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Sennu, Palanichamy,Park, Hyo Seok,Park, Kwang Uk,Aravindan, Vanchiappan,Nahm, Kee Suk,Lee, Yun-Sung Elsevier 2017 Journal of catalysis Vol.349 No.-
<P><B>Abstract</B></P> <P>A 3D structured NiCo<SUB>2</SUB>O<SUB>4</SUB>@Co<SUB>3</SUB>O<SUB>4</SUB> hybrid was prepared by a two-step hydrothermal approach and subsequently employed as a highly efficient catalyst in oxygen reduction reactions (ORRs)/oxygen evolution reactions (OERs) and from a Li–O<SUB>2</SUB> battery perspective. The Co-NC possesses interconnected NiCo<SUB>2</SUB>O<SUB>4</SUB> nanorods grown over a Co<SUB>3</SUB>O<SUB>4</SUB> nanosheet structure, which facilitates charge transfer and enhances the electrical conductivity. Moreover, the 3D structured hybrids are directly used as a cathode catalyst for the Li–O<SUB>2</SUB> system and displayed a maximum in-depth-specific discharge capacity of 4386mAhg<SUP>−1</SUP>. In addition, significantly improved and stable cycling performance up to 60 cycles is observed compared with Co<SUB>3</SUB>O<SUB>4</SUB> nanosheets at the limited capacity range of 500mAhg<SUP>−1</SUP>. The excellent electrochemical performance of the NiCo<SUB>2</SUB>O<SUB>4</SUB>@Co<SUB>3</SUB>O<SUB>4</SUB> hybrid is mainly associated with the oxygen-deficient 3D architecture providing more catalytic active sites and can accommodate more discharge products. Further, ORR/OER activities of NiCo<SUB>2</SUB>O<SUB>4</SUB>@Co<SUB>3</SUB>O<SUB>4</SUB> hybrid in aqueous media are also evaluated in 0.1M KOH solution using the rotating ring disk electrode technique. For instance, the OER activity of NiCo<SUB>2</SUB>O<SUB>4</SUB>@Co<SUB>3</SUB>O<SUB>4</SUB> hybrid (apex current is 4.18mAcm<SUP>−2</SUP>) is an approximately 2.25 times higher than that of commercial RuO<SUB>2</SUB> catalyst (1.84mAcm<SUP>−2</SUP>). Since the catalytic activity in aqueous and organic medium is not necessarily the same, but of NiCo<SUB>2</SUB>O<SUB>4</SUB>@Co<SUB>3</SUB>O<SUB>4</SUB> hybrid exhibiting excellent ORR/OER characteristics in both cases is worth mentioning.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 3D structured NiCo<SUB>2</SUB>O<SUB>4</SUB>@Co<SUB>3</SUB>O<SUB>4</SUB> hybrid is prepared as catalyst for Li-O<SUB>2</SUB> battery. </LI> <LI> Excellent ORR/OER activity is observed in both aqueous and organic media. </LI> <LI> Li–O<SUB>2</SUB> system displayed a maximum in-depth-specific discharge capacity of 4386mAhg<SUP>−1</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Correlation between Yellow Emission and Misoriented Structure in GaN Epilayers
Ok Hwan Cha,Mun Seok Jeong,고도경,Eun-Kyung Suh,Jongmin Lee,Kee Suk Nahm 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.3
A strong relationship between misoriented structure and yellow luminescence (YL) was found from the X-ray diffraction (XRD) and the photoluminescence measurements of GaN films grown by using radio-frequency induction-heated chemical vapor deposition and metal-organic chemical vapor deposition. YL was observed to be emitted from GaN films which contained peaks associated with the (10.10) and the (10.11) planes in their XRD spectra, and intensity variation of YL with some parameters, such as the growth temperature and the film thickness, had quite similar trends to that of the misoriented peak in XRD. We suggest that this tendency is due to point defects acting as YL centers trapped at the interface between the (0001) oriented structure and an unintentional structure oriented in the [10.10] and the [10.11] directions.0
Si(100)기판 위에 성장된 3C-SiC(100)의 특성 연구
박찬일,이상현,남기석,양영석,김광철,노재일 한국화학공학회 2000 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.38 No.5
고주파 유도 화학 증착(rf-inductive chemical vapor deposition)장치를 이용하여 여러 가지 성장 변수(성장 온도, 성장 압력, 반응기체유량, Si/C조성비 등)에서 Si(100) 기판 위에 입방정계 SiC(3C-SiC) 박막을 성장하였다. 1,170-1,300℃의 온도에서 SiC 박막은 Si(100) 기판 방향을 따라 단결정(single crystalline)으로 성장되었다. 또한 3.4-400torr의 감압에서 성장한 SiC 박막은 성장 압력이 증가함에 따라 성장박막의 두께가 증가하였으며 계면에서 형성되는 보이드(void)의 크기와 밀도 가 감소하였다. Si/C의 비를 변화(0.25-0.5)시키면서 Si 기판 위에 SiC 박막을 성장시킨 실험결과로부터, SiC/Si 계면에 생성되는 보이드는 Si 기판으로부터 Si 원자들이 외부로 확산되어 나와 형성됨을 수 있었다. 성장 중 박막 내에 생성되는 응력(stress)과 변형(strain)을 적외선 분광법(FT-IR)으로 분석하였으며, SiC/Si 계면에 생성되는 보이드는 Si/C의 비를 변화시킴으로써 제어될 수 있음을 보였다. Single crystal cubic SiC(100) thin films were grown on Si(100) at various growth conditions in a home made RF-inductive chemical vapor deposition system. The orientation of SiC films grown at the temperature range of 1,170-1,300 ℃ followed that of Si substrate used in the growth. The increase of the growth pressure (3.4-400 torr) increased the thickness of SiC films, whereas decreased the size and density of voids formed at SiC/Si interface during the growth. From the experiments in the growth of SiC film on Si substrate as a function of Si/C atomic ratio (0.25-0.5), it was found that the out-diffusion of Si atom from Si substrate caused the formation of voids at SiC/Si interface. The stress and strain generated in the grown film were analyzed using a fourier transformation infrared spectroscopy. The formation of voids was suppressed by adjusting Si/C atomic ratios during the growth.