특집 : 다기능성 나노 박막 복합구조화 기술 ; 나노결정 다이아몬드 박막 기술

강찬형 ( Chan Hyoung Kang ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 재료마당 Vol.23 No.4

전구체 공침 온도가 LiNi_1/3Co_1/3Mn_1/3O₂ 분말의 특성에 미치는 영향

최웅희,강찬형,Choi, Woonghee,Kang, Chan Hyoung 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.4

$Ni_{1/3}Co_{1/3}Mn_{1/3}(OH)_2$ powders have been synthesized in a continuously stirred tank reactor via a co-precipitation reaction between aqueous metal sulfates and NaOH using $NH_4OH$ as a chelating agent. The co-precipitation temperature is varied in the range of $30-80^{\circ}C$. Calcination of the prepared precursors with $Li_2CO_3$ for 8 h at $1000^{\circ}C$ in air results in Li $Ni_{1/3}Co_{1/3}Mn_{1/3}O_2$ powders. Two kinds of obtained powders have been characterized by X-ray diffraction (XRD), scanning electron microscopy, particle size analyzer, and tap density measurements. The co-precipitation temperature does not differentiate the XRD patterns of precursors as well as their final powders. Precursor powders are spherical and dense, consisting of numerous acicular or flaky primary particles. The precursors obtained at 70 and $80^{\circ}C$ possess bigger primary particles having more irregular shapes than those at lower temperatures. This is related to the lower tap density measured for the former. The final powders show a similar tendency in terms of primary particle shape and tap density. Electrochemical characterization shows that the initial charge/discharge capacities and cycle life of final powders from the precursors obtained at 70 and $80^{\circ}C$ are inferior to those at $50^{\circ}C$. It is concluded that the optimum co-precipitation temperature is around $50^{\circ}C$.

공기와 질소 분위기에서 공침법으로 합성된 Ni_1/3Co_1/3Mn_1/3(OH)₂ 분말의 특성 비교

최웅희,박세련,강찬형,Choi, Woonghee,Park, Se-Ryen,Kang, Chan Hyoung 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.2

As precursors of cathode materials for lithium ion batteries, $Ni_{1/3}Co_{1/3}Mn_{1/3}(OH)_2$ powders are prepared in a continuously stirred tank reactor via a co-precipitation reaction between aqueous metal sulfates and NaOH in the presence of $NH_4OH$ in air or nitrogen ambient. Calcination of the precursors with $Li_2CO_3$ for 8 h at $1,000^{\circ}C$ in air produces dense spherical cathode materials. The precursors and final powders are characterized by X-ray diffraction (XRD), scanning electron microscopy, particle size analysis, tap density measurement, and thermal gravimetric analysis. The precursor powders obtained in air or nitrogen ambient show XRD patterns identified as $Ni_{1/3}Co_{1/3}Mn_{1/3}(OH)_2$. Regardless of the atmosphere, the final powders exhibit the XRD patterns of $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ (NCM). The precursor powders obtained in air have larger particle size and lower tap density than those obtained in nitrogen ambient. NCM powders show similar tendencies in terms of particle size and tap density. Electrochemical characterization is performed after fabricating a coin cell using NCM as the cathode and Li metal as the anode. The NCM powders from the precursors obtained in air and those from the precursors obtained in nitrogen have similar initial charge/discharge capacities and cycle life. In conclusion, the powders co-precipitated in air can be utilized as precursor materials, replacing those synthesized in the presence of nitrogen injection, which is the usual industrial practice.

초경합금에 나노결정질 다이아몬드 코팅 시 금속 중간층의 효과

나봉권(Bong-Kwon Na),강찬형(Chan Hyoung Kang) 한국표면공학회 2013 한국표면공학회지 Vol.46 No.2

For the coating of diamond films on WC-Co tools, a buffer interlayer is needed because Co catalyzes diamond into graphite. W and Ti were chosen as candidate interlayer materials to prevent the diffusion of Co during diamond deposition. W or Ti interlayer of 1 μm thickness was deposited on WC-Co substrate under Ar in a DC magnetron sputter. After seeding treatment of the interlayer-deposited specimens in an ultrasonic bath containing nanometer diamond powders, 2 μm thick nanocrystalline diamond (NCD) films were deposited at 600oC over the metal layers in a 2.45 GHz microwave plasma CVD system. The crosssectional morphology of films was observed by FESEM. X-ray diffraction and visual Raman spectroscopy were used to confirm the NCD crystal structure. Micro hardness was measured by nano-indenter. The coefficient of friction (COF) was measured by tribology test using ball on disk method. After tribology test, wear tracks were examined by optical microscope and alpha step profiler. Rockwell C indentation test was performed to characterize the adhesion between films and substrate. Ti and W were found good interlayer materials to act as Co diffusion barriers and diamond nucleation layers. The COFs on NCD films with W or Ti interlayer were measured as less than 0.1 whereas that on bare WC-Co was 0.6~1.0. However, W interlayer exhibited better results than Ti in terms of the adhesion to WC-Co substrate and to NCD film. This result is believed to be due to smaller difference in the coefficients of thermal expansion of the related films in the case of W interlayer than Ti one. By varying the thickness of W interlayer as 1, 2, and 4 μm with a fixed 2 μm thick NCD film, no difference in COF and wear behavior but a significant change in adhesion was observed. It was shown that the thicker the interlayer, the stronger the adhesion. It is suggested that thicker W interlayer is more effective in relieving the residual stress of NCD film during cooling after deposition and results in stronger adhesion.

