Deposited Diamond Films Research Articles

STUDY ON THE PROPERTIES OF DIAMOND FILMS ON CEMENTED CARBIDE SUBSTRATES BY SURFACE IMPLANTATION PRETREATMENT PROCESS

The deposition of diamond films on tungsten carbide-based tools can greatly improve the life and performance of cutting tools. However, the deposition of diamond coatings on cemented carbide (WC-Co) suffers from poor film-base bond strength. In this paper, diamond coatings were deposited of phytocrystalline metal micropowders (pure, Nb, Ti, Ta) pretreatment method and the properties of diamond films were analyzed by energy spectrometry (EDS), scanning electron microscopy (SEM), Raman spectroscopy and bonding strength test of diamond films. The results show that through the experiment of the pretreatment process of surface implanted crystal metal micropowder, the best implanted crystal metal micropowder was obtained, the surface quality of implanted crystal titanium (Ti) coating was improved, the diamond Raman peaks were sharp and the indentation cracks had a crack diameter of 389 [Formula: see text]m, which is small and has the highest bond strength. The pretreatment process of phytocrystalline diamond micropowder can deposit high-performance diamond coatings and improve the bonding strength between the coating and the substrate film base.

Edge effect during microwave plasma chemical vapor deposition diamond-film: Multiphysics simulation and experimental verification

Edge effect during microwave plasma chemical vapor deposition diamond-film: Multiphysics simulation and experimental verification

Deposition of a low-stress diamond film on stainless steel with a Mo/Mo-N interlayer

Depositing an adhering diamond film on stainless steel is still challenging. In this work, Mo/Mo-N film is used as an interlayer to solve the problem. The results show that diamond film with good adhesion is obtained when the interlayer with the N2/Ar ratios of 50 %–100 % is used. It is ascribed to the formation of Mo2N phase in the interlayer through which it is more difficult for carbon atoms to diffuse than Mo phase. On the Mo/Mo-N interlayer, carbon atoms are easily gathered and a new phase MoC appeared as well as Mo2C phase at the interface of diamond/interlayer. Thermal expansion of MoC is obviously lower than that of Mo2C, resulting in the lower stress of diamond film. And MoC offers higher bond strength between the diamond and the interlayer compared to Mo2C phase. As a result, the diamond film presents good adhesion.

Effect of linear antenna chemical vapor deposition process parameters on the growth of nanocrystalline diamond-on-GaN films

The present work will systematically study the effect of different linear antenna microwave plasma enhanced chemical vapor deposition (LACVD) processing parameters on the optimal deposition of the diamond films. The low pressure and low temperatures of LACVD growth conditions is expected to deposit diamond films on otherwise reactive gallium nitride (GaN) surfaces, without any intermediate nitride buffer layer. First, the distances between the quartz tube and the samples put on the stage are varied (3–15 cm), which has a direct impact on the substrate temperature (415°–300 °C). Thereafter, the microwave input power was also altered (1.5–2.8 kW) to attain low substrate temperatures. It was found that 300 °C is the temperature limit, which can be attained by heating only with microwave plasma when the substrates are kept farthest (15 cm) away from the liner antenna quartz tube. An additional heater was used under the stage for rapidly achieving such minimum substrate temperature of 300 °C. Substrate heater was used for efficient growth of the diamond phase while using pulse mode frequency of microwave power input for optimization of the diamond films. The microstructure (plate-like and cauliflower-like) of the deposited nanocrystalline diamond (NCD) films and the cross-sectional images for thickness measurements was observed under the scanning electron microscope and the elemental analysis of the film surfaces was done by electron diffraction spectroscopy. Moreover, the diamond film quality and crystallinity were evaluated by Raman spectroscopy with 488 nm laser light. Diamond-on-GaN film results were compared with conventional Si substrate. Different LACVD reactor parameters like, antenna to stage distances, microwave input power in continuous wave mode, and growth temperatures have significant impacts on the grown films, both in terms of their quality and microstructure. It was found that the optimum deposition of nanocrystalline diamond film on GaN substrates without its surface etching was possible, under pulse mode (20 kHz, 45 % duty cycle) with 2 kW average input microwave power.

