• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.8
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• pp.875-880
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• 2014

Recently, three-dimensional scaffolds and nanofibers are being developed for bone tissue regeneration. In this study, we fabricated a hybrid scaffold using a nano-micro precision deposition system. The fabrication process involved the application of the solid freeform fabrication (SFF) technology and electrospinning. The hybrid scaffolds were combined using micro scaffolds and nanofibers. The nanofibers were deposited on each layer of the micro scaffolding using the electrospinning process. The micro scaffolds were fabricated using the SFF technology at a temperature of $100^{\circ}C$, pressure of 650 kPa, and scan velocity of 250 mm/s. Nanofiber fabrication was conducted by means of electrospinning using the flow rate, solution concentration, distance from the tip to the collector (TCD), and voltage. The nanofibers were fabricated using a flow rate of 0.1 ml/min, voltage of 5 kV, TCD of 1 mm, and 10 wt% of solution concentration. MG-63 cells were seeded into the hybrid scaffold for the purpose of its evaluation.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.489.2-489.2
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• 2014

The planar type flexible piezoelectric energy harvesters (PEH) based on PbZr0.52Ti0.48O3 (PZT) thin films on the flexible substrates are demonstrated to convert mechanical energy to electrical energy. The planar type energy harvesters have been realized, which have an electrode pair on the PZT thin films. The PZT thin films were deposited on double side polished sapphire substrates using conventional RF-magnetron sputtering. The PZT thin films on the sapphire substrates were transferred by PDMS stamp with laser lift-off (LLO) process. KrF excimer laser (wavelength: 248nm) were used for the LLO process. The PDMS stamp was attached to the top of the PZT thin films and the excimer laser induced onto back side of the sapphire substrate to detach the thin films. The detached thin films on the PDMS stamp transferred to adhesive layer coated on the flexible polyimide substrate. Structural properties of the PZT thin films were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). To measure piezoelectric power generation characteristics, Au/Cr inter digital electrode (IDE) was formed on the PZT thin films using the e-beam evaporation. The ferroelectric and piezoelectric properties were measured by a ferroelectric test system (Precision Premier-II) and piezoelectric force microscopy (PFM), respectively. The output signals of the flexible PEHs were evaluated by electrometer (6517A, Keithley). In the result, the transferred PZT thin films showed the ferroelectric and piezoelectric characteristics without electrical degradation and the fabricated flexible PEHs generated an AC-type output power electrical energy during periodically bending and releasing motion. We expect that the flexible PEHs based on laser transferred PZT thin film is able to be applied on self-powered electronic devices in wireless sensor networks technologies. Also, it has a lot of potential for high performance flexible piezoelectric energy harvester.

• Korean Journal of Materials Research
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• v.23 no.6
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• pp.304-308
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• 2013

The effect of a sputter deposition sequence of Cu, Zn, and Sn metal layers on the properties of $Cu_2ZnSnS_4$ (CZTS) was systematically studied for solar cell applications. The set of Cu/Sn/Zn/Cu multi metal films was deposited on a Mo/$SiO_2$/Si wafer using dc sputtering. CZTS films were prepared through a sulfurization process of the Cu/Sn/Zn/Cu metal layers at $500^{\circ}C$ in a $H_2S$ gas environment. $H_2S$ (0.1%) gas of 200 standard cubic centimeters per minute was supplied in the cold-wall sulfurization reactor. The metal film prepared by one-cycle deposition of Cu(360 nm)/Sn(400 nm)/Zn(400 nm)/Cu(440 nm) had a relatively rough surface due to a well-developed columnar structure growth. A dense and smooth metal surface was achieved for two- or three-cycle deposition of Cu/Sn/Zn/Cu, in which each metal layer thickness was decreased to 200 nm. Moreover, the three-cycle deposition sample showed the best CZTS kesterite structures after 5 hr sulfurization treatment. The two- and three-cycle Cu/Sn/Zn/Cu samples showed high-efficient photoluminescence (PL) spectra after a 3 hr sulfurization treatment, wheres the one-cycle sample yielded poor PL efficiency. The PL spectra of the three-cycle sample showed a broad peak in the range of 700-1000 nm, peaked at 870 nm (1.425 eV). This result is in good agreement with the reported bandgap energy of CZTS.

