• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.3
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• pp.112-117
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• 2018

The metal alkoxide, CuCo-glycerate nanospheres (NSs), were successfully synthesized as Cu-Co bimetallic sulfides hierarchical multi-shelled hollow nanospheres ($CuCo_2S_4$ HMHNSs) through solvothermal synthesis. In this reaction mechanism, the solvothermal temperature and the amount of glycerol as a cosurfactant play significant role to optimize the morphology of CuCo-glycerate NSs. Furthermore, $CuCo_2S_4$ HMHNSs were obtained under optimized sulfurization reaction time of 10 h via anion exchange reaction between glycerate and sulfur ions. Finally, the structural and chemical compositions of CuCo-glycerate NSs and $CuCo_2S_4$ HMHNSs were confirmed through field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and electrochemical performances.

• Journal of the Korean Society of Clothing and Textiles
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• v.35 no.11
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• pp.1297-1308
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• 2011

This research investigates the application of ZnO (zinc oxide) nanoparticles and $TiO_2$ (titanium dioxide) nanoparticles to polypropylene nonwoven fabrics via an electrospinning technique for the development of textile materials that can decompose harmful gases. To fabricate uniform ZnO nanocomposite fibers, two types of ZnO nanoparticles were applied. Colloidal $TiO_2$ nanoparticles were chosen to fabricate $TiO_2$ nano- composite fibers. ZnO/poly(vinyl alcohol) (PVA) and $TiO_2$/PVA nanocomposite fibers were electrospun under a variety of conditions that include various feed rates, electric voltages, and capillary diameters. The morphology of electrospun nanocomposite fibers was examined with a field-emission scanning electron micro- scope and a transmission electron microscope. Decomposition efficiency of gaseous materials (formaldehyde, ammonia, toluene, benzene, nitrogen dioxide, sulfur dioxide) by nanocomposite fiber webs with 3wt% nano-particles (ZnO or $TiO_2$) and 7$g/m^2$ web area density was assessed. This study shows that ZnO nanoparticles in colloid were more suitable for fabricating nanocomposite fibers in which nanoparticles are evenly dispersed than in powder. A heat treatment was applied to water-soluble PVA nanofiber webs in order to stabilize the electrospun nanocomposite fibrous structure against dissolution in water. ZnO/PVA and $TiO_2$/PVA nanofiber webs exhibited a range of degradation efficiency for different types of gases. For nitrogen dioxide, the degradation efficiency was 92.2% for ZnO nanocomposite fiber web and 87% for $TiO_2$ nanocomposite fiber web after 20 hours of UV light irradiation. The results indicate that ZnO/PVA and $TiO_2$/PVA nano- composite fiber webs have possible uses in functional textiles that can decompose harmful gases.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.1
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• pp.16-22
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• 2008

We fabricated thermally-evaporated 10 nm-Ni/30 nm and 70 nm Poly-Si/200 nm-$SiO_2/Si$ structures to investigate the thermal stability of nickel silicides formed by rapid thermal annealing(RTA) of the temperature of $300{\sim}1100^{\circ}C$ for 40 seconds. We employed for a four-point tester, field emission scanning electron microscope(FE-SEM), transmission electron microscope(TEM), high resolution X-ray diffraction(HRIXRD), and scanning probe microscope(SPM) in order to examine the sheet resistance, in-plane microstructure, cross-sectional microstructure evolution, phase transformation, and surface roughness, respectively. The silicide on 30 nm polysilicon substrate was stable at temperature up to $900^{\circ}C$, while the one on 70 nm substrate showed the conventional $NiSi_2$ transformation temperature of $700^{\circ}C$. The HRXRD result also supported the existence of NiSi-phase up to $900^{\circ}C$ for the Ni silicide on the 30 nm polysilicon substrate. FE-SEM and TEM confirmed that 40 nm thick uniform silicide layer and island-like agglomerated silicide phase of $1{\mu}m$ pitch without residual polysilicon were formed on 30 nm polysilicon substrate at $700^{\circ}C\;and\;1000^{\circ}C$, respectively. All silicides were nonuniform and formed on top of the residual polysilicon for 70 nm polysilicon substrates. Through SPM analysis, we confirmed the surface roughness was below 17 nm, which implied the advantage on FUSI gate of CMOS process. Our results imply that we may tune the thermal stability of nickel monosilicide by reducing the height of polysilicon gate.