The Stability of Straightened Ta Filament During Chemical Vapor Deposition of Diamond Film

Maintaining the geometrical stability of hot filament is a challenge in chemical vapor deposition (CVD) over a larger area since deformation varies the distance between the filament and the substrate and, consequently, destroys the uniformity of diamond deposition. Herein, Ta filament is straightened with a tensile stress ranging from 4.40 to 11 MPa to suppress deformation, and the stability during the CVD process of diamond film is evaluated. Scanning electron microscopy and energy dispersive X‐ray are further utilized to investigate the morphological and structural evolutions of Ta filament. Results show that straightened Ta filament maintains geometrical stability without any visible deformation or breakage and uniform deposition of diamond film is obtained through Ta filament undergone a transformation from Ta to Ta2C and then to TaC. At high deposition pressure (7 kPa) or a low concentration of methane (1%), the straightened Ta filament goes through a moderate transformation, which implies the cracks caused by rough transformation can be avoided, thus prolonging the lifetime of straightened Ta filament. These works provide significant guidelines for the large‐scale manufacture of diamond deposition.

Low-Temperature Deposition of Diamond Films by MPCVD with Graphite Paste Additive

Modern integrated circuits (ICs) take advantage of three-dimensional (3D) nanostructures in devices and interconnects to achieve high-speed and ultra-low-power performance. The choice of electrical insulation materials with excellent dielectric strength, electrical resistivity, strong mechanical strength, and high thermal conductivity becomes critical. Diamond possesses these properties and is recently recognized as a promising dielectric material for the fabrication of advanced ICs, which are sensitive to detrimental high-temperature processes. Therefore, a high-rate low-temperature deposition technique for large-grain, high-quality diamond films of the thickness of a few tens to a few hundred nanometers is desirable. The diamond growth rate by microwave plasma chemical vapor deposition (MPCVD) decreases rapidly with lowering substrate temperature. In addition, the thermal conductivity of non-diamond carbon is much lower than that of diamond. Furthermore, a small-grain diamond film suffers from poor thermal conductivity due to frequent phonon scattering at grain boundaries. This paper reports a novel MPCVD process aiming at high growth rate, large grain size, and high sp3/sp2 ratio for diamond films deposited on silicon. Graphite paste containing nanoscale graphite and oxy-hydrocarbon binder and solvent vaporizes and mixes with gas feeds of hydrogen, methane, and carbon dioxide to form plasma. Rapid diamond growth of diamond seeds at 450 °C by the plasma results in large-grained diamond films on silicon at a high deposition rate of 200 nm/h.

An investigation into low-temperature HFCVD and derivative techniques for the enhancement of diamond-coated cemented carbide tool performance

The performance of diamond-coated cemented carbide tools manufactured via the conventional hot filament chemical vapor deposition (HFCVD) technique exhibits certain limitations, including issues with poor toughness and reduced adhesive strength of film-substrate systems, primarily attributed to the cobalt diffusion at elevated temperatures (> 800 °C). In this study, a pioneering exploration of a low-temperature diamond film deposition technique on cemented carbide is developed, and a comprehensive evaluation of the film properties is conducted. The results indicate that owing to constraints related to growth rate and diamond film purity, it may not serve as an effective approach for enhancing the performance of conventional coated tools. Nonetheless, the inherent capability of this technique in inhibiting cobalt diffusion is strategically harnessed to pioneer the development of a derivative technique referred to as the “low-temperature to high-temperature HFCVD (LT-HT-HFCVD)”. This innovative method leverages a low-temperature deposited diamond layer as an intermediate layer to impede cobalt diffusion while serving as a densely nucleated layer for subsequent diamond growth. Subsequently, the conventional technique is employed to facilitate an effective growth rate and maintain high growth purity. The diamond-coated tools generated by this technique are subject to a comprehensive comparative analysis against those generated by low-temperature HFCVD (LT-HFCVD) and conventional HFCVD (CT-HFCVD) techniques. The results reveal that tools fabricated using the LT-HT-HFCVD combine the advantages inherent to both the LT-HFCVD and CT-HFCVD techniques, thereby manifesting superior toughness, enhanced film-substrate adhesive strength, and outstanding cutting performance.

Explore the growth mechanism of high-quality diamond under high average power density in the MPCVD reactor

Investigating the mechanism behind the high-efficiency deposition of high-quality diamond has always been a prominent topic in related research. This paper investigates the CH4-H2 plasma characteristics and related chemical reaction kinetics in the average power density range of 18–100 W·cm−3, which is a typical range for large-area diamond film deposition. The number densities of H, CH3 and C2H2 increase linearly with the average power density. C2H2 is the main hydrocarbon in the discharge, and CH3 is the main single-carbon hydrocarbon. The number density and radial uniformity of CH3 and C2H2 increase with the average power density, which is necessary for the high rate and uniform deposition of diamond films. The plasma's optical emission spectra indicate an acceleration in the C2 production rate at high power density. The diamond film deposition experiment demonstrates the efficacy of high average power density in achieving high-quality diamond deposition at a high growth rate.

