Numerical Analysis of Nd:YAG Pulsed Laser Polishing CVD Self-standing Diamond Film

Chemical vapor deposited （CVD） diamond film has broad application foreground in high-tech fields. But polycrystalline CVD self-standing diamond thick film has rough surface and non-uniform thickness that adversely affect its extensive applications. Laser polishing is a useful method to smooth self-standing diamond film. At present, attentions have been focused on experimental research on laser polishing, but the revealing of theoretical model and the forecast of polishing process are vacant. The paper presents a finite element model to simulate and analyze the mechanism of laser polishing diamond based on laser thermal conduction theory. The experimental investigation is also carried out on Nd：YAG pulsed laser smoothing diamond thick film. The simulation results have good accordance with the results of experimental results. The temperature and thermal stress fields are investigated at different incidence angles and parameters of Nd：YAG pulsed laser. The pyramidal-like roughness of diamond thick film leads to the non-homogeneous temperature fields. The temperature at the peak of diamond film is much higher than that in the valley, which leads to the smoothing of diamond thick film. The effect of laser parameters on the surface roughness and thickness of graphite transition layer is also carried out. The results show that high power density laser makes the diamond surface rapid heating, evaporation and sublimation after its graphitization. It is also found that the good polish quality of diamond thick film can be obtained by a combination of large incident angle, moderate laser pulsed energy, large repetition rate and moderate laser pulse width. The results obtained here provide the theoretical basis for laser polishing diamond film with high efficiency and high quality.

Simulations of the Dependence of Gas Physical Parameters on Deposition Variables during HFCVD Diamond Films

During the growth of the hot filament chemical vapor deposition （HFCVD） diamond films, numerical simulations in a 2-D mathematical model were employed to investigate the influence of various deposition parameters on the gas physical parameters, including the temperature, velocity and volume density of gas. It was found that, even in the case of optimized deposition parameters, the space distributions of gas parameters were heterogeneous due primarily to the thermal blockage come from the hot filaments and cryogenic pump effect arisen from the cold reactor wall. The distribution of volume density agreed well with the thermal round-flow phenomenon, one of the key obstacles to obtaining high growth rate in HFCVD process. In virtue of isothermal boundary with high temperature or adiabatic boundary condition of reactor wall, however, the thermal roundflow was profoundly reduced and as a consequence, the uniformity of gas physical parameters was considerably improved, as identified by the experimental films growth.

Microwave CVD Thick Diamond Film Synthesis Using CH4/H2/H2O Gas Mixtures

Thick diamond films with a thickness of up to 1.2 mm and a area of 20 cm^2 have been grown in a homemade 5 kW microwave plasma chemical vapor deposition （MPCVD） reactor using CH4/H2/H2O gas mixtures. The growth rate, radial profiles of the film thickness, diamond morphology and quality were evaluated with a range of parameters such as the substrate temperature of 700℃ to 1100℃, the fed gas composition CH4/H2 = 3.0%, H2O/H2 = 0.0%,-2.4%. They were characterized by scanning electron microscopy and Raman spectroscopy. Translucent diamond wafers have been produced without any sign of non-diamond carbon phases, Raman peak as narrow as 4.1 cm^-1. An interesting type of diamond growth instability under certain deposition conditions was observed in a form of accelerated growth of selected diamond crystallites of a very big lateral size, about 1 mm, and of a better structure compared to the rest of the film.

Fabrication and Characterization of FeNiCr Matrix-TiC Composite for Polishing CVD Diamond Film

Dynamic friction polishing （DFP） is one of the most promising methods appropriate for polishing CVD diamond film with high efficiency and low cost. By this method CVD diamond film is polished through being simply pressed against a metal disc rotating at a high speed utilizing the thermochemical reaction occurring as a result of dynamic friction between them in the atmosphere. However, the relatively soft materials such as stainless steel, cast iron and nickel alloy widely used for polishing CVD diamond film are easy to wear and adhere to diamond film surface, which may further lead to low efficiency and poor polishing quality. In this paper, FeNiCr matrix-TiC composite used as grinding wheel for polishing CVD diamond film was obtained by combination of mechanical alloying （MA） and spark plasma sintering （SPS）. The process of ball milling, composition, density, hardness, high-temperature oxidation resistance and wear resistance of the sintered piece were analyzed. The results show that TiC was introduced in MA-SPS process and had good combination with FeNiCr matrix and even distribution in the matrix. The density of composite can be improved by mechanical alloying. The FeNiCr matrix-TiC composite obtained at 1273 K was found to be superior to at 1173 K sinterin8 in hardness, high-temperature oxidation resistance and wearability. These properties are more favorable than SUS304 for the preparation of high-performance grinding wheel for polishing CVD diamond film.

