• Nuclear Engineering and Technology
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• v.41 no.1
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• pp.21-38
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• 2009

The use of multi scale modeling concepts and simulation techniques to study the destabilization of an ultrathin layer of oxide interface between a metal substrate and the surrounding environment is considered. Of particular interest are chemo-mechanical behavior of this interface in the context of a molecular-level description of stress corrosion cracking. Motivated by our previous molecular dynamics simulations of unit processes in materials strength and toughness, we examine the challenges of dealing with chemical reactivity on an equal footing with mechanical deformation, (a) understanding electron transfer processes using first-principles methods, (b) modeling cation transport and associated charged defect migration kinetics, and (c) simulation of pit nucleation and intergranular deformation to initiate the breakdown of the oxide interlayer. These problems illustrate a level of multi-scale complexity that would be practically impossible to attack by other means; they also point to a perspective framework that could guide future research in the broad computational science community.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.1
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• pp.71-75
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• 2022

Graphene oxide was stirred with a ZnCl₂:NaCl electrolyte and electrochemically coated by cyclic voltammetry to simplify the electron transpfer layer film forming process for organic solar cells and to fabricate an organic solar cell having it. The device structure is FTO/ZnO:graphene/P3HT:PCBM/PEDOT:PSS/Ag. Morphology and chemical properties of ETL were confirmed by scanning electron microscopy(SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. As a result of XPS measurement, ZnO metal oxide and carbon bonding were simultaneously confirmed, and ZnO and graphene peaks were confirmed by Raman spectroscopy. The electrical characteristics of the manufactured solar cell were specified with a solar simulator, and the ETL device coated twice at a rate of 0.05 V/s showed the highest photoelectric conversion efficiency of 1.94%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.166-169
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• 2000

The Organic Electroluminescence (OEL) device, that was consisted of ALq3(8-hydroxyquinoline aluminum) and TPD(N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine), has been used. We investigated characteristics of brightness and current density about OEL that was oxidated each layers. We used two samples that were fabricated each continuous and non-continuous method. Emission was observed above 10mA/$\textrm{cm}^2$ and luminance was measured to be 1530cd/$\textrm{cm}^2$ at a current density of 100mA/$\textrm{cm}^2$. A luminance of over 2600cd/$\textrm{cm}^2$ was also observed after the final fabrication process.

• Korean Journal of Metals and Materials
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• v.48 no.1
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• pp.90-100
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• 2010

Micro-conductive patterns were microfabricated on an insulating substrate ($SiO_2$) surface by a selective electroless nickel plating process in order to investigate the formation of seed layers. To fabricate micro-conductive patterns, a thin layer of metal (Cu.Cr) was deposited in the desired micropattern using laser-induced forward transfer (LIFT). and above this layer, a second layer was plated by selective electroless plating. The LIFT process. which was carried out in multi-scan mode, was used to fabricate micro-conductive patterns via electroless nickel plating. This method helps to improve the deposition process for forming seed patterns on the insulating substrate surface and the electrical conductivity of the resulting patterns. This study analyzes the effect of seed pattern formation by LIFT and key parameters in electroless nickel plating during micro-conductive pattern fabrication. The effects of the process variables on the cross-sectional shape and surface quality of the deposited patterns are examined using field emission scanning electron microscopy (FE-SEM) and an optical microscope.

• Carbon letters
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• v.26
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• pp.88-94
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• 2018

This manuscript explains the effective determination of urea by redox cyclic voltammetric analysis, for which a modified polypyrrole-graphene oxide (PPY-GO, GO 20% w/w of PPY) nanocomposite electrode was developed. Cyclic voltammetry measurements revealed an effective electron transfer in 0.1 M KOH electrolytic solution in the potential window range of 0 to 0.6 V. This PPY-GO modified electrode exhibited a moderate electrocatalytic effect towards urea oxidation, thereby allowing its determination in an electrolytic solution. The linear dependence of the current vs. urea concentration was reached using square-wave voltammetry in the concentration range of urea between 0.5 to $3.0{\mu}M$ with a relatively low limit of detection of $0.27{\mu}M$. The scanning electron microscopy was used to characterize the morphologies and properties of the nanocomposite layer, along with Fourier transform infrared spectroscopy. The results indicated that the nanocomposite film modified electrode exhibited a synergistic effect, including high conductivity, a fast electron-transfer rate, and an inherent catalytic ability.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.3
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• pp.276-283
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• 2005

