• Journal of Magnetics
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• 제12권3호
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• pp.103-107
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• 2007

Magnetic field induced structural transition has been systematically investigated for $La_{1-x}Ba_xMnO_3$ with the fine control of carrier doping $(0.15{\leq}x{\leq}0.20)$. Application of a magnetic field results in the suppression of the rhombohedral-orthorhombic transition temperature $(T_s)$ and the increase of insulator-metal transition temperature $(T_{MI})$. Near x = 0.17, where $T_S$ is similar to $T_{MI}$ at zero magnetic field, we found that the $T_S$ smoothly decreased with magnetic field even though it intersected the $T_{MI}$ near 3 T. Also, the magnetostructural phase diagram obtained from the temperature sweep and from the magnetic field sweep is not significantly modified. By comparing the magnetostructural transition in $La_{1-x}Sr_xMnO_3$, we have suggested that the large disorder originated from ionic size differences between La and Ba may weaken the sensitivity of the kinetic energy of $e_g$ electrons on the degree of lattice distortion in $La_{1-x}Ba_xMnO_3$.

• 한국분말재료학회지
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• 제12권6호
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• pp.399-405
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• 2005

Nanopowders of titanium dioxide $(TiO_2)$ incorporating the transition metal element(s) were synthesized by flame synthesis method. Single element among Fe(III), Cr(III), and Zn(II) was doped into the interior of $TiO_2$ crystal; bimetal doping of Fe and Zn was also made. The characteristics of transition-metal-doped $TiO_2$ nanopowders in the particle feature, crystallography and electronic structures were determined with various analytical tools. The chemical bond of Fe-O-Zn was confirmed to exist in the bimetal-doped $TiO_2$ nanopowders incorporating Fe-Zn. The transition element incorporated in the $TiO_2$ was attributed to affect both Ti 3d orbital and O 2p orbital by NEXAFS measurement. The bimetal-doped $TiO_2$ nanopowder showed light absorption over more wide wavelength range than the single-doped $TiO_2$ nanopowders.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.194.1-194.1
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• 2015

Transition metal dichalcogenide (TMD) with layered structure, has recently been considered as promising candidate for next-generation flexible electronic and optoelectronic devices because of its superior electrical, optical, and mechanical properties.[1] Scalability of thickness down to a monolayer and van der Waals expitaxial structure without surface dangling bonds (consequently, native oxides) make TMD-based thin film transistors (TFTs) that are immune to the short channel effect (SCE) and provide very high field effect mobility (${\sim}200cm^2/V-sec$ that is comparable to the universal mobility of Si), respectively.[2] In addition, an excellent photo-detector with a wide spectral range from ultraviolet (UV) to close infrared (IR) is achievable with using $WSe_2$, since its energy bandgap varies between 1.2 eV (bulk) and 1.8 eV (monolayer), depending on layer thickness.[3] However, one of the critical issues that hinders the successful integration of $WSe_2$ electronic and optoelectronic devices is the lack of a reliable and controllable doping method. Such a component is essential for inducing a shift in the Fermi level, which subsequently enables wide modulations of its electrical and optical properties. In this work, we demonstrate n-doping method for $WSe_2$ on poly-4-vinylphenol and poly (melamine-co-formaldehyde) (PVP/PMF) insulating layer and adjust the doping level of $WSe_2$ by controlling concentration of PMF in the PVP/PMF layer. We investigated the doping of $WSe_2$ by PVP/PMF layer in terms of electronic and optoelectronic devices using Raman spectroscopy, electrical measurements, and optical measurements.

