Diamond Nucleation Density Research Articles

High-temperature tribological properties and wear mechanisms of multilayered cubic-BN/nanocrystalline diamond tool coatings

Wear failure of cutting inserts is the main form of failure that occurs when cutting difficult-to-machine materials at high speeds. To obtain cutting inserts with outstanding tribological properties, multilayered cubic boron nitride (cBN) and nanocrystalline diamond (NCD) coatings (cBN/NCD) were prepared on WC-6 wt% Co tool substrates. The tribological properties of the multilayered cBN/NCD coatings were studied at different temperatures, and the results showed that the coefficient of friction (COF) and wear rate of the coatings were closely interrelated to the temperatures, and the COF gradually decrease and the wear rate gradually increase as the temperature increased from room temperature (25 °C) to 600 °C. The COF and wear rate of the multilayer coatings at 600 °C were ∼0.05 and 8.43 × 10−6 mm3/(N⋅m), respectively. The wear resistance of the cBN/NCD coatings was higher than that of TiAlN coatings and PcBN tool materials by more than 3 and 4.5 times, respectively. The high-temperature wear failure modes of the multilayered cBN/NCD coatings were abrasive wear, diamond graphitization, and BN hydrolysis. Coating wear accelerated when pores were formed on the cBN surface of a multilayered cBN/NCD coating due to the low nucleation density of diamond. These results would guide the application of cBN/NCD-coated cutting tools in high-speed cutting processes.

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.

Diamond nucleation with dynamic magnetic field in hot filament chemical vapor deposition

The magnetic field is an important non-contacting energy field that can affect material synthesis. In this study, a dynamic magnetic field with an angular frequency of 100 π rad/s was applied in hot filament chemical vapor deposition, and its effects on diamond nucleation were intensively investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscope, grazing incidence X-ray diffraction, and Raman spectroscopy. The results showed that the dynamic magnetic field enhanced diamond nucleation, with deposited diamonds having a large crystal grain size and high crystallinity. Furthermore, the angular frequency of the dynamic magnetic field was varied from 83 to 600 π rad/s, and the diamond nucleation density was measured to clarify the corresponding enhancement of the dynamic magnetic field. The diamond nucleation density zigzagged from 1.48 × 109 to 2.49 × 109 cm−2 over the investigated angular frequency range but was well-fitted to the electric field excited by a dynamic magnetic field. The enhancement of the dynamic magnetic field in diamond nucleation was ascribed to electron-stimulated hydrogen desorption.

The Effect of Interlayer Microstructure on the Thermal Boundary Resistance of GaN-on-Diamond Substrate

Diamond has the highest thermal conductivity of any natural material. It can be used to integrate with GaN to dissipate heat from AlGaN/GaN high electron mobility transistor (HEMT) channels. Much past work has investigated the thermal properties of GaN-on-diamond devices, especially the thermal boundary resistance between the diamond and GaN (TBReff,Dia/GaN). However, the effect of SiNx interlayer structure on the thermal resistance of GaN-on-diamond devices is less investigated. In this work, we explore the role of different interfaces in contributing to the thermal boundary resistance of the GaN-on-diamond layers, specifically using 100 nm layer of SiNx, 80 nm layer of SiNx, 100 nm layer of SiNx with a 20 nm × 20 nm periodic structure. Through combination with time-domain thermoreflectance measurement and microstructural analysis, we were able to determine that a patterning SiNx interlayer provided the lower thermal boundary resistance (32.2 ± 1.8 m2KGW−1) because of the diamond growth seeding and the diamond nucleation surface. In addition, the patterning of the SiNx interlayer can effectively improve the interface bonding force and diamond nucleation density and reduce the thermal boundary resistance of the GaN-on-diamond. This enables significant improvement in heat dissipation capability of GaN-on-diamond with respect to GaN wafers.

