Plasma-assisted Chemical Vapor Deposition System Research Articles

Diamond Structures for Tuning of the Finesse Coefficient of Photonic Devices.

Finesse coefficient is one of the most important parameters describing the properties of a resonant cavity. In this research, a mathematical investigation of the application of diamond structures in a fiber-optic Fabry–Perot measurement head to assess their impact on the finesse coefficient is proposed. We present modeled transmission functions of cavities utilizing a nitrogen-doped diamond, a boron-doped diamond, nanocrystalline diamond sheet and a silver mirror. The diamond structures were deposited using a microwave plasma-assisted chemical vapor deposition system. A SEM investigation of surface morphology was conducted. The modeling took into consideration the fiber-optic Fabry–Perot setup working in a reflective mode, with an external cavity and a light source of 1550 nm. A comparison of the mathematical investigation and experimental results is presented.

The correlation between tribological properties of nanostructure TiN coatings and deposition process parameters in PACVD system

Titanium base coatings are being used extensively for improving wear characteristics at the surface of different parts. Titanium nitride was deposited by Plasma Assisted Chemical Vapor Deposition (PACVD) techniques with purpose improve interface with substrate, as this can increase wearing of the entire part in spite of desirable wear behavior of TiN. Samples from H13 steel were prepared and they experienced plasma nitriding (PN) prior to TiN deposition. TiN coatings were deposited in different conditions of temperature (475, 500 and 525°C) and duty cycle (33, 40 and 50%). Topographic studies were preceded by Atomic Force Microscope (AFM). Surface hardness was evaluated using Vickers's micro-hardness test. In order to study the wear behavior, pin-on-disc test was chosen which included examining the sample's resistance against pins from steel and tungsten carbide-cobalt. Based on the results obtained it can be observed that increasing the deposition temperature from 475 to 525°C will lead to higher values of hardness, thus the obtained weight loss from samples decreased from 2.1 to 0 mg. In addition to that, with increasing the duty cycle of system from 33 to 50%, weight loss of the TiN coating has increased from 0 to 2mg due to an increase in the value of surface roughness.

