• Journal of Sensor Science and Technology
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• v.5 no.5
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• pp.1-10
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• 1996

Solar cells made of the edge-defined film-fed growth Si are characterized using current-voltage, surface photovoltage, electron beam induced current, electron microprobe, scanning electron microscopy, and electron backscattering. The weak temperature dependence of the I-V curves in the EFG solar cells is due to a voltage variable shunt resistance giving higher diode ideality factors than the ideal one. The voltage variable shunt resistance is modeled by a modified recombination mechanism which includes carrier tunneling to distributed impurity energy states in the band gap within the space-charge region. The junction integrity and the substrate quality are characterized simultaneously by combining I-V and surface photovoltage (SPV) measurements. The diode ideality factors and the surface photovoltages characterize the junction integrity while the SPV diffusion lengths characterizes the substrate quality. Most of the measured samples show the voltage variable shunt resistance although how serious it is depends on the solar cell efficiency. The voltage variable shunt resistance is understood as one of the most important factors of the degradation of EFG solar cells.

• Geomechanics and Engineering
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• v.28 no.3
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• pp.265-281
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• 2022

A set of slurry shield test system capable of cutter cutting and slurry automatic circulation is used to investigate the deformation characteristics, the evolution characteristics of support resistance and the distribution and evolution process of earth pressure during excavating and collapsing of slurry shield tunneling in circular-gravel layer. The influence of cover-span ratio on surface subsidence, support resistance and failure mode of excavation face is also discussed. Three-dimensional numerical calculations are performed to verify the reliability of the test results. The results show that, with the decrease of the supporting force of the excavation face, the surface subsidence goes through four stages: insensitivity, slow growth, rapid growth and stability. The influence of shield excavation on the axial earth pressure of the front soil is greater than that of the vertical earth pressure. When the support resistance of the excavation face decreases to the critical value, the soil in front of the excavation face collapses. The shape of the collapse is similar to that of a bucket. The ultimate support resistance increase with the increase of the cover-span ratio, however, the angle between the bottom of the collapsed body and the direction of the tunnel excavation axis when the excavation face is damaged increase first and then becomes stable. The surface settlement value and the range of settlement trough decrease with the increase of cover-span ratio. The numerical results are basically consistent with the model test results.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1715-1717
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• 2004

We attempt to investigate morphology of self-assembled dipyridinium dithioacetate on Au(111) substrate by Scanning Tunneling Microscopy(STM). Also, we measured electrical properties using Scanning Tunneling Spectroscopy(STS). Sample that use this experiment acquires thiol function beside quantity by dipyridinium dithioacetate, is structure that can be self-assembled easily to Au(111) substrate. The same self-assembly procedure was used for two different concentrations, 0.5mmol/ml and 1mmol/ml. Dilute density of sample by 0.5mmol/ml, 1mmol/ml and observed dipyridinium dithioacetate's image by STM after self-assembled on Au(111) substrate. The structure of Tip/SAMs/Au(111) has been used measurement for electrical properties(i-v) using STM. The current-voltage measurement result, observed negative differential resistance(NDR) properties.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.2
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• pp.116-125
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• 2006

We have presented a nanoelectromechanical (NEM) model based on atomistic simulations. Our models were applied to a NEM device as called a nanotube random access memory (NRAM) operated by an atomistic capacitive model including a tunneling current model. We have performed both static and dynamic analyses of a NRAM device. The turn-on voltage obtained from molecular dynamics simulations was less than the half of the turn-on voltage obtained from the static simulation. Since the suspended carbon nanotube (CNT) oscillated with the amplitude for the oscillation center under an externally applied force, the quantity of the CNT-gold interaction in the static analysis was different from that in the dynamic analysis. When the gate bias was applied, the oscillation centers obtained from the static analysis were different from those obtained from the dynamics analysis. Therefore, for the range of the potential difference that the CNT-gold interaction effects in the static analysis were negligible, the vibrations of the CNT in the dynamics analysis significantly affected the CNT-gold interaction energy and the turn-on voltage. The turn-on voltage and the tunneling resistance obtained from our tunneling current model were in good agreement with previous experimental and theoretical works.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.485-488
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• 2004

본 연구에서는 dipyridinium dithioacetate 분자를 Au(111) 표면에 자기조립하여 STM 탐침-유기 단분자막-Au(111)기판의 수직구조로 STM 측정시스템을 이용하여, 전기적 특성을 관찰하였다. 먼저 Au(111)기판을 Piranha용액$(H_2SO_4:H_2O_2=3:1)$으로 Au 표면을 전처리 하였다. 전처리한 Au(111) 기판을 dipyridinium dithioacetate 1mol/ml 농도로 자기조립 하였으며, 자기조립막의 표면 구조를 STM으로 관찰하였다. dipyridinium dithioacetate의 전기적 특성은 STM 탐침-유기단분자막-Au(111) 기판의 수직구조로 STS를 이용하여 조사하였다. 전압과 전류 측정에서 전압이 증가함에 따라 전류가 감소하는 부성 미분저항(NDR)의 특성이 관찰 되었다. NDR 수치가 $-545\;[m\Omega/cm^2]$였고, PVCR은 1.64:1 이었다.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1390-1391
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• 2006

