• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.666-672
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• 2014

We have investigated the gate insulator effects on the electrical performance of p-type tin monoxide (SnO) thin-film transistors (TFTs). Various SnO TFTs are fabricated with different gate insulators of a thermal $SiO_2$, a plasma-enhanced chemical vapor deposition (PECVD) $SiO_x$, a $150^{\circ}C$-deposited PEVCD $SiO_x$, and a $300^{\circ}C$-deposited PECVD $SiO_x$. Among the devices, the one with the $150^{\circ}C$-deposited PEVCD $SiO_x$ exhibits the best electrical performance including a high field-effect mobility ($=4.86cm^2/Vs$), a small subthreshold swing (=0.7 V/decade), and a turn-on voltage around 0 (V). Based on the X-ray diffraction data and the localized-trap-states model, the reduced carrier concentration and the increased carrier mobility due to the small grain size of the SnO thin-film are considered as possible mechanisms, resulting in its high electrical performance.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.185.2-185.2
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• 2014

We have studied the atomic and electronic structure of graphene nanoribbons (GNRs) on a hexagonal boron nitride (h-BN) sheet with intercalated atoms using first-principles calculations. The h-BN sheet is an insulator with the band gap about 6 eV and then it may a good candidate as a supporting dielectric substrate for graphene-based nanodevices. Especially, the h-BN sheet has the similar bond structure as graphene with a slightly longer lattice constant. For the computation, we use the Vienna ab initio simulation package (VASP). The generalized gradient approximation (GGA) in the form of the PBE-type parameterization is employed. The ions are described via the projector augmented wave potentials, and the cutoff energy for the plane-wave basis is set to 400 eV. To include weak van der Waals (vdW) interactions, we adopt the Grimme's DFT-D2 vdW correction based on a semi-empirical GGA-type theory. Our calculations reveal that the localized states appear at the zigzag edge of the GNR on the h-BN sheet due to the flat band of the zigzag edge at the Fermi level and the localized states rapidly decay into the bulk. The open-edged graphene with a large corrugation allows some space between graphene and h-BN sheet. Therefore, atoms or molecules can be intercalated between them. We have considered various types of atoms for intercalation. The atoms are initially placed at the edge of the GNR or inserted in between GNR and h-BN sheet to find the effect of intercalated atoms on the atomic and electronic structure of graphene. We find that the impurity atoms at the edge of GNR are more stable than in between GNR and h-BN sheet for all cases considered. The nickel atom has the lowest energy difference of ~0.2 eV, which means that it is relatively easy to intercalate the Ni atom in this structure. Finally, the magnetic properties of intercalated atoms between GNR and h-BN sheet are investigated.

• Journal of the Korean Institute of Intelligent Systems
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• v.23 no.6
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• pp.558-564
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• 2013

Wireless sensor networks (WSNs) contain limited energy resources and are left in open environments. Since these sensor nodes are self-operated, attacks such as sinkhole attacks are possible as they can be compromised by an adversary. The sinkhole attack may cause to change initially constructed routing paths, and capture of significant information at the compromised node. A localized encryption and authentication protocol (LEAP) has been proposed to authenticate packets and node states by using four types of keys against the sinkhole attack. Even though this novel approach can securely transmits the packets to a base station, the packets are forwarded along the constructed paths without checking the next hop node states. In this paper, we propose the next hop node selection method to cater this problem. Our proposed method evaluates the next hop node considering three factors (i.e., remaining energy level, number of shared keys, and number of filtered false packets). When the suitability criterion for next hop node selection is satisfied against a fix threshold value, the packet is forwarded to the next hop node. We aim to enhance energy efficiency and a detour of attacked areas to be effectively selected Experimental results demonstrate validity of the proposed method with up to 6% energy saving against the sinkhole attack as compared to the LEAP.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.145.1-145.1
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• 2016

Binding and unbinding between molecular oxygen and metallo-porphyrin is a key process for oxygen delivery in respiration. It can be also used to control spin state of magnetic metallo-porphyrin molecules. Controlling and sensing spin states of magnetic molecules in such reactions at the single molecule level is essential for spintronic molecular device applications. Here, we demonstrate that spin states of metallo-porphyrin on surfaces can be controlled over by binding and unbinding of oxygen molecule, and be sensed using scanning tunneling microscopy and spectroscopy. Kondo localized state of metallo-porphyrin showed significant modification by the binding of oxygen molecule, implying that the spin state was changed. Our density functional theory calculation results explain the observations with the hybridization of unpaired spins in d and ${\pi}^*$ orbitals of metallo-porphyrin and oxygen, respectively. Our study opens up ways to control molecular spin state and Kondo effect by means of molecular binding and unbinding reactions on surfaces.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.10
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• pp.438-442
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• 2005