Magnetic tunneling transistor (MTT) device using the amorphous n-type Si semiconductor film for base and collector consisting of the [CoFe/NiFe](free layer) and Si(top layer) multilayers was used to study the spin-dependent hot electron magnetocurrent (MC) and tunneling magnetoresistance (TMR) at room temperature. A large MC of 40.2 % was observed at the emitter-base bias voltage ( $V_{EB}$ ) of 0.62 V. The increasing emitter hot current and transfer ratio ( $I_{C}$/ $I_{E}$) as $V_{EB}$ are mainly due to a rapid increase of the number of conduction band states in the Si collector. However, above the $V_{EB}$ of 0.62 V, the rapid decrease of MC was observed in amorphous Si-based MTT because of hot electron spin-dependent elastic scattering across CoFe/Si interfaces.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.430-430
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• 2011

Graphene, one single atomic layer of graphite, has attracted extensive attention in various research fields since its first isolation from graphite. Application in the future electronics requires better understanding and manipulation of electronic properties of graphene supported on various solid substrates. Here, we present a study on charge doping and morphology of graphene prepared on atomically flat and highly polar mica substrates. Ultra-flat single-layer graphene was prepared by micro-exfoliation of graphite followed by deposition on cleaved mica substrates. Atomic force microscopy (AFM) revealed presence of ultra-thin water films formed in a layer-by-layer manner between graphene and mica substrates. Raman spectroscopy showed that a few angstrom-thick water films efficiently block electron transfer from graphene to mica. Hole doping in graphene caused by underlying mica substrates was also visualized by scanning Kelvin probe microscopy (SKPM).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.10
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• pp.820-826
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• 2009

The anisotropic phonon conductions with varying Joule heating rate of the silicon film in Silicon-on-Insulator devices are examined using the electron-phonon interaction model. It is found that the phonon heat transfer rate at each boundary of Si-layer has a strong dependence on the heating power rate. And the phonon flow decreases when the temperature gradient has a sharp change within extremely short length scales such as phonon mean free path. Thus the heat generated in the hot spot region is removed primarily by heat conduction through Si-layer at the higher Joule heating level and the phonon nonlocality is mainly attributed to lower group velocity phonons as remarkably dissimilar to the case of electrons in laser heated plasmas. To validate these observations the modified phonon nonlocal model considering complete phonon dispersion relations is introduced as a correct form of the conventional theory. We also reveal that the relation between the phonon heat deposition time from the hot spot region and the relaxation time in Si-layer can be used to estimate the intrinsic thermal resistance in the parallel heat flow direction as Joule heating level varies.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.5
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• pp.270-275
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• 2017

Current progress in the development of semiconductor technology in applications involving high electron mobility transistors (HEMT) and power devices is hindered by the lack of adequate ways todissipate heat generated during device operation. Concurrently, electronic devices that use gallium nitride (GaN) substrates do not perform well, because of the poor heat dissipation of the substrate. Suggested alternatives for overcoming these limitations include integration of high thermal conductivity material like diamond near the active device areas. This study will address a critical development in the art of GaN on diamond (GOD) structure by designing for ideal heat dissipation, in order to create apathway with the least thermal resistance and to improve the overall ease of integrating diamond heat spreaders into future electronic devices. This research has been carried out by means of heat transfer simulation, which has been successfully demonstrated by a finite-element method.

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.997-999
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• 1999

We fabricated white light-emitting organic electroluminescent device which have a mixed single emitting layer containing poly(N-vinylcarbazole)[PVK], tris(8-hydroxyquinoline)aluminum[Alq3] and poly(3-hexylthiophene)[P3HT] and investigated the emission properties of it. We expect to obtain a blue light from PVK, green light from Alq3 and red light from P3HT The fabricated device emits white light over 18V with slight orange light. We think that the energy transfer in a mixed layer occurred from PVK to $Alq_3$ and P3HT resulted in decreasing the blue light intensity from PVK. With mixing of N, N'-diphenyl-N, N'-(3-methylphenyl)-[1,1'-biphenyl]-4, 4'-diamine[TPD], hole transport material, to the emitting layer, the luminance intensity of device was increased 50 times than that of the device which not contain TPD. We find that the efficiency of the white light electroluminescent device can be improved by injecting electron more effectively and blue light need to improve the color purity of white light.