• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.159-159
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• 2011

최근 여러 화학 반응에 대해서 일층(1L) 그래핀(graphene)이 복층(multi-layered) 그래핀보다 10 배 이상의 높은 반응성을 보인다는 사실이 알려졌다. 본 실험에서는 기판의 편평도와 기판-그래핀 간의 상호작용이 그래핀의 반응성에 미치는 영향을 이해하기 위해서, AFM(atomic force microscopy)과 라만 분광법을 이용하여 그래핀의 기체상 고온 산화반응을 연구하였다. 기계적 박리법을 통해 산화실리콘(SiO2/Si)과 마이카(mica) 기판 위에 고착된 그래핀 시료를 대조군으로 비교하였다. AFM 형상 분석으로부터 편평도가 낮은 산화실리콘 위에서는 그래핀의 두께가 작을수록 산화 속도가 크다는 사실을 확인하였다. 그러나 편평도가 높은 마이카 기판 위에서는 단일층 그래핀의 산화 속도가 산화실리콘 기판 위에서보다 현저하게 감소하고 두 겹 이상의 두께에서는 반응성의 차이가 없음을 발견하였다. 특히 마이카 위의 단일층 그래핀에서는 복층 그래핀과는 달리 산화에 의한 식각이 거의 일어나지 않아 화학적 안정성이 증대되었음을 알 수 있었다. 본 연구는 기판의 표면구조와 상호 작용을 통해 그래핀의 화학적 특성을 조절 할 수 있다는 가능성을 보여 준다.

• Journal of Powder Materials
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• v.23 no.4
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• pp.317-324
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• 2016

Tin is one of the most promising anode materials for next-generation lithium-ion batteries with a high energy density. However, the commercialization of tin-based anodes is still hindered due to the large volume change (over 260%) upon lithiation/delithiation cycling. To solve the problem, many efforts have been focused on enhancing structural stability of tin particles in electrodes. In this work, we synthesize tin nano-powders with an amorphous carbon layer on the surface and surroundings of the powder by electrical wire explosion in alcohol-based liquid media at room temperature. The morphology and microstructures of the powders are characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The electrochemical properties of the powder for use as an anode material for lithium-ion battery are evaluated by cyclic voltammetry and a galvanometric discharge-charge method. It is shown that the carbon-coated tin nano-powders prepared in hexanol media exhibit a high initial charge specific capacity of 902 mAh/g and a high capacity retention of 89% after 50 cycles.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.8
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• pp.701-706
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• 2006

In addition to its similarity to genuine diamond film, diamond-like carbon (DLC) film has many advantages, including its wide band gap and variable refractive index. In this study, DLC films were prepared by the RF PECVD (Plasma Enhanced Chemical Vapor Deposition) method on silicon substrates using methane $(CH_4)$ and hydrogen $(H_2)$ gas. We examined the effects of the post annealing temperature on the structural variation of the DLC films. The films were annealed at temperatures ranging from 300 to $900^{\circ}C$ in steps of $200^{\circ}C$ using RTA equipment in nitrogen ambient. The thickness of the film and interface between film and substrate were observed by surface profiler, field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), respectively. Raman and X-ray photoelectron spectroscopy (XPS) analysis showed that DLC films were graphitized ($I_D/I_G$, G-peak position and $sp^2/sp^3$ increased) ratio at higher annealing temperature. The variation of surface as a function of annealing treatment was verified by a AFM and contact angle method.

• Current Optics and Photonics
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• v.1 no.4
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• pp.358-363
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• 2017

In this study, we present a detailed investigation of luminescence properties of a blue light-emitting diode using InGaN/GaN (indium component is 17.43%) multiple quantum wells as the active region grown on patterned sapphire substrate by low-pressure metal-organic chemical vapor deposition (MOCVD). High-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman scattering (RS) and photoluminescence (PL) measurements are employed to study the crystal quality, the threading dislocation density, surface morphology, residual strain existing in the active region and optical properties. We conclude that the crystalline quality and surface morphology can be greatly improved, the red-shift of peak wavelength is eliminated and the superior blue light LED can be obtained because the residual strain that existed in the active region can be relaxed when the LED is grown on patterned sapphire substrate (PSS). We discuss the mechanisms of growing on PSS to enhance the superior luminescence properties of blue light LED from the viewpoint of residual strain in the active region.

• Bulletin of the Korean Chemical Society
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• v.35 no.2
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• pp.431-435
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• 2014

Zinc peroxide nanoparticles ($ZnO_2$ NPs) were prepared by reacting zinc(II) isobutylcarbamate, as an organometallic precursor, with hydrogen peroxide ($H_2O_2$) at $60^{\circ}C$. Polyethylene glycol and polyvinylpyrrolidone were used as stabilizers, which suppressed aggregation of the $ZnO_2$ NPs. Conditions such as concentrations of $H_2O_2$ and the stabilizer were systemically controlled to determine their effect on the formation of nano-sized $ZnO_2$ NPs. The formation of stable $ZnO_2$ NPs was confirmed by UV-vis, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction. The TEM images revealed that polyvinylpyrrolidone-stabilized $ZnO_2$ NPs (diameter, 10-30 nm) were well dispersed in the organic solvent. Quite pure ZnO NPs were obtained from the peroxide powder by simple heat treatment of $ZnO_2$. The transition temperature of $170^{\circ}C$ was determined by differential scanning calorimetry.

