P. C. Yang

Oriented diamond films grown on nickel substrates

A previously reported multistep hot filament chemical vapor deposition process for nucleating diamond directly on nickel substrates has been further refined to increase the nucleation density and improve the orientation of diamond films. The process employed heavy seeding of both 〈100〉 and 〈111〉 oriented single crystal Ni surfaces with diamond powders to enhance the nucleation density of diamond films. The deposition conditions were adjusted to allow for 〈100〉 and 〈111〉 orientations to grow on similarly oriented substrates to form nearly complete films with grain boundaries being eliminated. Thus, the technique holds promise for developing heteroepitaxial diamond films for microelectronics applications.

Nucleation of oriented diamond films on nickel substrates

A seeding and multistep deposition process has been developed to nucleate and grow diamond films directly on Ni substrates in a hot filament chemical vapor deposition system. High quality diamond films have been deposited without graphite codeposition on both 〈100〉 oriented single-crystal Ni and polycrystalline Ni substrates. Both 〈100〉 and 〈111〉 oriented diamond nuclei have been observed depending upon the underlying substrate orientations. Molten metallic phases were found surrounding the diamond nuclei, and it is speculated that a liquid layer composed of nickel, carbon, and hydrogen also formed on the diamond surface during the growth. The oriented diamond is believed to have been achieved by the reorientation of seeded diamond particles into alignment with the Ni substrate due to interaction between the diamond and Ni lattices.

HETEROEPITAXIAL NUCLEATION OF DIAMOND ON NICKEL

Abstract Highly oriented diamond has been grown on (100) nickel substrates by the hot filament chemical vapor deposition method. Epitaxial nuclei were obtained by a diamond powder seeding and high temperature annealing process. Since the timing of the process was crucial for the achievement of a high degree of orientation and high density of diamond nuclei, a real-time, in-situ laser reflectometry system was developed to monitor changes in surface morphology observed during the high temperature annealing stage. Characteristic features observed in the intensities of reflected and scattered light were interpreted by comparison with scanning electron micrographs of the samples quenched at sequential stages of the process. It was concluded that the scattered light signal can be effectively used as a process steering parameter. Using this technique, oriented nucleation and growth of diamond on Ni was reproducibly achieved. Auger spectroscopy showed that up to 6 at% of carbon was dissolved in the nickel surface layer. The investigation of interfacial microstructures and phases involved by transmission electron microscopy revealed the formation of Ni4C already in the early stages of nucleation. This phase was manifested as coherent precipitates and is believed to have been the precursor for diamond nucleation. Perfectly epitaxial diamond was grown by this process. The epitaxial relationship was determined by cross-sectional transmission electron microscopy and selected area diffraction analysis.

Nucleation of oriented diamond particles on cobalt substrates

Nucleation of oriented diamond particles on cobalt substrates has been achieved by a multistep, hot‐filament chemical vapor deposition process, which involves seeding, annealing, nucleation, and then growth. The substrates were seeded with either diamond powders, graphite powders, or gaseous carbon species. Scanning electron microscopy showed that 〈111〉 oriented diamond particles were obtained on 〈0001〉 oriented single crystal cobalt substrates. Micro‐Raman indicated that the quality of the diamond grown on the cobalt substrate was high, with a full width at half maximum of 4.3 cm−1. A very weak graphitic peak was observed on regions of the substrate not covered by the diamond particles, indicating that graphite codeposition was significantly suppressed. Scanning Auger depth profile analysis was done to characterize the diamond nucleation. Based on the experimental observations, a nucleation model is proposed.

DIAMOND NUCLEATION AND GROWTH ON REACTIVE TRANSITION-METAL SUBSTRATES

Diamond deposition on group VIII transition metals of Cr, Mn, Fe, Co, and Ni has been achieved by a multi-step chemical vapor deposition process consisting of (i) seeding the substrate with diamond powders, (ii) annealing the seeded substrate in hydrogen at high temperatures, and (iii) diamond nucleation and growth. It was found that high quality diamond can be grown on these substrates, and the often accompanied graphite formation, which has been the main obstacle in the deposition of diamond on these metal surfaces, can be largely suppressed by the above step-deposition procedure. This technique was further extended to the processes of depositing diamond on steels and Co-bonded WC materials.

