• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.71-71
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• 1999

현재 소자 제작에 응용되는 수소화된 비정질 실리콘은 PECVD 방법으로 제작하는 것이 보편적인 방법이다. 그러나 비정질 실리콘 박막 트랜지스터는 band gap edge 근처에서 국재준위가 많아 mobility가 작으며 상온에서 조차 불안정하여 신뢰성이 높지 않고, 도핑된 비정질 실리콘의 높은 비저항 등의 단점으로 인하여 고속 회로에 응용이 불가능하다. 반면 다결정질 실리콘 박막 트랜지스터는 a-Si:H TFT 에 비해 재현성이 우수하고 high resolution, high resolution, high contrast LCD에 응용할 수 있다. 하지만, 다결정 실리콘의 grain boundary로 인해 단결정에 비해 많은 defect 들이 존재하여 전도성을 감소시킨다. 따라서 Mobility를 증가시키기 위해서 grain size를 증가시키고 grain boundary 내에 존재하는 trap center를 감소시켜야 한다. 따라서 본 실험에서는 PECVD 장비로 초기 기판을 plasma 처리하여 다결정 실리콘 박막을 제작하여, 기판 처리에 대한 다결정 실리콘 박막의 성장의 특성을 조사하였다. 실험 방법으로는 PECVD 시스템을 이용하여 SiH4 gas와 H2 gas를 선택적으로 증착시키는 LBL 방법을 사용하여 $\mu$c-Si:H 박막을 제작하였다. 비정질 층을 gas plasma treatment 하여 다결정질 실리콘의 증착 initial stage 관찰을 주목적으로 관찰하였다. 다결정 실리콘 박막의 구조적 성질을 조사하기 위하여 Raman, AFM, SEM, XRD를 이용하여 grain 크기와 결정화도에 대해 측정하여 결정성장 mechanism을 관측하였다. LBL 방법으로 증착시킨 박막의 Raman 분석을 통해서 박막 증착 초기에 비정질이 증착된 후에 결정질로 상태가 변화됨을 관측할 수 있었고, SEM image를 통해서 증착 회수를 증가시키면서 grain size가 작아졌다 다시 커지는 현상을 볼 수 있었다. 이 비정질 층의 transition layer를 gas plasma 처리를 통해서 다결정 핵 형성에 영향을 관측하여 적정한 gas plasma를 통해서 다결정질 실리콘 박막 증착 공정을 단축시킬 수 있는 가능성을 짐작할 수 있었고, 또한 표면의 roughnes와 morphology를 AFM을 통하여 관측함으로써 다결정 박막의 핵 형성에 알맞은 증착 표면 특성을 분석 할 수 있었다.

• Journal of the Korean Ceramic Society
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• v.28 no.8
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• pp.626-634
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• 1991

The specimens for the corrosion test were made by hot-pressing of SiC power with 2 wt% Nl2O3 and 10wt% Al2O3 additions at 200$0^{\circ}C$ and 205$0^{\circ}C$. The specimens were corroded in 37 mole% NaCl and 63 mole% Na2SO4 salt mixture at 100$0^{\circ}C$ up to 60 min. SiO2 layer was formed on SiC and then this oxide layer was dissolved by Na2O ion in the salt mixture. The rate of corrosion of the specimen containing 10 wt% Al2O3 was slower than that of the specimen containing 2 wt% Al2O3. This is due to the presence of continuous grain boundary phase in the specimen containing 10 wt% Al2O3. The oxidation of SiC produced gas bubbles at the SiC-SiO2 interface. The rate of corrosion follows a linear rate law up to 50 min. and then was accelerated. This acceleration is due to the disruption oxide layer by the gas evolution at SiC-SiO2 interface. Pitting corrosion has found at open pores and grain boundaries.

• Journal of Sensor Science and Technology
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• v.26 no.2
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• pp.122-127
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• 2017

Graphene grown on copper-foil substrates by chemical vapor deposition (CVD) has been attracting interest for sensor applications due to an extraordinary high surface-to-volume ratio and capability of large-scale device fabrication. However, CVD graphene has a polycrystalline structure and a high density of grain boundaries degrading its electrical properties. Recently, processes such as electropolishing for flattening copper substrate has been applied before growth in order to increase the grain size of graphene. In this study, we systemically analyzed the effects of the process condition of electropolishing copper foil on the quality of CVD graphene. We observed that electropolishing process can reduce surface roughness of copper foil, increase the grain size of CVD graphene, and minimize the density of double-layered graphene regions. However, excessive process time can rather increase the copper foil surface roughness and degrade the quality of CVD graphene layers. This work shows that an optimized electropolishing process on copper substrates is critical to obtain high-quality and uniformity CVD graphene which is essential for practical sensor applications.

