Good Quality Diamond Films Research Articles

The effect of MoW interlayer thickness on diamond growth on steel substrates

Abstract

Fourier Transform Infrared Spectroscopic Study of Boron-Doped Micro/Nano/Ultrananocrystalline Diamond Prepared by Chemical Vapor Deposition

Boron-doped diamond (BDD) films were grown with different grain sizes. The films were deposited on silicon substrate after a suitable pre-treatment in a hot filament assisted by chemical vapor deposition (CVD) reactor in Ar/H2/CH4 gas mixtures. The addition of argon to the growth gas mixture clearly revealed the transition from nanocrystalline (BDND) to ultrananocrystalline (BDUND) diamond films. Raman spectroscopy results of BDD, BDND and BDUND exhibited a good quality diamond films considering the diamond defined peak. Fourier Transform Infrared Spectroscopy (FTIR) spectra indicated carbonyl groups and B-C in BDND and BDUND films, while the microcrystalline BDD films showed only C-H bonds and boron-carbon (B-C), without the presence of oxygen and unsaturated species. Therefore, the carbonyl presence in the nanocrystalline films is mainly due to oxidation of transpolyacetylene present at the film grain boundaries. The transition became pronounced in the gas mixture with 60% of Ar, and the microcrystalline films were totally transformed in nanocrystalline diamond at 70% of Ar.

Toroidal plasma enhanced CVD of diamond films

An inductively coupled toroidal plasma source is used as an alternative to microwave plasmas for chemical vapor deposition of diamond films. The source, operating at a frequency of 400 kHz, synthesizes diamond films from a mixture of argon, methane, and hydrogen. The toroidal design has been adapted to create a highly efficient environment for diamond film deposition: high gas temperature and a short distance from the sample to the plasma core. Using a toroidal plasma geometry operating in the medium frequency band allows for efficient (≈90%) coupling of AC line power to the plasma and a scalable path to high-power and large-area operation. In test runs, the source generates a high flux of atomic hydrogen over a large area, which is favorable for diamond film growth. Using a deposition temperature of 900–1050 °C and a source to sample distance of 0.1–2.0 cm, diamond films are deposited onto silicon substrates. The results showed that the deposition rate of the diamond films could be controlled using the sample temperature and source to sample spacing. The results also show the films exhibit good-quality polycrystalline diamond as verified by Raman spectroscopy, x-ray diffraction, and scanning electron microscopy. The scanning electron microscopy and x-ray diffraction results show that the samples exhibit diamond (111) and diamond (022) crystallites. The Raman results show that the sp3 peak has a narrow spectral width (FWHM 12 ± 0.5 cm−1) and that negligible amounts of the sp2 band are present, indicating good-quality diamond films.

Effect of Nitrogen Addition Flow Rate on Bonding Strength of Diamond Films Synthesized by Flame Combustion Using High-Purity Acetylene Gas

Diamond films have been synthesized by flame combustion using a mixture of high-purity acetylene and oxygen gas. To obtain good quality diamond films and to achieve good adhesion, diamond films were synthesized by stable flame combustion using the mixture of high-purity acetylene and oxygen gas with nitrogen gas added as the diamond promotion agent; nitrogen flow rate was carefully varied. In previous study, the optimal nitrogen flow rate was 0.500 cm3/s, and good quality diamond films were synthesized. In this study, to investigate effects of nitrogen addition flow rate on the bonding strength of synthesized films, the scratch test by indenter of Rockwell to synthesized delamination-free diamond films was performed, and the bonding strength was discussed. In results, the bonding strength was increased with increasing the nitrogen flow rate from the nitrogen flow rate 0.000 cm3/s, and it was concluded that diamond films synthesized by nitrogen flow rate 0.500 cm3/s had the highest bonding strength. And, the bonding strength was decreased with increasing the nitrogen flow rate from the nitrogen flow rate 0.500 cm3/s. The bonding strength of synthesized diamond films was changed by varying the nitrogen flow rate. Thus, nitrogen addition to high-purity acetylene affects bonding strength. The reason for this is that the nitrogen affects the crystallite morphology of synthesized diamond films. The nitrogen flow rate 0.500 cm3/s is good condition for the bonding strength.

