• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.12
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• pp.1171-1176
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• 2012

The selective patterning of a carbon nanotube (CNT) forest on a Si substrate has been performed using a femtosecond laser. The high shock wave generated by the femtosecond laser effectively removed the CNTs without damage to the Si substrate. This process has many advantages because it is performed without chemicals and can be easily applied to large-area patterning. The CNTs grown by plasma-enhanced chemical vapor deposition (PECVD) have a catalyst cap at the end of the nanotube owing to the tip-growth mode mechanism. For the application of an electron emission and biosensor probe, the catalyst cap is usually removed chemically, which damages the surface of the CNT wall. Precise control of the femtosecond laser power and focal position could solve this problem. Furthermore, selective CNT cutting using a femtosecond laser is also possible without any phase change in the CNTs, which is usually observed in the focused ion beam irradiation of CNTs.

• Water for future
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• v.10 no.1
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• pp.95-100
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• 1977

The empirical area-reduction method by W.M. Borland and C.R. Miller and its revised procedure by W.T. Moody were made of fitting the area and storage curves to the Van't Hul distributions. It should be noted that the reservoir is classified into one of the four standard types on the basis of the topographical feature of the reservoir in application of the method. In other words, this method did not take into account several considerafble factors affecting the mode of sediment deposition, but only the shape of the reservoir as a governign factor. This is why the method occasionally creates ambiguity in classification and accordingly leads to unexpected mode of deposition. This paper describes a generating an formula to decide the standard classification of four types Van's Hul distributions, taking into consideration quantitatively sediment-loss percent and capacity-inflow ratio as well as the shape of the reservoirs by multiple regression analysis using the least square method to get a better fit to the design curves. The result is expressed as $Y=-1.95+55.8X_1+0.14X_2+0.12X_3$ in which the the values of Y locate the standard type I through type IV in the range from ten to forty with the interval of ten. The regression analysis was correlated well with the standard errors of estimate of around two except for the case of the type IV. This formula does not give big difference from the Borland's work in general sityation, but it demonstrates acceptable results, giving somewhat precise replys for the specific reservoirs. Its application to the Soyang Lake, one of the largest reservoirs in the country, defined clearly the type II, while the original method located it in the boundary of the type II and type III.

• Korean Journal of Optics and Photonics
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• v.16 no.4
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• pp.340-344
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• 2005

Microlens cells of Ge-doped BPSG (Boro-Phospho-Silicate Glass) are fabricated by dicing the film produced by FHD (Flame Hydrolysis Deposition). Microlens arrays of $53.4{\mu}m$ square unit are produced by the thermal reflow of the diced unit cells at $1200^{\circ}C$. The gap between the microlenses was about $70{\mu}m,$ and the thickness of the produced lens was about $28.4{\mu}m$. We analyzed the reflowed shape of the microlens cell by an image-process technique, and the focal length was about $62.2{\mu}m$. This method of fabricating a microlens is simple and inexpensive compared to the conventional method using the photolithographic process. Also, the control of the radius of curvature of the microlens is easier and a more precise microlens way of various types can be fabricated using this method.

• Journal of Ocean Engineering and Technology
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• v.32 no.2
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• pp.84-94
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• 2018

Subsea pipelines are designed to transport mixtures of oil, gas, and their associated impurities from a wellhead that can be in excess of approximately $100^{\circ}C$, while the external temperature may be approximately $5^{\circ}C$. Heat can be lost from a subsea pipeline containing a high-temperature fluid to the surrounding environment. It is important that the pipeline be designed to ensure that the heat loss is small enough to maintain sufficient flow from the unwanted deposition of hydrate and wax, which occurs at a critical temperature of about $40^{\circ}C$. Therefore, it is essential to estimate the heat loss of a subsea pipeline in various circumstances. In previous studies, overall heat transfer coefficient(OHTC) formulas were considered only for a single soil type. Thus, it is difficult to characterize the OHTC of the actual seabed with multiple soil layers. In this paper, an OHTC formula that considers multi-layered soils is proposed for more precise OHTC estimation.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.4
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• pp.455-460
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• 2012

The Electrostatic Inkjet system has many applications in cost and time effective manufacturing of printed electronics like RFIDs, OLEDs and flexible displays etc. This paper presents pneumatic ink supply system for an electrohydrodynamic deposition (EHD) setup for the precise pressure control to produce a small amount of discharge at the end of the capillary. The meniscus shape depends upon the applied pneumatic pressure to the ink supply system. Furthermore, this paper also compares meniscus shapes at different applied pneumatic pressures. It is concluded that patterning of constant line-width can be achieved better by controlling the meniscus shape using this technique.

