Deposited Diamond Films Research Articles

Polycrystalline diamond film fabrication using modulated inductively coupled thermal plasmas at different pressure conditions

This paper investigates pressure influence on polycrystalline diamond formation using sawtooth-waveform modulated induction thermal plasma. Modulated induction thermal plasma was used to promote nucleation of diamond particles in the first stage. The operating pressure was set to 32, 60, and 90 Torr. The deposited diamond films were analyzed by field emission scanning electron microscope and Raman spectroscopic observation. Experimental results indicated that a lower pressure condition provided a higher deposition rate and a qualitatively better diamond film. Spectroscopic and high-speed video camera observation showed that a lower pressure condition expanded the thermal plasma flow axially onto the substrate. Numerical simulation was also made for Ar/CH4/H2 induction thermal plasma to study the influence of pressure on the thermal plasma flow. Calculation results showed that lower pressure involves a higher particle flux of neutral hydrocarbon species on to the substrate surface because of higher convective transport of these species before their ionization. These results imply that neutral hydrocarbon would play a more important role for diamond deposition than hydrocarbon ions in the present thermal plasma diamond film deposition.

Investigating the Possible Origin of Raman Bands in Defective sp2/sp3 Carbons below 900 cm−1: Phonon Density of States or Double Resonance Mechanism at Play?

Multiwavelength Raman spectroscopy (325, 514, 633 nm) was used to analyze three different kinds of samples containing sp2 and sp3 carbons: chemical vapor deposited diamond films of varying microstructure, a plasma-enhanced chemical vapor deposited hydrogenated amorphous carbon film heated at 500 °C and highly oriented pyrolytic graphite exposed to a radio-frequent deuterium plasma. We found evidence that the lower part of the phonon density of states (PDOS) spectral region (300–900 cm−1) that rises when defects are introduced in crystals can give more information on the structure than expected. For example, the height of the PDOS, taken at 400 cm−1 and compared to the height of the G band, depends on the sp2 content, estimated by electron energy-loss spectroscopy. This ratio measured with 633 nm laser is more intense than with 514 nm laser. It is also correlated for diamond to the relative intensity ratio between the diamond band at 1332 cm−1 and the G band at ≈1500–1600 cm−1 when using 325 nm laser. Moreover, it is found that the shape of the PDOS of the exposed graphite samples is different when changing the wavelength of the laser used, giving evidence of a double resonance mechanism origin with the rise of the associated D3, D4 and D5 bands, which is not the case for a-C:H samples.

Numerical optimization of hydrogen microwave plasma reactor for diamond film deposition

We present the results of optimization of microwave plasma generation in a prototypical diamond film deposition device by means of numerical simulation. The modification of the device was done by changing the shape of microwave resonant chamber, where the plasma generation occurs, in a way to focus the discharge near the outlet nozzle. The best results were obtained for a configuration with an addition of a conducting rod located on the axis of the chamber. This modified configuration provided a two orders of magnitude increase in electron number density near the nozzle exit and about 10 time increase (up to 5%) in dissociation degree of hydrogen molecules.

Gas Jet Deposition of Diamond onto a Steel Surface Covered by a Tungsten Carbide or Molybdenum Layer

Results of studying the growth of diamond structures on steel specimens with the use of intermediate layers of molybdenum or tungsten carbide cemented by cobalt are reported. The interlayers are deposited by means of detonation spraying. Subsequent deposition of diamond films onto the clad steel specimens is formed by the gas jet method and a special thermocatalytic reactor with extended activating surfaces. The nucleation process on the interlayer surfaces is intensified by preliminary seeding of the specimens in a colloid solution containing nanodiamonds. Information about the phase and structural composition of the resultant specimens and about the film surface morphology is obtained by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction analysis. The tribology of the specimens is studied with the use of hardness nansensors and by the Rockwell hardness indentation method.