Diamond deposition on AlN using Q-carbon interlayer through overcoming the substrate limitations

Q-carbon, a quenched form of carbon, is a recently discovered carbon structure that has tremendous properties, compatibility, and potential for use in device fabrication and other electronic and mechanical applications. However, the non-equilibrium nature of the synthesis process and a very small window of growth parameters have limited the formation of Q-carbon to only low thermal conductive substrates. This study aims to overcome these limitations through extensive tuning of the parameters of diamond-like-carbon (DLC), the base structure required for the formation of Q-carbon. The as-deposited DLC films demonstrate ID/IG ratios ranging from 0.12 to 1.67, which are obtained through the optimization of laser energy density, rep rate, and deposition temperature during pulsed laser deposition. Utilizing Simulation of Laser Interaction with Materials, pulsed laser annealing (PLA) was used to directly transform the DLC films into Q-carbon while varying the PLA energy density from 0.3 J/cm2 to 1.2 J/cm2. Findings of Q-carbon formation on sapphire using different DLC films assisted in the preparation of a roadmap for overcoming the substrate limitations for Q-carbon formation. Further, Q-carbon is formed on AlN substrates for the direct deposition of diamond films without the requirement of a non-carbon interfacial layer or nanodiamond seeding layer. The large-area and uniform diamond growth on Q-carbon shows well-faceted and five-fold twinned growth with a 70 % improvement in the residual compressive stress of diamond on AlN. Such a method of diamond deposition on AlN provides the opportunity to address the thermal management issues in wide- and ultra-wide bandgap high-power electronic devices.

Effects of methane concentration on tribological properties of diamond films prepared on different ceramic substrates

ABSTARCT Diamond films were prepared on silicon nitride and zirconia ceramic substrates using hot filament chemical vapor deposition (HFCVD). The surface morphology, friction, and wear properties of the diamond films prepared with different methane concentrations (2%, 4%, and 6%) were compared using scanning electron microscopy, Raman spectroscopy, X-ray diffraction, and friction and wear testing machines. The results showed that, with an increase in the methane concentration, the diamond particles gradually changed from micro- to nanodiamonds, and the grain size first increased and then decreased. The diamond films on silicon nitride substrates were of excellent quality, with good wear resistance, strong adhesion, and wear rates of 2.857 × 10−8 mm−3•m−1•N−1, 5.151 × 10−8 mm−3•m−1•N−1, and 1.334 × 10−7 mm−3•m−1•N−1, respectively. The diamond films on zirconia substrates had more impurities on the surface, higher internal stress, poorer wear resistance, and weaker adhesion, with wear rates of 3.789 × 10−8 mm−3•m−1•N−1, 5.899 × 10−8 mm−3•m−1•N−1, and 2.074 × 10−7 mm−3•m−1•N−1, respectively. Hence, the deposition of diamond films on ceramic substrates significantly reduced the friction coefficient, and the performance of diamond films on silicon nitride substrates was excellent.

Deposition of uniform diamond films on three dimensional Si spheres by using faraday cage in MPCVD reactor

Deposition of a consistent diamond coating on intricate surfaces has historically posed a difficulty. This article presents the advancement in research on depositing a uniform diamond coating on three-dimensional (3D) silicon spheres, utilizing a faraday cage within a microwave plasma chemical vapor deposition (MPCVD) reactor. A self-consistent three-dimensional multi-physics field model has been established for simulating the microwave electric field and plasma inside a reactor with or without a faraday cage. Results indicate the cage effectively reduces the discharge at the top of the silicon sphere and improves uniformity of the distribution of the microwave electric field and plasma electron density on the sphere's surface. MPCVD trials have demonstrated that a powerful discharge takes place at the apex of the silicon sphere resulting in an excessive thermal gradient if the cage is not added. The apex of the silicon sphere is covered with a blend of diamond and graphite phases. Due to the excessive internal stress of the coating, approximately 50 % of the samples experience coating detachment. After the addition of the cage, the strong discharge is transferred to the top of the cage, effectively suppressing the microwave electric field and plasma inside the cage. Improved quality, reduced internal stress, and enhanced uniformity of the polycrystalline diamond coating are achievable on the silicon spheres within the cage. Moreover, this technique offers a novel approach to coat diamond on complex 3D geometries.