• Journal of Magnetics
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• 제16권1호
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• pp.15-18
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• 2011

We have studied the $TiO_2$ doping effects on the flux pinning behavior of an $MgB_2$ superconductor synthesized by the in-situ solid-state reaction. From the field-cooled and zero-field-cooled temperature dependences of magnetization, the reversible-irreversible transition of $TiO_2$-doped $MgB_2$ was determined in the H-T diagram (the temperature dependence of upper critical magnetic field and irreversibility line). For comparison, the similar measurements are also obtained from SiC-doped $MgB_2$. The critical current density was estimated from the width of hysteresis loops in the framework of Bean's model at different temperatures. The obtained results manifest that nano-scale $TiO_2$ inclusions served as effective pinning centers and lead to the enhanced upper critical field and critical current density. It was concluded that the grain boundary pinning mechanism was realized in a $TiO_2$-doped $MgB_2$ superconductor.

• 마이크로전자및패키징학회지
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• 제29권4호
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• pp.63-69
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• 2022

이산화 바나듐은 금속-절연체 전이라는 독특한 특성으로 인해 기초적인 소재 연구 및 산업에의 응용을 위한 연구가 꾸준하게 진행되고 있다. 본 연구에서는 통전활성소결법으로 제조한 이산화 바나듐의 금속-절연체 전이 특성에 마그네슘과 텅스텐 첨가가 미치는 영향을 연구하였으며, 덩어리 시편을 대상으로 그 거동을 고찰하였다. 상용 분말과 통전활성소결법을 이용하여 열처리를 진행하여 제작한 시편의 경우 격자 상수의 변화는 크지 않고 이차상이 존재하였으며, 이로 인해 상전이 온도는 64.2-64.6℃에 분포하는 것으로 나타났다. 반면 불순물의 종류와 함량에 따라 전기전도도는 최대 2.4배 증가하거나 최대 57.4배 감소하는 거동을 나타냈다. 열전도도는 불순물의 첨가에 따라 증가하는 거동을 나타냈으며, 상전이 온도 이전에서는 1.8~2.5 W/m·K, 성전이 온도 이후에서는 1.9~2.8 W/m·K의 값을 가졌다. 이러한 물성 변화는 불순물의 첨가로 인한 전하 나르개 농도의 변화, 불순물의 산란중심, 미세구조의 변화 등이 복합적으로 작용한 결과로 해석할 수 있다.

• Applied Science and Convergence Technology
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• 제27권5호
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• pp.90-94
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• 2018

The electron band structure of manganese-adsorbed graphene on an SiC(0001) substrate has been studied using angle-resolved photoemission spectroscopy. Upon introducing manganese atoms, the conduction band of graphene, that is observed in pristine graphene indicating intrinsic electron-doping by the substrate, completely disappears and the valence band maximum is observed at 0.4 eV below Fermi energy. At the same time, the slope of the valence band decreases by the presence of manganese atoms, approaching the electron band structure calculated using the local density approximation method. The former provides experimental evidence of the formation of nearly free-standing graphene on an SiC substrate, concomitant with a metal-to-insulator transition. The latter suggests that its electronic correlations are efficiently screened, suggesting that the dielectric property of the substrate is modified by manganese atoms and indicating that electronic correlations in grpahene can also be tuned by foreign atoms. These results pave the way for promising device application using graphene that is semiconducting and charge neutral.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.142.2-142.2
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• 2013

The effect of substrate on catalytic activity of CO oxidation with transition metal Platinum nanoparticles on doped and undoped TiO2 was investigated. Titanium dioxide was doped chemically with non-metal anions including nitrogen and fluorine. Undoped TiO2 was synthesized via simple conventional sol-gel route. Thin films of titania were developed by spin coating technique and the characterization techniques SEM, XRD, UV-Vis Absorption Spectroscopy and XPS were carried out to examine the morphology of films, crystal phase, crystallites, optical properties and elemental composition respectively. XPS analysis from doped TiO2 confirmed that the nitrogen site were interstitial whereas fluorine was doped into TiO2 lattice substitutionally. Catalytic activity systems of Pt/doped-TiO2 and Pt/undoped-TiO2 were fabricated to reveal the strong metal-support interaction effect during catalytic activity of CO oxidation reactions. By arc plasma deposition technique, platinum nanoparticles with mean size of 2.7 nm were deposited on the thin films of doped and undoped titanium dioxide. The CO oxidation was performed with 40 Torr CO and 100 Torr O2 with 620 Torr He carrier gas. Turn over frequency was observed two to three folds enhancement in case of Pt/doped TiO2 as compared to Pt/TiO2. The electronic excitation and the oxygen vacancies that were formed with the doping process were the plausible reasons for the enhancement of catalytic activity.

