• Polymer(Korea)
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• v.36 no.4
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• pp.536-541
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• 2012

The effects of silica content were studied on UV curing characteristics and defect formations in imprinted patterns of hundreads nanometer size for the photo-curable imprinting composites with silica particles. An increase in elasticity and a decrease in shrinkage were observed with an increase in silica content in the imprinting resin which was UV cured at room temperature. However, the patterned nano-pillars were stuck together with neighboring nano-pillars if the amount of silica is more than 7 wt%. This can be ascribed to the increased viscosity of imperfectly cured resin due to the obstruction of the photo-reaction by silica particles. Addition of silica to the imprinting resin is useful in enhancing the strength of the cured resin although it is difficult to get good imprinted patterns for the resin with more than 7 wt% of silica due to the reduction of photo-reaction conversion.

• Korean Journal of Materials Research
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• v.25 no.1
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• pp.1-8
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• 2015

This study suggested comprehensive structural characterization methods for the commercial blue light emitting diodes(LEDs). By using the Z-contrast intensity profile of Cs-corrected high-angle annular dark field scanning transmission electron microscope(HAADF-STEM) images from a commercial lateral GaN-based blue light emitting diode, we obtained important structural information on the epilayer structure of the LED, which would have been difficult to obtain by conventional analysis. This method was simple but very powerful to obtain structural and chemical information on epi-structures in a nanometer-scale resolution. One of the examples was that we could determine whether the barrier in the multi-quantum well(MQW) was GaN or InGaN. Plan-view TEM observations were performed from the commercial blue LED to characterize the threading dislocations(TDs) and the related V-pit defects. Each TD observed in the region with the total LED epilayer structure including the MQW showed V-pit defects for almost of TDs independent of the TD types: edge-, screw-, mixed TDs. The total TD density from the region with the total LED epilayer structure including the MQW was about $3.6{\times}10^8cm^{-2}$ with a relative ratio of Edge- : Screw- :Mixed-TD portion as 80%: 7%: 13%. However, in the mesa-etched region without the MQW total TD density was about $2.5{\times}10^8cm^{-2}$ with a relative ratio of Edge- : Screw- :Mixed-TD portion of 86%: 5%: 9 %. The higher TD density in the total LED epilayer structure implied new generation of TDs mostly from the MQW region.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.8
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• pp.1885-1890
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• 2013

In this paper, the electrical properties of nanoscale junctionless p-channel MuGFET at cryogenic temperature have been analyzed experimentally. The experiment was performed using a cryogenic probe station which uses the liquid Helium. It has been observed that the drain current oscillation at low drain voltage and cryogenic temperature was more pronounced in junctionless transistor than in accumulation mode transistor. The reason for more marked oscillation is due to the smaller electrical cross section area of the inversion channel which is formed at the center of silicon film in junctionless transistor. It was also observed that the drain current and maximum transconductance were increased as the measurement temperature increased. This is resulted from the increase of hole mobility and the decrease of the threshold voltage as the measurement temperature increases. The drain current oscillation due to the quantum effects can be occurred up to the room temperature when the device size scales down to the nanometer level.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.111-111
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• 2007

Further scaling the semiconductor devices down to low dozens of nanometer needs the extremely shallow depth in junction and the intentional counter-doping in the silicon gate. Conventional ion beam ion implantation has some disadvantages and limitations for the future applications. In order to solve them, therefore, plasma source ion implantation technique has been considered as a promising new method for the high throughputs at low energy and the fabrication of the ultra-shallow junctions. In this paper, we study about the effects of DC bias and base pressure as a process parameter. The diluted mixture gas (5% $PH_3/H_2$) was used as a precursor source and chamber is used for vacuum pressure conditions. After ion doping into the Si wafer(100), the samples were annealed via rapid thermal annealing, of which annealed temperature ranges above the $950^{\circ}C$. The junction depth, calculated at dose level of $1{\times}10^{18}/cm^3$, was measured by secondary ion mass spectroscopy(SIMS) and sheet resistance by contact and non-contact mode. Surface morphology of samples was analyzed by scanning electron microscopy. As a result, we could accomplish the process conditions better than in advance.