• Korean Journal of Materials Research
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• v.9 no.5
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• pp.509-514
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• 1999

Interest in the integrated capacitors, which make it possible to reduce the size of and to obtain improved electrical performance of an electronic system, is expanding. In this study, $Ta_2$O\ulcorner thin film capacitors for MCM integrated capacitors were fabricated on a Upilex-S polymer film by DC magnetron reactive sputtering and the effects of low temperature annealing at various atmospheres and substrate surface morphology on the capacitor characteristics were discussed. The low temperature($150^{\circ}C$) annealing produced improved capacitor yield irrespective of the annealing at mosphere. But the leakage current of the $O_2$-annealed film was larger than that of any other films. This is presumably mosphere. But the leakage current of the $O_2$-annealed film was larger than that of any other films. This is presumably due to the change of the $Ta_2$O\ulcorner film surface by oxygen, which was explained by conduction mechanism study. Leakage current and breakdown field strength of the capacitors fabricated on the Upilex-S film were 7.27$\times$10\ulcornerA/$\textrm{cm}^2$ and 1.0 MV/cm respectively. These capacitor characteristics were inferior to those of the capacitors fabricated on the Si substrate but enough to be used for decoupling capacitors in multilayer package. Roughness Analysis of each layer by AFM demonstrated that the properties of the capacitors fabricated on the polymer film were affected by the surface morphology of the substrate. This substrate effect could be classified into two factors. One is the surface morphology of the polymer film and the other is the surface morphology of the metal bottom electrode determined by the deposition process. Therefore, the control of the two factors is important to obtain improved electrical of capacitors deposited on a polymer film.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.275-277
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• 2003

최근 logic 소자의 gate oxide로 기존의 $SiO_2$, SiON보다 고유전, 작은 누설전류를 가지는 물질의 개발이 중요한 이슈가 되고 있다. 본 실험실에서는 Si 기판위에 $HfO_2$를 바로 증착하는 경우, 기판의 Si이 박막내로 확산하여 유전율이 저하되는 문제점을 인식하고, 기판과 $HfO_2$ 사이에 $AlO_x$를 방지막으로 사용하였다. 이 때, $AlO_x$의 Al precursor는 TMA로 고정하고, 산화제로는 $H_2O$, $O_2$-plasma, $O_3$를 각각 사용하였다. 모든 $AlO_x/\;HfO_y$ 박막에서 매우 우수한 누설전류특성을 얻을 수 있었는데, 특히 $O_3$를 산화제로 사용한 $AlO_x$방지막의 경우 가장 우수한 특성을 보였다. 또한 질소 분위기에서 $800^{\circ}C$ 10분간 열처리한 후, 방지막을 사용한 모든 경우에서 보다 향상된 열적 안정성을 관찰할 수 있었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.47-52
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• 2002

A processing method is developed for preparing sol-gel derived $Pb(Zr_{1-x}Ti_x)O_3$ (x=0.5) thin films on Pt-Ir($Pt_{80}Ir_{20}$)-alloy substrates. The as-deposited layer was dried on a plate in air at $70^{\circ}C$. And then it was baked at $1500^{\circ}C$, annealed at $450^{\circ}C$ and finally annealed for crystallization at various temperatures ranging from $580^{\circ}C$ to $700^{\circ}C$ for 1hour in a tube furnace. The thickness of the annealed film with three layers was $0.3{\mu}m$. Crystalline properties and surface morphology were examined using X-ray diffractometer (XRD). Electrical properties of the films such as dielectric constant, C-V, leakage current density were measured under different annealing temperature. The PZT thin film which was crystallized at $600^{\circ}C$ for 60minutes showed the best structural and electrical dielectric constant is 577. C-V measurement show that $700^{\circ}C$ sample has window memory volt of 2.5V and good capacitance for bias volts. Leakage current density of every sample show $10^{-8}A/cm^2$ r below and breakdown voltage(Vb) is that 25volts.