Three-dimensional micromachined diamond birdbath shell resonator on silicon substrate

This paper proposes a novel three-dimensional (3-D) micromachined birdbath shell resonator ($$\mathrm {\upmu }$$-BSR) fabricated from polycrystalline diamond on silicon substrate for potential MEMS gyroscope. Design, modal simulation, MEMS fabrication process and vibration test of the micromachined diamond birdbath shell resonator are presented. Key features of the 3-D fabrication process are the etching of the bulk silicon mold and deposition of high-Q polycrystalline diamond films onto the mold. The birdbath shell resonator is fabricated with a good structural symmetry, owing to its supporting anchor and shell are integrated manufactured through the MEMS fabrication process. By using piezoelectric actuation and optical characterization, the M = 2 elliptical vibration mode is determined to be at about 80.61 kHz with a normalized frequency split ($$\varDelta {f_{M = 2}}/{f_{M = 2}}$$) of 0.32%. The frequency separation between the M = 2 elliptical mode and the closest parasitic tilting mode of the $$\upmu $$-BSR is relatively large, which makes the resonator less sensitive to vibration and improves shock resistance. These resonators show great promise for being used as micro birdbath resonator gyroscopes ($$\upmu $$-BRGs) on a chip.

La-doped diamond films prepared through microwave plasma chemical vapor deposition

La-doped diamond films were deposited through a microwave plasma chemical vapor deposition (MPCVD) system. The effects of La addition on the morphology, microstructure, and quality of the diamond films were systematically investigated. The analysis of secondary ion mass spectroscopy and X-ray photoelectron spectroscopy indicates that lanthanum atoms were incorporated into the diamond films through MPCVD with lanthanum (III) acetate as a precursor. The characterization results reveal that different lanthanum dopant flows can affect the morphology, the preferred orientation of the crystal, and the diamond phase fraction in the films. Upon the lanthanum addition with the dopant flow of 30 sccm, the intensity ratio of the (220) to (111) peaks [I(220)/I(111)] decreases from 20% to 17% and the sp3/sp2 ratio is reduced from 8.53 to 5.89. However, with the increase of the lanthanum dopant flow to 90 sccm, the intensity ratio of I(220)/I(111) rises up to 39% and the sp3/sp2 ratio increases to 8.99. Therefore, a certain amount of lanthanum addition can promote the growth of (110) orientation grains and enhances the sp3 phase fraction in the deposited diamond films. The results obtained from this study provide a hint for adjusting the morphology and microstructure of diamond films with rare earth element doping.

Micro-manufacturing technology of a three-dimensional curved surface diamond structure for gyroscope applications

A novel three-dimensional (3D) micro-manufacturing technology of a curved surface diamond structure used for a micro birdbath resonator gyroscope (-BRG) with integrated curved electrodes is presented. The integrated curved electrodes with the same curvature as the birdbath shell are embedded using a self-aligned process, which avoids the extra assembly process, ensures the symmetry and improves the driving capacity of the -BRG. The capacitive gap is defined by the sacrificial layer, and a uniform and small gap distance (2 m) between the curved electrodes and the birdbath shell is obtained. The -BRGs with a diameter of 1.2 mm and a thickness of 2 m have been demonstrated by employing boron-doped microcrystalline diamond films deposited using hot filament chemical vapor deposition (HFCVD). In this paper, the device structure and basic working principle of the gyroscope are described. The key steps in the fabrication process, such as isotropic wet etching of the bulk silicon for a birdbath mold, photoresist spray-coating for patterning the curved electrodes, and deposition and etching of diamond films, are considered in detail and well solved. The radial deviation of the etched birdbath mold is about 0.31% for the ∼560 m radius shell and the surface roughness of the birdbath mold is favorable (Rq = 4.933 nm, Ra = 3.945 nm). The key techniques described in this paper can be applied to the fabrication of other 3D micro devices.

Superhydrophilic surface of oxidized freestanding CVD diamond films: Preparation and application to test solution conductivity

This work reports the surface features, wettability properties and application of the thermally oxidized freestanding chemical vapor deposited diamond films. The oxygen-terminated micrometer-sized diamond grains on growth side and the pyramid-shaped diamond nanotips on nucleation side of diamond films, having superhydrophilic feature, are realized by a thermal oxidation treatment process in air. The superhydrophilic surfaces were proposed to examine the conductivity properties of micro-solution droplets (with varying ion concentrations) spreading fast on the film surface. The corresponding conductivities of the micro-solutions are nearly linearly increased with increasing the ion-concentration in a large region. It is demonstrated that the chemical inert diamond films with the functionalized surfaces are favorable for fabricating high efficient, sensitive, and washable detectors.

