• Journal of the Korean institute of surface engineering
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• v.34 no.1
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• pp.10-16
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• 2001

Recently plasma etching research has been focused on the metal surfaces in the nuclear industry. In this study, surface etching reaction of metallic Co and Mo, principal contaminants in the spent nuclear components, in CF$_4$/O$_2$, gas plasma has been experimentally investigated to look into the applicability and the effectiveness of the technique for the surface decontamination. Experimental variables are $CF_4$/$O_2$ ratio and substrate temperature between 29$0^{\circ}C$ and 38$0^{\circ}C$. Experimental results Show that the optimum gas composition is 80%CF$_4$-20%$O_2$ and the metallic Co and Mo are etched out well enough in the temperatures range. Cobalt starts to be etched above $350^{\circ}C$ and the etching rate increases with increasing substrate temperature. Maximum rate achieved at 38$0^{\circ}C$ under 220 W r.f. plasma power is 0.06 $\mu\textrm{m}$/min. On the other hand, the metallic Mo is etched easily even at low temperature and the reaction rate drastically increases as the substrate temperature goes up. Highest rate obtained under the same conditions is $1.9\mu\textrm{m}$/min. OES (Optical Emission Spectroscopy) analysis reveals that the intensities of F atom and CO molecule reach maximum at the optimum gas composition, which demonstrates that the principal reaction mechanism is fluorination and/or carbonyl reaction. It is confirmed, therefore, that dry processing technique using reactive plasma is quite feasible and applicable for the decontamination of surface-contaminated parts or equipments.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.333-334
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• 2007

Diamond-like carbon (DLC)박막은 높은 경도, 화학적 안정성, 높은 광 투과성을 가지고 있어, 공구강, 광학렌즈 및 플라스틱의 보호 코팅을 위해 응용되어진다. 본 연구에는 DLC 박막은 Silicon을 기반으로 하는 태양전지 반사 반지막으로 응용을 위해, 13.56 MHz RF 플라즈마 화학기상 증착 (RF-PECVD)법을 통해 합성되었다. DLC 합성 시 RF power는 150 W, 메탄 (CH4)가스의 유량은 6%~10% 조절되었다. 합성되어진 DLC 박막의 광학적 특성은 UV spectrometry, Ellipsometry를 사용하여 분석되었고, 경도는 Nano-indenter를 사용하여 측정되었다. 측정 결과 투과도와 굴절률 등의 광학적 특성은 탄소 조성비가 6%정도에서 가장 좋은 결과 값을 얻었으나, 물리적 특성인 경도는 탄소 조성비가 높을수록 증가하는 경향을 보였으며, Si기판과의 접착력은 32N 이상의 높은 값을 나타내었다. 결과로써, DLC 박막은 합성시 적절한 탄소 조성비를 통해 silicon을 기반으로 하는 태양전지 반사방지막으로 응용할 수 있다.

• Korean Journal of Optics and Photonics
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• v.3 no.2
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• pp.77-85
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• 1992

The design of a flat-field XUV spectrograph is optimized for a high throughput, aberration-corrected spectral image in the wavelength region of 50-300 $\AA$ The varied-line spacing (VLS) concave grating theory for an XUV spectrograph with a toroidal mirror in front of an entrance slit is derived. Since the derived theory includes the arbitrary shaped source, it is able to correct the limit of the simple optimization theory which considers only a point source at the center of the entrance slit. The reflection matrix at the toroidal mirror and the diffraction matrix at VLS grating are derived and compared with those of a holographic grating. The absolute energy efficiency of a flat-field spectrograph is calculated by considering the reflectivities of the toroidal mirror and the Au coated concave grating and the grating efficiency. The alignment sensitivity of the toroidal mirror and the concave grating is investigated, and the method to achieve the best imaging of XUV spectrum is discussed. The calculated resolving power of the flat-field XUV spectrograph is more than 4000 in the aberration-corrected wavelength range. The focused spot size at the dispersion plane is less than $20\mu \textrm m\times \mu \textrm m$at the wavelength 100$\AA$ It is shown that a high throughput characteristic can also be achieved through a careful adjustment of alignment parameters.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.177-177
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• 2010

