Synthesis Of Diamond Films Research Articles

Evolution of the deposited carbon during diamond thin film synthesis evidenced by in-situ optical studies

Reactivity of silicon substrates in hydrogen and methane gaseous mixtures has been studied by means of in-situ differential reflectivity measurements, in a hot filament assisted chemical vapour deposition reactor. Reflectivity changes have been related to substrate etching by atomic hydrogen, and to carbon deposition. Comparison of the results obtained on substrates scratched with diamond paste (on which diamond growth takes place) and on unscratched ones (no diamond growth) has allowed us to evidence reflectivity changes specific to the diamond formation.

Low Temperature Synthesis of Diamond Films with Electron Cyclotron Resonance Plasma Chemical Vapor Deposition

In this paper we review our previous work and present additional results on polycrystalline diamond film synthesis in a CH4/H2/O2 microwave discharge at substrate temperatures down to 300° C. Low temperature diamond growth was achieved by combining three strategies: the low temperature limit for diamond growth was reduced by decreasing the total gas pressure in the deposition chamber to 1–3 Torr; low pressure diamond growth was enhanced by applying a static axial magnetic field to the plasma generation region to increase gas dissociation and ionization in the Torr pressure range; and the microwave input power was pulse modulated to control the relative fluxes of neutral atomic hydrogen and charged positive ions to the substrate. With these combined methods, high quality diamond films exhibiting a clearly defined Raman phonon peak could be grown at backside substrate temperatures from 300° C to 500° C.

Control of an MPACVD reactor for polycrystalline textured diamond films synthesis: role of microwave power density

We report here results concerning characterisations of polycrystalline textured diamond films with the purpose of determining the parameters responsible for the texture, growth rate and surface morphology. Beyond the influences of methane concentration and substrate temperature on these characteristics, the influence of microwave power density (pMW) is studied. An increase of both diamond film quality and growth rate are observed as the PMW increases. In addition, the role of nitrogen as impurities inCH4/H2 gas mixtures is observed. The quality is characterized by Raman spectroscopy, the morphology by SEM and optical goniometry. The texture was investigated by X-ray diffraction analysis.

Production, Characterization, and Wear Behaviour of Plasma Jet CVD Diamond Films on Hard Metal Cutting Tools

The dc plasma jet chemical vapour deposition (CVD) process is one of the most promising processes for the synthesis of polycrystalline diamond films. The obtainable linear growth rates in the range of 100 μm/h are much higher than the growth rates for other CVD processes like microwave or hot filament CVD (1 to 10 μm/h). Wear resistant diamond coatings on cutting tools are very interesting for industrial applications. The poor adhesion of the diamond films is the main problem with these systems. Therefore a mechanical or chemical pretreatment of the substrate surface is used to improve the adhesion of the coating. The influence of mechanical pretreatment by grinding and polishing with diamond powder as well as chemical etching with different solutions or combinations of these pretreatments were examined on WC-Co hard metals. The diamond films were synthesized on these pretreated cutting tools by dc plasma jet CVD. Scanning electron microscopy, EDS analysis, X-ray diffraction, and Raman spectroscopy have been used to characterize the coatings. Adhesion and wear resistance of the diamond films have been investigated using turning tests on metal matrix composites without lubricant. The improvement in adhesion of the diamond coatings is found to be highest after a combined mechanical and chemical pretreatment.

Influence of Methane Concentration on the Nucleation and Growth Stages in Diamond Film Deposition

Optical emission spectroscopy (OES) and mass spectrometry have been used to characterize the reaction species during the CVD synthesis of diamond films using methane and hydrogen gas mixtures in a microwave discharge. In the low methane concentration range. an increase in the nucleation rate with the methane content in the reactor has been detected by scanning tunneling microscopy (STM), which has been associated to the increase in the atomic hydrogen as well as to the presence of CH x (x < 3) radicals, considered as precursors of amorphous and diamond-like carbon films. Although the further growth of the diamond films is mainly associated with CH 3 radicals and/or C 2 H 2 molecules. present in the discharge. other ionized CH + species have been detected by OES. which are known to favor the attachment of methyl radicals on the growing surface.