Enhancing the adhesion of diamond films on cobalt-cemented tungsten carbide substrate using tungsten particles via MPCVD system

To increase the adhesion of diamond films and avoid the negative effects of using cobalt, previous treatments have employed tungsten particles to cover the surface of the 6 wt.% cobalt-cemented tungsten carbide (WC-Co) substrate. The surface of the tungsten particles is transformed into W 2C and WC, which attracts and traps carbon. Through the process of nucleation, the carbon forms around the tungsten particles, thereby satisfying the conditions necessary for the formation of diamond film. Using Raman spectroscopy, we determined that diamond films of good quality with excellent adhesive properties and a hardness level as high as 27.78 GPa could be produced following pretreatment with 2.0 μm tungsten particles. Rockwell indentation tests indicate that addition of tungsten particles promotes the interfacial adhesion of diamond films with WC-Co substrates. We determined that using smaller tungsten particles decreased the number of gaps and cavities on the surface of the substrate, thereby enhancing the adhesion of the diamond film.

Correlation between chemical vapor deposited diamond and carbon fibers substrates

Diamond film formation has been studied on carbon felts (CF) substrates produced from polyacrylonitrile precursor, at different heat treatment temperatures (HTT). Scanning electron microscopy images have revealed a polycrystalline and preferential (111) diamond film covering the whole CF surface, even for deeper planes. The average grain size increased from 3.0 up to 6.0 μm for films grown on CF treated between 1000 and 2000 °C. This behavior may be attributed to different contributions associated to the facility to extract carbons atoms from CF substrate. For CF treated at lower HTT, higher carbon atoms amount will promote higher nucleation density on diamond films and consequently a smaller grain size. Raman spectroscopy indicated good quality diamond films and the lower amount of graphitic phase was observed for diamond grown on CF obtained at 2000 °C HTT. The microstructural properties of the CF were obtained by X-ray diffraction (XRD) and show a strong dependence with HTT.

CVD Diamond Applications as TL Radiation Dosimeters

AbstractThe extraordinary characteristics of chemically vapor deposited (CVD) diamond such as tissue equivalence, radiation hardness, and lack of solubility in water; makes CVD diamond a very promising material for radiation dosimetry applications. Recent investigations have shown that CVD techniques allowed the growing of good quality diamond films in a diversity of substrates to be used in the form of ionization chambers, thermoluminescence (TL) detectors and dosimeters. In the present work, we report on the TL properties of MWCVD diamond exposed to gamma radiation in the 0.05 -1.0 kGy dose range and 43.5 and 81.11 Gy min−1 dose rates. The CVD diamond displays a linear dose behavior and 5% TL cycle reproducibility, without requiring any annealing or thermal treatment before using it as TL dosimeter. In spite of the significant results, some problems remain and a lot of research work is necessary to improve the synthetic material characteristics to optimize the TL/OSL radiation dosimeter properties.

100]-textured growth of polycrystalline diamond films on alumina substrates by microwave plasma chemical vapor deposition

In order to grow diamond film on alumina ceramic, it is essential to control the diamond nucleation properly. Under a gas pressure lower than that used for growth, a high nucleation density of diamond films on alumina, as high as 10 8/cm 2, is successfully achieved by microwave plasma-enhanced chemical vapor deposition method. Based on this, [100]-textured diamond films are successfully deposited on alumina by controlling the substrate temperature. From the results on SEM, XRD and Raman measurements, the substrate temperature has a strong influence on the textured growth and quality of diamond films on alumina substrates. Too low or too high temperature cannot obtain [100]-textured and good-quality films. The optimum substrate temperature range, for the growth of [100]-textured and good-quality diamond films on alumina, should be 800∼860 °C in our experiments.

