• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
• /
• pp.119-119
• /
• 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.

• 폴리머
• /
• 제38권1호
• /
• pp.38-42
• /
• 2014

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)]와 graphene oxide(GO)를 혼합하여 WPF-6-oxy-F-GO를 제조한 후 공기 중에서 감마선을 조사하였다. WPF-6-oxy-F-GO 복합재는 유기태양전지(organic solar cells, OSCs)의 정공수송층(hole transporting layer, HTL)으로서 적용하였다. GO와 비교해 보았을 때, 조사된 WPF-6-oxy-F-GO의 면저항(sheet resistance, $R_{sheet}$)은 약 2배 정도 감소하였다. 이는 감마선 조사를 통하여 WPF-6-oxy-F와 GO 사이의 C-N 결합의 형성으로 인한 ${\pi}-{\pi}$ 공유 결합의 영향과 효율적인 packing 때문이다. 결과적으로, 조사된 WPF-6-oxy-F-GO를 정공수송층으로 적용하였을 때 유기태양전지의 효율은 6.10%까지 증가하였다. 수용성 고분자 WPF-6-oxy-F-GO는 정공수송층으로서 사용되고 있는 PEDOT:PSS를 대체하는 대안 소재로서, 높은 효율과 저가의 유기태양전지를 구현할 수 있을 것으로 기대된다.

• 센서학회지
• /
• 제4권4호
• /
• pp.70-74
• /
• 1995

다공질 실리콘을 형성하는데 있어서 이방성 양극 반응 과정을 관찰하였다. 실험재료는 n형 기판 위에 $n^{+}$가 확산되고 그 위에 n에 피층이 있는 $n/n^{+}/n$ 구조의 (100) 실리콘 웨이퍼였다. 상충부 n실리콘 에피층을 식각하여 다공질 실리콘 층의 양극 반응 창을 내고 양극반응이 $n^{+}$매몰층까지만 일어나게 한다. 다공질 실리콘 층의 형성과정은 이방성이었다. 반응창의 형태들이 서로 다를 지라도 반응된 다공질 실리콘 영역의 모양은 모두 사각형 형태의 것이었다. 이 실험 결과는 다공질 실리콘 양극반응은 화학반응에 달려 있는 것이 아니고 전기전도 성질 즉 결정방향에 따른 정공의 서로 다른 전도도에 있다는 것을 보여 준다.

• 천문학논총
• /
• 제30권2호
• /
• pp.133-137
• /
• 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.

• 천문학회보
• /
• 제37권2호
• /
• pp.84.1-84.1
• /
• 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.

• 천문학회보
• /
• 제40권1호
• /
• pp.78.2-78.2
• /
• 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.

• 지질공학
• /
• 제28권1호
• /
• pp.1-9
• /
• 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.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1995년도 추계학술대회 논문집
• /
• pp.271-275
• /
• 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.

• 한국분말재료학회지
• /
• 제13권5호
• /
• pp.305-312
• /
• 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.

• 반도체디스플레이기술학회지
• /
• 제7권3호
• /
• pp.51-54
• /
• 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.