Si nanocrystal (Si NC) memory device has several advantages such as better retention, lower operating voltage, reduced punch-through and consequently a smaller cell area, suppressed leakage current. However, the physical and electrical reasons for this behavior are not completely understood but could be related to interface states of Si NCs. In order to find out this effect, we characterized electrical properties of Si NCs embedded in a SiO$_{2}$ layer by scanning probe microscopy (SPM). The Si NCs were generated by the laser ablation method with compressed Si powder and followed by a sharpening oxidation. In this step Si NCs are capped with a thin oxide layer with the thickness of 1$\~$2 nm for isolation and the size control. The size of 51 NCs is in the range of 10$\~$50 m and the density around 10$^{11}$/cm$^{2}$ It also affects the interface states of Si NCs, resulting in the change of electrical properties. Using a conducting tip, the charge was injected directly into each Si NC, and the image contrast change and dC/dV curve shift due to the trapped charges were monitored. The results were compared with C-V characteristics of the conventional MOS capacitor structure.

• Journal of Photoscience
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• v.9 no.2
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• pp.275-277
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• 2002

We have recently found that a detergent-resistant raft like membrane (DRM) can be prepared from bovine rod outer segment membranes as a low-density buoyant fraction in sucrose density gradient ultracentrifugation. G protein (transducin) and its effector enzyme (phosphodiesterase: PDE) drastically change their affinities to DRM in the process of phototransduction. We report here that the recruitment of transducin and/or $^2$PDE to DRM has close relationship with their states in signal transduction. Active T$\alpha$/PDE-complex has a high affinity to DRM, whereas inactive transducin, or inactive PDE are excluded from DRM. Active T$\alpha$/PDE-complex seems to bind to a GTPase activating protein (GRS9) in multi- protein complexes localized on DRM. Physiological significance of the multi-protein complex on the raft-like membrane in vertebrate phototransduction would be discussed.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.211-211
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• 2012

Using spin-polarized density-functional theory calculations, we find that the existence of either Peierls instability or antiferromagnetic spin ordering is sensitive to hydrogen passivation near the step. As hydrogens are covered on the terrace, the dangling bond electrons are localized at the step, leading to step-induced states. We investigate the competition between charge and spin orderings in dangling-bond (DB) wires of increasing lengths fabricated on an H-terminated vicinal Si(001) surface. We find antiferromagnetic (AF) ordering to be energetically much more favorable than charge ordering. The energy preference of AF ordering shrinks in an oscillatory way as the wire length increases. This oscillatory behavior can be interpreted in terms of quantum size effects as the DB electrons fill discrete quantum levels.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.472-472
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• 2013

본 논문은 InN와 GaN를 교대로 증착하는 교번성장법을 이용해 제작한 4주기 InN/GaN 박막의 구조적, 광학적, 특성을 X-ray diffraction, Atomic force microscopy, Transmission electron microscopy과 저온 Photoluminescence (PL) 장비를 사용하여 분석한 결과를 보고한다. Fig. 1은 4주기 InN/GaN박막의 XRD 스펙트럼으로 GaN(0002)와 InN(0002)의 회절 신호를 관찰할 수 있다. 그러나 두 피크뿐만 아니라 InN와 GaN 사이에 구분이 되지 않은 추가 신호를 확인할 수 있다. 추가신호는 InN와 GaN 계면에서 발생하는 상호확산 확률로서 해석할 수 있다. Fig. 2는 다양한 조건에서 성장한 InN/GaN 시료의 PL스펙트럼으로 방출 파장은 각각 1,380, 1,290, 1,280, 1,271, 1,246 nm로 측정되었다. 성장 조건 변화에 따른 발광특성 변화를 박막에서 III족 원자 특히, In 원자의 성장 거동에 따른 구속준위(Localized states) 변화로 논의할 예정이다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.5
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• pp.376-382
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• 2001

Magnetic and transport properties in the ceramic specimen of L $a_{0.7}$S $r_{0.3}$Fe $O_3$ with orthohombic structure has been investigated. Weak ferromagnetism has been observed in a ceramic sample of L $a_{0.7}$S $r_{0.3}$Fe $O_3$. Large dielectric relaxation of Debye type is observed in paramagnetic states within the temperature range of 130K~200K. From the temperature dependence of the characteristic frequency, we concluded that the elementary process of the dispersion is related to holes hopping between F $e^{3+}$ and F $e^{4+}$ ions. The temperature dependencies of thermoelectric power and Dc conductivity suggest that the charge carrier responsible for the conduction are strongly localized. These experimental results have been interpreted in terms of a hopping process involving small polaron.n.laron.n.

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.53-54
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• 2000

Measurements of the direct current resistivity, on multiwalled carbon nanotubes(MWNT) for field electron emitter source that had been screen printed in a thick film form were made as a function of temperature T in the range of 1.7K-390K. In this measuring temperature range, the electrical resistivity for the MWNT show that the main contribution to the conductivity comes form carries that hop directly between localized states executing variable range hopping processes. This thick-film form system for large area display showed a high bright light emission as well as very low turn-on field as like an individual MWNT system at room temperature. Furthermore, the electron emission characteristics followed well typical Fowler-Nordheim conduction under the vacuum.