A CVD diamond film detector for pulsed proton detection

A chemical vapour deposition （CVD） diamond film detector was prepared and the main characteristics for pulsed proton detection were studied at Beijing Tandem Accelerator. The result shows that the charge collection efficiency of the detector increases with increasing electric field intensity and reaches to 9.44% at 5 V/μm with the charge collection distance of 15.9 μm. The relationship between the sensitivity of the detector and proton energy is consistent with the Monte Carlo （MC） simulation result. Its plasma time for a pulse with 4.85×10^5 protons is 1l.2ns. The dose threshold for onset of damage under 9MeV proton irradiation in the detector is about 10^13 cm^-2. All of the results show that a CVD diamond detector has fast time response and high radiation hardness, and can be used in pulsed proton detection.

Microwave Plasma Chemical Vapor Deposition of Diamond Films on Silicon From Ethanol and Hydrogen

Diamond films with very smooth surface and good optical quality have been deposited onto silicon substrate using microwave plasma chemical vapor deposition (MPCVD) from a gas mixture of ethanol and hydrogen at a low substrate temperature of 450 ℃. The effects of the substrate temperature on the diamond nucleation and the morphology of the diamond film have been investigated and observed with scanning electron microscopy (SEM). The microstructure and the phase of the film have been characterized using Raman spectroscopy and X-ray diffraction (XRD). The diamond nucleation density significantly decreases with the increasing of the substrate temperature. There are only sparse nuclei when the substrate temperature is higher than 800 ℃ although the ethanol concentration in hydrogen is very high. That the characteristic diamond peak in the Raman spectrum of a diamond film prepared at a low substrate temperature of 450 ℃ extends into broadband indicates that the film is of nanophase. No graphite peak appeare

A MONTE CARLO SIMULATION OF THE CVD DIAMOND FILM

A Monte Carlo algorithm has been developed by the authors to simulate the chemical vapor deposition (CVD) processes of diamond films. The method considers both the diffusion and the incorporation of the growth radicals on the growing surface in simulating the evolution of the morphology and microstructure. The calculation of configuration energy is used to determine the orientation of adsorbed growth radicals. The effect of processing variables such as nucleation density and substrate temperature on the morphology and microstructure is discussed. It is found that competitive characteristic and coarsening effect exist in the simulation results, which agree with the experimental observations.

A novel approach of deposition for uniform diamond films on circular saw blades

Uniform diamond films are highly desirable for cutting industries, due to their high performance and long lifetime used on cutting tools. Nevertheless, they are difficult to obtain on cutting tools with complicated shapes, greatly limiting the applications of diamond films. In this study, a novel approach of deposition for uniform diamond films is proposed, on circular saw blades made of cemented carbide using reflectors of brass sheets. Diamond films are deposited using hot filament chemical vapor deposition（HFCVD）. A novel concave structure of brass sheets is designed and fabricated, improving the distribution of temperature field, and overcoming the disadvantages of the conventional HFCVD systems. This increases the energy efficiency of use without changing the structure and increasing the cost of HFCVD. The grains are refined and the intensities of diamond peaks are strengthened obviously, which is confirmed by scanning electron microscopy and Raman spectra respectively.

Friction Behaviors of the Hot Filament Chemical Vapor Deposition Diamond Film under Ambient Air and Water Lubricating Conditions

The friction behavior of the hot filament chemical vapor deposition（HFCVD） diamond film plays a critical role on its applications in mechanical fields and largely depends on the environment. Studies on the tribological properties of HFCVD diamond films coated on Co-cemented tungsten carbide （WC-Co） substrates are rarely reported in available literatures, especially in the water lubricating conditions. In this paper, conventional microcrystalline diamond（MCD） and fine-grained diamond（FGD） films are deposited on WC-Co substrates and their friction properties are evaluated on a reciprocating ball-on-plate tribometer, where they are brought to slide against ball-bearing steel and copper balls in dry and water lubricating conditions. Scanning electron microscopy（SEM）, atomic force microscopy（AFM）, surface profilometer and Raman spectroscopy are adopted to characterize as-deposited diamond films; SEM and energy dispersive X-ray（EDX） are used to investigate the worn region on the surfaces of both counterface balls and diamond films. The research results show that the friction coefficient of HFCVD diamond films always starts with a high initial value, and then gradually transits to a relative stable state. For a given counterface and a sliding condition, the FGD film presents lower stable friction coefficients by 0.02-0.03 than MCD film. The transferred materials adhered on sliding interface are supposed to have predominate effect on the friction behaviors of HFCVD diamond films. Furthermore, the effect of water lubricating on reducing friction coefficient is significant. For a given counterpart, the stable friction coefficients of MCD or FGD films reduce by about 0.07-0.08 while sliding in the water lubricating condition, relative to in dry sliding condition. This study is beneficial for widespread applications of HFCVD diamond coated mechanical components and adopting water lubricating system, replacing ofoil lubricating, in a variety of mechanical processing fields to implement the green production process.

