Enhancement Of Diamond Nucleation Research Articles

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.

Effect of Ta diffusion layer on the adhesion properties of diamond coating on WC-Co substrate

To enhance diamond nucleation and adhesion on cemented carbide substrates, the Ta diffusion layers with gradient structure were deposited by the combination with double glow plasma surface alloying technique (DGPSA) and the reverse-sputtering process. The effect of reverse-sputtering times on phase composition and morphology of the Ta surface layers was studied. It was found that both the thickness of the Ta deposition layer and the amount of Ta elements decreased during the removal of the Ta deposition layer. With the reverse-sputtering time increases from 0 to 60 min, the thickness of the Ta deposition layers decreased from 1.6 μm to 0 μm. When the reverse-sputtering time reached 30 min, the as-prepared sample surface exhibited the maximum micro-hardness (3496.3 HV1.96N). Rockwell C indentation tests were used to investigate the effect of the Ta diffusion layers on the adhesion between the WC-Co substrate and the diamond coating. The results show that diamond coating exhibits good adhesion performance on WC-Co substrate with the Ta diffusion layer after reverse-sputtering for 60 min, indicating that the barrier effect of cobalt diffusion is enhanced by introducing the Ta diffusion layer.

Tetramethysilane-assisted enhancement of diamond nucleation on silicon substrate

This paper describes the effect of tetramethylsilane (TMS) on diamond nucleation on Si substrate under an applied bias voltage of 120 V, performed in a modified microwave plasma chemical vapor deposition (MPCVD) reactor. The introduction of TMS in the CH4/H2 plasma leads to a significant enhancement of nucleation density of diamond nuclei, namely from (3.7 ± 0.2) × 107/cm2 without the introduction of TMS to (4.7 ± 0.5) × 1010/cm2 at the TMS flow rate of 4 sccm. On the contrary, further increasing in the TMS flow rate to 8 sccm slightly reduces the nucleation density of diamond nuclei to (2.1 ± 0.3) × 1010/cm2, along with the increase in average size of diamond nuclei. High-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) allow us to study the microstructural and chemical composition evolution of Si/diamond interface. The obtained results suggest that bias-enhanced nucleation of diamond on Si substrate exhibits a direct relationship with the TMS flow rate.

CVD 다이아몬드가 코팅된 알루미늄 방열판의 방열 특성

Nanocrystalline diamond(NCD) coated aluminium plates were prepared and applied as heat sinks for LED modules. NCD films were deposited on 1 mm thick Al plates for times of 2 - 10 h in a microwave plasma chemical vapor deposition reactor. Deposition parameters were the microwave power of 1.2 kW, the working pressure of 90 Torr, the CH4/Ar gas ratio of 2/200 sccm. In order to enhance diamond nucleation, DC bias voltage of �90 V was applied to the substrate during deposition without external heating. NCD film was identified by X-ray diffraction and Raman spectroscopy. The Al plates with about 300 nm thick NCD film were attached to LED modules and thermal analysis was carried out using Thermal Transient Tester (T3ster) in a still air box. Thermal resistance of the module with NCD/Al plate was 3.88 K/W while that with Al plate was 5.55 K/W. The smaller the thermal resistance, the better the heat emission. From structure function analysis, the differences between junction and ambient temperatures were 12.1 o C for NCD/Al plate and 15.5 o C for Al plate. The hot spot size of infrared images was larger on NCD/Al than Al plate for a given period of LED operation. In conclusion, NCD coated Al plate exhibited better thermal spreading performance than conventional Al heat sink.

Improved nanodiamond seeding on chromium by surface plasma pretreatment

Surface pretreatment by gas discharge plasmas of N2, O2 and CF4 is studied for enhanced diamond nucleation on Cr surfaces. The seeding density following the interaction of water-dispersed nanodiamonds (NDs) and the Cr surface is enhanced due to chemical modification of a surface. The surface that is untreated or pretreated with N2 plasma possesses a suppressed electrostatic attraction of NDs, while the pretreatment with O2 or CF4 plasmas render a strong electrostatic attraction and high seeding density. Finally, by this method thin nanocrystalline diamond films are achieved on Cr surfaces after O2 and CF4 plasma pretreatments.