고효율 비정질 실리콘 박막 태양전지 제작을 위해서는 광파장대에서 optical confinement 능력을 최대화할 수 있는 기술이 필수적이다. 효율적인 photon trapping을 위해서는 back reflector를 사용하거나 전면전극인 투명전도성막의 표면에 요철을 형성하여 포획된 태양광의 내부 반사를 증가시키거나 전면 투명전극에서 반사를 감소시켜 태양광의 travel length를 증가시키는 방법이 일반적이며, 이를 통해 흡수층의 효율을 최대화할 수 있다. 이 중 전면전극으로 사용되는 투명전도성막은 불소가 도핑된 tin-oxide가 주로 사용되었으나, 최근 들어 Al이 도핑된 산화아연막을 이용한 비정질 실리콘 박막 태양전지 개발에 대한 연구도 활발히 진행되고 있다. 투명전극 증착후 표면의 유효면적을 증가시키기 위해 염산 용액을 이용하여 표면 텍스쳐링을 수행한다. 그후 흡수층인 p-i-n 층을 플라즈마 화학기상증착법을 이용하여 형성하는 것이 일반적이다. 이때 표면처리 된 투명전극은 수소플라즈마에 대해 특성이 변하지 않아야 고효율 비정질 실리콘 박막 태양전지 제조에 적용될 수 있다. 본 연구에서는 표면처리 된 AZO 투명전극의 수소플라즈마에 의한 특성 변화에 대해 고찰하였다. 먼저 AZO 투명전극은 스퍼터링 공정을 적용하여 $1\;{\mu}m$두께로 증착하였고, 0.5 wt%의 HCl 용액을 이용하여 습식 식각을 수행하였다. 수소플라즈마 처리 조건은 $H_2$ flow rate 30 sccm, working pressure 20 mtorr, RF power 300 W, Temp $60^{\circ}C$ 이며 3분간 진행하였다. 표면형상은 수소플라즈마 전 후에는 큰 차이를 보이지 않았으며 AZO의 grain size는 각각 220 nm, 210 nm로 관찰되었다. 투명전극의 가장 중요한 특성인 가시광선 영역에서의 투과도는 수소플라즈마 처리전에는 90 % 이상의 투과도를 보였으나, 수소플라즈마 처리 후에는 85 %로 약간 저하된 특성을 보였다. 그러나 이는 박막 태양전지용 전면전극으로 사용하기 위한 투과도인 80 % 이상을 만족하는 결과로, 비정질 박막 실리콘 태양전지 제작에 사용될 수 있다. 또 하나의 중요한 특성인 Haze factor 역시 수소플라즈마 처리 전 후 모두 10 이상의 값을 나타냈다. 하지만 고효율 실리콘 박막 태양전지에 적용하기 위해서는 Haze factor를 증가시키는 공정 개발에 대한 추가 연구가 필요하다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.252.2-252.2
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• 2013

ZnO nanostructures have a lot of interest for decades due to its varied applications such as light-emitting devices, power generators, solar cells, and sensing devices etc. To get the high performance of these devices, the factors of nanostructure geometry, spacing, and alignment are important. So, Patterning of vertically- aligned ZnO nanowires are currently attractive. However, many of ZnO nanowire or nanorod fabrication methods are needs high temperature, such vapor phase transport process, metal-organic chemical vapor deposition (MOCVD), metal-organic vapor phase epitaxy, thermal evaporation, pulse laser deposition and thermal chemical vapor deposition. While hydrothermal process has great advantages-low temperature (less than $100^{\circ}C$), simple steps, short time consuming, without catalyst, and relatively ease to control than as mentioned various methods. In this work, we investigate the dependence of ZnO nanowire alignment and morphology on si substrate using of nanosphere template with various precursor concentration and components via hydrothermal process. The brief experimental scheme is as follow. First synthesized ZnO seed solution was spun coated on to cleaned Si substrate, and then annealed $350^{\circ}C$ for 1h in the furnace. Second, 200nm sized close-packed nanospheres were formed on the seed layer-coated substrate by using of gas-liquid-solid interfacial self-assembly method and drying in vaccum desicator for about a day to enhance the adhesion between seed layer and nanospheres. After that, zinc oxide nanowires were synthesized using a low temperature hydrothermal method based on alkali solution. The specimens were immersed upside down in the autoclave bath to prevent some precipitates which formed and covered on the surface. The hydrothermal conditions such as growth temperature, growth time, solution concentration, and additives are variously performed to optimize the morphologies of nanowire. To characterize the crystal structure of seed layer and nanowires, morphology, and optical properties, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and photoluminescence (PL) studies were investigated.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.245.2-245.2
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• 2013

Solution processed organic photovoltaic devices have relatively less attention compared to polymer photovoltaic devices even though they have high possibility to be developed because they have both advantages of polymer and organic, such as solution processable, no synthetic batch dependence of photovoltaic performance, high purity and high charge carrier mobility as well as relatively high efficiency (~7%). In addition, solution processed organic photovoltaic devices have an advantage of easiness to study the relationship between the molecular structure and photovoltaic performance due to its simple structure. In this work, five isoindigo based low band gap donor-acceptor-donor (D-A-D) small molecules with different electron donating strength were synthesized for investigating the relationship between the molecular structure and photovoltaic performance, especially, investigating the effects of different electron donating effect of donor group in isoindigo backbone to photovoltaic device performance. The variation of electron donating strength of donor group strongly affected the optical, thermal, electrochemical and photovoltaic device performances of isoindigo organic materials. The highest power conversion efficiency of ~3.2% was realized in bulk heterojuction photovoltaic device consisted of the ID3T as donor and PC70BM as acceptor. This work demonstrates the great potential of isoindigo moieties as electron deficient units as well as guideline for synthesis of donor-acceptor-donor (D-A-D) small molecules for realizing highly efficient solution processed organic photovoltaic devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.244.1-244.1
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• 2013

