• Applied Science and Convergence Technology
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• v.24 no.6
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• pp.268-272
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• 2015

We report the systematic study to reduce extrinsic doping in graphene grown by chemical vapor deposition (CVD). To investigate the effect of crystallinity of graphene on the extent of the extrinsic doping, graphene samples with different levels of crystal quality: poly-crystalline and single-crystalline graphene (PCG and SCG), are employed. The graphene suspended in air is almost undoped regardless of its crystallinity, whereas graphene placed on an $SiO_2/Si$ substrate is spontaneously p-doped. The extent of p-doping from the $SiO_2$ substrate in SCG is slightly lower than that in PCG, implying that the defects in graphene play roles in charge transfer. However, after annealing treatment, both PCG and SCG are heavily p-doped due to increased interaction with the underlying substrate. Extrinsic doping dramatically decreases after annealing treatment when PCG and SCG are placed on the top of hexagonal boron nitride (h-BN) substrate, confirming that h-BN is the ideal substrate for reducing extrinsic doping in CVD graphene.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.284-284
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• 2013

중 에너지 이온 산란 분석법(Medium Energy Ion Scattering Spectrometer, MEIS)은 50~500 keV로 이온을 가속 후 시료에 입사시켜 시료의 원자와 핵간 충돌로 산란되는 일차이온의 에너지를 측정하여 시료를 분석하는 기법으로, 원자층의 깊이 분해능으로 초박막의 표면 계면의 조성과 구조를 분석 할수 있는 유용한 미세 분석기술이다. 본 실험에서 에너지 70~100 keV의 He+ 이온을 사용하여 Pulse Width 1 ns의 Pulsed ion beam을 만들어 Start 신호로 사용하고 Delay-line-detector에 검출된 신호를 End 신호를 이용한 TOF-MEIS System을 개발하였다. 활용 가능한 분석시편으로 Ultra thin film 시편으로 1, 1.5, 2, 2.5, 3, 4 nm의 HfO2, 1.8, 4nm의 SiO2 시편을 분석 하였으며 Ultra Shallow Junction 시편으로 As Doped Si, Cs Doped Si 시편 및 Composition, Core/shell 구조의 Q-dot 시편으로 CdSe, CdSe/ZnS등 다양한 분석 실험을 진행 하였다. Composition, Core/shell 구조의 Q-dot 시편은 Diamond Like Carbon(DLC)의 Substrate에 Mono-layer로 형성하여 분석하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.463-463
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• 2013

This paper reports the synthesis and characterization of ZnO:Ga nano-structures deposited on Au/SiNx/Si(001) by radio-frequency sputtering. The effect of the temperature on the microstructure of the as-grown ZnO:Ga thin films was examined. The growth mode of ZnO:Ga nano-structures can be explained by the profile coating, i.e. the ZnO nano-structures were formed with a morphological replica of Au seeds. Initially, the ZnO:Ga nano-structures were overgrown on top of Au nano-crystals. Small ZnO:Ga nano-dots were then nucleated on hexagonal ZnO:Ga discs.

• Journal of the Korean Society of Radiology
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• v.4 no.4
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• pp.5-10
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• 2010

The $Ca_2SiO_4$ phosphors doped by La with 0.1 wt%, 0.3 wt%, 0.5 wt%, and 1.0 wt% concentration were prepared by sintering at $1000^{\circ}C$ for 90 minutes in N2 atmosphere. The phosphors were ground in powdered form and were grouped in $100{\mu}m$ size, then the samples had been exposed to low energy X-ray and UV light. The TL glow curves were measured by heating the phosphors at $10^{\circ}C/s$ rate. There was no significantly meaningful correlation between the TL intensity and the doping level. The intensities of the TL peak measured from X-ray irradiated samples doped with 0.1 wt% were relatively strong. The activation energy and the frequency factor were 0.434 ~ 0.516 eV and 0.5 ~ 0.56, respectively. The intensities of the TL peak measured from UV irradiated samples doped with 0.3 wt% were relatively strong. The activation energy and frequency factor were 0.415 ~ 0.477 eV and 0.5 ~ 0.53, respectively. The TL process were found to be the 2nd order for both X-ray and UV irradiation. The TL intensity was increased linearly with the increase of the radiation dose. In summary, the $Ca_2SiO_4 phosphors developed in this study showed good TL characteristics at low energy X-ray and UV light. We believe they will be used as TLDs in near future for personal and environmental radiation detection dosimetry.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.159-166
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• 1999

The physical properties and microstructural changes with heat-treatment of opacified silica aerogels doped by TiO2 were investigated. Monolithic SiO2-TiO2 aerogels were prepared by supercritical drying (25$0^{\circ}C$, 1250 psig) of wet gel obtained by adding titanium isopropoxide to prehydrolyzed TEOS-isopropanol solutions. The density and the porosity of SiO2-10 mol% TiO2 aerogels were 0.23 g/㎤ and 90%, respectively. During supercritical drying, the linear shrinkage of aerogels increased with increase in the titanium content an TiO2 was transformed to the anatase phase as well as particls agglomerates led to TiO2 clusters of 100~800 nm dispersed homogeneoulsy in the silica matrix. The IR transmittance of opacified silica aerogels was very low in the region of wavelengths below 8 ${\mu}{\textrm}{m}$ compared with pure silica aerogels and SiO2-TiO2 aerogels showed the high thermal stability of microstructures up to $600^{\circ}C$.

