• 한국세라믹학회지
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• 제48권4호
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• pp.312-315
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• 2011

The effect of slurry composition and wafer flatness on a material removal rate (MRR) and resulting surface roughness which are evaluation parameters to determine the CMP characteristics of the on-axis 6H-SiC substrate were systematically investigated. 2-inch SiC wafers were fabricated from the ingot grown by a conventional physical vapor transport (PVT) method were used for this study. The SiC substrate after the CMP process using slurry added oxidizers into slurry consisted of KOH-based colloidal silica and nano-size diamond particle exhibited the significant MRR value and a fine surface without any surface damages. SiC wafers with high bow value after the CMP process exhibited large variation in surface roughness value compared to wafer with low bow value. The CMPprocessed SiC wafer having a low bow value of 1im was observed to result in the Root-mean-square height (RMS) value of 2.747 A and the mean height (Ra) value of 2.147 A.

• 한국진공학회지
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• 제9권4호
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• pp.328-334
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• 2000

ECR-PECVD 방법을 이용하여 ECR power, $CH_4/H_2$ 가스 혼합비와 유량, 증착시간을 고정시켜놓고 기판 bias 전압을 변화 시켜가면서 DLC 박막을 제작하였고, 제작된 박막의 두께, Raman과 FTIR 스펙트럼 그리고 미소경도 등을 측정 및 분석하여 기판 bias전압에 따른 이온충돌이 박막의 특성 변화에 미치는 영향을 조사하였다. FTIR 분석 결과로부터 기판 bias 전압을 증가시킬수록 이온충돌 현상이 두드러져 탄소와 결합하고 있던 수소원자들의 탈수소화 현상을 확인할 수 있었고, 박막의 두께는 bias 전압을 증가시킬수록 감소되었다. 그리고 Raman 스펙트럼으로부터 Gaussian curve fitting을 통하여 $sp^3$/$sp^2$의 결합수에 비례하는 D와 G peak의 면적 강도비(ID/IG)는 기판 bias 전압을 증가시킬수록 증가하였고, 또한 경도도 증가하였다. 이 결과로부터 본 연구에서 제작된 수소를 함유한 비정질 탄소 박막은 기판 bias 전압의 크기를 증가시킬수록 DLC 특성이 더 향상됨을 알 수 있었다.

• 열처리공학회지
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• 제24권3호
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• pp.127-132
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• 2011

The silicon-containing Diamond-like Carbon (Si-DLC) film as an low friction coefficient coating has especially treated a different silicon content by plasma-enhanced chemical vapor deposition (PECVD) process at $500^{\circ}C$ on nitrided-STD 11 mold steel with (TMS) gas flow rate. The effects of variable silicon content on the Si-DLC films were tested with relative humidity of 5, 30 and 85% using a ball-on-disk tribometer. The wear-tested and original surface of Si-DLC films were analysed for an understanding of physical and chemical characterization, including a changing structure, via Raman spectra and nano hardness test. The results of Raman spectra have inferred a changing intra-structure from dangling bonds. And high silicon containing DLC films have shown increasing carbon peak ratio ($I_D/I_G$) values and G-peak values. In particular, the tribological tested surface of Si-DLC was shown the increasing hardness value in proportional to TMS gas flow rate. Therefore, at same time, the structure of the Si-DLC film was changed to a different intra-structure and increased hardness film with mechanical shear force and chemical reaction.

• 한국표면공학회지
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• 제39권3호
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• pp.105-109
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• 2006

The effects of negative carbon ion beam energy on the bonding configuration, hardness and surface roughness of DLC film prepared by a direct metal ion beam deposition system were investigated. As the negative carbon ion beam energy increased from 25 to 150 eV, the $sp^3$ fraction of DLC films was increased from 32 to 67%, while the surface roughness was decreased. The films prepared at 150 eV showed the more flat surface morphology of the film than that of the film prepared under another ion beam energy conditions. Surface roughness of DLC film varied from 0.62 to 0.22 nm with depositing carbon ion beam energy. Surface nano-hardness increased from 12 to 57 Gpa when increasing the negative carbon ion beam energy from 25 to 150 eV, and then decreased when increasing the ion beam energy from 150 to 200 eV.

• 한국결정성장학회지
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• 제24권1호
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• pp.33-40
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• 2014

전기방사법(Electrospinning technique)을 이용하여 PVdF-HFP(Poly vinylidene fluoride-co-hexafluoropropylene) 멤브레인을 제조하고, 그 멤브레인 표면위에 DLC(Diamond-like carbon) 코팅공정을 적용하여 멤브레인의 표면변화 및 접촉각 변화를 조사하였다. Ar 플라즈마 처리시간 및 처리조건에 따라 PVdF-HFP 멤브레인 파이버 표면이 주름(wrinkles)형태로 변화 하였다. 이러한 Ar 플라즈마 처리가 된 PVdF-HFP 멤브레인은 초친수성(super-hydrophilic) 특성으로 변했지만, 초친수성 PVdF-HFP 멤브레인에 DLC 코팅공정을 적용하면 반대로 초소수성(super-hydrophobic) 특성으로 변화되었다. 이러한 특성을 가진 표면을 접촉각 측정과 XPS, FE-SEM 측정으로 분석하였다. 따라서 화학적 조성과 표면 형상에 의해 접촉각 특성을 가지는 것으로 확인하였다.