• Korean Journal of Materials Research
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• v.13 no.8
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• pp.497-502
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• 2003

Crystallographic characteristics and interfacial structures of $Al_2$$O_3$and $ZrO_2$dielectric films prepared by atomic layer chemical vapor deposition (ALCVD) were investigated at atomic scale by high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS)/electron energy-loss spectroscopy (EELS) coupled with a field-emission transmission electron microscope. The results obtained from cross-sectional and plan-view specimens showed that the $Al_2$$O_3$film was crystallized by annealing at a high temperature and its crystal system might be evaluated as either cubic or tetragonal phase. Whereas the $ZrO_2$film crystallized during deposition at a low temperature of ∼$300^{\circ}C$ was composed of both tetragonal and monoclinic phase. The interfacial thickness in both films was increased with the increased annealing temperature. Further, the interfacial structures of X$ZrO_2$$O_3$and $ZrO_2$films were discussed through analyses of EDS elemental maps and EELS spectra obtained from the annealed films, respectively.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.1 s.38
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• pp.1-5
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• 2006

We prepared 80 nm-thick TiSix on each 70 nm-thick amorphous silicon and polysilicon substrate using an RF sputtering with $TiSi_2$ target. TiSix composite silicide layers were stabilized by rapid thermal annealing(RTA) of $800^{\circ}C$ for 20 seconds. Line width of $0.5{\mu}m$ patterns were embodied by photolithography and dry etching process, then each additional annealing process at $750^{\circ}C\;and\;850^{\circ}C$ for 3 hours was executed. We investigated the change of sheet resistance with a four-point probe, and cross sectional microstructure with a field emission scanning electron microscope(FE-SEM) and transmission electron microscope(TEM), respectively. We observe an abrupt change of resistivity and voids at the silicide surface due to interdiffusion of silicide and composite titanium silicide in the amorphous substrates with additional $850^{\circ}C$ annealing. Our result implies that the electrical resistance of composite titanium silicide may be tunned by employing appropriate substrates and annealing condition.

• Journal of the Korean Vacuum Society
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• v.16 no.4
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• pp.279-285
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• 2007

We have demonstrated structural evolution and optical properties of the Si-NWs on Si (111) substrates with synthesized nanoscale Au-Si islands by rapid thermal chemical vapor deposition(RTCVD). Au nano-islands (10-50nm in diameter) were employed as a liquid-droplet catalysis to grow Si-NWs via vapor-liquid-solid mechanism. Si-NWs were grown by a mixture gas of $SiH_4\;and\;H_2$ at pressures of $0.1{\sim}1.0$Torr and temperatures of $450{\sim}650^{\circ}C$. SEM measurements showed the formation of Si-NWs well-aligned vertically for Si (111) surfaces. The resulting NWs are 30-100nm in diameter and $0.4{\sim}12um$ in length depending on growth conditions. HR-TEM measurements indicated that Si-NWs are single crystals convered with about 3nm thick layers of amorphous oxide. In addition, optical properties of NWs were investigated by micro-Raman spectroscopy. The downshift and asymmetric broadening of the Si optical phonon peak with a shoulder at $480cm^{-1}$ were observed in Raman spectra of Si-NWs.

• Tissue Engineering and Regenerative Medicine
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• v.15 no.6
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• pp.735-750
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• 2018

BACKGROUND: The major challenge of tissue engineering is to develop constructions with suitable properties which would mimic the natural extracellular matrix to induce the proliferation and differentiation of cells. Poly(${\varepsilon}$-caprolactone)-poly(ethylene glycol)-poly(${\varepsilon}$-caprolactone) (PCL-PEG-PCL, PCEC), chitosan (CS), nano-silica ($n-SiO_2$) and nano-hydroxyapatite (n-HA) are biomaterials successfully applied for the preparation of 3D structures appropriate for tissue engineering. METHODS: We evaluated the effect of n-HA and $n-SiO_2$ incorporated PCEC-CS nanofibers on physical properties and osteogenic differentiation of human dental pulp stem cells (hDPSCs). Fourier transform infrared spectroscopy, field emission scanning electron microscope, transmission electron microscope, thermogravimetric analysis, contact angle and mechanical test were applied to evaluate the physicochemical properties of nanofibers. Cell adhesion and proliferation of hDPSCs and their osteoblastic differentiation on nanofibers were assessed using MTT assay, DAPI staining, alizarin red S staining, and QRT-PCR assay. RESULTS: All the samples demonstrated bead-less morphologies with an average diameter in the range of 190-260 nm. The mechanical test studies showed that scaffolds incorporated with n-HA had a higher tensile strength than ones incorporated with $n-SiO_2$. While the hydrophilicity of $n-SiO_2$ incorporated PCEC-CS nanofibers was higher than that of samples enriched with n-HA. Cell adhesion and proliferation studies showed that n-HA incorporated nanofibers were slightly superior to $n-SiO_2$ incorporated ones. Alizarin red S staining and QRT-PCR analysis confirmed the osteogenic differentiation of hDPSCs on PCEC-CS nanofibers incorporated with n-HA and $n-SiO_2$. CONCLUSION: Compared to other groups, PCEC-CS nanofibers incorporated with 15 wt% n-HA were able to support more cell adhesion and differentiation, thus are better candidates for bone tissue engineering applications.