• Transactions of Materials Processing
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• v.17 no.4
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• pp.240-248
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• 2008

The effect of alloying elements(Mn, S, Mo, B) on the high temperature deformation behavior of Fe-29%Ni-17%Co (Kovar) alloy were investigated. And the effect of high temperature oxidation on the hot ductility was also studied. The hot ductility of Kovar alloy was drastically increased with the addition of Mn and lowering of S content. It has been found that the brittle intergranular fracture at high temperature cracking is closely associated with the FeS sulfide along the grain boundary. When Mn was added, the type of sulfide was changed to MnS from FeS and ductile intergranular fracture and transgranular fracture were promoted. The formation of oxide layer was found to have minimized the hot ductility of the Kovar alloy significantly. Grain boundary micro-cracks in the internal oxide region were noted following deformation due to high temperature, one of which acting as a notch that caused the poor hot workability of the oxidized specimen. The addition of Mo to the Kovar alloy could also retard the decrease in the hot ductility of the oxidized specimen through the prevention of notching due to internal oxidation. Hot ductility was remarkably improved by the addition of Boron. The improvement of hot ductility results from the grain boundary migration mainly due to the dynamic recrystallization at lower temperature range ($900{\sim}1000^{\circ}C$).

• Journal of Powder Materials
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• v.23 no.6
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• pp.432-436
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• 2016

We investigate the microstructural and magnetic property changes of $DyH_2$, $Cu+DyH_2$, and $Al+DyH_2$ diffusion-treated NdFeB sintered magnets with the post annealing (PA) temperature. The coercivity of all the diffusion-treated magnets increases with increasing heat treatment temperature except at $910^{\circ}C$, where it decreases slightly. Moreover, at $880^{\circ}C$, the coercivity increases by 3.8 kOe in Cu and 4.7 kOe in Al-mixed $DyH_2$-coated magnets, whereas this increase is relatively low (3.0 kOe) in the magnet coated with only $DyH_2$. Both Cu and Al have an almost similar effect on the coercivity improvement, particularly over the heat treatment temperature range of $790-880^{\circ}C$. The diffusivity and diffusion depth of Dy increases in those magnets that are treated with Cu or Al-mixed $DyH_2$, mainly because of the comparatively easy diffusion path provided by Cu and Al owing to their solubility in the Nd-rich grain boundary phase. The formation of a highly anisotropic $(Nd,\;Dy)_2Fe_{14}B$ phase layer, which acts as the shell in the core-shell-type structure so as to prevent the reverse domain movement, is the cause of enhanced coercivity of diffusion-treated Nd-Fe-B magnets.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.40.2-40.2
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• 2007

• Journal of the Korean Ceramic Society
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• v.23 no.5
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• pp.55-60
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• 1986

A mechanism for formation of surface reoxidation layer in Surface Boundary Layer Capacitor (SBLC) has been studied. SBLC were prepared by reduction of $BaTiO_3$ doped with $Bi_2O_3$ and electrode firing of silver paste containing $Bi_2O_3$ The apparent dielectric constant was in the order of $10^5$ and the insulation resistance larger than $10^6$$\Omega$ It can be expected that $Bi_2O_3$ dopant in $BaTiO_3$ plays the role of inhibition of grain growth and decreasing the resistivity of $BaTiO_3$. In order to confirm the process of surface reoxidation layer effects of atmosphere and annealing time in electrode sintering were investigated.

• Journal of the Korean Ceramic Society
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• v.24 no.1
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• pp.63-69
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• 1987

Effect of MoO3 additiion on the semiconductive BaTiO3 ceramics doped with 0.2 mole% Nb2O5 and their frequency characteristics have been investigated on the view of intergranular barrier layer model through the observation of changes in their electrical properties. The resistivity increases with the increase of MoO3 addition, but the capacitance, the frequency dependence of capacitance and the effect of positive temperature coefficient of resistivity (PTCR) decrease. It is explained by the possible increase in the thickness of potential barrier due to the formation of insulating layer and thus decrease in the degree of energy band bending. Both the PTCR effect and resistivity decrease with the increase of frequency due to the possible elimination of barrier layer at the grain boundary.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1418-1420
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• 2003

In this study capacitance and dielectric loss tan${\delta}$were measured with frequency changes for commercial $Z_nO$ varistors with pin-type leads and equivalent circuit simulation was proposed. The leakage inductance in pin leads and the stray caoacitance could be seperated from the dielectric characteristics of $Z_nO$ varistors by the simulation of equivalent circuit. The equivalent circuit model considered semiconduction layer, dielectric layer and depletion layer as the grain boundary structure of varistor is well fitted to the observed data.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.252.1-252.1
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• 2013

Hexagonal boron nitride (h-BN) is a two dimensional material which has high band-gap, flatness and inert properties. This properties are used various applications such as dielectric for electronic device, protective coating and ultra violet emitter so on. 1) In this report, we were growing h-BN sheet directly on sapphire 2"wafer. Ammonia borane (H3BNH3) and nickel were deposited on sapphire wafer by evaporate method. We used nickel film as a sub catalyst to make h-BN sheet growth. 2) During annealing process, ammonia borane moved to sapphire surface through the nickel grain boundary. 3) Synthesized h-BN sheet was confirmed by raman spectroscopy (FWHM: ~30cm-1) and layered structure was defined by cross TEM (~10 layer). Also we controlled number of layer by using of different nickel and ammonia borane thickness. This nickel film supported h-BN growth method may propose fully and directly growing on sapphire. And using deposited ammonia borane and nickel films is scalable and controllable the thickness for h-BN layer number controlling.