• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.9-9
• /
• 2011

There has been strong demand for novel nonvolatile memory technology for low-cost, large-area, and low-power flexible electronics applications. Resistive memories based on metal oxide thin films have been extensively studied for application as next-generation nonvolatile memory devices. However, although the metal oxide-based resistive memories have several advantages, such as good scalability, low-power consumption, and fast switching speed, their application to large-area flexible substrates has been limited due to their material characteristics and necessity of a high-temperature fabrication process. As a promising nonvolatile memory technology for large-area flexible applications, we present a graphene oxide-based memory that can be easily fabricated using a room temperature spin-casting method on flexible substrates and has reliable memory performance in terms of retention and endurance. The microscopic origin of the bipolar resistive switching behaviour was elucidated and is attributed to rupture and formation of conducting filaments at the top amorphous interface layer formed between the graphene oxide film and the top Al metal electrode, via high-resolution transmission electron microscopy and in situ x-ray photoemission spectroscopy. This work provides an important step for developing understanding of the fundamental physics of bipolar resistive switching in graphene oxide films, for the application to future flexible electronics.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.438-438
• /
• 2011

White light-emitting diodes (LEDs), the so-called next-generation solid-state lighting, offer benefits in terms of reliability, energy-saving, maintenance, safety, lead-free, and eco-friendly. Recently, rare-earth-doped oxynitride or nitride compounds have attracted a great deal of interest as a photoluminescent material because of their unique luminescent property, especially for white LEDs applications. Ce doped ${\beta}$-SiAlON has been studied as a wavelength conversion phosphor in white LEDs thanks to its high absorption rates, high quantum efficiency, and excellent thermal stability. Previously researches were not enough to understand the detail mechanism and characteristics of ${\beta}$-SiALON. The bandgap structures and electronic structures were not exact due to limitation of calculation methods. In this study, to elucidate the Ce doping effect on the SiAlON system, accurate band structures and electronic structure of the Ce doped ${\beta}$-SiAlON was intensively investigated using density functional theory calculations. In order to get a better description of the band gaps, MBJLDA method were used. We have found a single Ce atom site in ${\beta}$-SiAlON super cell. Furthermore, the density of state, band structure and lattice constant were intensively investigated.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.384-384
• /
• 2011

양자점 감응형 태양전지는 염료감응형 태양전지와 비슷한 구조를 가지지만, 유기물 염료를 대신하여 무기물 양자점을 사용함으로서 기존 유기물 염료가 가지는 한계점을 극복할 수 있다. 양자점을 광감응 염료로 사용하는 경우 양자제한효과(quantum confinement effect)에 의해 양자점의 사이즈조절만으로 밴드갭을 조절할 수 있어 광학적 특성 조절이 용이하며, 유기물 염료보다 광흡수 능력도 뛰어나다. 더불어, 하나의 광자를 흡수하여 두개 이상의 전자-정공쌍을 만들 수 있는(multiple exciton generation) 가능성이 있어 기존 태양전지가 가지는 이론적 한계효율(Shockley-Queisser limit)을 뛰어넘을 수 있다. 본 연구에서는 고효율의 양자점 감응형 태양전지 개발을 위해, ZnO 나노선 구조에 CdS, CdSe 양자점을 증착한 CdSe/CdS/ZnO 나노선 헤테로구조를 수열합성법으로 합성하였다. 증착한 CdSe/CdS 양자점이 태양광의 가시광 전 영역을 흡수하여 전자-정공을 생성하며, 세 물질 간의 밴드구조를 통해 양자점에서 생성된 전자가 ZnO 나노선으로 포집되고, 바닥전극으로 직접연결이 되어있는 1차원의 나노선 구조를 통해 전자를 효율적으로 운반할 수 있다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.08a
• /
• pp.369-369
• /
• 2011

양자점 감응형 태양전지는 가시광 영역을 흡수, 이용할 수 있는 광감응 물질로 무기물 양자점을 사용하며, 이 경우 나노미터 크기의 무기물 양자점으로 인한 양자제한 효과 (quantum confinement effect)에 의해 양자점의 사이즈 조절 만으로 밴드갭을 조절할 수 있어 광학적 특성 조절이 용이하며, 하나의 광자를 흡수하여 두개 이상의 전자-정공쌍을 만들 수 있는 (multiple exciton generation) 가능성이 있어 기존 태양전지가 가지는 이론적 한계효율(Shockley-Queisser limit)을 뛰어넘을 수 있다. 본 연구에서는 양자점 및 염료 감응형 태양전지분야에서 가장 많이 사용되고 있는 TiO2 다공성 필름이 아닌, ZnO 나노선 구조를 이용하여 양자점 감응형 태양전지를 제작하였다. ZnO의 경우 TiO2보다 높은 전자이동도를 가지며, 나노선 구조가 바닥전극까지 수직 연결된 1차원의 전자전달경로를 제공하여 결과적으로 광전자 포집에 유리하다. 또한, CdS, CdSe 양자점을 동시에 사용하여 광흡수 범위를 가시광 전 영역으로 확장하였으며, 계단형 밴드구조를 통해 광전자-정공 분리 및 포집을 용이하게 하였다. 더 나아가 전해질의 조성, 나노선의 길이 등 다양한 부분을 조절하면서 각 변수가 소자의 효율에 미치는 영향을 관찰하였다.