Effect of Substrate Temperature on the Selective Deposition of Diamond Films

Selective deposition of diamond film on patterned Si (100) substrates has been achieved by using microwave plasma chemical vapor deposition (MPCVD) method. The films have been characterized by scanning electron microscope (SEM) and Raman spectrum. The influence of substrate temperature on the nucleation behavior of diamond was discussed in detail and the optimized deposition condition has been obtained.

Surface graphitization analysis of cerium-polished HFCVD diamond films with micro-raman spectra

The etching technique using Ce is a convenient and fast method for polishing and shaping diamond films. In this study, the influence of polishing parameters such as polishing temperature and time on the surface crystallinity and phase composition of diamond films was thoroughly investigated via the analysis of Raman spectra such as FWHM and ID/IG. Moreover, the issue on the graphitization of diamond after polishing with Ce was further researched through the detailed study of the depth distribution of Raman data including FWHM and ID/IG, and a result completely different from the hot-iron metal polished ones was obtained. The results showed that polished diamond films had considerably higher diamond content than those before polishing, and not a bit of graphitization was found in the polished ones, owing to a higher solubility of carbon in rare earth metal Ce than that in transition metals, and the original crystallinity of the films polished with Ce did not deteriorate.

Ohmic contact properties of p-type surface conductive layer on H-terminated diamond films prepared by DC arc jet CVD

With the advantages of high deposition rate and large deposition area, polycrystalline diamond films prepared by direct current （DC） arc jet chemical vapor deposition （CVD） are considered to be one of the most promising materials for high-frequency and high-power electronic devices. In this paper, high-quality self-standing polycrystalline diamond films with the diameter of 100 mm were prepared by DC arc jet CVD, and then, the p-type surface conductive layer with the sheet carrier density of 10^11-10^13 cm-2 on the H-terminated diamond film was obtained by micro-wave hydrogen plasma treatment for 40 min. Ti/Au and Au films were deposited on the H-terminated diamond surface as the ohmic contact electrode, respectively, afterwards, they were treated by rapid vacuum annealing at different temperatures. The properties of these two types of ohmic contacts were investigated by measuring the specific contact resistance using the transmission line method （TLM）. Due to the formation of Ti-related carbide at high temperature, the specific contact resistance of Ti/Au contact gradually decreases to 9.95 × 10^-5 Ω-cm2 as the temperature increases to 820℃. However, when the annealing temperature reaches 850℃, the ohmic contact for Ti/Au is degraded significantly due to the strong diffusion and reaction between Ti and Au. As for the as-deposited Au contact, it shows an ohmic contact. After annealing treatment at 550℃, low specific contact resistance was detected for Au contact, which is derived from the enhancement of interdiffusion between Au and diamond films.

Deposition of crackless freestanding diamond films on Mo substrates with Zr interlayer

The Mo substrate with Zr interlayer,namely composite substrate,was employed to solve the problem of crack formation in the freestanding diamond film deposition.Freestanding diamond films deposited on the composite substrates by the direct current arc plasma jet chemical vapor deposition（CVD） method were investigated with scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy （XPS）,X-ray diffraction（XRD）,and Raman spectroscopy.In addition,the stress distribution during the large area freestanding diamond film deposition on the composite substrate was analyzed based on the finite element model ANSYS.The results reveal that Zr interlayer can be easily destroyed during the post-deposition cooling process,which is helpful for stress release and crack avoiding in diamond films.

Simulations of Temperature Field in HFCVD Diamond Films over Large Area

A three-dimensional model was developed to investigate the influence of various hot filaments parameters on substrate temperature fields that significantly affect the nucleation and growth of diamond films over large area by hot-filament chemical vapordeposition (HFCVD). Numerical simulated results indicated that substrate temperature varies as a function of hot filamentsnumber, radius, temperature, emissivity, the distance between filaments, and the distance between substrate and filamentsarrangement plane. When these filaments parameters were maintained at the optimal values, the homogeneous substrate temperature region of 76 mm×76 mm with the temperature fluctuation no more than 5% could be obtained by a 80 mm×80 mmhot filaments arrangement plane. Furthermore, the homogeneous region could be enlarged to 100 mm×100 mm under thecondition of supplementary hot filaments with appropriate parameters. All of these calculations provided the basis for speciallyoptimizing the hot filaments parameters to deposit uniform diamond film over large area by HFCVD.