The Influence of B, N and Si Doping on the CH3 Adsorption on the Diamond Surface Based on DFT Calculations

To better understand the influence mechanism of boron, nitrogen and silicon dopants on the growth of chemical vapor deposition (CVD) diamond film, density functional calculations have been performed to reveal the different impact of the impurities on the CH3 adsorption on diamond surface. The substituted doping and radical doping of diamond (111) and (100) − 2 × 1 surface are both considered. The calculation results indicate that the CH3 radicals are hardly adsorbed on nitrogen atoms and thus may cause vacancy in the diamond lattice easily. Boron substituted doping will disfavor the adsorption of CH3 due to the lacking of valence electron. However, the empty p orbitals of boron atom will help the chemical adsorbing of CH3 radicals. The substituted silicon doping has little influence on the CH3 adsorption, as Si atom has the same outer valence electron structure with C atom. In the case of radical doping, the adsorption energy of CH3 will be reduced due to the steric hindrance between NH2 or SiH3 with CH3. The adsorption energy can be slightly enhanced when BH2 radical is pre-adsorbed on diamond (111) surface. However, the BH2 pre-adsorbed on diamond (100) − 2 × 1 surface may interact with surface radical carbon site and result in a large reduction of CH3 adsorption energy. Thus, the boron doping may hinder the formation of the (100) facet during the CVD diamond deposition under a certain condition.

Influence of the Heat Dissipation Mode of Long-Flute Cutting Tools on Temperature Distribution during HFCVD Diamond Films

The distribution of substrate temperature plays a decisive role on the uniformity of polycrystalline diamond films on cemented carbide tools with a long flute, prepared by a hot filament chemical vapor deposition (HFCVD). In this work, the heat dissipation mode at the bottom of tools is a focal point, and the finite volume method (FVM) is conducted to simulate and predict the temperature field of tools, with the various materials of the holder placed under the tools. The simulation results show that the thermal conductivity of the holder affects the temperature difference of the individual tools greatly, but only affects the temperature of different tools at the same XY plane slightly. Moreover, the ceramic holder can reduce the difference in temperature of an individual tool by 54%, compared to a copper one. Afterwards, the experiments of the deposition of diamond films is performed using the preferred ceramic holder. The diamond coatings on the different positions present a highly uniform distribution on their grain size, thickness, and quality.

Atmospheric-Pressure Microwave Plasma Torch for CVD Technology of Diamond Synthesis

An electrodeless microwave jet plasma source is considered, and its various applications in the technology of chemical vapor deposition of diamond films and dimension increasing of small diamond single crystals synthesized at high pressures and temperatures are discussed. The plasma jet is ignited in an atmospheric-pressure gas (argon) flow with hydrogen and methane additives. The operation of the microwave jet reactor is described, and the plasma characteristics measured using emission spectroscopy are presented. The brightly glowing atmospheric-pressure plasma jet is ignited and stably burns at a microwave power of ≤1 kW supplied from a microwave oven magnetron. The specific microwave power density absorbed by the compact plasma jet (≤104 W/cm3) is comparable with that absorbed by a dc arc. The growth rate of the polycrystalline diamond layer amounts to 40 µm/h. The process of film deposition on the substrate can be controlled by scanning the substrate surface with the jet.

Formation of Pentagonal Dimples in Icosahedral Diamond Crystals Grown by Hot Filament Chemical Vapor Deposition: Approach by Non-Classical Crystallization

In this study, acetone was used as a carbon source to deposit diamond films using tantalum filaments by hot filament chemical vapor deposition (HFCVD). For acetone fluxes of 80, 90, 130 and 170 standard cubic centimeters per min (sccm) and the respective hydrogen fluxes of 420, 410, 370, and 330 sccm, film thickness appeared to increase with increasing acetone, and high quality diamonds were deposited with well-defined facets of (111) and (100). For acetone fluxes of 210 and 250 sccm and the respective hydrogen fluxes of 290 and 250 sccm, however, the diamond quality was degraded with cauliflower-shaped structures evolving and the film thickness decreased with increasing acetone. The degradation of diamond quality was confirmed by Raman spectra and X-ray diffraction (XRD). Many diamond crystals grown at acetone fluxes of 80, 90, 130 and 170 sccm consisted of five (111) facets, indicating an icosahedral structure. At the corner where the five (111) facets met, there were pentagonal dimples, which implied that diamond crystals must have been etched. The decrease in film thickness at high acetone fluxes of 210 and 250 sccm also implied that the deposited film must have been etched. These results indicate that the two irreversible processes of deposition and etching occur simultaneously, which would violate the second law of thermodynamics from the classical concept of crystal growth by an individual atom. These puzzling results could be successfully explained by non-classical crystallization, where the building blocks for diamond films are nanoparticles formed in the gas phase.