• Journal of the Korean institute of surface engineering
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• v.51 no.2
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• pp.126-132
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• 2018

SnS thin films with different substrate temperatures ($150 {\sim}300^{\circ}C$) as process parameters were grown on soda-lime glass substrates by RF magnetron sputtering. The effects of substrate temperature on the structural and optical properties of SnS thin films were investigated by X-ray diffraction (XRD), Raman spectroscopy (Raman), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and Ultraviolet-visible-near infrared spectrophotometer (UV-Vis-NIR). All of the SnS thin films prepared at various substrate temperatures were polycrystalline orthorhombic structures with (111) planes preferentially oriented. The diffraction intensity of the (111) plane and the crystallite size were improved with increasing substrate temperature. The three major peaks (189, 222, $289cm^{-1}$) identified in Raman were exactly the same as the Raman spectra of monocrystalline SnS. From the XRD and Raman results, it was confirmed that all of the SnS thin films were formed into a single SnS phase without impurity phases such as $SnS_2$ and $Sn_2S_3$. In the optical transmittance spectrum, the critical wavelength of the absorption edge shifted to the long wavelength region as the substrate temperature increased. The optical bandgap was 1.67 eV at the substrate temperature of $150^{\circ}C$, 1.57 eV at $200^{\circ}C$, 1.50 eV at $250^{\circ}C$, and 1.44 eV at $300^{\circ}C$.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.155-155
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• 2017

Surface modifications are commonly utilized to adjust the properties of the titanium and its alloy surface to the specific needs of the medical applications, but there are disadvantages such as poor osteoconductive properties and low adhesion of bone cell to implant surface. In order to improve these disadvantages, changes in surface properties have an important effect on osseointegration during implantation. In this paper we applied new technological method for improving a unique surface modification using the characteristic of an electrolytic Solution. Thus, in the electrolyte containing NaF in Na2SO4, TiO2 nanoporous was uniformly formed, and HAp nanoparticles were electrodeposited around the TiO2 nanopores, but in the electrolyte containing NH4F in (NH4)H2PO4, the coarse protrusions including HAp nano particles were regularly deposited onto the TiO2 barrier layer. The surface characteristics and the distributed elements and have been investigated by EDS analysis, and ultra-fine structure of surface are carried out using FE-SEM. To investigate the behavior of the anion, the analysis of chemical states was performed by XPS, and the narrow spectrums for Ti2P, Ca 2p, and P 2p seems to be almost similar depending on the characteristics of the electrolyte solution respectively. In addition, Ca 2p spectrum could be resolved into two peaks for Ca 2p3/2 and 2p1/2 at 347.4 and 351.3 eV, which are related to hydroxyapatite. And, the P peak can also be deconvoluted into two peaks for P1/2 and P3/2 levels with binding energy 134.2 and 133.4 eV, respectively. From the result of soaking test, the apatite morphologys were well-formed onto the modified surface according to the different conditions.

• Journal of Korean Ophthalmic Optics Society
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• v.7 no.1
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• pp.75-78
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• 2002

Thirty three layer $TiO_2/SiO_2$ coating mirrors with high reflectance through a 620~820nm wavelength range have been designed and fabricated by electron beam evaporation method. Multilayer films were deposited on glass(BK7) and sequentially. The high reflector design is based on alternating high and low refractive index layers. $n_H$ and $n_L$ such that a "stopband"(or area of high reflectivity) is created that is centered around the design wavelength. ${\lambda}_0$. The measured transmittance spectrum with an incident wavelength at an incident angle of $40^{\circ}{\pm}7^{\circ}$ exhibited a reflectance of 99.9% at the wavelength of 620~820nm but high peak transmittance in the wavelength region from 700 to 740nm.

• Analytical Science and Technology
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• v.30 no.6
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• pp.319-328
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• 2017

The identification of explosive residues on specimens obtained from an explosion event is a crucial factor for assessing the cause of the explosion. In order to detect the components of explosives, the explosive residues deposited on surfaces are commonly extracted using swabbing materials pre-wetted with an organic solvent. The residues are then analyzed with analytical instruments such as LC/MS and CE/MS. Most conventionally used swabbing media such as cotton swabs or cotton tip swabs seem unsuitable for extracting explosive residues from the surface of a large area of clothes because the swabbing materials tend to be damaged easily, and because only a relatively small amount of explosives is collected. To overcome these problems, we have introduced a novel wiper ($215{\times}210mm$, single layer, Yuhan-Kimberly, Republic of Korea) as a swabbing material to recover representative organic explosives, namely, TNT, RDX, tetryl, HMX, PETN, and NG, from a large area of clothes. Different sides of the wiper, which was folded in half five times, was used to swab the surface of a clothing. We compared this novel wiper with a cotton swab and a cotton tip swab in terms of the recovery efficiency for the aforementioned organic explosives by pre-wetting with methanol, acetone, and acetonitrile, respectively. We identified that this novel wiper collected a significantly higher amount of organic explosive residues than a cotton swab or a cotton tip swab when using methanol as an extracting solvent.