Deposition of diamond films by microwave plasma CVD on 4H-SiC substrates

Diamond films were deposited on 4H-SiC substrates by microwave plasma chemical vapor deposition (MPCVD). The substrate pretreatment method of electrostatic adsorption of seed crystals by nanodiamond suspensions was used, and the nucleation density of diamond on the substrate surface reached 1010/cm2 compared with ultrasonic seed crystals of diamond micro-powder suspensions, and continuous dense diamond films were formed in a shorter growth time. Scanning electron microscopy and Raman spectroscopy were used to characterize the changes of diamond grain morphology and quality with methane concentration, deposition time and substrate temperature during the growth process. The experimental results show that the methane concentration, deposition time and substrate temperature are the key factors affecting the grain shape and quality of diamond. And the best quality of diamond film is obtained at 850 °C substrate temperature.

Super High-Concentration Si and N Doping of CVD Diamond Film by Thermal Decomposition of Silicon Nitride Substrate.

The high-concentration N doping of diamond film is still a challenge since nitrogen is limited during diamond growth. In this work, a novel method combined with the thermal decomposition of silicon nitride was proposed to form the activated N and Si components in the reactor gas that surrounded the substrate, with which the high-concentration N and Si doping of diamond film was performed. Meanwhile, graphene oxide (GO) particles were also employed as an adsorbent to further increase the concentration of the N element in diamond film by capturing the more decomposed N components. All the as-deposited diamond films were characterized by scanning electron microscopy, energy dispersive spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. For the pure diamond film with a growth time of 0.5 h, the N and Si concentrations were 20.78 and 41.21 at%, respectively. For the GO-diamond film, they reached 47.47 and 21.66 at%, which set a new record for super high-concentration N doping of diamond film. Hence, thermal decomposition for the substrate can be regarded as a potential and alternative method to deposit the chemical vapor deposition (CVD) diamond film with high-concentration N, which be favorable for the widespread application of diamond in the electric field.

Effect of frequency on low temperature synthesis of diamond by pulsed discharge MPCVD

Low-temperature synthesis of diamond has broader application prospects compared to traditional diamond synthesis, but it faces issues such as low deposition rate and poor diamond quality. In this study, CH4–CO–H2 were used as reaction gases, and a pulsed discharge MPCVD apparatus was used to deposit diamond films at a substrate temperature of 400 °C and different frequencies were investigated. The results showed that the deposition rate of the pulse discharge was faster than that of continuous microwave discharge. The fastest deposition rate was observed at 500Hz, and crystal size became finer with increasing frequency, while the crystal orientation changed from (100) to (111). A diamond peak at 1333 cm−1 was observed in the Raman spectrum, and the diamond grain size was found to be biggest at 750Hz based on the measured half-width of the peak. Plasma OES analysis revealed that the brightness of CO increased gradually with increasing frequency, while the brightness of H showed an initial increase followed by a decrease. Comparison of emission spectra during low-temperature deposition with a single carbon source showed that CO participated in the reaction for low-temperature diamond synthesis.

CVD Diamond Growth Enhanced by a Dynamic Magnetic Field

A dynamic magnetic field (DMF) with different angular frequencies (50, 100, and 150 π rad/s) was introduced during diamond growth via hot filament chemical vapor deposition (HFCVD). The effects of the dynamic magnetic field on the growth rate, diamond quality, growth orientation, and deposition uniformity of large-area diamond films were investigated with scanning electron microscopy (SEM), X-ray diffractometry (XRD), and Raman spectroscopy. The correlation between diamond growth and angular frequency was discussed. The results showed that a faster growth rate (about 2.5 times) and higher diamond quality were obtained by increasing the angular frequency of the DMF. A (100) textured polycrystalline diamond film was achieved, and the preferential orientation was found to evolve from (110) to (100), while the expected uniform deposition of a large-area diamond film under DMF was not achieved. The enhancement effect of the DMF was ascribed to the activation of more gas molecules, which participated in CVD diamond growth.

Combined HF+MW CVD Approach for the Growth of Polycrystalline Diamond Films with Reduced Bow

A combination of two methods of chemical vapor deposition (CVD) of diamond films, microwave plasma–assisted (MW CVD) and hot filament (HF CVD), was used for the growth of 100 µm-thick polycrystalline diamond (PCD) layers on Si substrates. The bow of HF CVD and MW CVD films showed opposite convex\concave trends; thus, the combined material allowed reducing the overall bow by a factor of 2–3. Using MW CVD for the growth of the initial 25 µm-thick PCD layer allowed achieving much higher thermal conductivity of the combined 110 µm-thick film at 210 W/m·K in comparison to 130 W/m·K for the 93 µm-thick pure HF CVD film.

