• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.119-119
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• 2011

This study examined the synthesis of large area graphene and the change of its characteristics depending on the ratio of CH4/H2 by using the thermal CVD methods and performed the experiments to control the electron-hole conduction and Dirac-point of graphene by using chemical doping methods. Firstly, with regard to the characteristics of the large area graphene depending on the ratio of CH4/H2, hydrophobic characteristics of the graphene changed to hydrophilic characteristics as the ratio of CH4/H2 reduces. The angle of contact also increased to 78$^{\circ}$ from 58$^{\circ}$. According to the results of Raman spectroscopy showing the degree of defect, the ratio of I(D)/I(G) increases to 0.42% from 0.25% and the surface resistance also increased to 950 ${\Omega}$ from 750 ${\Omega}$/sq. As for the graphene synthesis at the high temperature of 1,000$^{\circ}$ by using CH4/H2 in a Cu-Foil, the possibility of graphene formation was determined as a function of the ratio of H2 included in the fixed quantity of CH4 as per specifications of every equipment. It was observed that the excessive amount of H2 prevented graphene from forming, as extra H-atoms and molecules activated the reaction to C-bond of graphene. Secondly, in the experiment for the electron-hole conduction and the Dirac-point of graphene using the chemical doping method, the shift of Dirac-point and the change in the electron-hole conduction were observed for both the N-type (PEI) and the P-type (Diazonium) dopings. The ID-VG results show that, for the N-type (PEI) doped graphene, Dirac-point shifted to the left (-voltage direction) by 90V at an hour and by 130 V at 2 hours respectively, compared to the pristine graphene. Carrier mobility was also reduced by 1,600 cm2/Vs (1 hour) and 1,100 cm2/Vs (2 hours), compared to the maximum hole mobility of the pristine graphene.

• Polymer(Korea)
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• v.38 no.1
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• pp.38-42
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• 2014

The poly[(9,9-bis((6'-(N,N,N-trimethylammonium)hexyl)-2,7-fluorene)-alt-(9,9-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)-9-fluorene)) dibromide (WPF-6-oxy-F)] and graphene oxide (GO) was blended and irradiated with gamma ray under ambient condition. This WPF-6-oxy-F-GO composite was investigated as a hole-transporting layer (HTL) in organic solar cells (OSCs). Compared with the pristine GO, the sheet resistance ($R_{sheet}$) of irradiated WPF-6-oxy-F-GO was decreased about 2 orders of magnitude. The reason for the decrease of $R_{sheet}$ is the effect of efficient ${\pi}-{\pi}$ packing resulted from the formation of C-N bond between WPF6-oxy-F and GO. As a result, the efficiency of OSCs was dramatically enhanced ~ 6.10% by introducing irradiated WPF-6-oxy-F-GO as a HTL. WPF-6-oxy-F-GO is a sufficient candidate for HTL to facilitate the low-cost and high efficiency OSCs.

• Journal of Sensor Science and Technology
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• v.4 no.4
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• pp.70-74
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• 1995

We have observed anisotropic anodisation process for porous silicon formation. The starting material was (100) silicon $n/n^{+}/n$ wafer structured by $n^{+}$-diffusion on n-type substrate and by subsequent n-epitaxial growth. After the top n-silicon epitaxial layer was etched to open the porous silicon layer(PSL) anodisation window, anodisation takes place only to $n^{+}$-buried layer. The process of porous silicon formation on (100) sample was anisotropic, which was evident from that the shapes of the reacted porous silicon layer was all squarelike regardless of the shapes of reaction windows. The experimental results show that the PSL anodisation process does not depend on chemical reaction but does on electrical conduction property, which is hole mobility depending on the crystal direction.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.133-137
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• 2015

The Galactic center uniquely provides opportunities to resolve how star clusters form in neutral gas overdensities engulfed in a large-scale accretion flow. We have performed sensitive Green Bank 100m Telescope (GBT), Karl G. Jansky Very Large Array (JVLA), and Submillimeter Array (SMA) mapping observations of molecular gas and thermal dust emission surrounding the Galaxy's supermassive black hole (SMBH) Sgr $A^{\ast}$. We resolved several molecular gas streams orbiting the center on ${\gtrsim}10$ pc scales. Some of these gas streams appear connected to the well-known 2-4 pc scale molecular circumnuclear disk (CND). The CND may be the tidally trapped inner part of the large-scale accretion flow, which incorporates inflow via exterior gas filaments/arms, and ultimately feeds gas toward Sgr $A^{\ast}$. Our high resolution GBT+JVLA $NH_3$ images and SMA+JCMT 0.86 mm dust continuum image consistently reveal abundant dense molecular clumps in this region. These gas clumps are characterized by ${\gtrsim}100$ times higher virial masses than the derived molecular gas masses based on 0.86 mm dust continuum emission. In addition, Class I $CH_3OH$ masers and some $H_2O$ masers are observed to be well associated with the dense clumps. We propose that the resolved gas clumps may be pressurized gas reservoirs for feeding the formation of 1-10 solar-mass stars. These sources may be the most promising candidates for ALMA to probe the process of high-mass star-formation in the Galactic center.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.84.1-84.1
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• 2012