본 연구에서는 전도성 분자로 잘 알려진 4,4-Di(ethynyl phenyl) -2'-nitro-1-(thioacetyl)-benzene(nitro - benzene) 분자를 Au (111) 표면에 자기조립하고, ultra high vacuum scanning tunneling microscopy (UHV-STM)을 사용하여 STM tip과 sample 사이의 거리를 변화시키면서 전기전도 특성을 측정하였다. Au 기판제작은 연증착시스템 (Thermal Evaporation System)으로 제작하였으며, piranha 용액 ($H_{2}SO_{4}\;:\;H_{2}O_{2}$=3:1)을 사용하여 전치리한 후, 자기조립 단분자막 (SAMs)을 형성하였다. 먼저 1-octanethiol을 ethanol solution용액 1 mM/L 농도에서 24시간 동안 자기조립한 후에, ethanol를 solution 용액으로 이용하여 nitro-benzene를 0.1 nM/L 농도로 암실에서 30분간 자기조립 하였다. 자기조림 후 solution을 제거하기 위해 에탄올로 세척하여 $N_2$로 건조시켰다. 이 조건하에서 UHV-STM을 사용하여 nitro-benzene SAMs의 실시간 모폴로지의 변화에 따른 nitro-benzene의 전기전도 특성을 STM tip - SAMs - Au 기판의 수직구조로 STM tip과 nitro-benzene의 거리를 변화시키면서, tunneling current을 조사하였다. 측정 결과 Z-position 변화에 대한 tunneling current와 resistance의 변화를 확인할 수 있었다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.6
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• pp.433-438
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• 2020

To enhance the tunneling electroresistance (TER) ratio of a ferroelectric tunnel junction (FTJ) device using Al-doped HfO₂ thin films, a thin insulating layer was prepared on a TiN bottom electrode, for which TiN was preliminarily treated at various temperatures in O₂ ambient. The composition and thickness of the inserted insulating layer were optimized at 600℃ and 50 Torr, and the FTJ showed a high TER ratio of 430. During the heat treatments, a titanium oxide layer formed on the surface of TiN, that suppressed oxygen vacancy generation in the ferroelectric thin film. It was found that the fabricated FTJ device exhibits two distinct resistance states with higher tunneling currents by properly heat-treating the TiN bottom electrode of the HfO₂-based FTJ devices in O₂ ambient.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.24-24
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• 2003

Metallic magnetoelectronic devices have studied intensively and extensively for last decade because of the scientific interest as well as great technological importance. Recently, the scientific activity in spintronics field is extending to the hybrid devices using ferromagnetic/semiconductor heterostructures and to new ferromagnetic semiconductor materials for future devices. In case of the hybrid device, conductivity mismatch problem for metal/semiconductor interface will be able to circumvent when the device operates in ballistic regime. In this respect, spin-valve transistor, first reported by Monsma, is based on spin dependent transport of hot electrons rather than electron near the Fermi energy. Although the spin-valve transistor showed large magnetocurrent ratio more than 300%, but low transfer ratio of the order of 10$\^$-5/ prevents the potential applications. In order to enhance the collector current, we have prepared magnetic tunneling transistor (MTT) with single ferromagnetic base on Si(100) collector by magnetron sputtering process. We have changed the resistance of tunneling emitter and the thickness of baser layer in the MTT structure to increase collector current. The high transfer ratio of 10$\^$-4/ range at bias voltage of more than 1.8 V, collector current of near l ${\mu}$A, and magnetocurrent ratio or 55% in Si-based MTT are obtained at 77K. These results suggest a promising candidate for future spintronic applications.

• 보존과학연구
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• s.7
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• pp.246-264
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• 1986

Micoromorphological alterations of sea-waterlogged woods by marinemicro-oragnisms were investigated by the light and scanning electron microscopy as a part of serial investigations on the shipwrecked materials which were excavated at the sea shore of Wando-Kun, southern coast of Korea in 1984.Deterioration of sea-waterlogged wood by marine microorganisms were varied with the wood species. The degree of deterioration even in the same wood specieswas different according to the part where it was in mud of sea-water. However, the resistance of Torreya nucifera over the marine organisms was marked. Deterioration in cell wall may be classified into three types; thinning of cell wall, separation of secondary wall from compound middle lamella and tunneling of cell wall. Thinning and separation were frequently observed, while the tunneling was rare. Among the wood cell elements of hardwoods, vessel wall was the least deteriorated. The difference degree of degradation of cell wall constituents and the accumulation of inorganic substances in cell lumen indicate that some factors to be considered for the conservation treatment were discussed. The kinds of marine microorganisms invading and/or inhabiting in wrecked wooden ship were also discussed.

• JSTS:Journal of Semiconductor Technology and Science
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• v.2 no.3
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• pp.157-163
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• 2002

A new flash EEPROM device with p^＋ poly-Si control gate and n^＋ poly-Si floating side gate was fabricated and characterized. The n^＋ poly-Si gate is formed on both sides of the p^＋ poly-Si gate, and controls the underneath channel conductivity depending on the number of electron in it. The cell was programmed by hot-carrier-injection at the drain extension, and erased by direct tunneling. The proposed EEPROM cell can be scaled down to 50 nm or less. Shown were measured programming and erasing characteristics. The channel resistance with the write operation was increased by at least 3 times.