Surface engineering of WC-Co used in dental tools technology

Diamond films, deposited using chemical vapour deposition (CVD), were grown onto cemented tungsten carbide (WC-Co). The 'grade' of hard metal used in this study is commonly employed in dental tools, such as burrs and in microdrills. The WC-Co substrates consisted of 10% cobalt and ≤1 μm WC grain size. Critical to the formation of well bonded diamond layers is the initial nucleation process, which is highly dependent on WC grain size and cobalt concentration. It is shown that by appropriate surface treatment and process optimisation it is possible to grow good quality diamond films onto WC-Co used in dental tools. The as grown films were polycrystalline in nature and consisted of compressive stresses, which were measured using the Raman spectroscopy technique. Indentation test methods were used to characterise the coating adhesion. Two independent indentations were performed at 300 and 500 N loads on diamond coated samples. The different responses of the coatings to the indentations at the two loads are discussed. Coated WC-Co dental burrs were tested using drilling tests on extracted human teeth for performance. The polydiamond crystals deposited onto the burr remained completely intact on the dental tool even after drilling 500 holes into human teeth. However, conventional diamond burr results revealed that the majority of the imbedded diamond particles had been dislodged from their cavities after drilling 500 holes.

Synthesis of boron-doped diamond films by DC plasma CVD using a CH 4+CO 2+H 2 gas mixture at lower substrate temperature and formation of an n-Si/p-diamond heterojunction

Diamond films were synthesized by direct current plasma chemical vapour deposition using a CH 4+CO 2+H 2 gas mixture on Si substrates. The optimum deposition conditions were determined. It was found that 0.4 A/cm 2 current density, at applied voltage of 1 kV, resulted in good-quality diamond films. The substrate temperature was 750 K which is considerably lower than the conventional requirement of ∼1100 K. Boron doping was achieved by passing a portion of the gas mixture through boric acid dissolved in methanol. The boron-doped p-type diamond films were deposited on an n-type single crystalline Si substrate and an n-Si/p-diamond heterojunction was fabricated. The p–n junction was characterized in terms of current–voltage ( I– V) and capacitance–voltage ( C– V) measurements.

Investigations on nitrogen addition in the CH 4–H 2 gas mixture used for diamond deposition for a better understanding and the optimisation of the synthesis process

In this study, we report on some investigations on the effects of nitrogen addition in the conventional CH 4H 2 gas mixture employed for diamond synthesis by microwave plasma assisted chemical vapour deposition process. Diamond films have been achieved for CH 4 concentrations ranging between 0.5 and 3%, and nitrogen amounts introduced in the feed gas between 0 and 3000 ppm, for an averaged power density of 15 W cm −3. The analysis of the deposited films has been carried out using SEM, micro-Raman spectroscopy, profilometry, XRD and electrical characterisations. For the experimental conditions employed we have pointed out that the main and conjugated effects of nitrogen are to enhance the secondary germination formation and the {100} faces development. Consequently, these effects widely depend on CH 4 and N 2 concentrations and the use of an optimal gas mixture composition leads to a maximal growth rate, chemical purity and surface electrical resistance, with a {100}〈100〉 surface global morphology. Furthermore, the achievement of thicker diamond films using the optimal gas composition has permitted to confirm few mechanisms forecasted for thin films. In particular, these mechanisms are related to the {100}〈100〉 morphology formation and to the influence of nitrogen atom incorporation in the films on the surface electrical properties. Finally, the interest of nitrogen addition has been discussed in terms of process optimisation for the production of good quality diamond films for specific applications.

