• Current Photovoltaic Research
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• v.8 no.2
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• pp.45-49
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• 2020

Molybdenum (Mo) thin films are widely used as back contact in copper indium diselenide (CISe) solar cells. However, despite this, there are only few published studies on the properties of Mo and characteristics of CISe solar cells formed on such Mo substrates. In this studies, we investigated the properties of sputter deposited Mo bilayer, and fabricated non-vacuum CISe solar cells using bilayer Mo substrates. The changes in surface morphology and electrical resistivity were traced by varying the gas pressure during deposition of the bottom Mo layer. In porous surface structure, it was confirmed that the electrical resistivity of Mo bilayer was increased as the amount of oxygen bonded to the Mo atoms increased. The resulting solar cell characteristics vary as the bottom Mo layer deposition pressure, and the maximum solar cell efficiency was achieved when the bottom layer was deposited at 7 mTorr with a thickness of 100 nm and the top layer deposited at 3 mTorr with a thickness of 400 nm.

• Economic and Environmental Geology
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• v.53 no.4
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• pp.363-381
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• 2020

The polymetallic Co, Ni, Cu, As, Au, and Ag deposits of Bou Azzer East are located in the western part of the Bou Azzer inlier in the Central Anti Atlas, Morocco. Six stages of emplacement of the mineralization have been identified. Precious metals (native gold and electrum) are present in all stages of this deposit except the early nickeliferous stage. From the Statistical analysis of the Co, As, Ni, Au, and Ag contents of a set of 501 samples, shows that the Pearson correlation coefficient between As-Co elements (0.966) is the highest followed by that of the Au-Ag couple (0.506). Principal component analysis (PCA) and hierarchical ascending classification (HAC) of the grades show, that Ni is associated with the pair (As-Co) and Cu is rather related to the pair (Au-Ag). The kriging maps show that the highest values of the Co, As and Ni appear in the contact of the serpentinite with other facies, as for those of Au and Ag, in addition to anomalous zones concordant with those of Co, Ni and As, they show anomalies at the extreme South and North of the study area. The development of the anomalous Au and Ag zones is mainly along the N40-50°E and N145°E directions.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.60-60
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• 2000

The adhesion interface formation between copper and poly(ethylene terephthalate)(PET), poly(methyl methacrylate)(PMMA) and Polyimide films was treated using Ion assisted reaction system to sequential sputter deposition by High-Frequency ion source. The ion beam modification system used a new type of low power HF ion thruster for space application as new low thruster electric propulsion system. Low power HF ion thruster with diameter 100mm gives the opportunity to obtain beams of Ar+ with currents 20~150 mA (current density 0.5~3.5 mA/cm2) and energy 200~2500eV at HF power level 10~150 W. Using Ar as a working gas it is possible to obtain thrust within 3~8 mN. Contact angles for untreated films were over 95$^{\circ}$ and 80 for Pet, 10o for PMMA and 12o for PI samples as a condition of ion assisted reaction at the ion dose of 10$\times$1016 ions/cm2, the ion beam potential of 1.2 keV and 4 ml/min for environmental gas flow rate. 900o peel tests yielded values of 15 to 35 for PET, 18 to 40 and 12 to 36 g/min. respectively. High resolution X-ray photoelectron spectrocopy is the Cls region for Cu metal on these polymer substrates showed increases in C=O-O groups for polymide, whereas PET and PMMA treated samples showed only C=O groups with increase the ion dose. Finally, unstable polymer surface can be changed from hydrophobic to hydrophilic formation such as C-O and C=O that were confirmed by the XPS analysis, conclusionally, the ion assisted reaction is very effective tools to attach reactive ion species to form functional groups on C-C bond chains of PET, PMMA and PI.