• Applied Chemistry for Engineering
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• v.28 no.5
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• pp.565-570
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• 2017

Tobacco smoke emitted during smoking is divided into a main-stream and side-stream smoke. Most of the tobacco smoke that spreads to a room while smoking is a side-stream one. The side-stream tobacco smoke is two to three times more harmful than that of the main-stream tobacco smoke. In this study, the removal efficiency of CO, $H_2S$, $NH_3$ and HCHO in a side-stream tobacco smoke using the doping component of $TiO_2$ photocatalysts was confirmed. As a result, CO was removed up to 78.37%, which indicated that the $TiO_2$ photocatalytic process is effective for CO removal. Also, the removal efficiencies of CO, $H_2S$ and HCHO were greatly affected by the amount of doped O and Si components of the $TiO_2$ photocatalyst. In conclusion, the more doped O and Si components had, the higher removal efficiencies of harmful substances were achieved.

• Korean Journal of Materials Research
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• v.29 no.6
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• pp.356-362
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• 2019

$BaSiO_3:RE^{3+}$ (RE = Sm or Eu) phosphor powders with different concentrations of activator ions are synthesized using the solid-state reaction method. The effects of the concentration of activator ions on the structural, photoluminescent, and morphological properties of the barium silicate phosphors are investigated. X-ray diffraction data reveals that the crystal structure of all the phosphors, regardless of the type and the concentration of the activator ions, is an orthorhombic system with a main (111) diffraction peak. The grain particles agglomerate together to form larger clusters with increasing concentrations of activator ions. The emission spectra of the $Sm^{3+}$-doped $BaSiO_3$ phosphors under excitation at 406 nm consist of an intense orange band at 604 nm and three weak bands centered at 567, 651, and 711 nm, respectively. As the concentration of $Sm^{3+}$ increases from 1 to 5 mol%, the intensities of all the emission bands gradually increase, reach maxima at 5 mol% of $Sm^{3+}$ ions, and then decrease significantly with further increases in the $Sm^{3+}$ concentration due to the concentration quenching phenomenon. For the $Eu^{3+}$-doped $BaSiO_3$ phosphors, a strong red emission band at 621 nm and several weak bands are observed. The optimal orange and red light emissions of the $BaSiO_3$ phosphors are obtained when the concentrations of $Sm^{3+}$ and $Eu^{3+}$ ions are 5 mol% and 15 mol%, respectively.

• Proceedings of the Korean Magnestics Society Conference
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• 2005.06a
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• pp.200-201
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• 2005

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.446-446
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• 2011

One dimensional (1-D) structures of ZnO nanorods are promising elements for future optoelectronic devices. However there are still many obstacles in fabricating high-quality p-type ZnO up to now. In addition, it is limited to measure the degree of the doping concentration and carrier transport of the doped 1-D ZnO with conventional methods such as Hall measurement. Here we demonstrate the measurement of the electronic properties of p- and n-doped ZnO nanorods by the Kelvin probe force microscopy (KPFM). Vertically aligned ZnO nanorods with intrinsic n-doped, As-doped p-type, and p-n junction were grown by vapor phase epitaxy (VPE). Individual nanowires were then transferred onto Au films deposited on Si substrates. The morphology and surface potentials were measured simultaneously by the KPFM. The work function of the individual nanorods was estimated by comparing with that of gold film as a reference, and the doping concentration of each ZnO nanorods was deduced. Our KPFM results show that the average work function difference between the p-type and n-type regions of p-n junction ZnO nanorod is about ~85meV. This value is in good agreement with the difference in the work function between As-doped p- and n-type ZnO nanorods (96meV) measured with the same conditions. This value is smaller than the expected values estimated from the energy band diagram. However it is explained in terms of surface state and surface band bending.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.8
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• pp.852-858
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• 2004

An alkoxide-based sol-gel method was used to fabricate $Ba_{0.6}Sr_{0.4}TiO_{3}$thin films doped by Bi from 5 to 20 mol% on a Pt/Ti/$SiO_2$/Sisubstrate. The structural and dielectric properties of BST thin films were investigated as a function of Bi dopant concentration. The dielectric properties of the Bi doped BST films were strongly dependent on the Bi contents. The dielectric constant and dielectric loss of the films decreased with increasing Bi content. However, the leakage current density of the 10 mol% Bi doped $Ba_{0.6}Sr_{0.4}TiO_{3}$ thin film showed the lowest value of 5.13$\times 10^{-7} A/{cm}^2$ at 5 V. The figure of merit (FOM) reached a maximum value of 32.42 at a 10 mol% Bi doped $Ba_{0.6}Sr_{0.4}TiO_{3}$thin films. The dielectric constant, loss factor, and tunability of the 10 mol% Bi doped $Ba_{0.6}Sr_{0.4}Tio_{3}$ thin films were 333, 0.0095, and 31.1%, respectively.