• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.389-390
• /
• 2012

In this study, we fabricate a superhydrophobic surface made of hierarchical nanostructures that combine wax crystalline structure with moth-eye structure using vacuum cluster system and measure their hydrophobicity and durability. Since the lotus effect was found, much work has been done on studying self-cleaning surface for decades. The surface of lotus leaf consists of multi-level layers of micro scale papillose epidermal cells and epicuticular wax crystalloids [1]. This hierarchical structure has superhydrophobic property because the sufficiently rough surface allows air pockets to form easily below the liquid, the so-called Cassie state, so that the relatively small area of water/solid interface makes the energetic cost associated with corresponding water/air interfaces smaller than the energy gained [2]. Various nanostructures have been reported for fabricating the self-cleaning surface but in general, they have the problem of low durability. More than two nanostructures on a surface can be integrated together to increase hydrophobicity and durability of the surface as in the lotus leaf [3,5]. As one of the bio-inspired nanostructures, we introduce a hierarchical nanostructure fabricated with a high vacuum cluster system. A hierarchical nanostructure is a combination of moth-eye structure with an average pitch of 300 nm and height of 700 nm, and the wax crystalline structure with an average width and height of 200 nm. The moth-eye structure is fabricated with deep reactive ion etching (DRIE) process. $SiO_2$ layer is initially deposited on a glass substrate using PECVD in the cluster system. Then, Au seed layer is deposited for a few second using DC sputtering process to provide stochastic mask for etching the underlying $SiO_2$ layer with ICP-RIE so that moth-eye structure can be fabricated. Additionally, n-hexatriacontane paraffin wax ($C_{36}H_{74}$) is deposited on the moth-eye structure in a thermal evaporator and self-recrystallized at $40^{\circ}C$ for 4h [4]. All of steps are conducted utilizing vacuum cluster system to minimize the contamination. The water contact angles are measured by tensiometer. The morphology of the surface is characterized using SEM and AFM and the reflectance is measured by spectrophotometer.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.11 no.2
• /
• pp.225-229
• /
• 2011

In this study, capacitive type pressure sensors based on low temperature co-fired ceramics (LTCC) technology for environmental monitoring were demonstrated. The LTCC is one of promising technology than is based one since it has many advantages (e.g., low cost production, high manufacturing yields and easy realizing 3D structure etc.) for sensor application. Especially, it has good mechanical and chemical properties for robust environmental application. The 3D LTCC diaphragm with thickness of 400 ${\mu}m$ were fabricated by laminating 4 green sheets using commercial powder (NEG, MLS 22C). To evaluate the sensing properties of the different cavity areas, two types of diaphragm which had different cavity areas with 25, 49 $mm^2$ respectively, were fabricated. To realize capacitive type pressure sensor, the Au top electrode was fabricated using thermal evaporator and the bottome electrode was compressed using aluminium foil. The sensing properties of the fabricated sensors showed linear characteristic under different pressure (0~30 psi) using pressure measurement system.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.306.1-306.1
• /
• 2016

ZnO semiconductor material has been widely utilized in various applications in semiconductor device technology owing to its unique electrical and optical features. It is a promising as solar cell material, because of its low cost, n-type conductivity and wide direct band gap. In this work ZnO/Si heterojunctions were fabricated by using pulsed laser deposition. Vacuum chamber was evacuated to a base pressure of approximately $2{\times}10^{-6}Torr$. ZnO thin films were grown on p-Si (100) substrate at oxygen partial pressure from 5mTorr to 40mTorr. Growth temperature of ZnO thin films was set to 773K. A pulsed (10 Hz) Nd:YAG laser operating at a wavelength of 266 nm was used to produce a plasma plume from an ablated a ZnO target, whose density of laser energy was $10J/cm^2$. Thickness of all the thin films of ZnO was about 300nm. The optical property was characterized by photoluminescence and crystallinity of ZnO was analyzed by X-ray diffraction. For fabrication ZnO/Si heterojunction diodes, indium metal and Al grid patterns were deposited on back and front side of the solar cells by using thermal evaporator, respectively. Finally, current-voltage characteristics of the ZnO/Si structure were studied by using Keithly 2600. Under Air Mass 1.5 Global solar simulator with an irradiation intensity of $100mW/cm^2$, the electrical properties of ZnO/Si heterojunction photovoltaic devices were analyzed.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.247.1-247.1
• /
• 2016