Gaseous boronizing pretreatment for the deposition of nanocrystalline diamond films on cemented carbide substrates

A simple and efficient method-vacuum heat treatment gaseous boronizing was proposed to pretreat the YG6X cemented carbides for maintaining its toughness and strength of the pretreated cemented carbide, and promising for mass production. After this pretreatment, the substrate surface remained clean, and the nanocrystalline diamond (NCD) films were deposited on the pretreated cemented carbide by hot filament chemical vapor deposition (HFCVD) with methane, hydrogen and argon as reaction gases. The morphology, structure, roughness and film-substrate adhesion strength of the cemented carbide substrate and the diamond films were analyzed by x-ray diffraction (XRD), scanning electron microscopy (SEM), micro-Raman spectroscopy and adhesion performance test. The results show that this method of gaseous boronizing is stable and feasible. The boride layer with high temperature stability can be formed. The microhardness of the cemented carbide surface after boronizing treatment was increased by 18% compared with that of the original untreated one. The comprehensive treatment of the alkali etching followed by boronizing is more effective to improve the film-substrate adhesion performance than the two-step chemical etching pretreatment.

Theoretical Study of Sulphur Atoms’ Adsorption and Migration Behaviors on Diamond (001) Surface

The adsorption and migration of sulphur (S) atoms on the diamond (001) surface were investigated through first principles calculations to discover the inherent law in S-doped diamond film growth. Results indicated that deposited S atoms could abstract the hydrogen atom on the surface. The adsorption energies were in a range of 2.47 to 5.5 eV when S atoms were deposited on the hydrogen terminated surface or the surface with open radical sites (ORSs). The S atom could migrate on the surface of the 3ORS slabs and the energy barrier was approximately 1.35 eV. The calculations of the projected density of states and the analysis of the magnetic moments presented an interesting result, which demonstrated the evolving phenomena in S-doped diamond film growth and discovered the inherent laws. On the 2ORS slabs, the magnetic moment of the S atom became 0.000 μB after bonding with the two carbon atoms. In such case, a new doped C atom combined with the S atom with a triple bond, and then the C–S molecule was desorbed from the surface. The abstraction of the adsorbed S atom results from the fact that S atoms have six electrons in their outermost electron shell. This finding revealed the reason behind the low S incorporation and the growth rate decrease in S-doped diamond film deposition. This discovery also indicated that atoms with six electrons in their outermost electron shell might hardly be doped into the diamond films during the deposition process.

Selection of CVD Diamond Crystal Size on a CVD Pad Conditioner for Improved Lifetime

Pad conditioners are important consumables for semiconductor chemical mechanical planarization processes. Recently, a new concept has been developed to improve the performance and lifetime of a pad conditioner by depositing diamond film on a uniformly patterned substrate. In this study, we investigated the pad conditioner lifetime while varying the crystal size of the deposited diamond film, which was controlled via different methane (CH4) gas concentrations in hydrogen gas (H2). Microcrystalline diamond (MCD) film was formed using 2% CH4 in H2 flow and nanocrystalline diamond film (NCD) was formed with 4% CH4. The NCD film showed a longer lifetime and higher adhesion with the substrate than the MCD film.

Multivariable study on growth of diamond on diamond substrates by microwave plasma chemical vapour deposition

Substrate temperature and methane concentration in Hydrogen (H2) gas mixture is the main source for increasing the growth rate, nucleation and grain size of a synthetic diamond. The downside of such an approach is reduced quality. By increasing the chamber pressure, although the quality can be improved, however, it leads to a decrease in the crystal growth rate. Thin diamond films were deposited under hydrogen (H2) and methane (CH4) gas mixture using microwave plasma chemical vapor deposition (MPCVD) technique. The effect of methane concentration (1%–5%), growth temperature, and pressure on the nucleation of diamond thin films on diamond substrates was investigated. The growth temperature and pressure were maintained in the range of 925 °C–950 °C and 72–75 Torr, respectively. Single crystal diamond (SCD) thin films have been prepared on diamond substrates, which play an important role in the application of the diamond detectors. Different dimensions of films were obtained on diamond substrates with different thicknesses such as 209.17 μm, 401.73 μm, and 995.03 μm for the sample with 1%, 2% and 5% of methane concentration respectively. The roughness, as well as growth rate of these films, were also investigated and were found to be 4.23 nm and 5.02 μ h−1, respectively for 5% methane by optimizing the substrate temperature at 950 °C. Different characterization techniques were used to study the structural, morphological, and compositional properties of the deposited diamond films which confirmed the crystallographic order of the developed diamond film on the diamond substrates.

