• Journal of the Korean Chemical Society
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• v.29 no.2
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• pp.111-120
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• 1985

The oxidation reaction of CO on the catalysts 4 mol%, 8 mol%, and 12 mol% Cd-doped ${\alpha}-Fe_2O_3$ is individually investigated. Regardless of Cd doping level, over-all reaction order for the oxidation of CO is 1.5; the first order with respect to CO and the one-half order with respect to $O_2$. Over the temperature range of 350∼$460^{\circ}C$, the activation energy for CO oxidation is 10.10∼11.30Kcal/mol. From the agreement between the kinetic data and conductivity measurements, the reaction mechanism is suggested. Especially from the effect of Cd doping, the fact that catalytic activity of ${\alpha}-Fe_2O_3$ is due to the excitation of electrons which are traped on oxygen vacancy is found, and the adsorption sites for reactant molecules are found.

• Korean Journal of Materials Research
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• v.18 no.8
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• pp.450-453
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• 2008

Mg-doped and In-Mg co-doped p-type GaN epilayers were grown in a low-pressure metal organic chemical vapor deposition technique. The effect of In doping on the p-GaN layer was studied through photoluminescence (PL), persistent photoconductivity (PPC), and transmission electron microscopy (TEM) at room temperature. For the In-doped p-GaN layer, the PL intensity increases significantly and the peak position shifts to 3.2 eV from 2.95 eV of conventional p-GaN. Additionally, In doping greatly reduces the PPC, which was very strong in conventional p-GaN. A reduction in the dislocation density is also evidenced upon In doping in p-GaN according to TEM images. The improved optical properties of the In-doped p-GaN layer are attributed to the high crystalline quality and to the active participation of incorporated Mg atoms.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.12
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• pp.949-955
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• 2010

Nd and Ti co-doped bismuth ferrite $(Bi_{1-x}Nd_x)(Fe_{1-y}Ti_y)O_3$ (x, y = 0, 0.05, 0.1, 0.2) ceramics and thin films were synthesized through the conventional mixed-oxide process and pulsed laser deposition (PLD), respectively. Nd and Ti co-doping effect was examined with emphasis on how these impurities affect phase formation behavior as there could be the improvement in leakage current problems often associated with multiferroic $BiFeO_3$ (BFO) thin films. The lattice constants of BFO ceramics decreased with Nd doping concentration up to 10mol%, while they further decreased with Nd and Ti co-doping to about 20%. BFO thin films obtained by the PLD process revealed random polycrystalline structure. Similar to bulk BFO ceramic, Nd and Ti co-doping effectively suppressed the formation of unwanted secondary phase and thus stabilized the perovskite phase in BFO thin films.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.436-439
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• 2000

Change of dielectric loss of use in high relative permitivity capacitor BaTiO$_3$ ceramic depends on Mn doping have been investigated. The powders used in this study were commercial BaTiO$_3$, TiO$_2$and, MnCO$_3$. Sample was fabricated by conventional ceramic process. The quantity of Mn was changed gradually from 0.lmol% to 10mo1%. The sintering densities were reduced with increasing amount of MnCO$_3$. This result is because of increase of low density second phase BaMnO$_3$. When the samples were doped by over 0.2mol% of MnCO$_3$, average grain sizes were enlarge to several tens ${\mu}{\textrm}{m}$. The dielectric losses were reduced by Mn doping to lmol% but, increased from lmol% to 10mo1% gradually.

• Progress in Superconductivity and Cryogenics
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• v.20 no.1
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• pp.28-31
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• 2018

Phase diagrams of electron- and hole-doped $Sr_2VO_3FeAs$ are investigated using Co and Mn substitution at Fe site. Metallic nature survives only for Co (electron) doping, not for Mn (hole) doping. The conductivity of $Sr_2VO_3(Fe,M)As$ (M=Mn,Co) is sensitive to the structural modification of FeAs microstructure rather than carrier doping. This finding implies that the FeAs layer plays a dominant role on the charge conduction, thus the $SrVO_3$ layers should be considered as an insulating block. Also, we found that the superconductivity is rapidly suppressed by both dopants. This result is different from the conventional behavior that superconductivity is induced by doping in the most of Fe pnictides. Our finding strongly supports the uniqueness of $Sr_2VO_3FeAs$ among the Fe pnictide superconductors.

• Journal of the Korean Ceramic Society
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• v.37 no.6
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• pp.612-616
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• 2000

The effect of Co dopant on the (La, Sr)MnO3 cathode was investigated. La2Zr2O7 and SrZrO3 were formed as the reaction products between YSZ and LSMC. The reactivity of LSMC with YSZ increased with increasing Co content. However, the cathodic polarization resistance decreased with increasing Co doping. Therefore, doping Co at Mn site in the (La, Sr)MnO3 cathode was effective on controlling the polarization resistance of the cathode. The polarization property of LSMC-YSZ composite(60 wt%: 40 wt%) cathode was better than that of LSMC single cathode.