철강 위에 SiC 중간층을 사용한 나노결정질 다이아몬드 코팅

명재우(Jae-Woo Myung),강찬형(Chan Hyoung Kang) 한국표면공학회 2014 한국표면공학회지 Vol.47 No.2

Nanocrystalline diamond(NCD) films on steel(SKH51) has been investigated using SiC interlayer film. SiC was deposited on SKH51 or Si wafer by RF magnetron sputter. NCD was deposited on SiC at 600oC for 0.5~4 h employing microwave plasma CVD. Film morphology was observed by FESEM and FIB. Film adherence was examined by Rockwell C adhesion test. The growth rate of NCD on SiC/Si substrate was much higher than that on SiC/SKH51. During particle coalescence, NCD growth rate was slow since overall rate was determined by the diffusion of carbon on SiC surface. After completion of particle coalescence, NCD growth became faster with the reaction of carbon on NCD film controlling the whole process. In the case of SiC/SKH51 substrate, a complete NCD film was not formed even after 4 h of deposition. The adhesion test of NCD/SiC/SKH51 samples revealed a delamination of film whereas that of SiC/SKH51 showed a good adhesion. Many voids of less than 0.1 μm were detected on NCD/SiC interface. These voids were believed as the reason for the poor adhesion between NCD and SiC films. The origin of voids was due to the insufficient coalescence of diamond particles on SiC surface in the early stage of deposition.

ZnO/나노결정다이아몬드 적층 박막 SAW 필터

정두영(Doo Young Jung),강찬형(Chan Hyoung Kang) 한국표면공학회 2009 한국표면공학회지 Vol.42 No.5

A surface acoustic wave (SAW) filter structure was fabricated employing 4 μm thick nanocrystalline diamond (NCD) and 2.2 ㎛ thick ZnO films on Si wafer. The NCD film was deposited in an Ar/CH₄ gas mixture by microwave plasma chemical vapor deposition method. The ZnO film was formed over the NCD film in an RF magnetron sputter using ZnO target and Ar/O₂ gas. On the top of the two layers, copper film was deposited by the RF sputter and inter digital transducer (IDT) electrode pattern (line/space : 1.5/1.5 ㎛) was defined by the photolithography including a lift-off etching process. The fabricated SAW filter exhibited the center frequency of 1.66 ㎓ and the phase velocity of 9,960 ㎧, which demonstrated that a giga Hertz SAW filter can be realized by utilizing the nanocrystalline diamond thin film.

나노결정질 다이아몬드가 코팅된 SiC 마모시험기 볼

임종환(Jong Hwan Im),강찬형(Chan Hyoung Kang) 한국표면공학회 2014 한국표면공학회지 Vol.47 No.5

Nanocrystalline diamond(NCD) coated SiC balls were applied in a ball-on-disk tribometer. After seeding in an ultrasonic bath containing nanometer diamond powders, 2.2 μm thick NCD films were deposited on sintered 3 mm diameter SiC balls at 600℃ in a 2.45 GHz microwave plasma CVD system. Bare ZrO₂ and SiC balls were prepared for comparison as test balls. Tribology tests were performed in air with pairs of three different balls and mirror polished steel(SKH51) disk. The wear tracks on balls and disks were examined by optical microscope and alpha step profiler. Under the load of 3 N, the friction coefficients of steel against ZrO₂, SiC and NCD-coated balls were between 0.4 and 0.8. After a few thousands sliding laps, the friction coefficient of NCD-coated balls dropped from 0.45 to below 0.1 and maintained thereafter. Under a higher load of 10 N or 20 N with a long sliding distance of 2 km, ZrO₂ and SiC balls exhibited the similar friction coefficients as above. The friction coefficient of NCD-coated balls was less than 0.1 from the beginning and increased to above 0.1 steadily or with some fluctuations as sliding distance increased. NCD coating layers were found worn out after long duration and/or high load sliding test, which resulted in the friction coefficient higher than 0.1.

마이크로웨이브 플라즈마 CVD에 의한 나노결정질 다이아몬드 박막 성장 시 DC 바이어스 효과

김인섭(In-Sup Kim),강찬형(Chan Hyoung Kang) 한국표면공학회 2013 한국표면공학회지 Vol.46 No.1

The effect of DC bias on the growth of nanocrystalline diamond films on silicon substrate by microwave plasma chemical vapor deposition has been studied varying the substrate temperature (400, 500, 600, and 700℃), deposition time (0.5, 1, and 2h), and bias voltage (?50, ?100, ?150, and ?200 V) at the microwave power of 1.2 ㎾, working pressure of 110 torr, and gas ratio of Ar/1%CH₄. In the case of low negative bias voltages (?50 and ?100 V), the diamond particles were observed to grow to thin film slower than the case without bias. Applying the moderate DC bias is believed to induce the bombardment of energetic carbon and argon ions on the substrate to result in etching the surfaces of growing diamond particles or film. In the case of higher negative voltages (?150 and ?200 V), the growth rate of diamond film increased with the increasing DC bias. Applying the higher DC bias increased the number of nucleation sites, and, subsequently, enhanced the film growth rate. Under the ?150 V bias, the height (h) of diamond films exhibited an h = k√t relationship with deposition time (t), where the growth rate constant (k) showed an Arrhenius relationship with the activation energy of 7.19 ㎉/㏖. The rate determining step is believed to be the surface diffusion of activated carbon species, but the more subtle theoretical treatment is required for the more precise interpretation.

VLSI 설계를 위한 디지틀 통신용 타이밍 복원회로 모델링

김대순(Dae-Soon Kim),강찬형(Chan- Hyoung Kang) 대한전자공학회 1997 대한전자공학회 학술대회 Vol.1997 No.7

나노 다이아몬드 박막 합성 및 응용기술

이욱성 ( Wook Seong Lee ),강찬형 ( Chan Hyoung Kang ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 재료마당 Vol.19 No.1