• 대한수학회보
• /
• 제55권1호
• /
• pp.227-237
• /
• 2018

In this paper, we study some geometric structures of a weakly cyclic Z-symmetric manifold (briefly, $[W CZS]_n$). More precisely, we prove that a conformally flat $[W CZS]_n$ satisfying certain conditions is special conformally flat and hence the manifold can be isometrically immersed in an Euclidean manifold $E^n+1$ as a hypersurface if the manifold is simply connected. Also we show that there exists a $[W CZS]_4$ with one parameter family of its associated 1-forms.

• 대한수학회보
• /
• 제42권1호
• /
• pp.5-15
• /
• 2005

The conharmonic transformation is a conformal trans-formation which satisfies a specified differential equation. Such a transformation was defined by Y. Ishii and we have generalized his results. Twisted product space is a generalized warped product space with a warping function defined on a whole space. In this paper, we partially classified the twisted product space and obtain a sufficient condition for a twisted product space to be locally Riemannian products.

• Kyungpook Mathematical Journal
• /
• 제58권4호
• /
• pp.761-779
• /
• 2018

The object of the present paper is to study weakly Z symmetric spacetimes $(WZS)_4$. At first we prove that a weakly Z symmetric spacetime is a quasi-Einstein spacetime and hence a perfect fluid spacetime. Next, we consider conformally flat $(WZS)_4$ spacetimes and prove that such a spacetime is infinitesimally spatially isotropic relative to the unit timelike vector field ${\rho}$. We also study $(WZS)_4$ spacetimes with divergence free conformal curvature tensor. Moreover, we characterize dust fluid and viscous fluid $(WZS)_4$ spacetimes. Finally, we construct an example of a $(WZS)_4$ spacetime.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2009년도 하계학술대회 논문집
• /
• pp.28-28
• /
• 2009

Fabrications of antireflection structures on solar cell were investigated to trap the light and to improve quantum efficiency. Introductions of patterned substrate or textured layer for Si solar cell were performed to prevent reflectance and to increase the path length of incoming light. However, it is difficult to deposit conformally flat electrode on perpendicular plane. ZnO is II-VI compound semiconductor and well-known wide band-gap material. It has similar electrical and optical properties as ITO, but it is nontoxic and stable. In this study, Al-doped ZnO thin films are deposited as transparent electrode by atomic layer deposition method to coat on Si substrate with micro-scale structures. The deposited AZO layer is flatted on horizontal plane as well as perpendicular one with conformal 200 nm thickness. The carrier concentration, mobility and resistivity of deposited AZO thin film on glass substrate were measured $1.4\times10^{20}cm^{-3}$, $93.3cm^2/Vs$, $4.732\times10^{-4}{\Omega}cm$ with high transmittance over 80%. The AZO films were coated with polyimide and performed selective polyimide stripping on head of column by reactive ion etching to measure resistance along columns surface. Current between the micro-columns flows onto the perpendicular plane of deposited AZO film with low resistance.

• 청정기술
• /
• 제22권3호
• /
• pp.203-207
• /
• 2016

Here, we report a novel fabrication technique for patchable organic lasing sheet based on non-volatile liquid organic semiconductors and freestanding polymeric film with high flexibility and patchability. For this work, we have fabricated the second-order DFB grating structure, which leads to surface emission, embedded in the freestanding polymeric film. Using an ultra-violet (UV) curable polyurethaneacrylate (PUA) mixture, the periodic DFB grating structure can be easily prepared on the freestanding polymeric film via a simple UV curing process. Due to unsaturated acrylate remained in the PUA mixture after UV curing, the freestanding PUA film provides adhesive properties, which enable mounting of the patchable organic lasing sheet onto non-flat surfaces with conformal contact. To achieve laser actions in the freestanding resonator structure, a composite material of liquid 9-(2-ethylhexyl)carbazole (EHCz) and organic laser dyes was used as the laser medium. Since the degraded active materials can be easily refreshed by a simple injection of the liquid composite, such a non-volatile liquid organic semiconducting medium has degradation-free and recyclable characteristics in addition to other strong advantages including tunable optoelectronic responses, solvent-free processing, and ultimate mechanical flexibility and uniformity. Lasing properties of the patchable organic lasing sheet were also investigated after mounting onto non-flat surfaces, showing a mechanical tunability of laser emission under variable surface curvature. It is anticipated that these results will be applied to the development of various patchable optoelectronic applications for light-emitting displays, sensors and data communications.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
• /
• pp.401-401
• /
• 2016

Although vertically aligned one-dimensional (1D) structure has been considered as efficient forms for photoelectrode, development of efficient 1D nanostructured photocathode are still required. In this sense, we recently demonstrated a simple fabrication route for CuInS2 (CIS) nanorod arrays from aqueous solution by template-assisted growth-and-transfer method and their feasibility as a photoelectrode for water splitting. In this study, we further evaluated the photoelectrochemical properties surface-modified CIS nanorod arrays. Surface modification with CdS and ZnS was performed by successive ion layer adsorption and reaction (SILAR) method, which is well known as suitable technique for conformal coating throughout nanoporous structure. With surface modification of CdS and ZnS, both photoelectrochemical performance and stability of CuInS2 nanorod arrays were improved by shifting of the flat-band potential, which was analyzed both onset potential and Mott-schottky plot.