• 한국분말재료학회지
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• 제17권6호
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• pp.456-463
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• 2010

This paper describes the results of the application of Cr-Diamond-like carbon (DLC) films for efficiency improvement through surface modification of spur gear parts in the hydraulic gear pump. Cr-DLC films were successfully deposited on SCM 415 substrates by a hybrid coating process using linear ion source (LIS) and magnetron sputtering method. The characteristics of the films were systematically investigated using FE-SEM, nano-indentation, sliding tester and AFM instrument. The microstructure of Cr-DLC films turned into the dense and fine grains with relatively preferred orientation. The thickness formed in our Cr buffer layer and DLC coating layer were obtained the 487 nm and $1.14\;{\mu}m$. The average friction coefficient of Cr-DLC films considerably decreased to 0.15 for 0.50 of uncoated SCM415 material. The hardness and surface roughness of Cr-DLC films were measured 20 GPa and 10.76 nm, respectively. And then, efficiency tests were performed on the hydraulic gear pump to investigate the efficiency performance of the Cr-DLC coated spur gear. The experimental results show that the volumetric and mechanical efficiency of hydraulic gear pump using the Cr-DLC spur gear were improved up to 2~5% and better efficiency improvement could be attributed to its excellent microstructure, higher hardness, and lower friction coefficient. This conclusion proves the feasibility in the efficiency improvement of hydraulic gear pump for industrial applications.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.128-128
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• 2000

박막의 탄성 특성을 평가하는 방법으로 nano-indentation, Brillouin light scattering measurement, ultrasonic surface wave measurement, bulge test, vibration membrane method 등 여러 가지가 제시되어 왔다. 이러한 방법들은 필름의 두께가 일정 두께 이상이 되어야 정확한 측정이 가능한 방법으로 매우 얇은 박막에서도 탄성특성을 평가할 수 있는 freehang, bridge 방법이 제시되었으며, 이 방법은 간단한 식각 공정을 통해 매우 얇은 박막에도 적용시킬 수 있다는 장점을 가지고 있다. 본 연구에서는 아주 얇은 박막에서도 탄성특성을 평가할 수 있는 freehang 방법을 이용하여 순수한 Diamond-like carbon (DLC) 필름과 Sidl 첨가된 DLC 필름의 탄성 특성을 평가하고자 한다. 실험에서 사용한 필름은 rf-PACVD 장비를 이용하여 증착하였다. 이때 전극과 플라즈마 사이의 바이어스 음전압은 -400 Vb로 합성압력은 10mTorr로 고정하였다. 사용한 반응 가스는 벤젠(C6H6), 그리고 벤젠과 희석된 실렌(SiH4 : H2 = 10 : 90)이며, 희석된 실렌의 첨가량을 조절하여 필름 내에 일정량의 Si을 함유시켰다. 각각의 조건에서 증착시간을 조절하여 필름의 두께를 변화시켰으며, KOH(5.6mol) 용액을 이용하여 습식 식각을 함으로써 freehang을 제작하였다. 이때 식각액에 의한 DLC 필름의 손상은 관찰되지 않았다. 필름의 잔류 응력을 측정하기 위해 200$\pm$10 혹은 100$\pm$5$\mu\textrm{m}$ 두께의 얇은 (100) Si wafer를 5$\times$50 mm2의 strip 형태로 절단하여 사용하였다. 필름의 압축 잔류 응력에 의해 발생한 필름/기판 복합체의 곡률은 laser 반사법과 $\alpha$-step profiler를 이용하여 측정하였으며, 이 결과를 Brenner 등에 유도된 식을 이용하여 잔류 응력을 계산하였다. 또한 제작된 frddhang은 광학 현미경과 전자주사현미경에 의해 관찰되었다. 이렇게 제작된 freehang을 이용하여 필름이 기판에 부착되기 위해 필요한 변형률을 측정하고, 독립적으로 측정된 필름의 잔류 응력을 박막의 응력-변형률 관계식에 적용하여 biaxial elastic modulus, E/(1-v)를 구할 수 있었다. 측정 결과 필름의 잔류 응력과 biaxial elastic modulus는 필름의 두께가 감소함에 따라 감소하는 경향을 나타냈으며, 같은 두께의 필름인 경우, 식각 깊이에 따른 biaxial elastic modulus 의 변화를 통해 최적의 식각 깊이를 알 수 있었다.