Deposition of diamond coatings on Fe-based substrates with Al and Al/AlN interlayers

Abstract Because of the carbon diffusion into the substrate and the formation of graphite at the interface, direct deposition of adherent diamond coatings on Fe-based materials is difficult. To address the issue, Al-based interlayers including Al and Al/AlN interlayers were introduced on Fe based substrates (SS316, FeNiCo) to enhance diamond deposition, which was carried out in a microwave plasma chemical vapor deposition (MPCVD) reactor using a CH4–H2 mixture. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, synchrotron-based X-ray absorption spectroscopy (XAS), and indentation testing. The results show that single Al layer can effectively suppress the formation of graphite and the inward diffusion of carbon into the substrate, and thus enhance diamond nucleation and growth. The dual layers of Al/AlN can further enhance the adhesion of diamond coatings comparing to the single Al interlayer.

Effect of carburizing process in enhancing nickel interlayer adhesion to WC-6% Co-substrate and promoting diamond nucleation and growth

Nickel enables nucleation and growth of well-oriented diamond crystals from the small lattice mismatch with diamond. However, its high solubility for carbon results in carbon loss during diamond deposition and, consequently, results in poor nucleation density. In this study, Ni/WC-6%Co specimens were carburized in a high-temperature furnace with inert gas atmosphere in order to provide nickel with sufficient carbon prior to diamond deposition. Two carburizing temperatures (750 ℃ and 850 ℃) were set for 20 min and 60 min durations. The effect of this process in altering the nickel layer composition was characterized by microscopy, element analysis, and phase identification techniques. Scratch test was performed to evaluate the interface adhesion between the nickel layer and the substrate. The results show that the carburizing process led to the formation of different metallic phases, such as nickel carbide and cobalt nickel, which prevented carbon loss during diamond deposition as well as cobalt diffusion into diamond, and thus enhanced diamond nucleation and growth on the nickel surface.

Effect of Seed Size, Suspension Recycling and Substrate Pre-Treatment on the CVD Growth of Diamond Coatings

CVD growth of uniform conformal polycrystalline diamond (PCD) coatings over complex three dimensional structures is very important material processing technique. It has been found that the nucleation and subsequent growth period is very critical for successful development of CVD diamond based technologies. There are many methods of enhancing diamond nucleation on foreign substrates-ultrasonic treatment with diamond seed suspension being the best among them. A combination of ultrasonic seeding (US) technique with prior treatment (PT) of the substrate under CVD diamond growth conditions for brief period of time, has found to be very effective in enhancing the diamond nucleation during CVD growth—together they are known as NNP. But successive usage of the same seeding suspension up to ten cycles deteriorates the seeding efficiency. 6th seeding cycle onwards the silicon substrates are barely get covered by diamond crystallites. Five different diamond micron grits were used for seeding the silicon substrates and it is observed that US with the sub-micron particles (0.25 μm) is very effective in efficient nucleation of PCD on Si substrates. PT of the substrate somewhat negates the effect of successive use of the same seeding slurry but it is best to avoid recycling of the same seeding suspension using micron size diamond grits.

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.

Surface plasma pretreatment for enhanced diamond nucleation on AlN

The surface of polycrystalline aluminum nitride (AlN) thin films is exposed to different gas discharge plasmas (N2, O2, and CF4) followed by a water-based colloidal seeding of ultra-dispersed nanodiamond particles. Fluorination of the AlN surface enhances the seeding density, whereas the oxidized surface does not yield any nucleation sites. In the former case, the seeding density improves by almost three orders of magnitude as compared to the untreated and N2 pretreated samples, and allows to grow pinhole-free nanocrystalline diamond film on AlN. Finally, we demonstrate a route towards selective diamond growth on AlN thin films by employing CF4 plasma pretreatment together with photolithography.

