• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.189-189
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• 2012

Lead sulfide (PbS) nanocrystal quantum dots (NQDs) are promising materials for various optoelectronic devices, especially solar cells, because of their tunability of the optical band-gap controlled by adjusting the diameter of NQDs. PbS is a IV-VI semiconductor enabling infrared-absorption and it can be synthesized using solution process methods. A wide choice of the diameter of PbS NQDs is also a benefit to achieve the quantum confinement regime due to its large Bohr exciton radius (20 nm). To exploit these desirable properties, many research groups have intensively studied to apply for the photovoltaic devices. There are several essential requirements to fabricate the efficient NQDs-based solar cell. First of all, highly confined PbS QDs should be synthesized resulting in a narrow peak with a small full width-half maximum value at the first exciton transition observed in UV-Vis absorbance and photoluminescence spectra. In other words, the size-uniformity of NQDs ought to secure under 5%. Second, PbS NQDs should be assembled carefully in order to enhance the electronic coupling between adjacent NQDs by controlling the inter-QDs distance. Finally, appropriate structure for the photovoltaic device is the key issue to extract the photo-generated carriers from light-absorbing layer in solar cell. In this step, workfunction and Fermi energy difference could be precisely considered for Schottky and hetero junction device, respectively. In this presentation, we introduce the strategy to obtain high performance solar cell fabricated using PbS NQDs below the size of the Bohr radius. The PbS NQDs with various diameters were synthesized using methods established by Hines with a few modifications. PbS NQDs solids were assembled using layer-by-layer spin-coating method. Subsequent ligand-exchange was carried out using 1,2-ethanedithiol (EDT) to reduce inter-NQDs distance. Finally, Schottky junction solar cells were fabricated on ITO-coated glass and 150 nm-thick Al was deposited on the top of PbS NQDs solids as a top electrode using thermal evaporation technique. To evaluate the solar cell performance, current-voltage (I-V) measurement were performed under AM 1.5G solar spectrum at 1 sun intensity. As a result, we could achieve the power conversion efficiency of 3.33% at Schottky junction solar cell. This result indicates that high performance solar cell is successfully fabricated by optimizing the all steps as mentioned above in this work.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.186-186
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• 2015

We have introduced multifunctional ITO single thin films formed by normal sputtering system equipped with a plasma limiter which effectively blocks the bombardment of energetic negative oxygen ions. MFSS ITO also possesses high gas diffusion barrier properties simultaneously low resistivity even it deposited at room temperature without post annealing on plastic substrate. Nano-crystalline enhancement by Ar energy has energy window from 20 to 30 eV under blocking NOI condition. Effect of blocking NOI and optimal Ar energy window enhancement facilitate that resistivity is minimized to $3.61{\times}10^{-4}{\Omega}cm$ and the WVTR of 100 nm thick MFSS ITO is $3.9{\times}10^{-3}g/(m^2day)$ which is measured under environmental conditions of 90% relative humidity and 50oC that corresponds to a value of ${\sim}10^{-5}g/(m^2day)$ at room temperature. The multifunctional MFSS ITO with low resistivity, and low gas permeability will be highly valuable for plastic electronics applications.

• Journal of Electrical Engineering and Technology
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• v.6 no.1
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• pp.119-122
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• 2011

A new high speed AFM probe has been proposed and fabricated. The probe is integrated with PZT actuated cantilever realized in bulk silicon wafer using heavily boron doped silicon as an etch stop layer. The cantilever thickness can be accurately controlled by the boron diffusion process. Thick SCS cantilever and integrated PZT actuator make it possible to be operated at high speed for fast imaging. The resonant frequency of the fabricated probe is 92.9 kHz and the maximum deflection is 5.3 ${\mu}m$ at 3 V. The fabricated probe successfully measured the surface of standard sample in an AFM system at the scan speed of 600${\mu}m$/sec.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.5
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• pp.616-621
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• 2010

New type of the base material of the light-emitting diode requires copper wafer in view of heat and electrical conductance. Therefore, polishing process of the substrate level is needed to get a nanometer level of surface roughness as compared with pattern structure of nano-size in the semiconductor industry. In this paper, a series of lapping and polishing technique is shown for the rough and deflected copper substrate of thickness 3mm. Lapping by sand papers tried air cooling method. And two steps of polishing used the diamond abrasives and the $Al_2O_3$ slurry of size 100mm considering the residual scratch. White-light interferometer proved successfully a mirror-like surface roughness of Ra 6nm on the area of $0.56mm{\times}0.42mm$.