• Current Photovoltaic Research
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• v.9 no.3
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• pp.84-95
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• 2021

The power conversion efficiency of Cu₂ZnSnSe₄ (CZTSe) solar cells depends on the absorber layer thickness; however, changes in the characteristics of the cells with varying absorber layer thickness are unclear. In this study, we investigated the changes in the characteristics of CZTSe solar cells for varying absorber layer thickness. Five absorber thicknesses were employed: CZTSe1 2.78 ㎛, CZTSe2 1.01 ㎛, CZTSe3 0.55 ㎛, CZTSe4 0.29 ㎛, and CZTSe5 0.15-0.23 ㎛. The efficiency of the CZTSe solar cells decreased as the absorber thickness decreased, resulting in power conversion efficiencies of 10.45% (CZTSe1), 8.67% (CZTSe2), 7.14% (CZTSe3), 3.44% (CZTSe4), and 1.54% (CZTSe5). As the thickness of the CZTSe absorber layer decreased, the electron-hole recombination at the grain boundaries and the absorber-back-contact interface increased. This caused an increase in the current loss, owing to light loss in the long-wavelength region. In addition, as the thickness of the CZTSe absorber layer decreased, more ZnSe was produced, and the resulting defects and defect clusters led to an open-circuit voltage loss.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.6
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• pp.237-243
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• 2020

In this study, a silane-based coating was applied to improve corrosion resistance and thermal efficiency performance of a brazed plate heat exchanger (BPHE) composed of stainless plate and copper (Cu) brazing. Although the selected coating material was applied to the BPHE by evaluating the corrosion and contact angle according to the coating material, the result of the heat transfer performance evaluation showed that the thermal efficiency was lower than that of the uncoated BPHE. It was analyzed that the adhesion of the coating agent to the flow path inside the BPHE and the residual coating agent on the surface acted as heat resistance, preventing heat transfer. This is due to the structural characteristics of the BPHE in which a fine flow path exists inside, and it is believed that manufacturing after coating the surface of the flow path in advance in the manufacturing process of the BPHE can improve heat transfer performance.

• Transactions on Electrical and Electronic Materials
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• v.17 no.2
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• pp.92-97
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• 2016

This paper presents design and simulation of wide band RF microswitch that uses electrostatic actuation for its operation. RF MEMS devices exhibit superior high frequency performance in comparison to conventional devices. Similar techniques that are used in Very Large Scale Integration (VLSI) can be employed to design and fabricate MEMS devices and traditional batch-processing methods can be used for its manufacturing. The proposed switch presents a novel design approach to handle reliability concerns in MEMS switches like dielectric charging effect, micro welding and stiction. The shape has been optimized at actuation voltage of 14-16 V. The switch has an improved restoring force of 20.8 μN. The design of the proposed switch is very elemental and primarily composed of electrostatic actuator, a bridge membrane and coplanar waveguide which are suspended over the substrate. The simple design of the switch makes it easy for fabrication. Typical insertion and isolation of the switch at 1 GHz is -0.03 dB and -71 dB and at 85 GHz it is -0.24 dB and -29.8 dB respectively. The isolation remains more than - 20 db even after 120 GHz. To our knowledge this is the first demonstration of a metal contact switch that shows such a high and sustained isolation and performance at W-band frequencies with an excellent figure-of merit (fc=1/2.pi.Ron.Cu =1,900 GHz). This figure of merit is significantly greater than electronic switching devices. The switch would find extensive application in wideband operations and areas where reliability is a major concern.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.1
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• pp.9-15
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• 2019

Here, we present a facile route to fabricate a vertically stacked 3D porous structure-based triboelectric nanogenerator (TENG) that can be used to harvest energy from the friction in a repetitive contact-separation mode. The unit component of TENG consists of thin Al foil electrodes integrated with microstructured 3D foams such as Ni, Cu, and polyurethane (PU), which provide advantageous tribo-surfaces specifically to increase the friction area to the elastomeric counter contact surfaces (i.e., polydimethylsiloxane, PDMS). The periodic contact/separation-induced triboelectric power generation from a single unit of the 3D porous structure-based TENG was up to $0.74mW/m^2$ under a mild condition. To demonstrate the potential applications of our approach, we applied our TENGs to small-scale devices, operating 48 LEDs and capacitors. We envision that this energy harvesting technology can be expanded to the applications of sustainably operating portable electronic devices in a simple and cost-effective manner by effectively harvesting wasted energy resources from the environment.