Adherent diamond film deposited on Cu substrate by carbon transport from nanodiamond buried under Pt interlayer

Diamond film deposited on Cu suffered from poor adhesion mainly due to the large mismatch of thermal expansion coefficients and the lack of affinity between carbon and Cu. Enhancing diamond nucleation by carbon transport from buried nanodiamond through a Pt ultrathin interlayer, adherent diamond film was then deposited on Cu substrate without distinctly metallic interlayer. This novel nucleation mechanism increased diamond nucleation density to 1011cm−2, and developed diamond film with a composite structure of nano-crystalline diamond (NCD) layer and micro-crystalline diamond layer. Diamond film was characterized by the scanning electron microscope (SEM) and Raman spectroscope, respectively. The composition of diamond film/Cu substrate interface was examined by electron probe microanalysis (EPMA). The adhesion of diamond film was evaluated by indentation test. Those results show that a Pt ultrathin interlayer provides stronger chemically bonded interfaces and improve film adhesion.

Enhancement of Diamond Nucleation by Atomic Silicon Microaddition

The enhancement of diamond nucleation by atomic silicon microaddition is demonstrated. From the observation by surface-enhanced Raman scattering (SERS), the mechanism of bias-enhanced nucleation (BEN) with atomic silicon microaddition is discussed. We propose two nucleation processes, namely, i) generation in condensed amorphous carbon (a-C) and ii) carbon cohesion with the adsorbed silicon atom as the core. It is shown that the nucleation process ii) induces highly oriented diamond growth on Si substrates.

Enhancement of Diamond Nucleation by Atomic Silicon Microaddition

Enhancement of Diamond Nucleation by Atomic Silicon Microaddition

Enhanced diamond nucleation on copper substrates by employing an electrostatic self-assembly seeding process with modified nanodiamond particles

Nanodiamond seeding is a well-established approach to enhancing the nucleation density in chemical vapor deposition (CVD) diamond growth. However, the effects of nanodiamond seeding are highly dependent upon the dispersion properties of nanodiamond particles, the solvent and the interaction between nanoparticles and substrate surfaces. Surface modification and fractionalization were employed to improve the dispersion of nanodiamond particles and separate those particles into a more narrow range of particle size. Mono-dispersed nanodiamonds with a ζ-potential and average particle size of −41.5mV and ∼25.3nm, respectively, were then obtained. They can be charged on copper substrate without any contaminations. Two-dimensional self-assemblies of nanodiamond seeding were actualized. The density and homogeneity of nanodiamond particles which act as pre-existing sp3 seeds shorten the incubation time of diamond nucleation to less than 30min. High quality of 750nm thick continuous diamond film was deposited on copper substrate in 60min. Furthermore, we calculated electrostatic interaction energy between nanodiamond particle and copper substrate by using the nonlinear Poisson–Boltzmann theory, and discussed interaction energy of nanodiamond-Cu substrate and nanodiamond–nanodiamond in the seeding process.

Chemical vapor deposited diamonds on Re substrate for the application of field emission

Boron-doped diamond (BDD) films were deposited on rhenium substrates using methane/hydrogen as reactant gases by hot filament chemical vapor deposition (HFCVD). The morphology, band structures and crystalline structure of the BDD films were characterized by the scanning electron microscope (SEM), Raman spectroscopy and X-ray diffractometer (XRD), respectively. The effects of the pre-treated on nucleation and quality of the diamond film were investigated. The mixture of sulfur acid and nitric acid enhanced diamond nucleation much more greatly than that of single acid. The highly boron-doped diamond films were deposited on rhenium substrate. The field emission characteristics of these films were analyzed. The minimum resistivity of doped diamond films reached 10−2Ω cm. Field emission studies revealed that the BDD film grown on rhenium substrate had the low threshold field (3.3v/μm).

Ultrathin W−Al Dual Interlayer Approach to Depositing Smooth and Adherent Nanocrystalline Diamond Films on Stainless Steel

The adherence of diamond coated on steel is commonly low and needs to be strengthened with thick intermediate layers. In this paper, a nanoscale W-Al dual metal interlayer has been applied on SS304 substrates to facilitate deposition of continuous, adherent and smooth diamond thin films. During the microwave plasma-enhanced chemical vapor deposition process, the Al inner layer 30 nm thick diffuses into steel surface inhibiting carbon diffusion and graphitization. The W outer layer 20 nm thick is transformed into W carbides, both preventing carbon diffusion and enhancing diamond nucleation. The diamond films synthesized are of high purity and have smooth surfaces and dense structures. Indentation and shear deformation tests indicate high delaminating tolerance of the diamond films.

