• Tribology and Lubricants
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• 제37권5호
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• pp.179-188
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• 2021

Reputed for their low friction coefficient and wear protection effect, diamond-like carbon (DLC) materials are considered amongst the most important lubricant coatings for tribological applications. In this framework, this investigation aims to elucidate the effect of a few operating parameters, such as applied stress and sliding amplitude on the friction lifetime of DLC coatings. Fretting wear tests are conducted using a 12.7 mm radius counterpart of 52100 steel balls slid against a substrate of the same material coated with a 2 ㎛ thickness DLC. Approximately, 5 to 57 N force is applied, generating a maximum Hertzian contact pressure of 430 to 662 MPa, corresponding to the applied force. The coefficient of friction (CoF) generates three regimes, first a running-in period regime, followed by a steady-state evolution regime, and finally a progressive increase of the CoF reaching the steel CoF value, as an indicator of reaching the substrate. To track the wear scenario, interrupted tests are performed with analysis combining scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), 3D profilometer and micro-Raman spectroscopy. The results show two endurance values: one characterizing the coating failure (Nc₁), and the other (Nc₂) indicating the friction failure which is situated where the CoF reaches a threshold value of μ_th = 0.3 in the third regime. The Archard energy density factor is used to determine the two endurance values (Nc₁, Nc₂). Based on this approach, a master curve is established delimitating both the coating and the friction endurances.

• 센서학회지
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• 제31권4호
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• pp.255-259
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• 2022

In this study, we fabricated ZnS substrates with excellent transmittance in the mid-infrared region (3-5 ㎛) using hot pressing instead of conventional chemical vapor deposition (CVD). Diamond-like carbon (DLC) was coated on either one or both sides of the ZnS substrates to improve their mechanical properties and transmittance efficiency. To reduce the reflectance and further improve transmittance in the mid-infrared region, anti-reflection (AR) coating was designed for DLC/ZnS /AR and AR/ ZnS /AR structures. The coating structure, microstructure, and optical properties of the AR-coated ZnS substrates were subsequently investigated by employing energy dispersive X-ray spectroscopy, scanning electron microscopy, and Fourier-transform infrared (FTIR) spectroscopy. The FTIR spectroscopy results demonstrated that, in the mid-infrared region, the average transmittance of the samples with AR coating on one and both sides increased by approximately 18% and 27%, respectively. Thus, AR coating improved the transmittance of the ZnS substrates.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2003년도 추계학술발표회초록집
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• pp.54-54
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• 2003

DLC films were deposited on Si(100) substrates by inductively coupled plasma (ICP) assisted chemical vapor deposition (CVD). A mixture of acetylene (C$_2$H$_2$) and argon (Ar) gases was used as the precursor and plasma source, respectively. The structure of the films was characterized by the Raman spectroscopy. Results from the Raman spectroscopy analysis indicated that the property change of the DLC films is due to the sp$^3$ and sp$^2$ ratio in the films under various conditions such as ICP power, working pressure and RF substrate bias. The hydrogen content in the DLC films was determined by an electron recoil detector (ERB). The roughness of the films was measured by atomic force microscope (Am). A microhardness tester was used for the hardness and elastic modulus measurement. The DLC film showed a maximum hardness of 37㎬. In this work, the relationship between deposition parameters and mechanical properties were discussed.

• Design & Manufacturing
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• 제17권2호
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• pp.15-21
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• 2023

In this study, a diamond turning machine and a laser-assisted machining module were utilized for the complex combined cutting of aspheric shapes and fine patterns on the surface of high-hardness brittle material, silicon. The analysis of material's form accuracy and corrective machining was conducted based on key factors such as laser output, rotational speed, feed rate, and cutting depth to achieve form accuracy below 1 ㎛ and surface roughness below 0.1 ㎛. The cutting condition and corrective machining methods were investigated to achieve the desired form accuracy and surface roughness. The rotational speed of the spindle and the linear feed rate of the diamond turning machine were varied in five stages for the cutting condition test. Surface roughness and form accuracy were measured using both a contact surface profilometer and a non-contact surface profilometer. The experimental results revealed a tendency of improved surface roughness with increased rotational speed of the workpiece, and the best surface roughness and form accuracy were observed at a feed rate of 5 mm/min. Furthermore, based on the cutting condition experiments, corrective machining was performed. The experimental results demonstrated an improvement in form accuracy from 0.94 ㎛ to 0.31 ㎛ and a significant reduction in the average value of the surface roughness curve from 0.234 ㎛ to 0.061 ㎛. This research serves as a foundation for future studies focusing on the machinability in relation to laser output parameters.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.7-8
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• 2010