Kinetic studies of few-layer graphene grown by flame deposition from the perspective of gas composition and temperature.

Studies on depositions of chemical vapour deposition (CVD) diamond films have shown that flame combustion has the highest deposition rates without involving microwave plasma and direct current arc. Thus, here we report on our study of few-layer graphene grown by flame deposition. A horizontal CVD reactor was modified for the synthesis of flame deposition of few-layer graphene on a Cu substrate. It was found that graphene obtained has comparable quality to that obtained with other flame deposition setups reported in the literature as determined from Raman spectroscopy, sheet resistance, and transmission electron microscopy. Calculation of the chemical kinetics reveals a gas phase species that has a close correlation to the growth rate of graphene. This was further correlated with van't Hoff analysis of the reaction, which shows that the growth reaction has a single dominating mechanism for temperatures in the range of 400 °C to 1000 °C. Arrhenius analysis also was found to be in good agreement with this result. This study shows few-layer graphene growth proceeds through different pathways from a CVD grown graphene and also highlights flame deposition as a viable method for graphene growth.

Catalytic graphite mechanism during CVD diamond film on iron and cobalt alloys in CH4-H2 atmospheres

Iron and cobalt alloys were exposed to a CH4-H2 mixture at about 670 °C during the chemical vapor deposition (CVD) of diamond film. Severe carburization is observed on pure Fe and Co-10Al alloy, resulting voluminous graphite preferentially formed before diamond deposition. To clarify the catalytic graphite mechanism, microstructures and compositions around the substrates-graphite interfacial region have been comprehensively analyzed by transmission electron microscopy (TEM). Severe internal carburization on pure Fe leads to a metastable Fe3C carbide layer formed and then decomposed, finally resulting in the precipitation of graphite. Meanwhile, graphitization also occurs on low-Al alloy (Co-10Al), the graphite is precipitated from AlCo3C carbide as substrate carburization occurs. As a comparison, such a graphite interlayer is inhibited when the substrate carburization is effectively hindered on high-Al alloys (Fe-25Al, Co-30Al), attributed to the protection of an alumina-rich layer on the alloy surface.

Deposition of microcrystalline diamond films in H2 microwave plasma with graphite powder as hydrocarbon precursor

We report on high-quality microcrystalline diamond films deposited on Si substrates in microwave hydrogen plasma (without methane feed gas) using graphite powders with different sizes from 2 μm to 150 μm as the carbon source. Hydrocarbon radicals, necessary for diamond growth, are produced in course of the graphite etching by atomic hydrogen, and supplied into the plasma for further participation in diamond formation on the substrate. Owing to the large open surface area of the powder the approach allows a continuous long-term stable flux of hydrocarbons (as determined via in situ optical emission spectroscopy of the plasma) during the 10 h graphite etching process. The produced diamond films with grain size of ~1 μm were characterized with scanning electron microscopy and Raman spectroscopy, and exhibited similar morphology and crystallinity independent on the graphite powder dimensions.

Physics and application of gas discharge in millimeter wave beams

The microwave discharge produced in gases by millimeter wave radiation in wave beams is characterized by high plasma density, and wave beams allow one to control the form and size of plasma maintained both in free space and near surfaces of various materials. This paper reviews the results of studying dense plasmas in microwave discharges, which are produced in four and two crossing wave beams by continuous wave radiation of a gyrotron at frequencies of 30 GHz and 28 GHz, respectively. The results of using such discharges for advancing the technique of chemical vapor deposition of diamond films are described. Furthermore, new results on discharge characteristics at extreme values of power density up to 1000–1500 W cm−3 and the homoepitaxial growth of diamond under these conditions are presented.