• 마이크로전자및패키징학회지
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• 제30권4호
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• pp.32-43
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• 2023

저항 변화 메모리 소자(RRAM)는 저항 변화 특성을 기반으로 빠른 동작 속도, 간단한 소자 구조 및 고집적 구조의 구현을 통해 많은 양의 데이터를 효율적으로 처리할 수 있는 차세대 메모리 소자로 주목받고 있다. RRAM의 작동원리 중 하나로 알려진 interface type의 저항 변화 특성은 forming process를 수반하지 않고 소자 크기를 조절하여 낮은 전류에서 구동이 가능하다는 장점을 갖는다. 그 중에서도 전이 금속 산화물 기반 RRAM 소자의 경우, 정확한 물질의 조성 조절 방법과 소자의 신뢰성 및 안정성과 같은 메모리 특성을 향상시키기 위해 다양한 연구가 진행 중에 있다. 본 논문에서는 이종 원소의 도핑, 다층 박막의 형성, 화학적 조성 조절 및 표면 처리 등의 방법을 이용하여 interface type 저항 변화 특성의 저하를 방지하고 소자 특성을 향상시키기 위한 다양한 방법을 소개하고자 한다. 이를 통해 향상된 저항 변화 특성을 기반으로 한 고효율 차세대 비휘발성 메모리 소자의 구현 가능성을 제시한다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.33.1-33.1
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• 2011

Strontium doped lanthanum manganite (LSM) with perovskite structure for SOFC cathode material shows high electrical conductivity and good chemical stability, whereas the electrical conductivity at intermediate temperature below $800^{\circ}C$ is not sufficient due to low oxygen ion conductivity. The approach to improve electrical conductivity is to make more oxygen vacancies by substituting alkaline earths (such as Ca, Sr and Ba) for La and/or a transition metal (such as Fe, Co and Cu) for Mn. Among various cathode materials, $LaSrMnCuO_3$ has recently been suggested as the potential cathode materials for solid oxide fuel cells (SOFCs). As for the Cu doping at the B-site, it has been reported that the valence change of Mn ions is occurred by substituting Cu ions and it leads to formation of oxygen vacancies. The electrical conductivity is also affected by doping element at the A-site and the co-doping effect between A-site and B-site should be described. In this study, the $La_{1-x}Sr_xMn_{0.8}Cu_{0.2}O_{3{\pm}{\delta}}$ ($0{\leq}x{\leq}0.4$) systems were synthesized by a combined EDTA-citrate complexing process. The crystal structure, morphology, thermal expansion and electrical conductivity with different Sr contents were studied and their co-doping effects were also investigated.

• 대한화학회지
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• 제54권6호
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• pp.766-770
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• 2010

본 연구는 전이금속이 치환된 묽은 자성 반도체의 자기적 특성을 연구하였다. 울츠자이트(wurtzite) 구조를 가지는 화합물은 졸-겔(sol-gel)법을 이용하여 합성하였다. 열역학적 특성과 자기적 특성을 가진 $Zn_{1-x}Co_xO$은 단일상으로 나타났으며, 농도에 따라 다른 특성을 보여주었다. 묽은 자성 반도체의 특성을 조사하기 위해 X-ray diffraction (XRD), scanning electronic microscope (SEM) 및 vibrating sample magnetometer (VSM)을 사용하였다. 구조 분석을 통해 단일상이 확인된 시료에서는 모두 강자성 특성이 발견되었고, 전이금속 이온의 농도를 5%이상 치환이 되면 강자성이 감소하는 현상이 나타났다.