The surface conductive layer (SCL) of chemical vapor deposition (CVD) diamonds has attracting much interest. However, neither photoemission electron microscopic (PEEM) nor micro-spectroscopic (PEEMS) information is available so far. Since SCL retains in an ultra-high vacuum (UHV) condition, PEEM or PEEMS study will give an insight of SCL, which is the subject of the present study. The sample was made on a Ib-type HTHP diamond (001) substrate by non-doping CVD growthin a DC-plasma deposition chamber. The SCL properties of the sample in air were; a few tens K/Sq. in sheet resistance, ${\sim}180\;cm^2/vs$ in Hall mobility, ${\sim}2{\times}10^{12}/cm^2$ in carrier concentration. The root-square-mean surface roughness (Rq) of the sample was ~0.2nm as checked by AFM. A $2{\times}1$ LEED pattern and a sheet resistance of several hundreds K/Sq. in UHV were checked in a UHV chamber with an in-situ resist-meter [1]. The sample was then installed in a commercial PEEM/S apparatus (Omicron FOCUS IS-PEEM) which was composed of electro-static-lens optics together with an electron energy-analyzer. The presence of SCL was regularly monitored by measuring resistance between two electrodes (colloidal graphite) pasted on the two ends of sample surface. Figure 1 shows two PEEM images of a same area of the sample; a) is excited with a Hg-lamp and b) with a Xe-lamp. The maximum photon energy of the Hg-lamp is ~4.9 eV which is smaller that the band gap energy ($E_G=5.5\;eV$) of diamond and the maximum photon energy of the Xe-lamp is ~6.2 eV which is larger than $E_G$. The image that appear with the Hg-lamp can be due to photo-excitation to unoccupied states of the hydrogen-terminated negative electron affinity (NEA) diamond surface [2]. Secondary electron energy distribution of the white background of Figs.1a) and b) indeed shows that the whole surface is NEA except a large black dot on the upper center. However, Figs.1a) and 1b) show several features that are qualitatively different from each other. Some of the differences are the followings: the two main dark lines A and B in Fig.1b) are not at all obvious and the white lines B and C in Fig.1b) appear to be dark lines in Fig.1a). A PEEMS analysis of secondary electron energy distribution showed that all of the features A-D have negative electron affinity with marginal differences among them. These differences can be attributed to differences in the details of energy band bending underneath the surface present in SCL [3].

• 한국조리학회지
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• 제14권2호
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• pp.1-17
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• 2008

This study analyzed the factors related to the stress which the top-rated chefs in Jeju suffer and conducted the multiple regression analysis to look into the effect of job-related stress on the stress reaction and the satisfaction with job, in order to examine the effect of job-related stress faced by hotel kitchen employees in performing duties and determine the effect of job-related stress on the reaction of individuals in the peculiar environment of a kitchen in a hotel. Job-related stresses were classified into five factors which were physical, individual, vocational, organizational, and social. The result of regression analysis, which was performed to figure out the effect of job-related stress on the stress reaction and the satisfaction with the job, indicated that the physical factor of job-related stress had the greatest effect on the physiological reaction, followed by the organizational factor, individual factor, and social factor, while the organizational factor of job-related stress had the greatest effect on the psychological reaction, followed by the individual factor, social factor, vocational factor, and physical factor. Meanwhile, the vocational factor of job-related stress had the greatest effect on behavioral re-action, followed by organizational factor and individual factor. The vocational factor of job-related stress had the greatest effect on the satisfaction with the job, followed by individual factor, organizational factor, social factor, and physical factor.

• Journal of the Korean Data and Information Science Society
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• 제18권2호
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• pp.515-524
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• 2007

This paper deals with local linear estimation of fuzzy regression models based on Diamond(1998) as a new class of non-linear fuzzy regression. The purpose of this paper is to introduce a use of smoothing in testing for lack of fit of parametric fuzzy regression models.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 춘계학술대회 논문집
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• pp.1033-1034
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• 2009

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1998년도 PROCEEDINGS OF THE 15TH KACG TECHNICAL MEETING-PACIFIC RIM 3 SATELLITE SYMPOSIUM SESSION 4, HOTEL HYUNDAI, KYONGJU, SEPTEMBER 20-23, 1998
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• pp.33-33
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• 1998

Invisible charged clusters are suggested to form in the gas phase and to become the growth unit in the thin film process. Similar suggestion had been made by Glasner el al. in the crystal growth of KBr and KCL in the solution where the lead ions were added. The charged cluster model, which was suggested in the diamond CVD process by our group, will be extended to the other thin film processes. It will be shown based on both the theoretical analysis and the experimental evidences that the charged clusters are formed in the gas phase and become the growth unit of the crystal in the thin film process.

• 한국항해항만학회지
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• 제46권3호
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• pp.203-208
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• 2022

최근 해사 분야에서는 제4차 산업혁명을 기반으로 e-Navigation, 자율운항선박, 스마트선박 등 다양한 디지털 기술 이슈가 끊임없이 등장하고 있다. 국제해사기구(IMO)는 해양안전 및 해양환경보호를 위한 규제를 점차 강화하고 있으며, 이러한 강화된 규제 이행은 해양안전 및 해양환경보호 분야의 신산업 창출로 이어지고 있다. 이에 본 연구에서는 해사 분야의 대표적 신산업인 자율운항기술 분야에 대한 산업경쟁력 분석을 위해 포터(Porter)의 다이아몬드 모델을 기반으로 산업경쟁력 분석 모델을 설계하고, 총 5개 평가요소 및 13개 세부요소를 기반으로 국내 자율운항기술 산업에 대한 산업경쟁력을 정성적·정량적으로 평가하였다. 산업발전 초기 단계인 자율운항기술 산업은 산업경쟁력 지수화 결과 16.9점으로 평가되었으며, 현재 산업의 범위 정립부터 관련 규제 및 핵심기술 개발 등이 동시에 진행되고 있는 것이 특징이었다. 이러한 산업특성을 고려한 산업경쟁력 분석·평가는 신산업에 대한 전략적 지원 및 정책 추진을 위한 근거를 마련하고, 신산업 경쟁력 강화를 통해 해운·물류, 항만, 조선·기자재 산업 등 광범위한 연관 산업까지 영향을 미칠 것으로 기대된다.