• Ocean and Polar Research
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• v.32 no.1
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• pp.73-84
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• 2010

A terrestrial LiDAR was used to acquire precise and high-resolution topographical information of Malipo beach, Korea. Terrestrial LiDAR and RTK-DGPS (VRS) were mounted on top of a survey vehicle and used to scan 20 times stop-and-go method with 250 m spacing intervals at ebb tides. In total, 7 measurements were made periodically from 2008 to 2009 and after each beach replenishment event. We carried out GIS-based 3D spatial analysis such as slope and volume calculations in order to assess topographical changes over time. In relation to beach replenishment, comparative analysis of each volume change revealed them to be similar. This result indicates that the terrestrial LiDAR measurements are accurate and can be used to analyze temporal topographical changes. In conclusion, the methodology employed in this study can be used efficiently to exercise coastal management through monitoring and analyzing beach process such as erosion and deposition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.9
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• pp.720-727
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• 2008

Microfluidic single chip integrating thermopneumatic micropump and micro check valve are developed. The micropump and micorvalve are made of biocompatible materials, glass and PDMS, so as to be applicable to the biochip. By using the passive-type check valve, backward flow and fluid leakage are blocked and flow control is stable and precise. The chip is composed of three PDMS layers and a glass substrate. In the chip, flow channel and pump chamber were made on the PDMS layers by the replica molding technique and pump heater was made on the glass substrate by Cr/Au deposition. Diameter of the pump chamber is 7 mm and the width and depth of the channel are 200 and $180{\mu}m$, respectively. The PDMS layers chip and the heater deposited glass chip are combined by a jig and a clamp for pumping operation, and they are separable so that PDMS chip is used as a disposable but the heater chip is able to be used repeatedly. Pumping performance was simulated by CFD software and investigated experimentally. The performance was the best when the duty ratio of the applied voltage to the heater was 33%.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.114-114
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• 2012

Metal-oxide-semiconductor field-effect transistors (MOSFETs)의 critical dimension (CD)가 sub 45 nm로 줄어듬에 따라 기존에 gate dielectric으로 사용하고 있는 SiO2에서 발생되는 high gate leakage current 때문에 새로운 high dielectric constant (k) 물질들이 연구되기 시작하였다. 여러 가지 high-k 물질 중에서, aluminum-oxide (Al2O3)는 높은 dielectric constant (~10)와 전자 터널링 barrier height (~2eV) 등을 가지기 때문에 많은 연구가 되고 있다. 그러나 Al2O3를 anisotropic한 patterning을 하기 위해 주로 사용되고 있는 halogen-based 플라즈마 식각 과정에서 나타나는 Al2O3와 하부 layer간의 낮은 식각 selectivity 뿐만 아니라 표면에 발생되는 defect, stoichiometry modification, roughness 변화 등의 많은 문제점들로 인하여 device performance가 감소하기 때문에 이를 해결하기 위한 많은 연구들이 진행중이다. 따라서 본 연구에서는 실리콘 기판위의 atomic layer deposition (ALD)로 증착된 Al2O3를 BCl3/Ar 중성빔을 이용하여 원자층 식각한 후 식각 특성을 분석해 보았다. Al2O3 표면을 BCl3로 absorption시킨 후 Ar 중성빔으로 desorption 시키는 과정에서 volatile한 aluminum-chlorides와 boron oxychloride가 형성되어 layer by layer로 제거됨을 관찰 할 수 있었다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.614-614
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• 2013

The effect of graphene growth parameters on the number of graphene layers were systematically studied and growth mechanism on copper substrate was proposed. Parameters that could affect the thickness of graphene growth include the pressure in the system, gas flow rate, growth pressure, growth temperature, and cooling rate. We hypothesis that the partial pressure of both the carbon sources and hydrogen gas in the growth process, which is set by the total pressure and the mole fraction of the feedstock, could be the factor that controls the thickness of the graphene. A synthetic method to produce such large area graphene films with precise thickness from mono- to few-layer would be ideal for chemists and physicists to explore the promising electronic applications of these materials. Here, large-area uniform mono-, bi-, and few-layer graphene films were successfully synthesized on copper surface in selective growth windows, with a finely tuned total pressure and $CH_4$/$H_{2gas}$ ratio. Our findings may facilitate both the large-area synthesis of well-controlled graphene features and wide range of applications of graphene.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.38-38
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• 2010

Ever since the experimental discovery of graphene exfoiliated from the graphite flakes by Geim et at., this area has drawn a lot of attention for its possible application in IT industry. For the growth of graphene, chemical vapor deposition (CVD) has been widely used to fabricate the large area graphene. The lateral size of this graphene can be easily controlled by the size of the metal substrate though the chemical etching to remove this substrate is somewhat troublesome. Another problem which is hard to avoid is the folding at the grain boundary. We will discuss the origin of the folding first and introduce the way to avoid this folding. To solve this problem, we have used the various types of micro-thin metal foils. The precise control of hydro-carbon and the carrier gas results in the formation of the graphene on top of substrate. The thickness of graphene layers can be controlled with the control of gas flow on top of Cu substrate in contrast to the previously reported self-limiting growth $behavior^1$. Uniformity of this graphene layer has been checked by micro-raman spectroscopy and SEM. The size of grain can be enhanced by thermal treatment or use of other metal substrate. The dependence of grain size on the lattice size of the substrate will be discussed. By selecting the shape of substrate, we can grow various types of graphene. We will introduce the micron size graphene tube and its application.