Enhanced nucleation and large-scale growth of CVD diamond via surface-modification of silicon-incorporated diamond-like carbon thin films

Herein we report a method to tailor the surface of silicon-incorporated diamond-like carbon (Si-DLC) thin films to enhance the diamond nucleation density and growth. In this technique, the surfaces of Si-DLC films were modified by fluorine and oxygen species utilizing a reactive-ion etching (RIE) method. The surface properties of Si-DLC, oxygen-terminated Si-DLC (O Si-DLC), and fluorine-terminated Si-DLC (F Si-DLC) films were investigated and compared. The analyses depicted that the sp2/sp3 ratio of carbon‑carbon bonds has diminished from 20.28% for Si-DLC film down to 8.96% and 4.41% for O Si-DLC and F Si-DLC films, respectively. Moreover, a significant amount of new sp3 hybridized bonds formed on the surface of the modified Si-DLC thin films, particularly in F Si-DLC film. The deposition of micro-diamond on the films was performed using hot filament chemical vapor deposition (HFCVD). SEM, XRD, and Raman results showed the enhancement in nucleation density and growth of micro-diamond on F Si-DLC and O Si-DLC films and the in-plane stress reduction up to 60%. Owing to the lower number of sp2 bonds and the greater number of new sp3 sites, the F Si-DLC thin film provided a superior platform for diamond nucleation than O Si-DLC film. The continuous diamond coverage on F Si-DLC film was up to ~2 mm2 versus ~0.4 mm2 for O Si-DLC film.

Enhancement of diamond seeding on aluminum nitride dielectric by electrostatic adsorption for GaN-on-diamond preparation

Abstract

Preparation of cemented carbide diamond films by gaseous boronizing pretreatment combines with self-assembly seeding process

In order to enhance the adhesion of cemented carbide diamond film and improve the cutting performance of cemented carbide diamond coating tools. This paper was the first to combine gaseous boronizing pretreatment with self-assembly seeding process to prepare diamond films on cemented carbide substrate. It not only eliminated the negative influence of cobalt (Co), but also improved the nucleation density of diamond. The gaseous boronizing pretreatment completed the boronation of the cemented carbide in a short time and obtained the CoWB phase which effectively prevented the diffusion of Co. By application of a self-assembly seeding process with the help of [2-(Methacryloyloxy) ethyl] trimethylammonium chloride (TMAEMC) highly improved the colloidal stability of nanodiamond (ND) particles. When the concentration of TMAEMC was 5 × 10−6 mol/l, the nucleation density of diamond was the highest. Rockwell indentation shows that the combination of gaseous boronizing pretreatment and TMAEMC self-assembly seeding process significantly improved the film-substrate adhesion. The reciprocating friction test shows that the diamond films prepared by this method had low friction coefficient and excellent wear resistance. Therefore, gaseous boronizing pretreatment combines with self-assembly seeding process is an effective way to achieve strong adhesion and high cutting performance of industrial diamond coating tools.

Unprecedented differences in the diamond nucleation density between carbon- and silicon-faces of 4H-silicon carbides

4H-silicon carbides deposited by diamond films have wide applications in many fields such as semiconductor heterojunction, heat sink and mechanical sealing. Nucleation plays a critical role in the deposition of the diamond film on 4H-silicon carbides. Nevertheless, as a typical polar material, the fundamental mechanism of diamond nucleation on different faces of 4H-silicon carbides has not been fully understood yet. In this contribution, nucleation of diamond was performed on the carbon- and silicon-faces of 4H-silicon carbides in a direct current chemical vapor deposition device. The nucleation density on the carbon-face is higher by 2–3 orders of magnitude compared to the silicon-face. Transmission electron microscopy verifies that there are high density diamond nuclei on the interface between the carbon-face and the diamond film, which is different from columnar diamond growth structure on the silicon-face. Transition state theory calculation reveals that the unprecedented distinction of the nucleation density between the carbon-face and the silicon-face is attributed to different desorption rates of the absorbed hydrocarbon radicals. In addition, kinetic model simulations demonstrate that it is more difficult to form CH2(s)-CH2(s) dimers on silicon-faces than carbon-faces, resulting in much lower nucleation densities on silicon-faces.

