• 한국전기전자재료학회논문지
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• 제20권6호
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• pp.487-490
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• 2007

In this paper, the formation and thermal stability characteristics of Ni silicide using Ni-V alloy on Boron cluster ($B_{18}H_{22}$) implanted bulk and SOI substrate were examined in comparison with pure Ni for nano-scale CMOSFET. The Ni silicide using Ni-V alloy on $B_{18}H_{22}$ implanted SOI substrate after high temperature post-silicidation annealing showed the lower sheet resistance, no agglomeration interface image and lower surface roughness than that using pure Ni. The thermal stability of Ni silicide was improved by using Ni-V alloy on $B_{18}H_{22}$ implanted SOI substrate.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.170.1-170.1
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• 2016

$Bi_2Te_3$ has long been studied for its excellent thermoelectric characteristics. Recently, this material has been known as a topological insulator (TI). The surface states within the bulk band gap of a TI, which are protected by the time reversal symmetry, contribute to the conduction at the surface, while the bulk is in insulating state. In contrast to the bulk defects tuning the chemical potential to the Dirac energy, the native defects near the surface are expected not to change the shape of the Fermi surface and the related spin structure. Using scanning tunneling microscopy (STM), we have systematically characterized surface or near surface defects in p- and n- doped $Bi_2Te_3$, and identified their structure by first principles calculations. In addition, bias-polarity dependences of STM images revealed the electron donor/acceptor nature of each defect. A detailed theoretical study of the surface states near the Dirac energy reveals the robustness of the Dirac point, which verifies the effectiveness of the disturbance on the backscattering from various kinds of defects.

• 한국분말재료학회지
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• 제21권3호
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• pp.207-214
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• 2014

In this study, nano-scale copper powders were reduction treated in a hydrogen atmosphere at the relatively high temperature of $350^{\circ}C$ in order to eliminate surface oxide layers, which are the main obstacles for fabricating a nano/ultrafine grained bulk parts from the nano-scale powders. The changes in composition and microstructure before and after the hydrogen reduction treatment were evaluated by analyzing X-ray diffraction (XRD) line profile patterns using the convolutional multiple whole profile (CMWP) procedure. In order to confirm the result from the XRD line profile analysis, transmitted electron microscope observations were performed on the specimen of the hydrogen reduction treated powders fabricated using a focused ion beam process. A quasi-statically compacted specimen from the nano-scale powders was produced and Vickers micro-hardness was measured to verify the potential of the powders as the basis for a bulk nano/ultrafine grained material. Although the bonding between particles and the growth in size of the particles occurred, crystallites retained their nano-scale size evaluated using the XRD results. The hardness results demonstrate the usefulness of the powders for a nano/ultrafine grained material, once a good consolidation of powders is achieved.

• 한국정밀공학회지
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• 제21권10호
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• pp.7-13
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• 2004

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1154-1155
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• 2008

본 연구에서는 전자 주개 물질(electron donor)인 regioregular poly(3-hexylthiophene)(P3HT)와 전자 받개 물질(electron acceptor)인 phenyl-$C_{61}$-butyric acid methyl ester (PCBM)을 혼합한 복합 박막 구조(Bulk Heterojunction)를 이용하여 태양전지를 제작하고 광활성층(Active layer)의 두께를 변화시키면서 광학적 특성 및 전기적 특성에 대해 분석하였다. 광활성층의 두께가 두꺼워 질수록 광흡수율이 높기 때문에 태양전지의 효율이 증가하여 200nm정도의 두께에서 가장 좋은 특성을 보였으며, 그 이상의 두께에서는 광흡수율이 높더라도 직렬저항(Series resistance)의 증가로 개방 회로 전압이 감소하는 것을 볼 수 있었으며, 최적화된 광활성층의 두께(190nm)에서 개방 회로 전압($V_{oc}$)은 0.6V, 단락 회로 전류($J_{sc}$)는 8.29mA, Fill factor(FF)는 0.59, 전력변환효율($\eta$)은 2.94%였다.