The p-type GaN which act as a hole injection layer in GaN-based LEDs has fundamental problems. The first one arises from the difficulty in growing a highly doped p-GaN (with a carrier concentration exceeding ~1018 $cm^{-3}$). And the second one is the absence of appropriate metals or conducting oxides having a work function that is larger than that of p-type GaN (7.5 eV). Moreover, the LED efficiency is decreases gradually as the injection current increases (the so-called 'efficiency droop' phenomenon). The efficiency droop phenomenon in InGaN quantum wells (QWs) has been a large obstacle that has hindered high-efficiency operation at high current density. In this study, we introduce the new approaches to improve the light-output power of LEDs by using graphene oxide sheets. Graphene oxide has many functional groups such as the oxygen epoxide, the hydroxyl, and the carboxyl groups. Due to nature of such functional groups, graphene oxide possess a lot of hole carriers. If graphene oxide combine with LED top surface, graphene oxide may supply hole carriers to p-type GaN layer which has relatively low free carrier concentration less than electron concentration in n-type GaN layer. To prove the enhancement factor of graphene oxide coated LEDs, we have investigated electrical and optical properties by using ultra-violet photo-excited spectroscopy, confocal scanning electroluminescence microscopy.

• Korean Journal of Materials Research
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• v.21 no.11
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• pp.592-595
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• 2011

It is well known that modified 9Cr-1Mo steel has a low thermal expansion and high thermal conductivity with excellent high temperature properties compared to austenitic stainless steel. For these advantages, the steel is very popular for the boiler tube of thermal power plants. Normalizing is commonly utilized to obtain martensite in this steel, which shows an unusual toughness for martensite. However, some accidents related to this steel have been reported recently, opening the necessity for further study. As a particular behavior of the steel, an abrupt drop of the impact value has been identified upon tempering at 750$^{\circ}C$ for about 1 hour. It is well known that $Fe_3C$ forms during autotempering and turns to $Cr_2C$ at an early stage and then transforms to $Cr_{23}C_6$. In this study, the cause of the abrupt drop of the impact value was investigated with an impact test, microstructural observation, nanodiffraction and phase analyses using instruments such as optical and transmission electron microscopes (TEM) with an extraction carbon replica of the carbides. The analyses revealed that the $M_2C$ that formed when retained for about 1 hour at 750$^{\circ}C$ causes a drastic decrease in the mechanical properties. The sharp drop in mechanical properties, however, disappeared as the $M_2C$ transformed into $M_{23}C_6$ with longer retention.

• Journal of the Korean Magnetics Society
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• v.25 no.5
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• pp.149-155
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• 2015

The ECR (Electron Cyclotron Resonance) Ar ion milling was manufactured to fabricate the device of thin film. The ECR ion milling system applied to the device etching operated by a power of 600W, a frequency of 2.45 GHz, and a wavelength of 12.24 cm and transferred by a designed waveguide. In order to match one resonant frequency, a magnetic field of 908 G was applied to a cavity inside of ECR. The Ar gas intruded into a cavity and created the discharged ion beam. The surface of target material was etched by the ion beam having an acceleration voltage of 1000 V. The formed devices with a width of $1{\mu}m{\sim}9{\mu}m$ on the GMR-SV (Giant magnetoresistance-spin valve) multilayer after three major processes such as photo lithography, ion milling, and electrode fabrication were observed by the optical microscope.

• Korean Journal of Optics and Photonics
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• v.1 no.1
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• pp.7-11
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• 1990

Resonant multi photon ionization (RMPD of Hg atoms is studied by focusing a high-power laser into the ionization cell. The intermediate resonant state is taken as $6d^1D_2$ with the 4-photon resonance wavelength of 560.7 nm. The ionization signal is measured as Hg vapor pressure (0.1-3.0 Torr), laser intensity $(10-120GW/\textrm{cm}^2)$, and laser wavelength (559-569 nm) vary. AC Stark shift and line broadening of the resonant state $(6d^1D_2)$ are observed and the shift factor is measured to be $-0.6(cm^{-1}/GW/\textrm{cm}^2$. It is also observed that the ionization signal increases as the Hg vapor pressure increases up to a certain value of pressure, however, if the pressure further increases, the signal decreases. The order of non-linearity, which discribes the laser intensity dependence of ionization rate, is measured to be 3 at the resonance, and compared with the theoretical results.esults.