The influence of dielectric layer on the thermal boundary resistance of GaN‐on‐diamond substrate

The cooling behavior of GaN‐on‐diamond substrate can be enhanced by reducing the thermal boundary resistance (TBR), which is mainly determined by the nature of interlayer. Although SiN film is considered as the primary candidate of dielectric layer, it is still needed to be optimized. In order to facilitate the understanding of the influence of dielectric layer on the TBR of GaN‐on‐Diamond substrate, aluminum nitride (AlN), and silicon nitride (SiN) film were compared systematically, both of which are 100 nm. The time‐domain thermoreflectance (TDTR) measurements, adhesion evaluation, and microstructural analysis methods were adopted to analyse these two interlayers. The results show the TBR of SiN interlayer is as low as 38.5 ± 2.4 m2K GW−1, comparing with the value of 56.4 ± 5.5 m2K GW−1 for AlN interlayer. The difference of TBR between these two interlayers is elucidated by the diamond nucleation density, and the adhesion between the diamond film and GaN substrate, both of which are affected by the surface charge and chemical groups of the dielectric layer.

High-speed synthesis of heavily boron-doped diamond films by in-liquid microwave plasma CVD

Here, we report the first synthesis of polycrystalline boron-doped diamond (BDD) by an In-liquid microwave plasma CVD (IL-MPCVD) process from a mixture of alcohols and boron trioxide (B2O3). We simultaneously achieved high growth rates (up to 287 μm/h) and high boron concentrations (up to 7 × 1021 cm−3). We examined the growth mechanism and show that water generated by dissolution of B2O3 in the alcohol is key to rapid growth of BDD. Even with the same C:H:O ratio, diamond growth rate and nucleation density drastically decreased by addition of water. Water has a strong etching effect, which shifts diamond to grow in carbon rich conditions. Finally, we evaluated the as-grown BDD film as a diamond electrode. Our IL-MPCVD-grown BDD showed electrochemical properties comparable to those of BDD grown by the conventional CVD process in terms of its potential window (3.2 V) and peak separation (85 mV) in 1 mM K3[Fe(CN)6]. Owing to the high growth rate, IL-MPCVD is an effective technique for synthesizing BDD.

Electrostatic self-assembly seeding strategy to improve machining performance of nanocrystalline diamond coated cutting tools

To tackle the issue of insufficient adhesion low wear resistance of diamond coated WC-Co inserts during machining Al-13 wt% Si alloy, nanocrystalline diamond films were deposited by HFCVD employing electrostatic self-assembly seeding strategy. The diamond film adhesion, wear resistance, tool lifetime and surface quality were extraordinary enhanced by increasing the diamond nucleation density via stabilizing the seeding solution by [2‑(Methacryloyloxy)ethyl]trimethylammonium chloride (TMAEMC). Due to the unprecedented high nucleation density of 1.2 × 1011 cm−2 on the tools, obtained with this stabilizing agent at pH 4, its flank wear after 90 min machining is at least 15 times lower than the commercially diamond coated insert and the diamond coating seeded without additive. The tool lifetime of the diamond film seeded with TMAEMC at pH 4 was at least 7 times higher than uncoated one and 4 times higher than the untreated one. A long tool lifetime with long phase of nearly constant low flank wear (46 μm till 150 min) was achieved at a diamond nucleation density higher than 1011 cm−2. Meanwhile, the surface roughness of the workpiece machined by optimized insert was 4 times lower than the untreated one. Therefore, the self-assembly seeding approach with the assistance of organic molecule represents a potent solution in order to achieve adherent and high wear resistant diamond coatings for industrial applications.

Enhanced nucleation of diamond on three dimensional tools via stabilized colloidal nanodiamond in electrostatic self-assembly seeding process

Nanocrystalline diamond particles are promising candidates for copious applications in materials science, biology and electronics. In this work, diamond nucleation density was unprecedentedly enhanced via a non-invasive electrostatic self-assembly seeding approach. By addition of glutamic acid to the nanodiamond seeding solution, the positively charged amino-group of glutamic acid, which is adsorbed on nanodiamond particles, enhances the adsorption on negative charged cemented carbide substrate. The highest nucleation density (1.0×1010cm−2) was achieved by utilizing glutamic acid at pH 4 as well as DI water at pH 2.2. This density was 20–1000 times higher than most earlier published results on WC-Co substrate. The concentration of the organic molecule, pH, concentration of ND particles and ultrasonication seeding time were found to be important for the seeding process. The colloidal stability was tweaked by pH of the dispersion and concentration of glutamic acid. The optimized parameters for nanodiamond adsorption on WC-Co substrate were found to be pH 4 at a concentration of 7×10−5M of glutamic acid at a nanodiamond concentration of 0.005wt%, while the seeding was conducted for 30min. The short ultrasonication time inhibits aggregation and void formation due to peeling off of nanodiamond patches at prolonged seeding times. Moreover, diamond thin films were deposited uniformly and densely on end mills made of cemented carbide. This work indicates that electrostatic induced adsorption of diamond nanoparticles is crucial for the development of ultra-high nucleation densities for the growth of high performance nanocrystalline diamond films, especially for micro sized tools with sharp cutting edges. It may serve as an approach for pinhole-free ultra-thin films deposition on micro-electromechanical system, and encapsulation coating in harsh environment.