Electrochemical Properties of Polycrystalline Phosphorus-Doped Diamond

Introduction Since a p-type boron-doped diamond (BDD) has excellent electrochemical properties, such as wide potential window, low background current, and so on, it has been investigated for both of fundamentals and electrochemical applications1. On the other hand, few studies have reported on the electrochemical properties of n-type diamond. The electrons in the conduction band of the diamond have the quite high reducing ability because it is situated at much higher energy level than that of other semiconductors. Hence, the n-type diamond electrode may present new electrochemical properties. In this work, we study on the preparation and the characterization of polycrystalline phosphorus-doped diamond (PDD), which is the most promising candidate for n-type diamond, and investigate the electrochemical properties of PDD. Experimental The polycrystalline PDD films were deposited on Si wafer substrates by a microwave plasma-assisted chemical vapor deposition system in following steps. Firstly, undoped diamond layer was deposited in CH4/H2 plasma for 4 hours. Subsequently, red phosphorus sublimed at 400ºC was introduced into CH4/H2 plasma for 1 hour in order to deposit PDD layer. The surface morphology was characterized by scanning electron microscopy (SEM), and structure was investigated by Raman spectroscopy and X-ray diffraction (XRD). Phosphorus doping level was evaluated by secondary ion mass spectroscopy (SIMS). The hall effect measurement was performed using van der Pauw method. Electrical contacts were made by sputtering Ti and Au on the PDD surface, followed by annealing in vacuum at 450ºC for 45 min to form the Ti-C layer. Electrochemical properties were characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) in an aqueous solution of 0.1 M H2SO4. Mott-Schottky plots were obtained by EIS measurements. Moreover, these results were compared with electrochemical properties of BDD electrode. Results and discussion The SEM images showed a polycrystalline nature with grain size of ca. 2 μm. Raman spectrum showed a sharp peak from center zone optical phonon of diamond at 1332 cm−1 and a wide band from sp2-bonded carbon at around 1500 cm−1. Phosphorus concentration in the synthesized film was 1.36×1018 cm−3. From Hall effect measurement, it was confirmed that the PDD film was n-type semiconductor because hall coefficient was negative. From the CV measurement, the cathodic current was much larger than the anodic current, which is a characteristic of the interface between n-type semiconductor and solution (Fig. 1). Since p-type BDD showed the reverse behavior, this characteristic is ascribed to the influence of phosphorus doping. In order to estimate the position of band edges of PDD and BDD, the space charge capacitance C was measured by EIS measurement. The obtained C as a function of potential E was fitted with Mott-Schottky equation (1): 1/C 2 = (±2/eε0εSCN)(E−Efb −kT/e) (1) where the plus and minus signs represent the type of semiconductors, ε0 and εSC are the permittivities of free space and diamond, respectively, e is the electron charge, and N is the donor or acceptor density. The Mott-Schottky plots obtained by EIS measurement (Fig. 2) revealed that the synthesized PDD film is n-type semiconductor because a positive slope was obtained. Moreover, from the intercept of the potential axis, flat band potential (Efb ) of the PDD and BDD was estimated because kT/e is almost zero at room temperature (298 K). These obtained Efb values were used to determine the band edge positions. The difference between Efb and EVB of BDD was assumed to be ~0.4 eV from the acceptor level of boron. On the other hand, the difference between Efb and ECB of PDD was assumed to be ~0.6 eV from the donor level of phosphorus. From the result of comparing PDD and BDD, the band edges of PDD were found to agree well with the ones of BDD and also the single-crystalline PDD reported on the previous research2. References (1) Y. Einaga, J. Appl. Electrochem. 40. 1807 (2010). (2) Y. Mukuda, T. Watanabe, A. Ueda, Y. Nishibayashi, and Y. Einaga, Electrochim. Acta 179. 599 (2015). Figure 1

The effects of V/III gas ratios on the catalyst-assisted growths of InGaN nanowires

Single crystalline InGaN nanowires were grown on Si(100) using Au catalysts at 700°C in a plasma-assisted chemical vapor deposition system. Under the low V/III (nitrogen radicals/(Ga+In vapor)) ratio in the gas phase, poor quality InGaN nanowires were grown along [0001] orientation (c-axis) containing a high concentration of stacking faults and a low indium content of 12%. However, under the high V/III gas ratio, very high quality InGaN nanowires could be grown along [1 0 1¯ 0] orientation (m-axis) free of stacking faults containing a high indium content of 24%.The transformation of nanowire orientation was likely due to the decrease of indium and gallium compositions in gold catalysts from >85% to <60% with increasing the V/III gas ratios. Besides, the increase of V/III gas ratios enhanced the incorporation efficiency of indium into the nanowires and significantly improved the crystal quality of nanowires by stabilizing the formation of InN under a high concentration of nitrogen radicals for reversing the fast thermal decomposition reaction of InN at 700°C.

Large Area Single-Crystal Diamond Synthesis by 915 MHz Microwave Plasma-Assisted Chemical Vapor Deposition

A 75 kW, 915 MHz microwave plasma-assisted chemical vapor deposition system was adapted and utilized to scale up production of high-quality single-crystal diamonds at high growth rates. A 300 mm diameter plasma discharge was achieved with uniform temperature distributions of ±250 °C on up to 300 single-crystal diamond substrates. Diamond single crystals were synthesized from H2/CH4/N2 gas mixtures at pressures between 90 and 180 Torr, with recorded growth rates from 10 to 30 μm/h. The source of N2 was from vacuum chamber leakage, and it greatly affected synthesis chemistry. Optical emission spectroscopy was used to probe the localized plasma chemistry and plasma uniformity at different gas pressures. Production rates of up to 100 g/day of single-crystal diamonds were demonstrated, with 25% of the material categorized as colorless. Crystals up to 3.5 mm in thickness could be produced during a single deposition run. The quality of the crystals produced was assessed by photoluminescence and UV–visible absorp...