• Current Optics and Photonics
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• v.2 no.5
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• pp.474-481
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• 2018

We propose a polarization phase-shifting technique to investigate the thickness of $Ta_2O_5$ thin films deposited on BK7 substrates, using a modified Sagnac interferometer. Incident light is split by a polarizing beam splitter into two orthogonal linearly polarized beams traveling in opposite directions, and a quarter-wave plate is inserted into the common path to create an unbalanced phase condition. The linearly polarized light beams are transformed into two circularly polarized beams by transmission through a quarter-wave plate placed at the output of the interferometer. The proposed setup, therefore, yields rotating polarized light that can be used to extract a relative phase via the self-reference system. A thin-film sample inserted into the cyclic path modifies the output signal, in terms of the phase retardation. This technique utilizes three phase-shifted intensities to evaluate the phase retardation via simple signal processing, without manual adjustment of the output polarizer, which subsequently allows the thin film's thickness to be determined. Experimental results show that the thicknesses obtained from the proposed setup are in good agreement with those acquired by a field-emission scanning electron microscope and a spectroscopic ellipsometer. Thus, the proposed interferometric arrangement can be utilized reliably for non-contact thickness measurements of transparent thin films and characterization of optical devices.

• Korean Journal of Materials Research
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• v.27 no.12
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• pp.705-709
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• 2017

The electronic and optical characteristics of molybdenum disulphide ($MoS_2$) film significantly vary with its thickness, and thus a rapid and accurate estimation of the number of $MoS_2$ layers is critical in practical applications as well as in basic researches. Various existing methods are currently available for the thickness measurement, but each has drawbacks. Transmission electron microscopy allows actual counting of the $MoS_2$ layers, but is very complicated and requires destructive processing of the sample to the point where it will no longer be useable after characterization. Atomic force microscopy, particularly when operated in the tapping mode, is likewise time-consuming and suffers from certain anomalies caused by an improperly chosen set point, that is, free amplitude in air for the cantilever. Raman spectroscopy is a quick characterization method for identifying one to a few layers, but the laser irradiation causes structural degradation of the $MoS_2$. Optical microscopy works only when $MoS_2$ is on a silicon substrate covered with $SiO_2$ of 100~300 nm thickness. The last two optical methods are commonly limited in resolution to the micrometer range due to the diffraction limits of light. We report here a method of measuring the distribution of the number of $MoS_2$ layers using a low voltage field emission electron microscope with acceleration voltages no greater than 1 kV. We found a linear relationship between the FESEM contrast and the number of $MoS_2$ layers. This method can be used to characterize $MoS_2$ samples at nanometer-level spatial resolution, which is below the limits of other methods.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.3
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• pp.71-76
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• 2017

The electrical behavior and flexibility of the screen printed Ag circuits were investigated with infrared radiation sintering times and sintering temperatures. Electrical resistivity and radio frequency characteristics were evaluated by using the 4 point probe measurement and the network analyzer by using cascade's probe system, respectively. Electrical resistivity and radio frequency characteristics means that the direct current resistance and signal transmission properties of the printed Ag circuit. Flexibility of the screen printed Ag circuit was evaluated by measuring of electrical behavior during IPC sliding test. Failure mode of the Ag printed circuits was observed by using field emission scanning electron microscope and optical microscope. Electrical resistivity of the Ag circuits screen printed on Pl substrate was rapidly decreased with increasing sintering temperature and durations. The lowest electrical resistivity of Ag printed circuit was up to $3.8{\mu}{\Omega}{\cdot}cm$ at $250^{\circ}C$ for 45 min. The crack length arisen within the printed Ag circuit after $10{\times}10^4$ sliding numbers was 10 times longer than that of after $2.5{\times}10^4$ sliding numbers. Measured insertion loss and calculated insertion loss were in good agreements each other. Insertion loss of the printed Ag circuit was increased with increasing the number of sliding cycle.