Seed-free deposition of large-area adhesive diamond films on copper surfaces processed and patterned by femtosecond lasers

We demonstrate that femtosecond (fs) laser patterning of Cu can be exploited to realize seed-free deposition of large-area adhesive diamond films on Cu. Fs-laser-induced nanostructures promote diamond nucleation density and result in diamond film formation within a laser fluence window from 2.6 to 3.6Jcm−2. Diamond films deposited on Cu surfaces prepared outside this window experience either complete film detachment or formation of low-quality ball-like diamond grains. Diamond/substrate interface roughness plays a critical role in controlling diamond quality and adhesion between substrates and diamond films. Large-area adhesive diamond films have been achieved on Cu substrate surfaces that were first modified with fs-laser irradiation and then scribed into grid patterns. The scribed channels function as expansion joints for stress relief. Strain-free diamond films have been achieved by optimizing the grid size. Using fs-laser processing for seed-free deposition of large-area diamond films on Cu is of great significance for diverse applications, such as thermal management and power electronic devices.

The diffusion behavior of carbon in sputtered tungsten film and sintered tungsten block and its effect on diamond nucleation and growth

Diamond was done on sintered tungsten block with or without sputtered tungsten films. The effects of various depositing conditions, including methane concentration, temperature, pressure, the diamond seeding step and reaction time, on diamond growth were investigated in detail. The results show that the sputtered tungsten film has a dual effect on diamond growth. Firstly, after ultrasonication with diamond slurry, the tungsten film will adsorb a large number of diamond nanoparticles. Therefore, the nucleation density of diamond will be substantially improved. Secondly, the film will be carbonized during the deposition process and the carbon on the surface of the film will decrease. Methane concentration generally does not affect the carbonization level of the tungsten film but higher temperature will lead to a higher level of carbonization. The carbonization process of sputtered tungsten films during deposition is made up of two steps. Also, the nucleation surface of diamond was revealed. The nucleation surface was a layer of ultrasmooth and seamless nanocrystalline diamond film with high-quality and special surface architecture (tiny peaks arrays), which is potential to be applied in MEMS and field-emission devices. A potential method to prepare ultrasmooth nanocrystalline diamond films is proposed.

The XRD Patterns Analysis of Diamond/Porous Composite Membrane Deposited by Bias Voltage Assisted HFCVD

Bias voltage assisted hot filament chemical vapor deposition (HFCVD) was adopted to deposit boron-doped diamond (BDD) film on porous titanium substrate, and diamond composite membrane materials were prepared and characterized by X-ray diffraction method. The influence of carbon concentration, boron source concentration, substrate temperature were discussed respectively on the diamond quality and the transition layer TiC. Results showed that: The concentration of carbon source was related to crystal orientation and the growth rate of diamond. The increase of diamond nucleation density and growth rate prevented the formation of TiC, and improved adhesion between diamond and the substrate; The increasing of boron source concentration promoted the orientation growth of diamond film (111) lattice plane, while reduced the content of TiC; Temperature affected the formation of TiC, and TiC diffraction peaks intensity decreased with the increase of substrate temperature; As the substrate temperature increased, secondary nucleation rate caused cauliflower-like structure which dominated growth mechanism transitting from MCD (Microcrystalline diamond) to the NCD (Nanocrystalline diamond).