• Economic and Environmental Geology
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• v.9 no.3
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• pp.143-156
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• 1976

The Cretaceous metal ore deposits in the Gyeongsang basin of Gyeongsangbuk-do are characterized by the formation of metallogenic provinces which show zonal distribution pattern around Yeonil province where pneumatolytic type is dominated and hydrothermal type are distributed in the order of decreasing temperature type outward. Some Cretaceous granitic rocks include zoned alkali feldspars which reflect rapid variation of $H_2O$ during emplacement and crystallization of the water-saturated granitic magma. The ore deposits are considered to be originated from upward transportation of ore solution from the excess of water exhausted from uprising magma, which seems to be intimately related to the fact that the majority of the ore deposits in Daegu area are cummulated around the granites including zoned alkali feldspars. In order to collect geochemical data necessary for geochemical exploration in the study area, certain trace elements were chosen as pathfinders from monzonite and soil in the vicinity of Dalsung Tungsten Mine by studying the dispersion patterns of trace elements: Ba and Sr show trends to decrease toward ore deposit while Cu, Pb, and Mo increase. Around mining area there are distributed apparently Equisetum arvense Linne and Mentha sachinensis Kudo which may be used as index plants. In the viewpoint of geologic structure, the trends of the ore veins in contact aureole around the Palgongsan granite body correspond with the pre- and syn- plutonism joint pattern in hornfels in the area.

• Journal of the Korean Ceramic Society
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• v.49 no.5
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• pp.417-422
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• 2012

Copper nano particles have been considered as the materials for conductive ink due to its good thermal, electrical conductivity and low cost. However, copper nanoparticles oxidize easily, decreasing dispersion stability and electrical conductivity. Therefore, it is important to develop a method to minimize oxidation of copper nano particles to improve its dispersion stability property in copper nano ink. In this study, copper nano particles were coated with 1-Octanethiol VSAM(Vaporized Self Assembled Multilayers) to prevent oxidation and coated copper powders were dispersed in conductive ink successfully by studying its relationship of different chain length of solvents to 1-Octanethiol coating layer to fabricate nano ink. Various alcohol solvents, such as 1-Hexanol, 1-Octanol, and 1-Decanol were used. The coating layer was observed using FESEM and TEM. Furthermore, dispersion of copper nano particles in nano inks, was characterized using Turbiscan analyzer, viscometer, and contact angle measurement tool.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05b
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• pp.90-93
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• 2002

In the surface pressure-area isotherms of mixed monolayers, mixtures containing as much as 30 mol% of AA form stable condensed monolayer while the monolayer without AA is in the expanded state because PVK take on 3D collapsed. All of the mixed monolayers with 0, 10, 20 and 30 mol% of AA could be readily transferred onto ITO substrate at 16, 17, 24 and 26 mN/m, respectively. The monolayer containing 30 mol% of AA, however, showed a roughness value of 28A and became homogeneous decreasing with the phase separation. We fabricated organic EL device of ITO/CuPc/MEL/BBOT/iLiF/Al using mixed monolayer of 13, 19 and 25 layer deposited by LB method as a emitting layer. In the voltage-current characteristics of EL device, current density was much smaller than that of the spin-coated devices. It may due to the large contact resistance existed at the interface of LB layer/organic layer inhibit carrier injection to the emitting layer. EL spectra of device showed peaks at 450. 470, 505, 555 and 650 nm and the white light emission indicate the CIE coordinate x=0.306, y=0.353.