Large-Scale Synthesis of Boron Nitride Nanotubes with Iron-Supported Catalysts

Boron nitride nanotubes (BNNTs) were synthesized in a large scale with iron-supported catalysts (Fe/SiO2−Al2O3) at low temperatures (900 °C) in a plasma-assisted chemical vapor deposition system. The structural morphology, chemical composition, and optical and photoluminescence properties of BNNTs were characterized. The obtained BNNTs are crystalline and with tubular structures, and the preferential zigzag arrangement of BNNTs was discovered for the first time for BNNT grown at low temperature (<1000 °C). The O2 additives were found to affect the growth yield significantly and it was attributed to the enhanced dehydrogenation from the catalyst surface and improved balancing of excess H radicals during our synthetic process. In addition, results from elemental-mapping revealed that the boron dissolved in iron tends to precipitate and react with nitrogen to form a BN sheet on the catalyst surface.

Synthesis of boron-doped homoepitaxial single crystal diamond by microwave plasma chemical vapor deposition

The deposition of boron-doped homoepitaxial single crystal diamond is investigated using a microwave plasma-assisted chemical vapor deposition system. The objective is to deposit high-quality boron-doped single crystal diamond and establish the relationships between the deposition conditions and the diamond growth rate and quality. Experiments are performed using type Ib HPHT diamond seeds as substrates and growing diamond with varying amounts of diborane in a methane–hydrogen gas mixture. The deposition system utilized is a 2.45 GHz microwave plasma-assisted CVD system operating at 135–160 Torr. Experiments are performed with methane concentrations of 4–6% and diborane concentrations of 5–50 ppm in the feedgas. Diamond is deposited with growth rates of 2 to 11 µm/h in this study. The deposited diamond is measured to determine its electrical conductivity and optical absorption versus wavelength in the UV, visible and IR portions of the spectrum. Data is presented that relates the growth rate and diamond properties to the deposition conditions including substrate temperature and feedgas composition.

SiC Formation Through Interface Reaction between C60 and Si in Plasma Environment

The formation of SiC through the interface reaction between C60and Si in a plasma-assisted chemical vapour deposition system(PACVD) is investigated with a C60 film previously depositedon Si wafers. The composition and structure of the deposited sampleswere characterized by micro-Raman spectroscopy and X-ray diffraction(XRD). The results showed that SiC film was formed successfully inhydrogen plasma at a substrate temperature of 800°C. Thehydrogen atoms in plasma were found to enhance the production ofSiC. Furthermore, the effects of the added CH4 on the formationof film were studied. Introduction of CH4 simultaneously withH2 at the beginning would suppress the formation of the initiallayer of SiC due to a carbon-rich environment on the substrate,which would be disadvantageous to the further growth of the SiCfilm.

Improvement of the biocompatibility and mechanical properties of surgical tools with TiN coating by PACVD

TiN film has been applied for medical cutting tools to improve the mechanical properties such as surface hardness and wear resistance, and also to provide the biocompatible property of the surgical tools. TiN film has been deposited by using a plasma-assisted chemical vapor deposition system. Bipolar-pulsed DC discharge has been used for optimal plasma discharge condition, and the gas mixture of TiCl 4, N 2, H 2 and Ar has been used. TiN layer enhanced the surface hardness of 2000 kg/mm 2 HK 0.01 and the corrosion property of the film. The corrosion resistance of TiN films has been estimated using Hank's solution and the corrosion rates of bare stainless steel substrate and the specimen coated with TiN were 1300 and 66 nA/cm 2, respectively. TiN film also shows a good biocompatibility in the standard cytotoxicity test (ISO10993-5: Tests for Cytotoxicity—In Vitro Methods), which is the normal method for ensuring the biocompatibility of a medical tool. In the standard cytotoxicity test, we obtained an excellent characteristic of biocompatibility from the medical tool coated with TiN layer. This means that the TiN-coated specimen is free of harmful extractables or has not much of them to cause any acute effects even under exaggerated conditions with isolated cells.