• Journal of Integrative Natural Science
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• v.2 no.1
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• pp.13-17
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• 2009

A newly developed OTFT manufacturing process using the combination of self-assembly techniques and vapor phase polymerization method revealed that a thick $SiO_2$ dielectric layer (100~200 nm) is not well compatible with conducting polymer electrode, thereby resulting in still recognizable contact resistance, unstable $V_{th}$ and leaking off current. A couple of very recent studies showed that this issue may be solved by replacing such inorganic dielectric with a self-assembled monolayer or multilayer (organic) dielectric. Therefore, this short review introduces recent trends in the development of high performance thin film transistor consisting of both organic semiconductor and SAM dielectric.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.4
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• pp.338-342
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• 2010

Carbon nanotubes (CNTs) have excellent electrical, chemical stability, mechanical and thermal properties. The MWCNT films were investigated as a transparent electrode for the solar cell, OLED, and field-emission display. MWCNT films were fabricated by air spray method, whose process is quite low-costed, using the multi-walled CNTs solution on glass substrates. Moreover, the most stable film was fabricated when the spraying time was 60 sec. The film that was sprayed with the MWCNT dispersion for 60 sec, has 300nm thick. And its electric resistivity, transmittance rate, mobility and carrier concentration are $6{\times}10^{-2}{\Omega}{\cdot}cm$, 50% at ${\lambda}=550mm$, $4.3{\times}10^{-2}cm^2/V{\cdot}s$ and $2.1{\times}10^{21}cm^{-3}$, respectively. Also, absorption energy of MWCNT films show from 3.9 eV to 4.6 eV. Furthermore, we can use MWCNT films fabricated by the spray method for the transparent electrode.

• Journal of the Optical Society of Korea
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• v.5 no.4
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• pp.136-139
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• 2001

We investigated a high-output ower, periodically poled lithium niobate(PPLN) optical parametric oscillator(OPO) pumped by a Q-switched Nd:YAG laser. Given the low optical damage threshold and the limited aperture (0.5mm thick) of PPLN, we tried to maximize the signal output power in a linear cavity consisting of two flat mirrors with a loosely focused pump beam. It is found that this simple cavity structure allowed a robust OPO operation, which was not sensitive to alignment compared with the conventional ones using concave mirrors. A maximum energy of 100$\mu$J/pulse was achieved for the signal at 1.36${\mu}{\textrm}{m}$, while the oscillation threshold was 0.3 mJ/pulse for the pump at 1064 nm.

• Applied Microscopy
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• v.43 no.2
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• pp.98-101
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• 2013

In the present study, formation of yard and shell has been investigated in as-melt-spun $Gd_{30}Ti_{25}Al_{25}Co_{20}$ alloy using a variety of transmission electron microscopy techniques. The phase separation during cooling leads to the formation of the microstructure consisting of amorphous droplets with different size scales embedded in the amorphous matrix. Due to the interdiffusion at the interface after the first-step phase separation, ~50 nm-thick yard develops on the surface of the primary droplet particle. Due to the critical wetting phenomenon, ~5 nm thickness shell enveloping the droplet forms. The sell is enriched in Co and Ti, implying that the composition is close to that of the droplet.

• Corrosion Science and Technology
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• v.9 no.4
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• pp.171-174
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• 2010

MAO (micro-arc oxidation) is an eco-friendly convenient and effective technology to deposit high-quality oxide coatings on the surfaces of Ti, Al, Mg and their alloys. The roles of the electrolyte concentration and relative cathode electrode area sizes in the grown oxide film during titanium MAO were investigated. The higher the concentration of the electrolyte, the lower the $R_{total}A$ value. The oxide film produced by the lower concentration of the electrolyte is thinner and less uniform than the film by the higher concentration, which is thick and porous. The cathode area size must be bigger than the anode area size in order to minimize the voltage drop across the cathode. The ratio of the cathode area size to the anode area size must be bigger than 8. Otherwise, the cathode will be another source for voltage drop, which is detrimental to and slows down the oxide growth.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.15.1-15.1
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• 2009

Nano transfer printing and micro contact printing is well known printing method based on soft lithography which uses conformal soft elastomer with designed surface relief structures. Here I introduce another class of novel 3D nanofabrication technique by using the same elastomer but in a different manner. The approach, which we refer to as proximity field nanopatterning, uses the surface-reliefed elastomers as phase masks to pattern thick layers of transparent, photosensitive materials. Aspects of the optics, the materials, and the physical chemistry associated with this method are outlined. A range of 3D structures illustrate its capabilities, and several application examples demonstrate possible areas of use in technologies ranging from microfluidics to photonic materials to density gradient structures for chemical release and high-energy density science.