Low-cost, high efficiency solar cells are tremendous interests for the realization of a renewable and clean energy source. ZnTe based solar cells have a possibility of high efficiency with formation of an intermediated energy band structure by impurity doping. In this work, ZnO/ZnTe:Cr and ZnO/i-ZnTe structures were fabricated by pulsed laser deposition (PLD) technique. A pulsed (10 Hz) Nd:YAG laser operating at a wavelength of 266 nm was used to produce a plasma plume from an ablated a ZnTe target, whose density of laser energy was 10 J/cm2. The base pressure of the chamber was kept at approximately $4{\times}10-7Torr$. ZnTe:Cr and i-ZnTe thin films with thickness of 210 nm were grown on p-Si substrate, respectively, and then ZnO thin films with thickness of 150 nm were grown on ZnTe:Cr layer under oxygen partial pressure of 3 mTorr. Growth temperature of all the films was set to $250^{\circ}C$. For fabricating ZnO/i-ZnTe and ZnO/ZnTe:Cr solar cells, indium metal and Ti/Au grid patterns were deposited on back and front side of the solar cells by using thermal evaporator, respectively. From the fabricated ZnO/ZnTe:Cr and ZnO/i-ZnTe solar cell, dark currents were measured by using Keithley 2600. Solar cell parameters were obtained under Air Mass 1.5 Global solar simulator with an irradiation intensity of 100 mW/cm2, and then the photoelectric conversion efficiency values of ZnO/ZnTe:Cr and ZnO/i-ZnTe solar cells were measured at 1.5 % and 0.3 %, respectively.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2015.08a
• /
• pp.206.1-206.1
• /
• 2015

최근에 금속산화물을 증착하는 방법으로 용액공정이 주목 받고 있다. 용액 공정은 대기압에서 매우 간단한 방법으로 복잡한 공정과정을 요구하지 않기 때문에 박막을 경제적으로 간단하게 형성할 수 있다. 하지만 용액공정을 통해 형성한 박막에는 소자의 특성을 열화 시키는 solvent와 탄소계열의 불순물을 많이 포함하고 있어 고온의 열처리가 필수적이다. 박막의 품질을 향상시키기 위해서 다양한 열처리 방법들이 이용되고 있으며, 일반적인 열처리 방법으로는 furnace를 이용한 conventional thermal annealing (CTA)이 많이 이용되고 있다. 하지만, 최근에는 microwave를 이용한 공정이 주목 받고 있다. Microwave energy는 CTA보다 효과적으로 비교적 낮은 온도에서 높은 열처리 효과를 나타낸다. 본 실험은 n-type Silicon 기판에 solution-ZrO2 산화막을 형성 후, oven baking을 한 뒤, CTA와 microwave를 이용하여 solvent와 불순물을 제거 하였다. 전기적 특성을 확인하기 위해 solution ZrO2 산화막 위에 E-beam evaporator를 이용해 Ti 금속 전극을 증착하여 Metal-Oxide-Semiconductor (MOS) capacitor를 제작하였다. 다음으로, PRECISION SEMICONDUCTOR PARAMETER ANALYZER (4156B)를 이용하여, capacitance-voltage (C-V) 특성 및 current-voltage (I-V) 특성을 비교하였다. 다음으로, CTA를 통하여 제작한 소자와 전기적 특성을 비교하였다. 그 결과, Microwave irradiation으로 열처리한 MOS capacitor 소자에서 capacitance 값과 flat band voltage, hysteresis 등이 개선되는 효과를 확인하였다. Microwave irradiation 열처리는 100oC 미만의 온도에서 공정이 이루어짐에도 불구하고 시료 내에서의 microwave 에너지의 흡수가 CTA 공정에서의 열에너지 흡수보다 훨씬 효율적으로 이루어지며, 결과적으로 ZrO2 용액의 불순물과 solvent를 낮은 온도에서 제거하여 고품질 박막 형성에 매우 효과적이라는 것을 나타낸다. 따라서, microwave irradiation 열처리 방법은 비정질 산화막이 포함되는 박막 transistor 소자 제작에 대하여 결정적인 열처리 방법이 될 것으로 기대한다.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.6
• /
• pp.734-749
• /
• 1998

A numerical study t predict the characteristics on transient operation of the heat pipe cooling system with multiple heaters for electronic system has been performed. The heat pipe cooling system of 45 cm length and 16 mm diameter was composed of evaporator section with four heaters which simulate electronic components, insulated transport section, and condenser section with a conductor which was cooled under the constant heat flux boundary condition. Two test cases were investigated in present study; Case 1 indicated that the 1st and 2nd heaters among four heaters were heated off, while the 3rd and the 4th heaters were heated on. Case 2 was the inverse situation switched from heating locations of Case 1. Case 3 indicated that the 1st and 4th heaters among four heaters were heated off, while the 2nd and 3rd heaters were heated on. The results showed that the transient time to reach the steady state is shorter for Case 1 than for Case 2. Especially, the maximum temperature among the heaters which simulate electronic components during switching operation is relatively small compared to the maximum allowable operating temperature in electronic system. It is concluded that the heat pipe cooling system in present study operate with the good thermal reliability even for sudden switching situation of the heaters.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.5 no.4
• /
• pp.297-308
• /
• 2007