Enhanced spontaneous nucleation of diamond nuclei in hot and cold microwave plasma systems

In this work, the diamond nucleation is studied using two different deposition systems: (i) focused microwave plasma (labeled as “hot plasma”) and (ii) pulsed-linear antenna microwave plasma (“cold plasma”). For the hot plasma, the influence of CH4 concentration in the hydrogen rich gas mixture on the self nucleation is investigated. It is found that higher CH4 concentration leads to increased diamond nucleation density, but also the amount of sp2 carbon bonds increases within the deposits. In the cold plasma, we investigate the influence of CO2 addition into CH4/H2 and total process pressure. Experimental results reveal a strong dependence of CO2 and pressure on spontaneous nucleation. The nucleation density (Nd) typical for non-treated substrates (∼105 cm−2) is improved by four orders to 109 cm−2 in cold plasma thanks to increased CH4 and CO2 concentrations. The highest nucleation density in the hot plasma system is still one order lower (∼4 × 107 cm−2). Moreover, in cold plasma a bimodal distribution function of diamond clusters is observed for low ratios of CO2/H2. Observed differences in Nd values are attributed to plasma properties and surface chemistry. Based on the experimental results, possible mechanisms contributing to the spontaneous nucleation process are discussed.

Enhanced Diamond Nucleation by Surface Texturing of Si Substrate in SF<sub>6</sub>/O<sub>2</sub> Plasmas

SF6/O2 plasma surface texturing was employed to pretreat Si substrate for achieving enhanced diamond nucleation density. Surface roughness of the textured Si was found to be strongly dependent on the process pressure and normalized roughness values in the range of 2-16 were obtained. Remarkably enhanced nucleation densities of ~1010 cm-2 compared to conventional mechanical abrasion were obtained after seeding for the surface textured Si substrates. Raman spectroscopy revealed that ultrananocrystalline diamond films with grain size below 10 nm were grown on the surface textured Si.

Influence of titanium ion implantation on nucleation of diamond films on tungsten carbide

Diamond film has been deposited on substrate of cobalt cemented tungsten carbide (WC–Co). An exploration is carried out to reveal effect of Ti ion implantation and ion implantation energy on the diamond nucleation and growth on tungsten carbide. Diamond nucleation density is enhanced with Ti ion implantation and a dense nucleation belongs to a sample at 35 kV. A diamond film growing subsequently consists of oriented diamond crystals with columnar structure and such crystals uniformly distribute and grow well on tungsten carbide.

Nucleation and Chemical Vapor Deposition Growth of Polycrystalline Diamond on Aluminum Nitride: Role of Surface Termination and Polarity

We have investigated the growth and atomic interface structures of diamond on aluminum nitride (AlN). The two-step chemical vapor deposition technique is used to control diamond nucleation density, crystal size, and AlN surface orientation and polarity. Highly uniform diamond layers with a nucleation density in the range of 105–1011 cm–2 and a grain size of 0.1–5 μm are fabricated. Crystallographically abrupt interfaces between polycrystalline diamond and single-crystal AlN(0001) layers have been observed via high-resolution transmission electron microscopy and electron energy-loss spectroscopy. A majority of the diamond crystals have been found to have the diamond(111)/AlN(0001) interface relationship. Atomistic models of the bonding mechanism at the heterointerface are used to elucidate experimental observations and the role of hydrogen plasma on the growth of diamond on AlN. Nonpolar and semipolar AlN surfaces have been found to have higher resistance to process plasma and led to better crystallinity o...

Effect of sputtered Mo interlayers on Si (100) substrates for the deposition of diamond film by hot filament chemical vapor deposition

Dense, ultra-smooth and well-distributed nanocrystalline diamond films have been grown by hot filament chemical vapor deposition (HFCVD) on Si (100) substrates with a sputtered Mo interlayer in only 20min. In order to investigate the effect of a Mo interlayer on the growth of CVD diamond films, each substrate was mounted over a range of HF-substrate separations, df. Spatially resolved scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, X-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS) and focused ion beam (FIB) milling of the deposited material provide a detailed relation of the evolution of film morphology, growth rate, surface roughness, grain size, sp3/sp2 content and phases with df in deposited samples. The deposited diamond film shows no internal stress. It is also found that the diamond nucleation density on sputtered Mo substrate after diamond powder pretreatment is more than 1014/m2, which is a remarkable improvement compared with 1011/m2 on bulk Mo substrate. The reason for the improvement is discussed in detail. This method can be a potential way to produce ultra-smooth nano-crystalline diamond for various applications. Also, the growth time of diamond can be greatly reduced.