One of the most intriguing questions regarding black hole (BH)-galaxy co-evolution picture is how the BH accretion, or active galactic nucleus (AGN) activity is linked to star formation (SF) activity. While it is suggested that AGN luminosity of quasars correlates with SF luminosity, it is still unclear how AGN activity is connected to SF activity based on host galaxy properties. Utilizing AKARI's unique slit-less spectroscopic capability and wavelength coverage, we probed star formation activity of several types of AGNs by measuring the PAH 3.3 ${\mu}m$ emission. First, we detected the PAH 3.3 ${\mu}m$ emission from seven out of 27 Seyfert type-1 galaxies at z~0.36. While these galaxies deviate significantly from the local Mbh-${\sigma}$ relation meaning their black holes proceed the host galaxies in terms of evolution, they appear to follow the correlation between nuclear SF and AGN activities of local Seyfert type-1 galaxies. This implies that SF and AGN activities are directly connected at the nuclear region for these Seyfert type-1 AGNs. We also obtained 2-5 ${\mu}m$ spectra for subsamples of Quasar Spectroscopic Observation in Near-infrared Grism (QSONG) which consists of reverberation-mapped AGNs and PG-QSOs. We detected the PAH 3.3 ${\mu}m$ emission from 16 out of 31 reverberation-mapped AGNs and 10 out of 49 PG-QSOs and measured their line strengths. We present the correlations between SF and AGN activities and discuss if there is any dependency of the correlations on properties of host galaxies, such as morphology, or the presence of radio jets.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.78.2-78.2
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• 2015

Powered by a supermassive black hole, active galactic nuclei (AGNs) are characterized by prominent emission lines including Blamer lines. The unification scheme of AGNs requires the existence of a thick molecular torus that may hide the broad emission line region. In this configuration, it is expected that the far UV radiation from the central engine can be Raman scattered by neutral hydrogen to reappear around Balmer lines which can be identified observationally with broad Balmer wings. Another mechanism that can form Balmer wings is considered by invoking a fast moving medium around the central engine. In this presentation, we produce Balmer wings that are formed through Raman scattering and also those expected from a fast moving emission flow. It is noted that Raman Balmer wings exhibit stronger red part whereas the opposite behavior is seen in the Balmer wings obtained from a fast moving emission flow.

• The Journal of Engineering Geology
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• v.28 no.1
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• pp.1-9
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• 2018

We propose a borehole test technique to estimate permeability of rocks in borehole. The borehole tests are hydraulic injection tests such as leak-off test and hydraulic fracturing tests, which are originally conducted for stress or casing integrity assessment and not for permeability measurement. We use one-dimensional radial diffusion equation to interpret fluid injection test results in terms of permeability. We apply this technique to a leak-off test conducted at a depth of 700 m in a wellbore, where rock formation is mudstone. The estimated permeability is at an order of $10^{-16}m^2$, which is somewhat high but within the range reported for mudstones previously. Quantitative rick assessment suggests that an accurate measurement of open hole section length is important to improve reliability of results. More data may be needed to ensure the reliability of this technique. If validated, however, this technique can provide cost-effective estimation of in situ permeability without conducting independent permeability tests in borehole.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.271-275
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• 1995

Chip control is a major problem in automatic machining process, especially in finish operation. Chip breaker is one of the important factors to be determined for the scheme of chip control. As unbroken chips are grown, there deteriorate quality of the surface roughness and process automation can be carried out. In this study, to get rid of chip curling problem while turning internal hole, optimal chip breaker is selected form the experiment. The experiment is planned with Taguchi's method that is based on the orthogonal arrary of design factor. From the respose table, cutting speed, feedrate, depth of cut, and tool geometry are major factors affecting chip formation. Then, optmal chip breaker is selected and this is verified good enough for chip control from the experiment.

• Journal of Powder Materials
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• v.13 no.5 s.58
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• pp.305-312
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• 2006

Amorphous carbon nanotubes were synthesized by a reaction of benzene, ferrocene and Na mixture in a small autoclave at temperatures as low as $400^{\circ}C$. The resulting carbon nanotubes were short and straight, but their inner hole was filled with residual products. The addition of quartz to the reacting mixture considerably promoted the formation of carbon nanotubes. A careful examination of powder structure suggested that the nanotubes in this process were mainly formed by surface diffusion of carbon atoms at the surface of solid catalytic particles, not by VLS(vapor-liquid-solid) mechanism.

• Journal of the Semiconductor & Display Technology
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• v.7 no.3
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• pp.51-54
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• 2008

In this study, we investigated variations in undoped ZnO thin film properties with working pressure, $O_2$/Ar ratio, and annealing ambient. Higher vacuum pressure during deposition was observed to bring about slower growth rate resulting in samples with better crystallinity as well as hole generation efficiency through formation of shallower oxygen interstitial. Given that $O_2$/Ar ratio is greater than unity, O provided from the ambient to ZnO during annealing was found to preferably situate at interstitial sites. When He was used for the second annealing, significant changes were not observed. On the other hand, O ambient caused increased density of oxygen interstitial, thereby making the film more intrinsic-like high resistivity ZnO.