Deposition and characterization of diamond coatings on WC-Co cutting tools with W/Al interlayer

A new double interlayer W/Al was developed for chemical vapor deposition (CVD) of diamond coatings on cemented WC-Co cutting tools to enhance diamond nucleation and adhesion. A thin layer of Al directly deposited on WC-Co is used to suppress the interfacial graphitization induced by Co and an additional thin layer of W is used to enhance diamond nucleation. The microstructure and adhesion of diamond coatings grown on the W/Al/WC-Co and, for comparison, on W/WC-Co as well as bare WC-Co were investigated. The results demonstrate that diamond coatings grown on W/Al are continuous and well adhesive. The advantage of the interlayer includes that nano-crystalline diamond can be achieved even under typical microcrystalline diamond growth conditions. In addition, the W/Al interlayer of overall 50–65 nm thickness would cause marginal lost of cutting edge sharpness and mechanical integrity of coated cutting tools.

Surface Science Contribution to the BEN Control on Si(100) and 3C‐SiC(100): Towards Ultrathin Nanocrystalline Diamond Films

AbstractDeposition of thin and smooth nanocrystalline diamond films requires a high degree of control of the nucleation stage. The nature of the interface between diamond film and substrate is also important for some applications. The successive steps of the bias‐enhanced nucleation (BEN) process are studied in‐situ on Si(100) and 3C‐SiC(100) using electron spectroscopies. Thin nanodiamond films (80–900 nm) have been achieved on Si(100). The formation of a thin covering SiC layer (2–3 nm) during the plasma exposure for parameters stabilization (PEPS) step leads us to study the plasma/surface interactions on 3C‐SiC(100) surfaces. The C‐terminated 3C‐SiC(100) demonstrates a large inertia under microwave plasma (MP)CVD conditions. An enhancement of diamond nucleation on this surface is observed. Moreover, surface analysis reveals very little damage after BEN on 3C‐SiC surfaces.

Bias enhanced diamond nucleation onto 3C–SiC(100) surfaces studied by high resolution X-ray photoelectron and high resolution electron energy loss spectroscopies

The nature of hydrogen and carbon bonding configuration formed onto 3C–SiC(100) surfaces by the diamond bias enhanced nucleation process consisting of stabilization and biasing stages were investigated by high resolution electron energy loss spectroscopy and high resolution X-ray photoelectron spectroscopy. During the stabilization stage a sp 3-CH x bonded carbonaceous mono-layer is formed onto a hydrogenated 3C–SiC(100)–C–H terminated surfaces. After the biasing stage a hydrogenated nano-diamond film is formed. It was determined that hydrogen is strongly bonded to these nano-diamond surfaces and boundaries in sp 3-C–H and sp 2-C–H mono-hydride configuration. In addition, CH x ( x > 1) weakly bonded surface or sub-surface species were detected. Regions which are not fully covered by the nano-diamond film expose the SiC surface covered with a very thin carbonaceous layer.

Microstructure investigation of positive/negative direct current bias-enhanced diamond deposition

A two step process, positive/negative direct current (dc) biasing during the substrate pretreatment stage without biasing during the subsequent deposition stage, was used in this study. Microstructure of positive/negative dc bias-enhanced diamond deposition by microwave plasma chemical vapor deposition on silicon substrate was investigated by Raman spectroscopy, scanning electron microscopy and high resolution transmission electron microscopy (HRTEM). In positive dc biasing pretreatment, high methane concentration (25.9% CH 4 in H 2) was used to enhance diamond nucleation and resulted in the co-deposition of diamond nuclei and amorphous carbon phase. Continuous polycrystalline diamond film was observed after positive dc biasing for 5 min and growth deposition. From HRTEM cross-section analysis, it is observed that an amorphous carbon interlayer was obtained between diamond–silicon interface after pretreatment and deposition processes. The process for negative dc biasing enhanced diamond deposition was also studied and discussed. HRTEM result shows that neither SiC nor other intermediate layer is revealed between the diamond and silicon after negative dc biasing and growth processes.