マイクロ波プラズマＣＶＤ法による高温酸化クロム基板上でのダイヤモンド膜の合成

マイクロ波プラズマＣＶＤ法による高温酸化クロム基板上でのダイヤモンド膜の合成

Diamond thin film deposition in low-pressure premixed flames

A study of combustion synthesis of diamond films has been carried out using low-pressure, fuel-rich hydrocarbon/oxygen flames. Diamond growth results are reported for acetylene/oxygen, propylene/oxygen, and propane/oxygen flames. The best results are achieved with acetylene/oxygen flames, in which we have grown uniform, 5-cm-diameter polycrystalline films at up to 2.3 μm/h. The deposition rate in propane/oxygen is much lower (0.15 μm/h), and the diamond film quality is also lower. The experimental results are compared to the predictions of a numerical model that includes both detailed flame chemistry and simplified diamond surface chemistry. The comparison of the experimental conditions with the simulation results shows that diamond growth occurs for stoichiometries where a small amount of hydrocarbon ( The model correctly predicts the variation of film growth rate with changes in pressure, substrate temperature, and fuel type. For all flames, the absolute predicted growth rate is somewhat higher than measured, but the agreement is reasonable considering the modeling uncertainties associated with the high peak flame temperatures and incompletely understood diamond surface kinetics.

Effect of CO2 Addition on Diamond Growth by DC Arc Plasma Jet Chemical Vapour Deposition

The effect of adding carbon dioxide ( CO2) to the reactant gases was studied in a dc arc plasma jet chemical vapour deposition (CVD) for the synthesis of diamond films. The fabricated films were characterized by Raman scattering spectroscopy and scanning electron microscopy. Without CO2, Raman spectra of these films display only graphitic peaks. As CO2 is added, faceted diamond crystal is observed in micrographs from scanning electron microscopy and a sharp diamond peak in the Raman spectrum appears. At a CO2/ CH4 ratio of 2.0, diamond films exhibit a pure diamond Raman peak at 1333 cm-1 with small nondiamond carbon peaks. In addition, plasma diagnosis was performed using optical emission spectroscopy.

Particle-Assisted Oriented Deposition of Diamond Thin Films

AbstractWe have developed a method for &lt;111&gt; oriented diamond film synthesis using micron-sized diamond particles. Different size of diamond powders were electrophoretically seeded on silicon substrates using diamond suspensions in organic solvents (acetone, methanol, and ethanol). Diamond suspension in acetone was found to be the best for obtaining uniform diamond seeding by electrophoresis. The thickness of diamond seeded films was changed by varying the applied voltage to observe the effect on the orientation of diamond particles. Then diamond films were deposited by the hot filament chemical vapor deposition (HFCVD) process. A preferred orientation with &lt;111&gt; direction normal to the substrate was obtained for monolayer coatings. The surface morphology, crystal orientation, and quality of diamond films were investigated using scanning electron microscopy, x-ray diffractometry, and Raman spectroscopy.

Diamond film synthesis in low pressure premixed flames of different fuel types

Various aspects of diamond film growth in low pressure flames are presented. Experiments are performed in a low pressure flat flame facility and diamond films are deposited on molybdenum substrates over areas of at least 2 cm2 or 5.5 cm2. Pure acetylene-oxygen (C2H2-O2), ethylene-oxygen (C2H4-O2), and methane-oxygen (CH4-O2) premixed flames are studied and compared for their use in depositing high quality diamond films. It is found that uniformity and quality are very sensitive to substrate temperatures Ts and flame equivalence ratios φ and vary between flames of different fuel types. The growth behavior in response to changes in fuel types is interpreted in terms of burning velocities, which determines the residence times of intermediate species in the post-flame region and strongly influences the flux of reactants to the substrate surface. These results can be used to project alternative, perhaps more cost-effective flame synthesis strategies to deposit diamond coatings.