The electrical conduction mechanism for the polycrystalline diamond membrane in the voltage range of ±50 V

Polycrystalline diamond films were deposited on the silicon substrate using a methane/hydrogen gas mixture in a microwave plasma-assisted chemical vapor deposition system. The polycrystalline diamond membrane was obtained by etching the backside of the silicon wafer with KOH solution. The conduction mechanisms for the Al/diamond/Al sandwich structure of the polycrystalline diamond membrane were established in the voltage range of −300 to 300 V. The equivalent circuit for the polycrystalline diamond membrane was represented by a back-to-back Schottky diode for the bulk diamond crystallites, in parallel with the grain boundary impedance for the diamond grain boundaries. It was found that the field-activated transport mechanism, in which the grain boundary impedance can be represented by the modified Frenkel–Poole equation, was for the diamond grain boundaries. The electrical conduction properties of the bulk diamond crystallites was found to be expressed by the Schottky emission conduction mechanism with the generation current, which played an important role in the low voltage measurement region of ±50 V.

Successive current–voltage measurements of a thick isolated diamond film

Polycrystalline diamond films were deposited on p-type (1 0 0) silicon substrate using a methane/hydrogen gas mixture in a microwave plasma-assisted chemical vapor deposition system. After the back-etched process, the Al contacts were evaporated on both sides of a 150 μm thick isolated diamond film for consecutive high-voltage measurements. It was found that the current–voltage ( I– V) characteristics of the Al/diamond/Al structure exhibited two Schottky barrier diodes in a back-to-back configuration. Since the top diamond surface possessed better diamond quality than the bottom surface, the top Schottky diode with a breakdown voltage of 897 V and a lower breakdown voltage of −515 V for the bottom Schottky diode was observed for the first I– V measurement. However, the breakdown voltage was decreased by 37 and 140 V for the top and bottom Schottky diodes after the consecutive sixth repeated measurements. It was found that the oxygenated phenomenon was more prominent; in addition, the quality of the isolated diamond film was also degraded after the consecutive high-voltage measurements. It was indicated that decrease of the breakdown voltage was due to the oxidation layer and the non-diamond components on both surfaces of the isolated diamond film.

Physical characteristics of the annealed/isolated-diamond film

Abstract The polycrystalline diamond films were deposited on the silicon substrate using a methane/hydrogen gas mixture in a microwave plasma-assisted chemical vapor deposition system. Prior to deposition, the silicon wafers were pretreated by a photoresist in which 0.1 μm powder is suspended. The isolated-diamond film was obtained by etching the backside of silicon wafer with KOH solution. From X-ray photoelectron spectroscopy analysis, the oxygenated phenomenon was detected for the as-deposited diamond film and increased for both surfaces of the isolated-diamond film after the back-etching process. A thick SiC (282.7 eV) and non-diamond components (285 eV) interface layer was found on the bottom surface of the isolated-diamond film. However, it was found that part of the interface layer (SiC and non-diamond components) was removed and the amorphous carbon (285.8 eV) was appeared for the bottom surface of the annealed/isolated-diamond film and the silicon signal was appeared for the top surface of the annealed/isolated-diamond film. It was also found that the oxygenated phenomenon increased considerably after the 800°C annealing process. However, from the Raman analysis, it was observed that the full width half maximum was changed from 5.0 to 4.6 cm−1 and from 6.0 to 5.4 cm−1 for the top and the bottom surfaces of the annealed/isolated-diamond film, respectively. It was concluded that the oxygenated phenomenon increased on both of the top and bottom surface layers of the annealed/isolated-diamond film. However, it was found that the oxygenated phenomenon did not degrade the film quality since the quality of the isolated-diamond film was improved after the high-temperature annealing process.