Deposition of an adherent diamond film on stainless steel using Cr/Cr[sbnd]Al[sbnd]N as an interlayer

Cr/CrAlN films were chosen as an interlayer to deposit an adherent diamond film on stainless steels by using hot filament chemical vapor deposition (HFCVD). The results show that diamond film with good adhesion is successfully deposited on 3Cr13 stainless steel when the interlayer with Al content from 0 to 18 at.%, which is ascribed to high chemical adhesion by a certain amount of chromium carbide. When Al content in the interlayer further increases, an excessive Al2O3 is formed on the surface of the interlayer, carbon supersaturation is easily arrived, so that the amount of the carbide at the diamond/interlayer interface decreases evidently. This decreases the strength of the covalent bonding from the carbide, producing poor adhesion. Moreover, with the raise of Al content in the interlayer, the hardness of the multilayer coated stainless steel increases due to the increase of the interlayer's hardness and the slight increase of the diamond content in the film.

Mechanical properties evaluation of diamond films via nanoindentation

Diamond film is considered ideal tool coating material for processing difficult-to-machine materials due to the high hardness and wear resistance. However, precisely evaluating the mechanical properties of diamond films has been a considerable obstacle, which hinders further design and application. In this work, various diamond films were deposited on cemented carbide substrates ranging from 0.1 to 1.0 kPa in CH4/H2 by hot filament chemical vapor deposition. The mechanical properties of diamond films were systematically and rigorously evaluated by nanoindentation adopting a series of loads. However, it is found that hardness calculated at different loads has a significant deviation, although all obey the well-known 10 % rule of thumb. On basis of the massive nanoindentation on polished diamond film with roughness <20 nm, we propose a stricter 5 %, instead of the well-known 10 % rule of thumb, for the limit of maximum penetration depth divided by film thickness in the diamond nanoindentation measurements. Notably, the mechanical properties of the deposited diamond films improved as the pressure increased, especially hardness gradually increased from 75.5 ± 1.4 GPa to 87.3 ± 5.0 GPa, which is attributed to the increase of the ratio of sp3 carbon content.

Effects of metal layers on chemical vapor deposition of diamond films

Abstract Diamond is recognized as one of the most promising wide bandgap materials for advanced electronic applications. However, for many practical uses, hybrid diamond growth combining metal electrodes is often demanded. Here, we present the influence of thin metal (Ni, Ir, Au) layers on diamond growth by microwave plasma chemical vapor deposition (MWCVD) employing two different concepts. In the first concept, a flat substrate (GaN) was initially coated with a thin metal layer, then exposed to the diamond MWCVD process. In the second concept, the thin diamond film was firstly formed, then it was overcoated with the metal layer and finally, once again exposed to the diamond MWCVD. It should be mentioned that this concept allows the implementation of the metal electrode into the diamond bulk. It was confirmed that the Ni thin films (15 nm) hinder the formation of diamond crystals resulting in the formation of an amorphous carbon layer. Contrary to this finding, the Ir layer resulted in a successful overgrowth by the fully closed diamond film. However, by employing concept 2 (ie hybrid diamond/metal/diamond composite), the thin Ir layer was found to be unstable and transferred into the isolated clusters, which were overgrown by the diamond film. Using the Au/Ir (30/15 nm) bilayer system stabilized the metallization and no diamond growth was observed on the metal layer.

Current Transient Spectroscopic Study of Vacancy Complexes in Diamond Schottky p-i-n Diode

The present state-of-the-art of junction-based diamond electronic devices is limited by the challenges inherent to the synthesis of n-type layers, where the dopant itself forms defect complexes that are donor compensating centers. Recently, the fabrication of diamond Schottky p-i-n diodes (SPINDs) by chemical vapor deposition (CVD) of intrinsic diamond films followed by an n-type layer on p-type diamond substrates has been reported to demonstrate excellent diode-like behavior with high rectification factors and surface barrier height at elevated temperatures. However, due to the ultrawide bandgap of diamond and small contact area of the devices, it is challenging to characterize the defect centers that limit the performance of the SPINDs using conventional capacitance transient spectroscopy. In this article, we report the characterization of defect centers in the diamond SPINDs with a contact area of 280 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}\,\,\times \,\,280\,\,\mu \text{m}$ </tex-math></inline-formula> using current transient spectroscopy (CTS), which measures thermally induced emission rates from trap centers through change in device current instead of junction capacitance. The CTS scans in the temperature range 80–800 K revealed the presence of five trap-related peaks. Results from density functional theory (DFT) calculations were used to identify the nature of the traps. While most of the detected traps were identified to be vacancy complexes coupled to phosphorus and hydrogen impurities, one trap has been identified as single carbon vacancy. Most of the phosphorus-related defect complexes were observed to be in neutral and/or negative charge states and were identified as acceptor-like states.