Diamond film synthesis in low pressure premixed flames of different fuel types

Various aspects of diamond film growth in low pressure flames are presented. Experiments are performed in a low pressure flat flame facility and diamond films are deposited on molybdenum substrates over areas of at least 2 cm 2 or 5.5 cm 2. Pure acetylene-oxygen (C 2H 2-O 2), ethylene-oxygen (C 2H 4-O 2), and methane-oxygen (CH 4-O 2) premixed flames are studied and compared for their use in depositing high quality diamond films. It is found that uniformity and quality are very sensitive to substrate temperatures T s and flame equivalence ratios φ and vary between flames of different fuel types. The growth behavior in response to changes in fuel types is interpreted in terms of burning velocities, which determines the residence times of intermediate species in the post-flame region and strongly influences the flux of reactants to the substrate surface. These results can be used to project alternative, perhaps more cost-effective flame synthesis strategies to deposit diamond coatings.

Thermal conductivity of dc-plasma assisted chemical vapor deposited diamond films

The dc-plasma assisted chemical vapor deposition method has been used to synthesize diamond films. Thermal diffusivity of these films has been measured in 120–800 K with a modified Angstrom method. Phonon scattering processes are considered to analyze thermal conductivity with the full Callaway model. In analysis, microstructure of grain boundaries and extended defect concentration give significant effects to the mean free path of phonons in low temperatures. At high temperatures, the thermal conductivity is governed by the intrinsic thermal resistive process, the umkalpp process. Thermal conductivity of the films above 500 K is shown to close to a recent measurement of natural diamond. This supports that the crystal structure of the films is not different with the bulk diamond.

Effects of electrode arrangement and pressure on synthesis of diamond films by arc discharge plasma jet chemical vapor deposition

Abstract The setup and deposition conditions of electrode arrangement and pressure have been studied to synthesize diamond films at high growth rate on wide area efficiently by arc discharge plasma jet chemical vapor deposition. An apparatus has been used in which four plasma torches, one is used for cathode and the others for divided anodes, are arranged and the positions of these torches are changeable. Growth rate, deposition area and thickness of diamond films have increased with changing the electrode arrangements without improvement of thickness variation. Maximum growth rate of our apparatus has occurred at the pressure of 6.7 kPa and diamond films that have less variations of quality and surface roughness have been synthesized at lower pressure during deposition. Moreover, a high conversion rate, which is the ratio of carbon atoms that form diamond in supplied methane gas, of 16% has been obtained at the pressure of 6.7 kPa and methane concentration of 2%.

Diamond film synthesis in low-pressure premixed methane-oxygen flames

We present the successful demonstration of diamond film synthesis in low-pressure premixed methane-oxygen flames. Experiments are performed in a low-pressure flat-flame facility that has been employed previously to study diamond synthesis in premixed acetylene-oxygen and ethylene-oxygen flames. The quality of the diamond films deposited is comparable to that deposited using these other flames, and the growth rate is approximately 0.2–0.3 μm/h; some factor of 10 less than acetylene-oxygen flames and one-third of that obtained for ethylene-oxygen flames. However, carbon conversion efficiencies are remarkably similar, since the cold gas velocities used here are substantially less, because of the lower burning velocities. The equivalence ratios employed in these methane-oxygen flames are in the 1.8–2.0 range. These values correspond to C:O ratios that are substantially lower than those that have been used to grow good quality diamond in acetylene-oxygen and ethylene-oxygen flames at low and atmospheric pressure. General observations suggest that the quality is only slightly sensitive to changes in equivalence ratios and very sensitive to substrate temperature. Uniform diamond films over areas of about 5.5 cm2 are deposited with substrate temperatures of approximately 900 °C.