Phosphorus-doped chemical vapor deposition of diamond

Abstract The semiconducting properties of phosphorus-doped diamond thin films grown using a metal-chamber-type microwave plasma-assisted chemical vapor deposition system have been investigated by Hall measurements over a wide temperature range. On {111} surfaces of Ib diamond substrates, the n-type conductive diamond thin films showing a mobility over 100 cm 2 /(V s) can be reproducibly obtained under doping conditions of P/C of 500 ppm in the gas phase. The best sample has shown a mobility of 240 cm 2 /(V s) at room temperature. The activation energy of the carrier was about 0.6 eV. Hopping conductivity has not been observed for these samples as a dominant conduction mechanism even at room temperature, as confirmed by temperature-dependent Hall measurements. However, the carrier mobility shows a slow temperature dependence (∝∼ T −0.7 ) even for the best sample; this implies the existence of another scattering mechanism with phonon scattering, which limits the carrier mobility at low temperature.

Electrical Conduction Mechanism of Al Contacts and Undoped Polycrystalline Diamond Films

Polycrystalline diamond films were deposited using a methane/hydrogen gas mixture in a microwave plasma-assisted chemical vapor deposition system. In this research, a conduction mechanism was successfully established for the Al/undoped diamond structure in the temperature range of 30–300°C. It was found that the rectifying properties of the Al/undoped diamond structure at room temperature exhibited more ohmic behavior at high temperatures. It was suggested that the oxidation layer in the metal/diamond interface was degraded, and more currents flowed through the bulk diamond crystallites and the diamond grain boundaries after the high-temperature measuring process. It was suggested that a Schottky contact was also formed in the diamond grain boundaries. The modified equivalent circuit for the Al/undoped diamond structure is an ideal Schottky diode in series with the bulk resistance for the bulk diamond crystallites, which is also parallel to an opposite pole of the ideal Schottky diode in series with the grain boundary resistance for the diamond grain boundaries. Both the space-charge-limited transport mechanism and the field-activated transport mechanism were considered for the Al/undoped diamond structure. It was found that the field-activated transport mechanism, in which the series resistance can be represented by the Frenkel-Poole equation, had a better fit to the experimental data.

Enhanced nucleation and growth of diamond thin films using a nanodiamond monolayer

