• Journal of the Korean Ceramic Society
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• v.49 no.3
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• pp.221-225
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• 2012

It is possible to enhance the color of the natural diamond with a high pressure high temperature(HPHT) process. We employed a pyrophyllite tube cell and cubic press apparatus for HPHT treatment on the brown colored Type II (5.6 GPa/ $1700^{\circ}C$/ 52 min), and Type I aB(5.6 GPa/ $1650^{\circ}C$/ 30 min) diamond samples. We investigated the microstructure, Types, fluorescence, properties of the diamonds with an optical microscopy, FT-IR, photoluminescence(PL) spectroscopy, Diamond-View, and micro-Raman spectroscopy. Two tinted brown diamonds changed into colorless just after the HPHT process. Optical microscopy showed that no crack and significant inclusion evolution occurred during the HPHT process except the small graphite spot appeared in Type I aB sample. FTIR spectrum confirmed that no Type, amber center, and platelet defect change with the HPHT treatment. Diamond-View could not distinguish the HPHT treated diamonds from the naturals. PL spectroscopy showed that N3 and H3 color centers remained even after HPHT process. Consequently, we successfully changed the color of diamonds into colorless by 5.6 GPa HPHT process.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.77-78
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• 2009

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.614-619
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• 2012

We investigated color and graphite layer formation on the surface of Type I tinted brown diamonds exposed for 5 minutes under a high-pressure high-temperature (HPHT) condition in a stable graphite regime. We executed the HPHT processes of Process I, varying the temperature from $1600^{\circ}C$ to $2300^{\circ}C$ under 5.2 GPa pressure for 5 minutes, and Process II, varying the pressure from 4.2 to 5.7 GPa at $2150^{\circ}C$ for 5 minutes. Optical microscopy and micro-Raman spectroscopy were used to check the microstructure and surface layer phase evolution. For Process I, we observed a color change to vivid yellow and greenish yellow and the growth of a graphite layer as the temperature increased. For Process II, the graphite layer thickness increased as the pressure decreased. We also confirmed by 531 nm micro-Raman spectroscopy that all diamonds showed a $1440cm^{-1}$ characteristic peak, which remained even after HPHT annealing. The results implied that HPHT-treated colored diamonds can be distinguished from natural stones by checking for the existence of the $1440cm^{-1}$ peak with 531 nm micro-Raman spectroscopy.

• Korean Journal of Materials Research
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• v.4 no.5
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• pp.566-573
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• 1994

The diamond synthesis by combustion flame method is considerably affected by the substrate surface temperature and its distribution which are mainly controlled by the ratio of mixed gas, $O_2/C_2H_2$. In order to elucidate the role of gas ratio in the diamond synthetic process by combustion flame, under various gas ratios (R=0.87~0.98; R=ratio of flow-rate of $O_2/C_2H_2$ gas) the substrate temperature was measured by using thermal video system and the morphological change of diamond crystals was analysed by using SEM, Raman spectroscope, and X-ray diffraction method. With increasing the gas ratio, i.e., decreasing the hydrocarbon content, the nucleation rate of diamond crystal was lowerd. It was also found that the morphology of diamond crystals changed from the cubo-octahedron type consisting of (100), (111) plane to the octahedron type of (111) plane. The increase of the substrate temperature consistently resulted in the increase of the nucleation rate as well as the growth rate of diamond crystals in which the surface of diamond crystal dominantly consisting of (100) plane.

• Journal of the Korean institute of surface engineering
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• v.29 no.5
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• pp.505-511
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• 1996

The field emission characteristics of diamond films deposited by microwave plasma enhanced chemical vapor deposition (MPECVD) method were investigated. Diamond films were deposited on n-type Si(100) wafer using various mixtures of hydrogen and methane gas, and the I-V characteristics are measured. We observed that the field emission characteristics depend on the $CH_4$ concentration and the diamond film thickness. All the films show remarkable emission characteristics; low turn-on voltage, high emission current density at lower voltage, uniform stable current density, and good stability and reproducibility. The threshold field for producing a current density of 1mA/$\textrm{cm}^2$ is found as low as 7.6V/$\mu\textrm{m}$.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.59-64
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• 2002

One of the exciting research areas of the X-ray microscope is the observation of a living cell. In order to study a living cell with high resolution the order of the several tens nm, we need to improve the efficiency of mirrors which are components of an X-ray microscope system. In this paper we present the mirror design and manufacture to give a high resolution and reflectivity. We designed Wolter type I the condenser and objective mirror with the several tens of nm resolution. According to mirror design. we made the program using the visual basic. Using the new processing method as well as the ultra-precision diamond cutting, we directly processed the inside of an aluminum hulk in order to manufacture mirrors. From the experimental result, we think that the new processing method will improve a high reflectivity through the improved cutting tools and optimum cutting conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.5
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• pp.817-822
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• 2006

Diamonds have been widely employed as polishing media for precise machining and noble substrates for microelectronics. The recent development of the split sphere press has led to the enhancement of low quality natural diamonds. Synthesized and treated diamonds are sometimes traded deceptively as high quality natural diamonds because it is hard to distinguish among these diamonds with conventional gemological characterization method. Therefore, we need to develop a new identification method that is cheap, fast, and non-destructive. We proposed using a new method of micro-Raman spectroscopy for checking the local HPHT residual stress to distinguish these diamonds from natural ones. We observe unique ~10f compressive and tensile strains at Type I and Type II diamonds after HPHT treatment. Our result implies that our proposed methods may be appropriate fur identification of the treated diamonds with appropriate reference samples.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.290-290
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• 2011

In this study Diamond-like carbon (DLC) films were deposited on p-type Si substrates using a Radio-Frequency magnetron Sputtering system. The DLC film was deposited by bombarding graphite target with a N2/Ar plasma mixture with various conditions: substrate, pressure, deposition time, temperature of substrate, power and ratio of gas mixture. The effect on the conduction and hardness of DLC thin films were investigated. The conduction of DLC films were measured by I-V measurement. In addition, Raman analysis was performed to study the chemical bonding structure. The hardness was measured by Nano indentation. Atomic Force Microscopy was used for determined surface morphology of DLC film.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1223-1227
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• 2005

Fine microgroove is the key component to fabricate micro-grating, micro-grating lens and so on. Conventional groove fabrication methods such as etching and lithography have some problems in efficiency and surface integrity. This study deals with the creation of ultra-precision micro grooves using non-rotational diamond tool and CNC machining center. The shaping type machining method proposed in the study allows to produce V-shaped grooves of $40\mu{m}$ in depth with enough dimensional accuracy and surface. For the analysis of machining characteristics in micro V-grooving, three components of cutting forces and AE signal are measured and processed. Experimental results showed that large amplitude of cutting forces and AE appeared at the beginning of every cutting path, and cutting forces had a linear relation with the cross-sectional area of uncut chip thickness. From the results of this study, proposed micro V-grooving technique could be successfully applied to forming the precise optical parts like prism patterns on light guide panel of TFT-LCD.

• Journal of radiological science and technology
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• v.27 no.2
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• pp.45-50
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• 2004

Synthesis diamond films have been deposited on the molybdenum substrates using an microwave plasma enhanced chemical vapor deposition method. The effects of deposition time, surface morphology, infrared transmittance and Raman scattering have been studied. Diamond deposited on molybdenum substrate for 100 hours by MW plasma CVD from $CH_4-H_2-O_2$ gas mixture had good crystallity with $100[{\mu}m]$ thickness needed for radiation detector. Diamond radiation detector of M-I-M type was made and the current of radiation detector was increased by increasing X-ray dose.