Control of diamond heteroepitaxy on nickel by optical reflectance

Real time in situ laser reflectometry was used to investigate changes in surface morphology observed during the nucleation of oriented diamond on Ni in a hot filament chemical vapor deposition reactor. Characteristic features observed in the intensities of reflected and scattered light were interpreted by comparison with scanning electron micrographs of the diamond seeded substrates quenched at sequential stages of the process. Based on this analysis, a process was developed in which the scattered light signal was used as a steering parameter. Using this process, oriented nucleation and growth of diamond on Ni can be repeatedly achieved.

Surface melting in the heteroepitaxial nucleation of diamond on Ni

Abstract Surface melting associated with the heteroepitaxial nucleation of diamond on Ni was investigated. Scanning electron microscopy of quenched samples revealed flow patterns and a recrystallized surface morphology. A combination of techniques including in situ optical monitoring, differential thermal analysis, Auger depth profile analysis, and cross-section transmission electron microscopy (TEM) analysis were performed to identify the nature of the molten layer. Data obtained from different experiments were in good mutual agreement. All experimental results strongly indicated that a molten Ni–C–H surface layer was involved in the nucleation process. The presence of both carbon and atomic hydrogen played an important role in the depression of the melting point which was measured to be >300°C less than the melting point of pure Ni.

Coalesced oriented diamond films on nickel

The growth of coalesced, highly oriented diamond films has been achieved on nickel substrates using a multistep process that consisted of (i) seeding the Ni surface with 0.5 μm diamond powder, (ii) annealing at 1100 °C in a hydrogen atmosphere, and (iii) growth at 900 °C in a mixture of hydrogen and 0.5% methane. Auger depth profile analysis of a sample quenched after the annealing stage showed the presence of significant amounts of carbon (6 at. %) close to the substrate surface and about 3 at.% deeper in the substrate. The loss of carbon into the substrate resulted in relatively low nucleation density. The addition of methane into the gas phase during the annealing stage proved very effective in compensating for the diffusion. An addition of 0.5% methane in the gas phase produced optimum results, as the nucleation density, orientation of diamond particles, and uniformity were substantially improved. Substrates nucleated under these conditions were grown out into coalesced, 30 μm thick films. Both (100) and (111) oriented films showed a high degree of orientation and Raman spectra obtained from these orientations showed intense and narrow diamond signature peaks with FWHMs of 5 and 8 cm -1 , respectively.

Transmission electron microscopy analysis of the oriented diamond growth on nickel substrates

Transmission electron microscopy (TEM) was used to investigate the interfacial microstructure and the phases that developed during the nucleation and growth of oriented diamond on Ni by a hot filament process. Oriented Ni4C nuclei were identified by plan-view TEM in a sample quenched during the nucleation stage. Likewise, the presence of the Ni4C phase between the diamond and the Ni substrate was observed by cross-section TEM in samples grown for several hours. The orientational relationship among the diamond, Ni4C, and Ni substrate was examined by selected area diffraction. Diamond and Ni4C interfacial phase had a good epitaxial relationship, while the interfacial Ni4C phase and the Ni substrate developed with a small misfit and rotation. Based on these experimental results, the nucleation mechanism of oriented diamond growth on Ni is proposed.

Tem Analysis of the Observed Phases During the Growth of Oriented Diamond on Nickel Substrates

Transmission electron microscopy (TEM) was used to investigate the interfacial microstructures and phases involved in the nucleation and growth of the oriented diamond on Ni substrates by a multi-step growth process. A molten surface layer is formed during the process, which appears to be critical for both promotion of the diamond nucleation and suppression of graphite formation. Cross-section TEM analysis revealed that a polycrystalline nickel carbide interfacial structure exists between the diamond particles and the single crystal Ni substrate. X-ray diffraction analysis (XRD) identified the carbide phase as Ni 4 C. It is suggested that the Ni 4 C is formed in the molten layer and stabilizes sp 3 C precursor for diamond nucleation.