It is well known that the nucleation density during diamond film growth can be enhanced by simply scratching the substrates. The abrading particles need not be diamond, as high nucleation densities have been reported on substrates treated with particles of SiC [1], BN [2] etc. However, preferential growth of diamond on diamond has also been reported when diamond is present on the substrate surface as a residue from the polishing [3, 4]. Providing diamond or other nucleation sites is essential as the diamond nuclei formed in the gas phase as a result of the homogeneous nucleation remain unstable until they have reached a certain critical size. This is because the addition of carbon atoms to the nucleus decreases the bulk contribution to the free energy but increases the surface contribution. Therefore, the nuclei formed from the gas phase under normal conditions are unlikely to survive long enough to have an adequately low surface to volume ratio [5]. Thus nucleation on untreated surfaces is slow and leads to a very slow growth rate of the film [6]. Different techniques have been utilized to enhance the nucleation and growth rate of diamond thin films during chemical vapour deposition (CVD). Nonabrasive techniques have been sought since the polishing process is generally manual and seldom exactly reproducible. Stoner et al. [7] used a combination of negative bias and high methane concentration at the beginning of the deposition run in order to produce an SiC layer followed by carbon cluster formation which eventually led to diamond nucleation. A nucleation density three to five orders of magnitude higher than with conventional polishing was obtainable. Several investigators have also successfully used bucky balls [8] and bucky tubes [9] for diamond nucleation. Hartnett et al. [10] used laser ablated amorphic carbon layer for diamond nucleation and reported a nucleation density of 106 cmy2. In this letter we report the growth of diamond films on Si substrates using a nanodiamond monolayer as the nucleation enhancement layer. Enhancements of almost an order of magnitude in the nucleation density and more than a factor of three in the deposition rate over conventional polishing techniques have been realized. The substrate treatment involved making a slurry of commercially available du Pont nanodiamond powder and methanol. The nanoparticles in the nanodiamond powder were typically 5–10 nm in size. The slurry was formed by mixing approximately 4 g nanodiamond powder in 1 l methanol. The substrates were then placed in this slurry such that the slurry covered the surface of the substrates, and the methanol was allowed to evaporate. By controlling the amount of nanodiamond powder in methanol it is possible to deposit a monolayer of the nanodiamond particles. The substrate was never mechanically abraded in this experiment. Diamond films were deposited in an ASTEX microwave plasma assisted CVD system, which has been described elsewhere [11]. The plasma contained 0.6% CH4 and H2 excited by a 2.45 GHz source with 1500 W power. Deposition was carried out at 850 8C substrate temperature and 500 sccm flow rate. For comparison, films were also deposited on Si substrates that had been mechanically polished with diamond paste. Films were deposited for 15, 30 and 240 min. Fig. 1b shows a SEM micrograph of a sample grown with the nanodiamond layer for 15 min. The nucleation density calculated from this micrograph was 1:5 3 108 cmy2. Parallel samples grown on the Si substrates that were mechanically polished using diamond paste gave a nucleation density of 1:7 3 107 cmy2 after 15 min growth, as shown in Fig. 1a. After 30 min growth the nucleation densities were 2:7 3 109 and 1:8 3 108 cmy2 on the substrates with a nanodiamond layer and on mechanically polished substrates, respectively. Films grown for longer times were used to measure the deposition rate. The deposition rate for the diamond film with the nanodiamond interlayer was measured to be 1.3 μm hy1 as compared to 0.4 μm hy1 obtained for the deposition on the polished substrate under identical deposition conditions. Fig. 2 shows Raman spectra obtained from diamond films on the substrates with nanodiamond interlayer and with mechanically polished substrates. The spectra are virtually identical, indicating similar quality film growth in both cases, despite a very high deposition rate for the sample with the nanodiamond nucleation layer. In both cases, in addition to the sharp peak at 1332 cmy1 attributed to the crystalline sp3 fraction of the film, there is a broad peak

A combined MW/ECR-PACVD apparatus for the deposition of diamond and other hard coatings

We present an apparatus which is well suited for the chemical vapour deposition (CVD) process of diamond and diamond-like carbon (DLC) thin films as well as other hard coatings. The basic unit of the deposition arrangement is an ASTeX (Applied Science and Technology, Inc.) magnetized microwave (MW) plasma deposition source, which is attached to a newly designed large reactor. Owing to some changes in the substrate heater-holder assembly, the apparatus can be employed as an MW plasma-assisted CVD (PACVD) system in the medium-high pressure region as well as an electron resonance (ECR) PACVD system in the low pressure region. First results on diamond deposition in the high pressure MW PACVD regime ( p≈50 mbar) and on DLC deposition under ECR PACVD conditions ( p≈1 × 10 −3 mbar) with silicon substrates are given. In forthcoming investigations the use of the DLC layers for enhancing diamond nucleation will be checked in detail.

A pretreatment process for enhanced diamond nucleation on smooth silicon substrates coated with hard carbon films

Diamond nucleation on unscratched silicon substrates coated with thin films of hard carbon was investigated experimentally with a microwave plasma-assisted chemical vapor deposition system. A new pretreatment process was used to enhance the nucleation of diamond. Relatively high diamond nucleation densities of ∼108 cm−2 were achieved by pretreating the carbon-coated silicon substrates with a methane-rich hydrogen plasma at a relatively low temperature for an hour. Scanning electron microscopy and laser Raman spectroscopy studies revealed that diamond nucleation occurred from nanometer-sized spherical particles of amorphous carbon produced during the pretreatment. The nanoparticles possessed a structure different from that of the original hard carbon film, with a broad non-diamond Raman peak centered at ∼1500 cm−1, and a high etching resistance in pure hydrogen plasma. The high diamond nucleation density is attributed to the significant percentage of tetrahedrally bonded (sp3) atomic carbon configurations in the nanoparticles and the presence of sufficient high-surface free-energy sites on the pretreated surfaces.