• Macromolecular Research
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• v.16 no.6
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• pp.549-554
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• 2008

Proton conducting crosslinked membranes were prepared using polymer blends of polystyrene-b-poly(hydroxyethyl acrylate)-b-poly(styrene sulfonic acid) (PS-b-PHEA-b-PSSA) and poly(vinyl alcohol) (PVA). PS-b-PHEA-b-PSSA triblock copolymer at 28:21:51 wt% was synthesized sequentially using atom transfer radical polymerization (ATRP). FT-IR spectroscopy showed that after thermal ($120^{\circ}C$, 2 h) and chemical (sulfosuccinic acid, SA) treatments of the membranes, the middle PHEA block of the triblock copolymer was crosslinked with PVA through an esterification reaction between the -OH group of the membrane and the -COOH group of SA. The ion exchange capacity (IEC) decreased from 1.56 to 0.61 meq/g with increasing amount of PVA. Therefore, the proton conductivity at room temperature decreased from 0.044 to 0.018 S/cm. However, the introduction of PVA resulted in a decrease in water uptake from 87.0 to 44.3%, providing good mechanical properties applicable to the membrane electrode assembly (MEA) of fuel cells. Transmission electron microscopy (TEM) showed that the membrane was microphase-separated with a nanometer range with good connectivity of the $SO_3H$ ionic aggregates. The power density of a single $H_2/O_2$ fuel cell system using the membrane with 50 wt% PVA was $230\;mW/cm^2$ at $70^{\circ}C$ with a relative humidity of 100%. Thermogravimetric analysis (TGA) also showed a decrease in the thermal stability of the membranes with increasing PVA concentration.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.75.2-75.2
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• 2013

Atomic layer deposition (ALD), utilizing self-limiting surface reactions, could offer promising perspectives for future efficient energy conversion devices. The capabilities of ALD for surface/interface modification and construction of novel architectures with sub-nanometer precision and exceptional conformality over high aspect ratio make it more valuable than any other deposition methods in nanoscale science and technology. In the context, a variety of researches on fabrication of active materials for energy conversion applications by ALD are emerging. Among those materials, one-dimensional nanotubular titanium dioxide, providing not only high specific surface area but also efficient carrier transport pathway, is a class of the most intensively explored materials for energy conversion systems, such as photovoltaic cells and photo/electrochemical devices. The monodisperse, stoichiometric, anatase, TiO2 nanotubes with smooth surface morphology and controlled wall thickness were fabricated via low-temperature template-directed ALD followed by subsequent annealing. The ALD-grown, anatase, TiO2 nanotubes in alumina template show unusual crystal growth behavior which allows to form remarkably large grains along axial direction over certain wall thickness. We also fabricated dye-sensitized solar cells (DSCs) introducing our anatase TiO2 nanotubes as photoanodes, and studied the effect of blocking layer, TiO2 thin films formed by ALD, on overall device efficiency. The photon convertsion efficiency ~7% were measured for our TiO2 nanotubebased DSCs with blocking layers, which is ~1% higher than ones without blocking layer. We also performed open circuit voltage decay measurement to estimate recombination rate in our cells, which is 3 times longer than conventional nanoparticulate photoanodes. The high efficiency of our ALD-grown, anatase, TiO2 nanotube-based DSCs may be attributed to both enhanced charge transport property of our TiO2 nanotubes photoanode and the suppression of recombination at the interface between transparent conducting electrode and iodine electrolytes by blocking layer.

• Journal of the Korean institute of surface engineering
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• v.47 no.5
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• pp.263-268
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• 2014