Diamond Film Synthesis with a DC Plasma Jet:Effect of the Contacting Interface between Substrate and Base on the Substrate Temperature

The contacting interface between the substrate and water-cooled base is vital to the substrate temperature during diamond films deposition by a DC （direct current） plasma jet. The effects of the solid contacting area,conductive materials and fixing between the substrate and the base were investigated without affecting the other parameters. Experimental results indicated that the preferable solid contacting area was more than 60% of total contacting areal; the particular Sn-Pb alloy was more suitable for conducting heat and the concentric fixing ring was a better setting for controlling the substrate temperature. The result was explained in terms of the variable thermal contact resistance at the interface between substrate and base. The diamond films were analyzed by scanning electron microscopy （SEM） for morphology, X-ray diffraction （XRD） for the intensity of characteristic spectroscopy and Raman spectroscopy for structure.

Effect of nitrogen on deposition and field emission properties of boron-doped micro-and nano-crystalline diamond films

In this paper,we report the effect of nitrogen on the deposition and properties of boron doped diamond films synthesized by hot filament chemical vapor deposition.The diamond films consisting of micro-grains(nano-grains) were realized with low(high) boron source flow rate during the growth processes.The transition of micro-grains to nano-grains is speculated to be strongly(weekly) related with the boron(nitrogen) flow rate.The grain size and Raman spectral feature vary insignificantly as a function of the nitrogen introduction at a certain boron flow rate.The variation of electron field emission characteristics dependent on nitrogen is different between microcrystalline and nanocrystalline boron doped diamond samples,which are related to the combined phase composition,boron doping level and texture structure.There is an optimum nitrogen proportion to improve the field emission properties of the boron-doped films.

Effects of the electric field at the edge of a substrate to deposit a φ100 mm uniform diamond film in a 2.45 GHz MPCVD system

In this study,uniform diamond films with a diameter of 100 mm were deposited in a 15 kW/2.45 GHz ellipsoidal microwave plasma chemical vapour deposition system.A phenomenological model previously developed by our group was used to simulate the distribution of the electric strength and electron density of plasma.Results indicate that the electric field in the cavity includes multiple modes,i.e.TM_(02) and TM_(03).When the gas pressure exceeds 10 kPa,the electron density of plasma increases and plasma volume decreases.A T-shaped substrate was developed to achieve uniform temperature,and the substrate was suspended in air fromφ70 to 100 mm,thus eliminating vertical heat dissipation.An edge electric field was added to the system after the introduction of the T-shaped substrate.Moreover,the plasma volume in this case was greater than that in the central electric field but smaller than that in the periphery electric field of the TM_(02) mode.This indicates that the electric field above and below the edge benefits the plasma volume rather than the periphery electric field of the TM_(02) mode.The quality,uniformity and surface morphology of the deposited diamond films were primarily investigated to maintain substrate temperature uniformity.When employing the improved substrate,the thickness unevenness of theφ100 mm diamond film decreased from 22%to 7%.

Optical and electronic performances of CVD diamond film andits applications in radiation detectors

The outstanding properties of CVD diamond film such as electronic, optical, thermal and mechanical and the high radiation hardness have made it an ideal candidate material for radiation detectors in severe environments. Fabrication of ＇detector grade＇ CVD diamond films and development of CVD diamond detectors have been leading edge subjects. Micro-strip gas chamber （MSGC） fabricated on CVD diamond substrate would overcome the charge-up effect and the substrate instability, which has been a hotspot in the research of gas detectors.

Preparation and Characterization of High Quality Diamond Films by DC ArcPlasma Jet CVD Method

Under optimal conditions free-standing high quality diamond films were prepared by DC arc plasma jet CVD method at a growth rate of 7-10 Pm/h. Surface and cross section morphologies of the diamond films were observed by SEM. Raman spectrometer wasused to characterize the quality of diamond films. The IR transmittivity measured by IR spectrometer is close to the theoretical value ofabout 71% in the far infrared band. The thermal conductivity measured by photothermal deflection exceeds 18 W/cm' K. <l 10> is thepreferential growth orientation of the films detected by X-ray diffractometer. As s result, the extremely high temperature of DC arc plasma jet can produce supersaturated atomic hydrogen, which played an important role in the process for the deposition of high quality diamond films.

Phase Transformation and Enhancing Electron Field Emission Properties in Microcrystalline Diamond Films Induced by Cu Ion Implantation and Rapid Annealing

Cu ion implantation and subsequent rapid annealing at 500℃ in N2 result in low surface resistivity of 1.611 ohm/sq with high mobility of 290 cm2 V-1S-1 for microcrystalline diamond （MCD） films. Its electrical field emission behavior can be turned on at Eo = 2.6 V/μm, attaining a current density of 19.5μA/cm2 at an applied field of 3.5 V/#m. Field emission scanning electron microscopy combined with Raman and x-ray photoelectron mi- croscopy reveal that the formation of Cu nanoparticles in MCD films can catalytically convert the less conducting disorder/a-C phases into graphitic phases and can provoke the formation of nanographite in the films, forming conduction channels for electron transportation.