• Bulletin of the Korean Chemical Society
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• v.28 no.4
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• pp.533-537
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• 2007

This paper describes the heteroepitaxial growth of single-crystalline 3C-SiC (cubic silicon carbide) thin films on Si (100) wafers by atmospheric pressure chemical vapor deposition (APCVD) at 1350 oC for micro/nanoelectromechanical system (M/NEMS) applications, in which hexamethyldisilane (HMDS, Si2(CH3)6) was used as a safe organosilane single-source precursor. The HMDS flow rate was 0.5 sccm and the H2 carrier gas flow rate was 2.5 slm. The HMDS flow rate was important in obtaing a mirror-like crystalline surface. The growth rate of the 3C-SiC film in this work was 4.3 μm/h. A 3C-SiC epitaxial film grown on the Si (100) substrate was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Raman scattering, respectively. These results show that the main chemical components of the grown film were single-crystalline 3C-SiC layers. The 3C-SiC film had a very good crystal quality without twins, defects or dislocations, and a very low residual stress.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.265-265
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• 2013

We have investigated the influences of dangling bonds generated by alpha particle irradiation on friction and adhesion properties of graphene. Single layer of graphene grown with chemical vapor deposition on copper foil was irradiated by the alpha beam with the average energy of 3.04 MeV and the irradiation dosing between $1{\times}10^{14}$ and $1{\times}10^{15}$/$cm^3$. Raman spectroscopic showed that the ${\pi}$ electron states below Fermi level arises and the $I_D$/$I_G$ increases as increasing the dosing of alpha particle irradiation. The core level X-ray photoelectron (XPS) revealed that these defects represent the creation of various carbon-related defects and dangling bond. The nanoscale tribological properties were investigated with atomic force microscopy in ultrahigh vacuum. The friction appeared to increase remarkably as increasing the amount of dosing, indicating that the dangling bonds on graphene layers enhances the energy dissipations in friction. This trend can be explained by the additional channel of energy dissipation by dangling bond or O- and H- terminated clusters created by alpha particle irradiation.

• Journal of the Korean Vacuum Society
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• v.7 no.s1
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• pp.160-166
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• 1998

The field emission characteristics of defective diamond films grown by microwave plasma enhanced chemical vapor deposition (MPECVD) have been studied. X-ray diffraction, the poor crystal quality and/or small grain sizes of the diamond phase and the inclusion of the non-diamond carbon phases in these films have been condirmed by raman spectroscopy, scanning electron microscopy, atomic force microscopy, and the reflectance measurements. The degrees of the film defectiveness and the emission characteristics were dependent on the methane concentration. Current-versus-voltage measurements have demonstrated that the defective diamond films have good electron emission characteristics. characteristics strongly suggests the defect-related electron-emission mechanism. The defective diamond films deposited on Si substrates show the field emission current density of 1$\mu\textrm{A}/\textrm{cm}^2$ and 1mA/$\textrm{cm}^2$ have been measured at electric fields as low as 4.5V/$\mu\textrm{m}$ and 7.6V/$\mu\textrm{m}$, respectively. We also observed the similar emission characteristics from the defective diamond film deposited on Cr/Si substrate and could decrease the deposition temperature to $600^{\circ}C$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.3
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• pp.303-308
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• 1999

As a semiconductor material for electronic devices operated under extreme environmental conditions, silicon carbides(SiCs) have been intensively studied because of their excellent electrical, thermal and other physical properties. The growth characteristics of single-crystalline 4H-SiC homoepitaxial layers grown by a thermal chemical vapor deposition (CVD) were investigated. Especially, the successful growth condition of 4H-SiC homoepitaxial layers using a SiC-uncoated atmospheric pressure chamber and carried out using off-oriented substrates prepared by a modified Lely method. In order to investigate the crystallinity of grown epilayers, Nomarski optical microscopy, Raman spectroscopy, photoluninescence(PL), scanning electron microscopy(SEM) and other techniques were utilized. The best quality of 4H-SiC homoepitaxial layers was observed in conditions of growth temperature $1500^{\circ}C$ and C/Si flow ratio 2.0 of $C_{3}H_{8}\;0.2\;sccm\;&\;SiH_{4}\;0.3\;sccm$. The growth rate of epilayers was about $1.0\mu\textrm{m}/h$ in the above growth condition.

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.36-37
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• 2006

Both negative and positive substrate bias effects on the structural properties and field-emission characteristics are investigated. carbon nanotubes (CNTs) are grown on Ni catalysts employing an inductively-coupled plasma chemical vapor deposition (ICP-CVD) method. Characterization using various techniques, such as field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Auger spectroscopy (AES), and Raman spectroscopy, shows that the physical dimension as well as the crystal quality of CNTs grown can be changed and controlled by the application of substrate bias during CNT growth. It is for the first time observed that the prevailing growth mechanism of CNTs, which is either due to tip-driven growth or based-on-catalyst growth, may be influenced by substrate biasing. It is also seen that negative biasing would be more effectively role in the vertical-alignment of CNTs compared to positive biasing. However, the CNTs grown under the positively bias condition display much better electron emission capabilities than those grown under negative bias or without bias. The reasons for all the measured data regarding the structural properties of CNTs are discussed to confirm the correlation with the observed field-emissive properties.