Nanocrystalline diamond(NCD) coated SiC balls were applied in a ball-on-disk tribometer. After seeding in an ultrasonic bath containing nanometer diamond powders, $2.2{\mu}m$ thick NCD films were deposited on sintered 3 mm diameter SiC balls at $600^{\circ}C$ in a 2.45 GHz microwave plasma CVD system. Bare $ZrO_2$ and SiC balls were prepared for comparison as test balls. Tribology tests were performed in air with pairs of three different balls and mirror polished steel(SKH51) disk. The wear tracks on balls and disks were examined by optical microscope and alpha step profiler. Under the load of 3 N, the friction coefficients of steel against $ZrO_2$, SiC and NCD-coated balls were between 0.4 and 0.8. After a few thousands sliding laps, the friction coefficient of NCD-coated balls dropped from 0.45 to below 0.1 and maintained thereafter. Under a higher load of 10 N or 20 N with a long sliding distance of 2 km, $ZrO_2$ and SiC balls exhibited the similar friction coefficients as above. The friction coefficient of NCD-coated balls was less than 0.1 from the beginning and increased to above 0.1 steadily or with some fluctuations as sliding distance increased. NCD coating layers were found worn out after long duration and/or high load sliding test, which resulted in the friction coefficient higher than 0.1.

• Applied Chemistry for Engineering
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• v.32 no.4
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• pp.379-384
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• 2021

A microneedle is a tool that used for drug delivery and diagnosis. Unlike general injections, the microneedle is short in length, enabling effective drug delivery while minimizing pain and risk of infection. Conventionally, microneedles have been manufactured precisely at a nanometer level based on microelectro mechanical systems (MEMS) technology, requiring expensive equipments & maintenance and complicated processes. To address the issues, 3D printing research has been conducted to fabricate microneedles simply, economically, and rapidly. Since 3D printing facilitates to manufacture prototypes and apply feedbacks, it is advantageous for the development and commercialization of microneedle for pharmaceuticals and cosmetics. Therefore, this review will introduce stereolithography (SLA), two-photon polymerization (2PP), dynamic light processing (DLP), continuous liquid interface production (CLIP), and fused deposition modeling (FDM) 3D printing technologies and also highlight research trends for microneedle production using them. Furthermore, the limitation of the current microneedle technology and the direction to be solved in the future will be discussed.

• Advances in nano research
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• v.13 no.2
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• pp.187-197
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• 2022

The synthesis of organic and hybrid organic-inorganic perovskites directly from solution improves the cost- and energy-efficiency of processing. To date, numerous research efforts have been devoted to investigating the influence of the various solvent parameters for the synthesis of lead halide perovskites, focused on the effects of different single solvents on the efficiency of the resulting perovskites. In this work, we investigated the effect of solvent blends for the first time on the structure and phase of perovskites produced via the Lewis base vapor diffusion method to develop a new synthetic approach for water-stable CsPbBr₃ particles with nanometer-sized dimensions. Solvent blends prepared with DMF and water-miscible solvents with different Gutmann's donor numbers (D_N) affect the Pb ions differently, resulting in a variety of lead bromide species with various colors. The use of a DMF/isopropanol solvent mixture was found to induce the formation of the Ruddlesden-Popper perovskite based on lead bromide. This perovskite undergoes a blue color shift in the solvated state owing to the separation of nanoplatelets. In contrast, the replacement of isopropanol with DMSO, which has a high DN, induces the formation of spherical CsPbBr₃ perovskite nanoparticles that exhibit green emission. Finally, the integration of acetone in the solvent system leads to the formation of lead bromide complexes with a yellow-orange color and the perovskite CsPbBr₃.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.5
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• pp.205-211
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• 2022

The Granule Spray in Vacuum (GSV) process is a method of forming a dense nanostructured ceramic coating film by spraying ceramic granules on a substrate at room temperature in a vacuum. In the Granule Spray, the granules made by agglomerating particles with the size from submicrometer to micrometer can be sprayed into the substrate. Once the granules were squashed upon collision with the substrate, they become several dozens of nanometer-sized crystals in vacuum process. The zirconia of the monoclinic phase transform into tetragonal phase at 1150℃. At this time, its volume is changed by about 6.5 %. For this reason, it is widely held that it is difficult to acquire a compact of monoclinic zirconia sinter. In this study, the effect of particle treatment temperature and standoff distance on the substrate of zirconia granules were investigated in GSV. Also, particle treatment temperature, standoff distance, coating efficiency, and microstructure of the film were considered in forming the monoclinic zirconia coating film in GSV without any heating process. The deposited films exhibited monoclinic zirconia phase without any other detectable phase by X-ray diffractometer (XRD).