Plasma diagnostics in the growth of c-BN films

In order to obtain insights into the role of ion bombardment on the properties of BN thin films grown by plasma-assisted chemical vapour deposition (PACVD) from borane-ammonia (BH 3-NH 3), the nitrogen plasma was studied by optical emission spectrometry at different r.f. powers, applying otherwise the same deposition conditions. With increased r.f. power, the intensity of all the peaks due to N 2 and N + 2 were increased, but the increase of the N + 2 peak was very sharp. At 400 W, the peak due to N + 2 was increased by a factor of 25 times that at 100 W, whereas the most prominent peak due to N 2 was increased by a factor of only 7.5. Thus the additional power increases the ion density and, therefore, the ion flux onto the substrate. This increased ion flux to the more negatively biased substrate contributed to increasing the volume fraction of cubic phase. For a specific substrate and filament temperature in this PACVD system, a threshold value 160 W of r.f. power was found where the phase of the films started to convert from the hexagonal to the cubic phase. A good correlation was obtained between the properties of the films and the level of excited species in the plasma.

Application of nickel plating for the synthesis of chemical vapour deposition of diamond on steels

The major problem with wear-resistant diamond coatings in applications is the poor adhesion. The application of a buffer material holds some promise and has shown some successes. In this study, a commercially available process of electroless nickel plating was applied to steel as an intermediate layer for diamond chemical vapour depositions, by reason of the buffering material being softer than diamond and the stress relaxing, with increasing nickel thickness. Both continous diamond film on a nickel plate and discrete diamond particles embedded in a nickel matrix were formed in a microwave plasma-assisted chemical vapour deposition system. The results of tribotesting indicated that the continuous diamond film as top coating usually suffers from the microcracks, while the composite-like coating improves the wear resistance significantly, though at the expense of losing some surface hardness in comparison with that of the pure diamond coating.

Formation of diamond films from low pressure radio frequency induction discharges

Diamond films have been deposited in a low pressure, radio frequency (r.f.) induction plasma-assisted chemical vapor deposition system. The r.f.-induction system confines the plasma at the low pressures of operation 0.010–10.00 Torr to permit efficient dissociation of the reactant gases. A variety of chemical systems have been used to deposit diamond, including traditional H 2-CH 4 discharges containing 0.5–2.0% CH 4; H 2-CF 4 discharges containing 4–16% CF 4, and water vapor discharges containing high concentrations of alcohol and/or acetic acid vapors. No molecular hydrogen is admitted to the growth chamber for the water-based processes. The water vapor becomes the functional equivalent of the molecular hydrogen used in more traditional H 2-CH 4 discharges. The success of the low pressure r.f.-induction plasma for diamond growth from the wide variety of chemical systems is predicated on the generation of a high electron density plasma. Parent gaseous molecules are converted into appropriate high temperature stable products such as H, H 2, CO, and C 2H 2 as they traverse the plasma. Quadrupole mass spectroscopy has been used to study the conversion of the water-alcohol vapors to H 2, CO, and C 2H 2 as they pass through the r.f. plasma, 99% of the CH 4O is converted into H 2, H 2O, and C 2H 2. These studies show plasma conversion of H 2O into molecular H 2. The excess oxygen is rapidly converted into CO through interactions of the O, presumably with solid carbon sources. Optical emission from both the water-based discharges and the molecular hydrogen-based discharges shows the propensity for atomic hydrogen generation from these low pressure r.f.-induction discharges.