• 한국정밀공학회지
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• 제23권8호
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• pp.171-177
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• 2006

This study was performed as a part of the research on the development of a maskless and electroless process for fabricating metal micro/nanostructures by using a nanoindenter and an electroless deposition technique. $2-{\mu}m$-deep indentation tests on Ni and Cu samples were performed. The elastic recovery of the Ni and Cu was 9.30% and 9.53% of the maximum penetration depth, respectively. The hardness and the elastic modulus were 1.56 GPa and 120 GPa for Ni and 1.51 GPa and 104 GPa for Cu. The effect of single-point diamond machining conditions such as the Berkovich tip orientation (0, 45, and $90^{\circ}$ ) and the normal load (0.1, 0.3, 0.5, 1, 3, and 5 mN), on both the deformation behavior and the morphology of cutting traces (such as width and depth) was investigated by constant-load scratch tests. The tip orientation had a significant influence on the coefficient of friction, which varied from 0.52-0.66 for Ni and from 0.46- 0.61 for Cu. The crisscross-pattern sample showed that the tip orientation strongly affects the surface quality of the machined are a during scratching. A selective deposition of Cu at the pit-like defect on a p-type Si(111) surface was also investigated. Preferential deposition of the Cu occurred at the surface defect sites of silicon wafers, indicating that those defect sites act as active sites for the deposition reaction. The shape of the Cu-deposited area was almost the same as that of the residual stress field.

• The Journal of Advanced Prosthodontics
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• 제11권4호
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• pp.215-222
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• 2019

PURPOSE. To evaluate the polishing effect on roughness and color change of pressed and layering ceramics after immersion in coffee solution. MATERIALS AND METHODS. 88 ceramic discs ($1.0mm{\times}10.0mm$) were manufactured - 44 nano-fluorapatite layering ceramics (IPS e.max Ceram. Group C) and 44 pressed lithium disilicate ceramic discs (IPS e. max Press - Group P). Each group was divided into 4 subgroups according to surface treatments: (G) Glaze, (S) Shofu polishing system (Shofu Inc.), (E) Edenta AG polishing System, (KG) $30-{\mu}m$ diamond granulation tip. Surface roughness (Ra) and color change (${\Delta}E$) measurings after the surface treatments were performed, before and 12 days after the immersion in coffee solution. A samples' qualitative analysis was conducted with a scanning electron microscopy (SEM). Data were statistically-treated with one-way-ANOVA and Duncan's tests, apart from paired t-test and Pearson's correlation test (${\alpha}=5%$). RESULTS. The decrescent order, both for surface roughness (Ra) and ${\Delta}E$ for both ceramics were: KG > E > S > G (P<.05). With exception for PG and CG subgroups, which did not present statistical difference between them, all other pressed ceramics subgroups presented smaller Ra values and greater ${\Delta}E$ values than the layering ceramics subgroups (P<.05). CONCLUSION. Although mechanical polishing systems presented intermediate Ra values, their colors were considered clinically acceptable. There is a strong correlation between the surface roughness and the color change of tested ceramics.

• Advances in nano research
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• 제12권5호
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• pp.529-547
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• 2022

Graphene is one of the strongest, stiffest, and lightest nanoscale materials known to date, making it a potentially viable and attractive candidate for developing lightweight structural composites to prevent high-velocity ballistic impact, as commonly encountered in defense and space sectors. In-plane twist in bilayer graphene has recently revealed unprecedented electronic properties like superconductivity, which has now started attracting the attention for other multi-physical properties of such twisted structures. For example, the latest studies show that twisting can enhance the strength and stiffness of graphene by many folds, which in turn creates a strong rationale for their prospective exploitation in high-velocity impact. The present article investigates the ballistic performance of twisted bilayer graphene (tBLG) nanostructures. We have employed molecular dynamics (MD) simulations, augmented further by coupling gaussian process-based machine learning, for the nanoscale characterization of various tBLG structures with varying relative rotation angle (RRA). Spherical diamond impactors (with a diameter of 25Å) are enforced with high initial velocity (V_i) in the range of 1 km/s to 6.5 km/s to observe the ballistic performance of tBLG nanostructures. The specific penetration energy (E_p^*) of the impacted nanostructures and residual velocity (V_r) of the impactor are considered as the quantities of interest, wherein the effect of stochastic system parameters is computationally captured based on an efficient Gaussian process regression (GPR) based Monte Carlo simulation approach. A data-driven sensitivity analysis is carried out to quantify the relative importance of different critical system parameters. As an integral part of this study, we have deterministically investigated the resonant behaviour of graphene nanostructures, wherein the high-velocity impact is used as the initial actuation mechanism. The comprehensive dynamic investigation of bilayer graphene under the ballistic impact, as presented in this paper including the effect of twisting and random disorder for their prospective exploitation, would lead to the development of improved impact-resistant lightweight materials.