Diffusion-modified boride interlayers for chemical vapour deposition of low-residual-stress diamond films on steel substrates

The feasibility of using a boriding pretreatment for the chemical vapour deposition (CVD) of adherent, low-residual-stress diamond films on ferritic tool and AISI type 316 austenitic stainless steels was investigated. The steel samples were borided by means of a pack cementation process at a temperature of 950 °C using an interrupted thermal cycling process. Boriding of the alloy steels results in a very high surface hardness of approximately 3780 VHN due to the precipitation of alloy borides such as chromium boride in the predominantly FeB and/or Fe 2B case. The boriding conditions, and hence the microstructural state of the as-borided steels, was found to have a strong influence on the diamond film characteristics, particularly on the adherence. Detailed characterisation of the as-borided steels, as well as the deposited diamond films and interlayer modification during the CVD process, is discussed based on scanning electron microscopy, X-ray diffraction and micro-Raman spectroscopy investigations. Under optimised conditions, adherent and continuous diamond films of good quality have been obtained on both the ferritic tool and austenitic stainless steels. In the case of borided surface structures without the presence of a FeB phase, diffusion-modified gradient microstructures were found to accommodate efficiently the high thermal stress expected between the steel substrate and the diamond film, resulting in low-residual-stress films.

Effects of argon dilution of an ethanol/hydrogen gas feed on the growth of diamond by hot-filament chemical vapor deposition

We studied the effects on the growth kinetics and properties of diamond and carbon-like diamond films obtained by the introduction of argon at low to high concentrations (0–85 vol.% Ar) into the feed mixture (ethanol and hydrogen) of a hot-filament chemical vapor deposition (CVD) reactor. Scanning electron microscopy (SEM) analysis revealed that the addition of argon induces an increase in the diamond grain size, and increases the flaws between the grains and the density of vacancy defects. Well-faceted diamond films of good quality (measured by Raman spectroscopy) have been obtained using up to 65 vol.% of argon in the gaseous mixture, while higher concentrations (85 vol.% Ar) produce diamond-like carbon or other complex carbon structures. We also observed an increase in the diamond growth rate with argon addition that was associated with an increase in carbon free radicals (up to ∼40 vol.% Ar) or to the increase in the filament temperature necessary to keep the substrate temperature constant at higher Ar concentrations (above ∼40 vol.% Ar). Room temperature photoluminescence spectroscopy also confirmed that argon addition increases the density of vacancy defects in the diamond structure.

Characterization of diamond films deposited with a 915-MHz scaled-up surface-wave-sustained plasma

The operating frequency of a microwave plasma system designed for polycrystalline diamond film deposition is lowered from 2450 to 915 MHz to allow for larger diameter substrate processing. The substrate diameter is limited to 80 mm by the size of the cathode heater utilized as susceptor; 76-mm (3-inch) Si(100) wafers have actually been processed. Good-quality diamond films are obtained over the whole substrate surface with a thickness uniformity of ±10%. The plasma of these systems is sustained by an electromagnetic surface wave and adjusted for uniform coverage of the substrate. We compare the characteristics of these discharges at 915 and 2450 MHz and their corresponding diamond films.

Growth of polycrystalline diamond films on stainless steel without external barrier layers using oxy-acetylene flame

Polycrystalline diamond films have been successfully deposited on stainless steel substrates using oxy-acetylene flame. Films have been characterized using scanning electron microscopy, X-ray diffraction and micro-Raman spectroscopy. Good quality diamond films were obtained by employing a short duration pretreatment of the substrates by the oxidizing outer zone of the flame, prior to film deposition using inner zone (acetylene feather) of the flame. Low growth temperatures (∼625 °C) and formation of oxides at the steel surfaces during pretreatment are suggested to be responsible for the growth of diamond films.

Nano-diamond films produced from CVD of camphor

Abstract Nano-diamond films were deposited by chemical vapour deposition (CVD) of camphor (C 10 H 16 O) and hydrogen (∼ 75 vol.%) on glass (at 523–623 K) and quartz/Si substrate (at 523–713 K). The films had low values of surface roughness (∼ 17 nm on quartz) along with high values of hardness and band gap. IR studies of the films deposited on Si substrate indicated the films to be transparent in the IR region. Optical properties of the films deposited on quartz (fused silica) and glass (Corning) substrates were studied. The absorption data in the below band gap region were utilized to estimate the strain (2–12 × 10 −3 ), stress (1.9–8.4 GPa) and hardness (47–62 GPa) in the films. The FTIR studies of the films did not show absorption around 2900 cm −1 , while the Raman spectra indicated a sharp peak (with FWHM ∼8 cm −1 ) at 1337 cm −1 corresponding to good quality diamond films.

