, developed at the University of Science and Technology Beijing (USTB) in the mid 1990s of the 20th century. Thanks to the continuous efforts made in the technological improvement in the past 15 years, considerable progresses have been achieved in the commercialization of this high power dc arcjet CVD system, which is now capable of mass production of large area high quality freestanding diamond films for optical, thermal, and mechanical (tool) applications. The present status in the commercialization and the property level of the resultant diamond films in optical, thermal, mechanical, dielectric, oxidation resistance, sand erosion resistance, and laser damage threshold etc. are presented. Based on the same high power dc arcjet technology, a novel high current extended dc arc plasma (HCEDCA) CVD system has been developed which successfully changed the diamond film deposition mode from 2D planar deposition in to 3D deposition (as confined by two hollow (virtue) columns). It is demonstrated to be advantageous for mass production of diamond thin film coated WC-Co cutting tools. Recent results in the R&D of thin diamond film coated WC-Co drills and end mills, and the results in field tests are discussed.

Effect of Input Power on the Deposition of Optical Grade Thick Diamond Film in a DCPJ CVD Jet System

High quality optical grade thick diamond film wafers with different thickness are prepared by high power DC arc plasma jet CVD (DCPJ CVD) method using a CH4/Ar/H2 gas mixture. Three different powers, 13.65, 15.40 and 17.94kW, were employed during the investigation. The aim was to investigate the effect of these powers on the deposition of thick diamond film. The controlled system was discussed together. The results show that the average diamond grain size and growth rate increase with input plasma power, but a further increase in input power, diamond thick-film defects and amorphous carbon content increased.

Study on Mechanical Polishing for CVD Diamond Films of Forming Nucleus Surface and Growing Surface

In the present work, high power DC arc plasma jet chemical vapor deposition (CVD) is used to prepare diamond films with full width half magnitude (FWHM) less than 10 wave numbers at 1332 cm−1 Raman peak. During the polishing process, diamond film is hold against the stainless steel holder, which rotates and swings when the sample comes into contact with the cast-iron plate. Average surface roughness of the forming nucleus polished surface and growing polished surface is 560nm, 90nm respectively. And the materials removal rate is quite different. Fine crystal grain of the forming nucleus surface and the thick column crystal of growing surface are dominant in structure. In the meantime, effects of the size of the abrasive power, the applied force and polishing direction are also discussed. A profilometer, an Raman spectroscopy, X-ray diffraction and a scanning electron microscope have been used to evaluate the surface states of diamond films before and after polishing. This result reveals an. improvement of polishing efficiency and a great potential for commercial application.

Fabrication of layered self-standing diamond film by dc arc plasma jet chemical vapor deposition

Layered self-standing diamond films, consisting of an upper layer, buffer layer, and a lower layer, were fabricated by fluctuating the ratio of methane to hydrogen in high power dc arc plasma jet chemical vapor deposition. There were micrometer-sized columnar diamond crystalline grains in both upper layer and lower layer. The size of the columnar diamond crystalline grains was bigger in the upper layer than that in the lower layer. The orientation of the upper layer was (110), while it was (111) for the lower layer. Raman results showed that no sp3 peak shift was found in the upper layer, but it was found and blueshifted in the lower layer. This indicated that the internal stress within the film body could be tailored by this layered structure. The buffer layer with nanometer-sized diamond grains formed by secondary nucleation was necessary in order to form the layered film. Growth rate was over 10μm∕h in layered self-standing diamond film fabrication.

Investigation of Technology and Analysis of Residual Stress in Large Area Diamond Films

We investigated the residual stress in diamond films grown on molybdenum substrates as a function of different places in the same large sample. The diamond film wafers of Ф60 mm diameter were deposited at 900°C by high power DC arc plasma jet CVD method using a gas mixture of methane (1.8% vol.) and hydrogen ( 90% vol.). The grain sizes, obtained from the top view scanning electron microscopy (SEM) images, were found to become larger from center to the border in the same sample, and the x-ray diffraction indicated that the intensity of characteristic spectroscopy in same diamond film was changed from (220) to (111) with the increases of (311). Profile curves presented the appreciable difference of surface texture from center to edge. The film had 4.3GPa of residual compressive stress. Examination of the Raman spectra of the film revealed that residual stress in the film of up to approximately 0.70GPa, and the Raman spectroscopy shifts from 1332.99cm-1 at the center to 1331.17cm-1 at the border, which means the stress mode changed from compressive to tensile. These demonstrated a significant inhomogeneity of stress in diamond films. The differences have been attributed partly to high temperature inhomogeneity arc jet during growth and morphological aspects of the film growth. The relationships between stress and methane concentration, and substrate temperature are discussed in detail.