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2008년도 International Meeting on Information Display
• /
• pp.86-88
• /
• 2008

Organosiloxane based spin on planarizing dielectrics (PTS-E and PTS-R) were developed for application in flat panel displays as a replacement to conformal chemical vapor deposited SiNx. Here we demonstrate the successful use of siloxane-based material as a passivation layer for active matrix $\alpha$-Si thin film transistors (TFT) on both rigid and flexible substrates.

• 한국정밀공학회지
• /
• 제20권5호
• /
• pp.218-224
• /
• 2003

This paper describes a novel MEMS integration technique on a CMOS chip. MEMS integration on CMOS circuit has many advantages in view of manufacturing cost and reliability. The surface topography of a CMOS chip from a commercial foundry has 0.9 ${\mu}{\textrm}{m}$ bumps due to the conformal coating on aluminum interconnect patterns, which are used for addressing each MEMS element individually. Therefore, it is necessary to achieve a flat mirror-like CMOS chip fer the microelectromechanical system (MEMS) such as micro mirror array. Such CMOS chip needs an additional thickness of the dielectric passivation layer to ease the subsequent planarization process. To overcome a temperature limit from the aluminum thermal degradation, this study uses RF sputtering of silicon nitride at low temperature and then polishes the CMOS chip together with the surrounding dummy pieces to define a polishing plane. Planarization reduces 0.9 ${\mu}{\textrm}{m}$ of the bumps to less than 25 nm.

• 한국재료학회지
• /
• 제22권11호
• /
• pp.636-641
• /
• 2012

In this study, we have investigated highly efficient nanoscale surface corrugated light emitting diodes (LEDs) for the enhancement of light extraction efficiency (LEE) of nitride semiconductor LEDs. Nanoscale indium tin oxide (ITO) surface corrugations are fabricated by using the conformal nanoimprint technique; it was possible to observe an enhancement of LEE for the ITO surface corrugated LEDs. By incorporating this novel method, we determined that the total output power of the surface corrugated LEDs were enhanced by 45.6% for patterned sapphire substrate LEDs and by 41.9% for flat c-plane substrate LEDs. The enhancement of LEE through nanoscale surface corrugations was studied using 3-dimensional Finite Different Time Domain (FDTD) calculation. From the FDTD calculations, we were able to separate the light extraction from the top and bottom sides of device. This process revealed that light extraction from the top and bottom sides of a device strongly depends on the substrate and the surface corrugation. We found that enhanced LEE could be understood through the mechanism of enhanced light transmission due to refractive index matching and the increase of light scattering from the corrugated surface. LEE calculations for the encapsulated LEDs devices also revealed that low LEE enhancement is expected after encapsulation due to the reduction of the refractive index contrast.

• 한국의학물리학회지:의학물리
• /
• 제13권4호
• /
• pp.202-208
• /
• 2002

본 논문에서는 표면조직에 있는 종양 치료 시 사용되고 있는 고에너지 전자선의 monitor unit을 다양한 방법에 의해 계산하여 평가 하고자 한다. 본 병원에서 6, 9, 그리고 12 MeV 전자선으로 치료한 33명의 유방암 환자가 선택되었다. 각 환자마다 모의 치료기에서 얻어진 시뮬레이션 필름에 불규칙한 모양의 전자선 블록이 제작되었다. 이러한 불규칙한 모양의 블록을 이용하여 최대선량 깊이에 100 cGy의 선량을 주기 위해 필요한 monitor unit 이 3차원 치료계획 시스템 (Pinnacle 6.0, ADAC Lab)을 사용하여 계산되었고 측정되었다. 선원과 표면 거리(SSD)가 100 cm 인 곳에서 plane parallel (PP) 이온전리함(Roos, OTW Germany) 을 사용하여 고체 물 팬텀 내에서 측정하였다. 불균등 조직에 대한 효과를 평가하기 위해 CT 데이터를 사용하였고 monitor unit을 균등조직 및 비균등조직 내에서 계산하였다. 균등조직으로 계산하기 위해 CT의 밀도를 1 g/㎤로 지정하였다. 이러한 방법에 의해 구해진 monitor unit 값들을 비교하였다. 한 지점에서 측정된 선량과 RTP에서 구해진 선량을 비교 할 때 측정된 값이 치료계획에 의해 계산된 값보다 조금 높았다. 평평한 고체 물 표면에 조사된 경우 측정된 값과 계산된 값에는 6 MeV 전자선의 경우 4%, 그리고 9 및 12 MeC 전자선의 경우 2%의 차이가 있었다. 또한 다양한 조사방향에서 CT 데이터를 사용하여 monitor unit을 계산한 경우 불균등한 조직의 밀도를 고려하여 계산된 값과 고려하지 않고 계산된 값은 모든 에너지에서 3% 이내의 차이가 있었다. 이러한 결과는 전자선을 사용하여 유방암 치료 시 조직내의 불균등한 밀도를 고려하지 않고 monitor unit을 계산해도 큰 차이가 발생하지 않는다는 것을 의미한다.