The granulation equipment of concentrated wastes is manufactured for the polymer solidification of concentrated wastes. It uses liquid sodium silicate as a granulating agent for the granulating of dried powder containing boric acid. The granulating agent is sprayed in the form of droplet and mean size of dried granules is $2{\sim}4mm$. The new technology which has been used for the polymer solidification of spent resin in U.S. and certified by Nuclear Regulatory Commission (NRC) is successfully applied to concentrated wastes. This uses in-situ solidification process within drum without mechanical mixing. Maximum loading of waste can be achieved without increasing of waste volume. Polymer waste forms were evaluated with several test such as fire test, compressive strength test, leaching test, immersion test, irradiation test, and thermal cycling test according to standard test procedures.

• Journal of Advanced Marine Engineering and Technology
• /
• v.36 no.8
• /
• pp.1036-1042
• /
• 2012

This paper describes an analysis on exergy efficiency of R744 OTEC power system to optimize the design for the operating parameters of this system. The operating parameters considered in this study include subcooling and superheating degree, evaporation and condensation temperature, and turbine and pump efficiency, respectively. The main results are summarized as follows : As the evaporation temperature, superheating degree, and turbine and pump efficiency of R744 OTEC power system increases, the exergy efficiency of this system increases, respectively. But condensation temperature and subcooling degree of R744 OTEC power system increases, the exergy efficiency of this system decreases, respectively. The effect of evaporation temperature and pump efficiency on R744 OTEC power system is the largest and the lowest among operation parameters, respectively. Therefore, the refrigerant temperature in the evaporator must be closely to the surface seawater temperature to enhance the exergy efficiency of R744 OTEC power system.

• Korean Journal of Materials Research
• /
• v.21 no.2
• /
• pp.115-119
• /
• 2011

Si Nanowire (NW) field effect transistors (FETs) were fabricated on hard Si and flexible polyimide (PI) substrates, and their electrical characteristics were compared. Si NWs used as channels were synthesized by electroless etching method at low temperature, and these NWs were refined using a centrifugation method to get the NWs to have an optimal diameter and length for FETs. The gate insulator was poly(4-vinylphenol) (PVP), prepared using a spin-coating method on the PI substrate. Gold was used as electrodes whose gap was 8 ${\mu}m$. These gold electrodes were deposited using a thermal evaporator. Current-voltage (I-V) characteristics of the device were measured using a semiconductor analyzer, HP-4145B. The electrical properties of the device were characterized through hole mobility, $I_{on}/I_{off}$ ratio and threshold voltage. The results showed that the electrical properties of the TFTs on PVP were similar to those of TFTs on $SiO_2$. The bending durability of SiNWs TFTs on PI substrate was also studied with increasing bending times. The results showed that the electrical properties were maintained until the sample was folded about 500 times. But, after more than 1000 bending tests, drain current showed a rapid decrease due to the defects caused by the roughness of the surface of the Si NWs and mismatches of the Si NWs with electrodes.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.04c
• /
• pp.15-17
• /
• 2008

$CuInS_2$ thin films were synthesized by sulpurization of Cu/In Stacked elemental layer deposited onto glass Substrates by vacuum furance annealing at temperature 200[$^{\circ}C$]. And structural and electrical properties were measured in order to certify optimum conditions for growth of the ternary compound semiconductor $CuInS_2$ thin films with non-stoichiometry composition. $CuInS_2$ thin film was well made at the heat treatment 200[$^{\circ}C$] of SLG/Cu/In/S stacked elemental layer which was prepared by thermal evaporator, and chemical composition of the thin film was analyzed nearly as the proportion of 1 : 1 : 2. Physical properties of the thin film were investigated at various fabrication conditions substrate temperature, annealing and temperature, annealing time by XRD, FE-SEM and hall measurement system. At the same time, carrier concentration, hall mobility and resistivity of the thin films was $9.10568{\times}10^{17}[cm^{-3}]$, 312.502[$cm^2/V{\cdot}s$] and $2.36{\times}10^{-2}[{\Omega}{\cdot}cm]$, respectively.