Gas phase study and oriented self-standing diamond film fabrication in high power DC arc plasma jet CVD

Gas phase species were diagnosed by in situ spatially resolved OES in high power DC arc plasma jet CVD system. CH, C 2, H were found as main species in this deposition plasma environment. Concentration of species was studied with the variation of deposition parameters such as methane concentration, substrate temperature and gas flow rate. C 2 was found to be the most sensitive species to deposition parameters. The electron mean temperature was deduced from H γ/H β, and changed little no matter how the deposition parameters varied. Self-standing diamond films with (111) orientation were grown within the modified species atmosphere where the intensity ratio of CH/C 2 was higher than 0.41.

Application of optical emission spectra in controlling dominant crystalline surface of diamond films deposited by DC arc plasma jet CVD

Dominant crystalline surface of diamond film growth was tried to control by the help of optical emission spectroscopy in situ detection in high power DC arc plasma jet chemical vapor deposition system. The radicals, like CH, C 2, H γ, H 2 and H β, were strongly influenced by the substrate temperature and the concentration of Ar, H 2 and CH 4 in the feed gas. Altering the deposition parameters, the emission intensities of various radicals changed, and the intensity ratio of C 2/H β varied more sensitively than that of CH/H β. The diamond films with excellent (111) dominant crystalline surface were deposited by modifying the radicals atmosphere that had a higher intensity ratio of CH/H β and a lower intensity ratio of C 2/H β, i.e. the intensity ratio of CH/C 2 was higher than 0.41. Very clear columnar crystals shown in the cross-section of the as-grown films indicated the stability of dominant surfaces growth within this atmosphere of radicals. The stable growth was also proven by the results of X-ray diffraction detection vs. deposition time.

Effects of Methane Concentration on Growth of Carbon Balls in Anode Nozzle and Arc Stability of DCPJ CVD Plasma Torch

High quality diamond film wafers with different thickness are prepared by high power DC arc plasma jet CVD (DCPJ CVD) method using a CH4/Ar/H2 gas mixture. The effects of methane concentration on the growth of carbon balls in anode nozzle and arc stability are studied with theoretical analysis and experimental investigation. The results indicate that different sizes of carbon balls may rapidly grow in the anode nozzle with methane concentration higher than 2 Vol-%, symmetry and uniformity of the rotating arc are strongly affected with the occurrence of carbon balls, which will result in non-uniform deposition of diamond films over a large substrate area. The methane concentration should be controlled at a low level to keep diamond film wafers growth stable. Characterization by X-ray diffraction, Raman spectroscopy and SEM analysis are also carried out.

OES study of the gas phase during diamond films deposition in high power DC arc plasma jet CVD system

This paper used optical emission spectroscopy (OES) to study the gas phase in high power DC arc plasma jet chemical vapour deposition (CVD) during diamond films growth processes. The results show that all the deposition parameters (methane concentration, substrate temperature, gas flow rate and ratio of H2/Ar) could strongly influence the gas phase. C2 is found to be the most sensitive radical to deposition parameters among the radicals in gas phase. Spatially resolved OES implies that a relative high concentration of atomic H exists near the substrate surface, which is beneficial for diamond film growth. The relatively high concentrations of C2 and CH are correlated with high deposition rate of diamond. In our high deposition rate system, C2 is presumed to be the main growth radical and CH is also believed to contribute the diamond deposition.

Large area high quality diamond film deposition by high power DC arc plasma jet operating at gas recycling mode

Principles of a high power DC arc plasma torch with rotating arc roots and the semi-closed gas recycling system are presented. Recent results on large area high quality free standing diamond film deposition by a high power DC arc plasma jet CVD system operating at gas recycling mode is discussed. It was shown that the uniformity of diamond film deposition over a large substrate area was closely dependent on the uniformity and symmetry of the plasma, which can be adjusted by proper manipulation of the magnetic field and the effects of fluid dynamics. Effect of gas recycling on the quality of diamond films is discussed. By proper design of the whole system and process optimization, thick uniform diamond wafers of Φ60–110 mm in diameter with a thickness up to 2 mm and transparent diamond wafers of Φ30–60 mm in diameter has been deposited successfully. It is demonstrated that gas recycling can be used even for high quality diamond film synthesis. This is of technical and economical importance in the development of high power DC arc plasma jet CVD systems for economical fabrication of high quality diamond wafers.

Economical deposition of a large area of high quality diamond film by a high power DC arc plasma jet operating in a gas recycling mode

Abstract In the present paper, details of a semi-closed gas recycling system incorporated with a high power jet, which allows more than 90% of the feed gas to be recycled while exhausting and feeding a small amount of fresh gas is disclosed. Recent experimental results of diamond deposition by the high power jet system operating in gas recycling mode are presented. The effect of gas recycling on diamond deposition and the quality of the deposited diamond films was discussed. By proper design of the whole system, and optimization of process parameters, thick uniform diamond wafers of Φ60–100 mm in diameter with a thickness up to 2 mm and transparent diamond wafers of Φ60 mm in diameter has been deposited successfully. It is demonstrated by the present study that gas recycling can be used even for high quality diamond film synthesis. This is of technical and economical importance in the development of high power DC arc plasma jet CVD systems for economical fabrication of large area high quality diamond wafers.