• Nuclear Engineering and Technology
• /
• v.40 no.6
• /
• pp.439-450
• /
• 2008

The KSTAR device succeeded in first plasma generation on $13^{th}$ June of 2008 through comprehensive system test and commissioning. Among various kinds of the key factors that decisively affected the project, success in the construction and assembly of the major tokamak structure was most important one. Every engineering aspects of each structure were finally confirmed in the integrated commissioning period, and there were no severe troubles and failures prevented the KSTAR device from operating during the commissioning and the first plasma experiments. As a result, all of the experiences and technologies achieved through the KSTAR construction process are expected to be important fundamentals for future construction projects of superconducting fusion devices. This paper summarizes key engineering features of the major structures and of the machine assembly.

• Journal of the Korean Vacuum Society
• /
• v.17 no.4
• /
• pp.253-261
• /
• 2008

Programmable metallizaton cell (PMC) memory device has been known as one of the next generation non-volatile memory devices, because it includes non-volatility, high speed and high ON/OFF resistance ratio. This paper reviews the operation principle of the device. Besides, the recent research results of professor Kozicki who firstly invented the device and investigated it for the memory applications, NEC corporation which studied it for the FPGA (field programmable gate array) switch applications, ETRI and chungnam national university which examined Te-based devices are introduced.

• Proceedings of the Korean Vacuum Society Conference
• /
• 1995.06a
• /
• pp.151-151
• /
• 1995

Nitrogen implantation process has been applied for improvement of wear resistance of Z Zircaloy-4 fuel cladding materials. Nitrogen was implanted at 120 ke V to a total do range of 1xHP ions/cm2 to 8xlO17 ions/cm2 at various temperatures of 298"C to 676"C. The m microstructure changes by nitrogen implantation were analyzed by using TEM, XRD 뻐d A AES, cmd then wear behavior was evaluated by ball-on-disc wear testings at various loads a and sliding velocity under unlubricated condition. Nitrogen implantation produced ZrNx nitride above 4.37x1017 ions!cm2 as well as heavy d dislocations, which enhanced microhardness of the implanted surface of up to 900 Hk from 2 200 Hk of unimplanted substrate. Hardness was also found to be increased with increasing i implantation temperature and enhanced up to OOOHk at 620 "C. the wear resistance was g greatly improved with increasing total ion do않 as well as implantation temperature. The effective enhancement of wear resistance at high dose and tem야ratures is believed d due to significant hardening associated with high degree of precipitation of Zr nitrides and g generation of prismatic dislocation I$\infty$ps.infty$ps.

• Journal of Korean Vacuum Science & Technology
• /
• v.2 no.2
• /
• pp.78-84
• /
• 1998

ZnO:Al films were prepared by an rf magnetron sputtering and targets for the experiments were fabricated by sintering the mixture of ZnO and Al2O3. The most conductive film was obtained from the target with 2.0∼2.2 wt.% of Al2O3. Optical properties studied with spectroscopic ellipsometry showed band gap widening, i.e., the Burstein-Moss shift, with aluminum doping as well as with the elevation of deposition temperature. And it is found that the optical and electrical properties were related to the density of states as well as the variation of donor level. when hydrogen atoms were introduced into the films, the activation energy for the generation of oxygen vacancy was smaller for the films showing higher conductivity. This indicates that the optimum deposition condition for highly conductive ZnO:Al film has strong relation to the optimum doping condition.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.379-379
• /
• 2010

Recent technical advances in OLEDs (organic light emitting devices) requires more and more the improvement in low operation voltage, long lifetime, and high luminance efficiency. Inverted top emission OLEDs (ITOLED) appeared to overcome these problems. This evolved to operate better luminance efficiency from conventional OLEDs. First, it has large open area so to be brighter than conventional OLEDs. Also easy integration is possible with Si-based driving circuits for active matrix OLED. But, a proper buffer layer for carrier injection is needed in order to get a good performance. The buffer layer protects underlying organic materials against destructive particles during the electrode deposition and improves their charge transport efficiency by reducing the charge injection barrier. Hexaazatriphenylene-hexacarbonitrile (HAT-CN), a discoid organic molecule, has been used successfully in tandem OLEDs due to its high workfunction more than 6.1 eV. And it has the lowest unoccupied molecular orbital (LUMO) level near to Fermi level. So it plays like a strong electron acceptor. In this experiment, we measured energy level alignment and hole current density on inverted OLED structures for hole injection. The normal film structure of Al/NPB/ITO showed bad characteristics while the HAT-CN insertion between Al and NPB greatly improved hole current density. The behavior can be explained by charge generation at the HAT-CN/NPB interface and gap state formation at Al/HAT-CN interface, respectively. This result indicates that a proper organic buffer layer can be successfully utilized to enhance hole injection efficiency even with low work function Al anode.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.432-432
• /
• 2010

Organic light emitting diodes (OLED) thin films were fabricated by Electrostatic spray deposition (ESD). In this study, we reported the thickness, morphology, current efficiency, luminescence of OLED fabricated by ESD. These results were compared with the spin coating method, and showed that also ESD is a good fabrication method for OLED because of its characteristics similar with the results using spin coating. The active layer consists of organic blends with Poly(N-vinylcarbazole) (PVK), 2-(4-Biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), N,N'-Bis(3-methylphenyl) -N,N'-bis(phenyl)-benzidine (TPD), Tris(2-phenylpyridine)iridium(III) (Ir(ppy)3), and the structure of OLED consists of aluminum (Al), lithium fluoride (LiF), organic blends, PEDOT:PSS and Indium-tin-oxide (ITO), which was used as the top cathode, cathode interfacial layer, emitting layer and bottom anode, respectively. The results suggest that Electrostatic spray deposition is a promising method for the next generation of OLED fabrication since it has a probability fabricating large-area thin films.