• 한국분말재료학회지
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• 제14권1호
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• pp.26-31
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• 2007

Manufacturing bulk nanostructured materials with least grain growth from initial powders is challenging because of the bottle neck of bottom-up methods using the conventional powder metallurgy of compaction and sintering. In this study, bottom-up type powder metallurgy processing and top-down type SPD (Severe Plastic Deformation) approaches were combined in order to achieve both real density and grain refinement of metallic powders. ECAP (Equal Channel Angular Pressing), one of the most promising processes in SPD, was used for the powder consolidation method. For understanding the ECAP process, investigating the powder density as well as internal stress, strain distribution is crucial. We investigated the consolidation and plastic deformation of the metallic powders during ECAP using the finite element simulations. Almost independent behavior of powder densification in the entry channel and shear deformation in the main deformation zone was found by the finite element method. Effects of processing parameters on densification and density distributions were investigated.

• Journal of Welding and Joining
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• 제27권6호
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• pp.43-48
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• 2009

In this study, Cu-based bulk metallic glass (BMG) coatings were deposited by atmospheric plasma spraying (APS) process with different process conditions (with- and without hydrogen gas). As adding the hydrogen gas, thermal energy in the plasma flame increased and induced difference in the melting state of the Cu-based BMG particles. The microstructure and mechanical properties of the coatings were analyzed using a scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) and nano-indentation tester in the light of phase analysis. It was elucidated by the nano-indentation tests that un-melted region was a mainly amorphous phase which showed discrete plasticity observed as the flow serrations on the load.displacement (P - h) curves, and the curves of solidified region showed lower flow serrations as amorphous phase mingled with crystalline phase. Oxides produced during the spraying process had the highest hardness value among the phases and were well mixed with other phases resulted from the increase in melting degree.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2007년도 The 1st International Symposium on Advanced Magnetic Materials
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• pp.180.1-180.1
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• 2007

• Smart Structures and Systems
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• 제23권2호
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• pp.141-153
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• 2019

This research deals with wave propagation of the functionally graded (FG) nano-beams based on the nonlocal elasticity theory considering surface and flexoelectric effects. The FG nano-beam is resting in Winkler-Pasternak foundation. It is assumed that the material properties of the nano-beam changes continuously along the thickness direction according to simple power-law form. In order to include coupling of strain gradients and electrical polarizations in governing equations of motion, the nonlocal non-classical nano-beam model containg flexoelectric effect is used. Also, the effects of surface elasticity, dielectricity and piezoelectricity as well as bulk flexoelectricity are all taken into consideration. The governing equations of motion are derived using Hamilton principle based on first shear deformation beam theory (FSDBT) and also considering residual surface stresses. The analytical method is used to calculate phase velocity of wave propagation in FG nano-beam as well as cut-off frequency. After verification with validated reference, comprehensive numerical results are presented to investigate the influence of important parameters such as flexoelectric coefficients of the surface, bulk and residual surface stresses, Winkler and shear coefficients of foundation, power gradient index of FG material, and geometric dimensions on the wave propagation characteristics of FG nano-beam. The numerical results indicate that considering surface effects/flexoelectric property caused phase velocity increases/decreases in low wave number range, respectively. The influences of aforementioned parameters on the occurrence cut-off frequency point are very small.

• Elastomers and Composites
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• 제34권1호
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• pp.45-52
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• 1999

본 논문에서는 미세 상분리된 블럭 공중합체 박막의 특이상에서 금 입자들이 어떻게 자기응집(self assemble) 되고 잘 배열된 패턴을 형성하는지를 살펴보았다. 본 연구에서는 원통형 모폴로지를 갖는 PS-PB-PS 삼블럭 공중합체(30wt% PS) 박막(${\sim}100nm$)을 0.1wt% 톨루엔 용액으로부터 캐스팅하여 고분자 박막 형판(template)으로 사용하였다. 각각의 상이한 용매 증발조건으로부터 PB matrix내에 수평배열 PS cylinder와 수직 PS cylinder를 함께 갖는 막이 얻어졌다. 블럭 공중합체박막의 표면 및 bulk 몰폴로지를 살펴보기 위하여 단면투과전자현미경(TEM)을 사용하였다. Nano-scale 패턴을 얻기 위하여는 소량의 금입자를 블럭 공중합체 박막상에 증발시켰다. 캐스팅된 상태 그 대로의 박막형판이 사용되어질때 금입자들은 표면 장력이 적은 PB상에 우선적으로 자기응집(self as-semble)하여 비교적 잘 배열된 nano-scale의 패턴을 형성하였다. 그러나 열처리(annealing)에 의하여 표면장력이 적은 PB-rich충이 형성된 후에는 금입자의 자기응집에 의한 패턴은 관찰되지 않았다.