Kwang-Yong Eun

Behaviour of Co binder phase during diamond deposition on WCCo substrate

Abstract The movement of the Co-rich binder phase and its interaction with growing diamond particles during deposition were investigated by repeated observations of the same site on a WC-Co substrate surface. Both etched and unetched (as-polished) specimens of WC-5Co were used for deposition. The diamond deposition was carried out using the tungsten filament chemical vapour deposition method. Raman spectra have shown that the quality of the diamond deposited on the etched substrate was better than that on the as-polished substrate. The facet size of the diamond film surface on the as-polished substrate was smaller than that on the etched specimen. These effects were caused by the atomic-scale interaction of Co atoms in the binder phase. A special feature of the diamond film on the as-polished specimen was a very rough diamond film surface. This phenomenon was observed to result from the abnormal movement of the Co-rich binder phase to the deposited diamond particle surface and the subsequent non-uniform growth of particles during deposition. The phenomenological characteristics of the Co-rich binder phase movement were also explained.

Stress relief behaviour of diamond-like carbon films on glasses

Abstract The stress relief behaviour of diamond-like carbon (DLC) films on glass substrates was investigated. The r.f.-plasma-enhanced chemical vapour deposition method was used for the deposition with variable negative bias voltages of the cathode from −100 to −700 V. Beyond a critical thickness of the film, film delamination starts to occur after its removal from the reaction chamber. In addition to the previously observed stress relief morphologies, sinusoidal cracking and sinusoidal removal of the film are also observed. The stress relief morphology is dependent on the film thickness and the negative bias voltage. The measured wavelength of sinusoidal buckling increases with both increasing film thickness and increasing negative bias voltage. This behaviour is qualitatively consistent with a phenomenological equation derived by Nir. It was suggested that the elastic modulus of the DLC film can be calculated using the dependence of the wavelength of sinusoidal buckling on the film thickness and the negative bias voltage.

A method of determining the elastic properties of diamond-like carbon films

The elastic properties of diamond-like carbon (DLC ) films were measured by a simple method using DLC bridges which are free from the mechanical constraints of the substrate. The DLC films were deposited on a Si wafer by radio frequency (RF ) glow discharge at a deposition pressure of 1.33 Pa. Because of the high residual compressive stress of the film, the bridge exhibited a sinusoidal displacement on removing the substrate constraint. By measuring the amplitude with a known bridge length, we could determine the strain of the film which occurred by stress relaxation. Combined with independent stress measurement using the laser reflection method, this method allows the calculation of the biaxial elastic modulus, E/(1’n), where E is the elastic modulus and n is Poisson’s ratio of the DLC film. The biaxial elastic modulus increased from 10 to 150 GPa with increasing negative bias voltage from 100 to 550 V. By comparing the biaxial elastic modulus with the plane‐strain modulus, E/(1’n2), measured by nano-indentation, we could further determine the elastic modulus and Poisson’s ratio, independently. The elastic modulus, E, ranged from 16 to 133 GPa in this range of the negative bias voltage. However, large errors were incorporated in the calculation of Poisson’s ratio due to the pile up of errors in the measurements of the elastic properties and the residual compressive stress.

Generation of pulsed direct-current plasma above 100 torr for large area diamond deposition

A high-temperature, large-size plasma was successfully generated at a pressure above 100 torr using a pulsed direct current (DC) electric power for the application of wafer-scale diamond thick film growth. A diode type electrode configuration was used, with a Mo disk of 13 cm in diameter as a cathode and a W disk of 10 cm in diameter as a substrate. By adjusting the pulse condition and maintaining the cathode temperature between 1000°C and 1100°C, the arc between the electrodes was suppressed completely and the plasma was maintained very stably for over 100 h. Above and below this cathode temperature range, solid carbon was deposited on the cathode, which induced either the arc or non-uniformity of plasma state. A diamond wafer with a thickness up to 1 mm was successfully grown using this plasma of methane and hydrogen mixed gas. The plasma characteristics were analyzed using an optical emission spectroscopy.

Morphology dependence of cathodoluminescence spectra of CVD diamond film

Abstract Translucent polycrystalline diamond film made by a DC plasma CVD method was investigated with cathodoluminescence spectroscopy and topography. Shift and/or splitting were found in peaks of several luminescence bands, 575, 532, 480, 460, 389, 270 (5RL) and 235 nm (FE), suggesting considerable magnitude of residual stress is present in the film. The behavior of the splitting was different for the different peak, indicating that the symmetries of the associated defects are different. The film after heat treatment at 6 GPa and 1800 °C was found to exhibit new luminescence bands approximately 300 and 500 nm. Splitting of the 575 nm peak was recognized to decrease with the heat treatment, suggesting that the residual stress was reduced.

SiC enhanced nucleation of diamond under high pressure and high temperature

Abstract Three kinds of catalyst have been prepared to investigate the role of SiC in diamond nucleation under high pressure and high temperature: (1) a fresh Ni-SiC powder mixture; (2) a heat-treated Ni-SiC mixture at 1300 °C for 2 h in vacuum, and (3) a heat-treated Ni-Si mixture at 1100 °C for 3 h in vacuum. When carbon black was treated with each catalyst at 4.7 GPa, 1450 °C for 5 min, diamond was synthesized only in the specimen containing the fresh mixture of Ni-SiC catalyst. The added fresh SiC enhanced drastically diamond formation. SiC thus appears to act as direct nucleation sites of diamond under the experimental condition.