Plasma-assisted chemical vapour deposition in a tunable microwave cavity

We describe a microwave plasma-assisted chemical vapour deposition facility with some novel features including the ability to adjust the microwave cavity tuning during operation, thereby maximizing the overall device efficiency. The initial application of the facility was for diamond thin film synthesis. Microwave power, generated by a magnetron obtained from a commercial microwave oven, enters the cylindrical resonant cavity from the top face, which can be adjusted to position the maximum electric field at the desired location within the cavity; this tuning can be done while the equipment is running, allowing fine adjustment of the field distribution when the cavity is plasma-loaded. The microwave power activates the reactant gases, which are at low pressure inside a quartz bell jar specimen chamber, and the cavity base plate has a window through which the rear face of the hot substrate can be viewed, allowing pyrometric temperature measurement. A moveable sample holder allows control of the sample position in relation to the plasma ball. The system is stable and the deposition rate is about 1.25 mu m h-1.

Synthesis of diamond films using sequential chemistry: Enhanced growth rate by atomic oxygen

The growth of diamond films by sequentially exposing a heated silicon substrate to fluxes of carbon, atomic hydrogen, and atomic oxygen is reported on. High quality diamond films can be grown sequentially using only the hydrogen and carbon sources. Here the use of an additional source of atomic oxygen is reported on. Film growth for both the possible exposure sequences to the three sources has been attempted. No film is grown if the exposure sequence is carbon-oxygen-hydrogen. When the exposure sequence is carbon-hydrogen-oxygen it is found that the flux of hydrogen necessary for the growth of high quality diamond films is less than that for runs in which no oxygen is present. The growth rate of diamond is also enhanced up to 500% with atomic oxygen. The role of atomic oxygen in modifying the growth surface is discussed to explain the improvement of growth rate and quality of these films.

Purification of diamond films by applying current into the plasma stream in the arc discharge plasma jet chemical vapor deposition technique

A synthesis method that provides high-purity diamond films is proposed employing direct current arc discharge plasma jet chemical vapor deposition. In the method, an electric current was supplied to a plasma jet stream by applying a bias voltage between a cathode and the substrate on which diamond films were deposited. The Raman spectral analysis showed that the purity of the synthetic diamond was remarkably improved by the application of the bias voltage during deposition. The alternating current calorimetric method was employed to measure the thermal diffusion coefficient of the synthesized diamond films. The thermal diffusion coefficient greatly increased for films deposited with biasing. This improved thermal diffusion coefficient suggests higher purity diamond films. Emission spectral analysis revealed that the quantity of the dissociated hydrogen contributing to the plasma emission near the substrate is greater when biasing is used. Thus, the dissociated and excited hydrogen atoms are considered to play a key role in removing the carbon allotropes other than diamond.

In situ optical investigations of diamond thin film growth on molybdenum substrates

Abstract In situ optical measurements have been performed during synthesis of diamond thin films by hot filament assisted chemical vapour deposition on molybdenum substrates. Monochromatic measurements of reflectivity and elastic scattered light intensity have enabled us to follow in real time the evolution of the diamond particle size. Hence, growth kinetic domains have been inferred. Spectroscopic measurements of differential reflectivity have evidenced diamond absorption processes during the diamond crystal growth.

Jumps and Hysteresis Effects in CH4-H2 Plasma Discharges

In typical conditions of diamond film synthesis in a EACVD device (ElectronAssisted Chemical Vapor Deposition), we report on the sudden jumps, bistability, multistability and negative resistance phenomena in methane-hydrogen mixture discharge plasma. We studied the variations of these phenomena with gas pressure, filament current. The difference of discharge characteristic between pure hydrogen and methane-hydrogen mixture system is presented

Carbon Atom, Dimer and Trimer Chemistry on Diamond Surfaces from Molecular Dynamics Simulations

ABSTRACTSpectroscopic investigations of various atmospheres appearing in diamond film synthesis suggest evidence for carbon atoms, dimers or trimers. Molecular dynamics simulations with the Brenner hydrocarbon potential are being used to investigate the elementary reactions of these species on a hydrogen-terminated diamond (111) surface. In principle these types of simulations can be extended to simulations of growth morphologies, in the 1-2 monolayer regime presently.