Evaluation of buffer layers for hot filament chemical vapor deposition diamond films on silicon substrates

Deposition of high-quality diamond films on technology important substrates such as semiconductor silicon is a difficult problem due to inherent interdiffusion problems between substrates and diamond overlayers. To overcome this difficulty the concept of the buffer layer has been utilized and good quality diamond films have been deposited on Si (100) substrates with different kinds of buffer layers. Aluminum nitride (AlN), titanium nitride (TiN), carbon nitride (CN x), and tungsten carbide (WC) as buffer layers have been studied for diamond nucleation enhancement. Scratching the silicon substrate surface with a diamond paste has also been investigated for diamond nucleation enhancement on Si (100) substrates. The deposited diamond films have been characterized with Raman spectroscopy, and scanning electronic microscopy (SEM) techniques. This study shows that the use of a buffer layer is very effective in enhancing the nucleation rate of diamond films. Finite-volume based computational fluid dynamics has been used to model flow, transport, gas-phase, and surface chemical reactions.

The synthesis and characterization of phosphorus-doped diamond films using trimethyl-phosphite as a dopping source

Producing impurity-doped diamond films is a critical task for modern electronic applications. In this study, the effects of phosphorus in the gas phase on the morphological features of polycrystalline diamond films were investigated. The diamond films were prepared on n-type Si(100) substrates by the microwave plasma chemical vapour deposition. A trimethyl-phosphite vapour was introduced to the CH 4CO 2 gas mixture as a dopant source. Surface morphology changed from well-defined facets to ball-like features by increasing the dopant concentration in the gas phase. Phosphorus-doped diamond films of good quality and well defined facets could be obtained by reducing the carbon concentration of reactant gases. This reduction could be achieved by decreasing the CH 4 flow rates during the deposition process. An increase in the the dopant source caused the growth rate to become lower, the nucleation density to reduce drastically, and the relative intensity of XRD characteristic (110) peak to increase significantly.

Diamond synthesis by capacitively coupled radio frequency plasma with the addition of direct current power

Diamond films were synthesized by using radio frequency (RF) power in a capacitively coupled mode with a parallel plate electrode configuration in which direct current (DC) power was also applied simultaneously. This new plasma method is superior to plain DC plasma chemical vapor deposition (CVD) techniques for diamond deposition since it is very stable and seems readily scaleable. Good quality diamond films were synthesized by this modified plasma CVD method. The effect of variation of both RF and DC parameters on the deposited diamond films is discussed.

Effect of nitrogen on diamond growth using unconventional gas mixtures

The influence of nitrogen on the growth of diamond using unconventional gas mixtures of CH 4CO 2 by microwave plasma chemical vapor deposition was investigated. A clear improvement in the surface morphology and quality of the diamond films indicates the beneficial effect of adding nitrogen to CH 4-CO 2 gas mixtures. However, most interestingly, for lower methane concentration, the addition of small amounts of nitrogen resulted in the formation of isolated diamond particles possessing a vacant “cage-like” structure with completed {100} facets This result indicates that the continued addition of nitrogen gives rise to the deterioration of {111} facets and the retention of {100} facets. Analysis using Auger electron spectroscopy and secondary ion mass spectroscopy shows very low and uniform levels of nitrogen in the diamond films. Although the amount of atomic hydrogen in the ground state decreased and CN radicals increased with increasing amounts of added nitrogen, good-quality diamond films were deposited resulting from a larger amount of atomic oxygen and the decrease in the C 2 emissions in the gas phase under optimum conditions.