• Korean Journal of Materials Research
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• v.19 no.11
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• pp.607-612
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• 2009

We investigated the effects of Co doping on the NO gas sensing characteristics of ZnO-carbon nanotube (ZnO-CNT) layered composites fabricated by coaxial coating of single-walled CNTs with ZnO using pulsed laser deposition. Structural examinations clearly confirmed a distinct nanostructure of the CNTs coated with ZnO nanoparticles of an average diameter as small as 10 nm and showed little influence of doping 1 at.% Co into ZnO on the morphology of the ZnO-CNT composites. It was found from the gas sensing measurements that 1 at.% Co doping into ZnO gave rise to a significant improvement in the response of the ZnO-CNT composite sensor to NO gas exposure. In particular, the Co-doped ZnO-CNT composite sensor shows a highly sensitive and fast response to NO gas at relatively low temperatures and even at low NO concentrations. The observed significant improvement of the NO gas sensing properties is attributed to an increase in the specific surface area and the role as a catalyst of the doped Co elements. These results suggest that Co-doped ZnOCNT composites are suitable for use as practical high-performance NO gas sensors.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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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.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.292-292
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• 2016

Transition metal dichalcogenides (TMDs) with a two-dimensional layered structure have been considered highly promising materials for next-generation flexible, wearable, stretchable and transparent devices due to their unique physical, electrical and optical properties. Recent studies on TMD devices have focused on developing a suitable doping technique because precise control of the threshold voltage ($V_{TH}$) and the number of tightly-bound trions are required to achieve high performance electronic and optoelectronic devices, respectively. In particular, it is critical to develop an ultra-low level doping technique for the proper design and optimization of TMD-based devices because high level doping (about $10^{12}cm^{-2}$) causes TMD to act as a near-metallic layer. However, it is difficult to apply an ion implantation technique to TMD materials due to crystal damage that occurs during the implantation process. Although safe doping techniques have recently been developed, most of the previous TMD doping techniques presented very high doping levels of ${\sim}10^{12}cm^{-2}$. Recently, low-level n- and p-doping of TMD materials was achieved using cesium carbonate ($Cs_2CO_3$), octadecyltrichlorosilane (OTS), and M-DNA, but further studies are needed to reduce the doping level down to an intrinsic level. Here, we propose a novel DNA-based doping method on $MoS_2$ and $WSe_2$ films, which enables ultra-low n- and p-doping control and allows for proper adjustments in device performance. This is achieved by selecting and/or combining different types of divalent metal and trivalent lanthanide (Ln) ions on DNA nanostructures. The available n-doping range (${\Delta}n$) on the $MoS_2$ by Ln-DNA (DNA functionalized by trivalent Ln ions) is between $6{\times}10^9cm^{-2}$ and $2.6{\times}10^{10}cm^{-2}$, which is even lower than that provided by pristine DNA (${\sim}6.4{\times}10^{10}cm^{-2}$). The p-doping change (${\Delta}p$) on $WSe_2$ by Ln-DNA is adjusted between $-1.0{\times}10^{10}cm^{-2}$ and $-2.4{\times}10^{10}cm^{-2}$. In the case of Co-DNA (DNA functionalized by both divalent metal and trivalent Ln ions) doping where $Eu^{3+}$ or $Gd^{3+}$ ions were incorporated, a light p-doping phenomenon is observed on $MoS_2$ and $WSe_2$ (respectively, negative ${\Delta}n$ below $-9{\times}10^9cm^{-2}$ and positive ${\Delta}p$ above $1.4{\times}10^{10}cm^{-2}$) because the added $Cu^{2+}$ ions probably reduce the strength of negative charges in Ln-DNA. However, a light n-doping phenomenon (positive ${\Delta}n$ above $10^{10}cm^{-2}$ and negative ${\Delta}p$ below $-1.1{\times}10^{10}cm^{-2}$) occurs in the TMD devices doped by Co-DNA with $Tb^{3+}$ or $Er^{3+}$ ions. A significant (factor of ~5) increase in field-effect mobility is also observed on the $MoS_2$ and $WSe_2$ devices, which are, respectively, doped by $Tb^{3+}$-based Co-DNA (n-doping) and $Gd^{3+}$-based Co-DNA (p-doping), due to the reduction of effective electron and hole barrier heights after the doping. In terms of optoelectronic device performance (photoresponsivity and detectivity), the $Tb^{3+}$ or $Er^{3+}$-Co-DNA (n-doping) and the $Eu^{3+}$ or $Gd^{3+}$-Co-DNA (p-doping) improve the $MoS_2$ and $WSe_2$ photodetectors, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.134-137
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• 2004

새로운 리튬 2차전지용 양극활물질인 Li[NiMnCo]O2를 간단히 합성할 수 있는 방법과 Si의 doping에 의해 그 특성을 향상하였다. 원하는 당량비의 Li, Ni, Co, Mn의 nitrate를 고순도의 에탄올에 용해하고 여기에 Si의 원료물질로서 poly(methyl phenyl siloxane)을 원하는 양(전체 전이금속 이온의 $2{\sim}10\;mol%$)만큼 첨가한 후 약 30분 정도 교반하였다. 이 용액을 약 $70{\sim}80^{\circ}C$ 정도의 온도에서 고점도의 진흙 상태가 될 정도로 가열하고 $450{\sim}500^{\circ}C$의 온도에서 약 5시간 정도 열처리 하여 유기물이 없는 상태의 전구체를 제조하였다. 이 전구체를 분말형태로 분쇄하고 $600{\sim}650^{\circ}C$ 정도의 온도에서 3시간, $900{\sim}950^{\circ}C$ 정도의 온도에서 5시간 연속적으로 열처리 하여 최종 활물질을 제조하였다. 이렇게 제조된 활물질은 175mAh/g 정도의 높은 비용량을 나타내었으며 4.5V 충전 조건에도 우수한 수명특성을 나타내었다. Si이 doping되지 않은 활물질에 비해 Si이 doping된 물질은 율특성, 수명특성에서 보다 우수한 특성을 나타내었는데 이것은 층상구조 활물질의 격자상수 증가와 impedance 증가 억제에 기인한 것으로 분석되었다.