• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.2
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• pp.97-103
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• 2014

Phase transition properties of the copolymer films of polyvinylidene fluoride (PVDF) and trifluoroethylene(TrFE), P(VDF-TrFE), were studied with X-ray diffraction (XRD) and polarization modulated ellipsometry (PME). XRD studies on both Langmuir-Blodgett (LB) films and spin coated films exhibit conversions from ferroelectric phase to paraelectric phase at $108{\pm}2^{\circ}C$ on heating and paraelectric phase to ferroelectric phase at $78{\pm}2^{\circ}C$ on cooling. The presence of the ferroelectric-paraelectric phase transition is also confirmed by the PME technique for the first time in this study. PME was proved to be a very sensitive tool in the measurement of the structural changes at the nano-thickness films.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.3
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• pp.97-101
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• 2005

ZnO thin films were grown at different plume-substrate (P-S) angles of 90$^{\circ}$ (on-axis PLD), 45$^{\circ}$ and 0$^{\circ}$ (off-axis PLD) using pulsed laser deposition. The x-ray diffraction pattern exhibiting a dominant (002) and a minor (101) peak of ZnO indicates all films were strongly c-axis oriented. By observing of (002) peak, the FWHMs of ZnO (002) peaks decreased and c-axis lattice constant approached the value of bulk ZnO as P-S angle decreased. Whereas the carrier concentration of ZnO thin film deposited at P-S angle of 90$^{\circ}$ was ~ 10$^{19}$ /cm$^{3}$, the Hall measurement of ZnO thin films deposited at P-S angles of 0$^{\circ}$ and 45$^{\circ}$ was impossible due to the decrease of the carrier concentration by the improvement of stoichiometry and crystalline quality. By decreasing P-S angle, the grain size of the films and the UV intensity investigated by photoluminescence (PL) increased and UV peak position showed red shift. The improvement of properties in ZnO thin films deposited by off-axis technique was due to the decrease of repulsive force between a substrate and the particle in plume and the relaxation of supersaturation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.04b
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• pp.101-102
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• 2009

We described the growth of undoped ZnO thin films and their optical properties changing with a various growth temperature. The un doped ZnO thin films were grown on c-$Al_2O_3$ substrates using pulsed laser deposition (PLD) at room temperature, 200, 400, and $600^{\circ}C$, respectively. Field emission microscopy (FE-SEM) measurements showed that the grain size of undoped ZnO thin films are increasing as a increase of growth temperature. In addition, we were investigated that the structural and optical properties of undoped ZnO thin films by x-ray diffraction (XRD) and photoluminescence (PL) studied. Also, we could confirmed that the exciton luminescence was strongly related to charge trap by grain boundary of the samples using micro-PL measurement.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.361.1-361.1
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• 2014

PbVO3 (PVO), a polar magnetic material considered as a candidate of multiferroic, has ferroelectricity along the c-axis and 2-dimensional antiferromagnetism lying in the in-plane through epitaxial growth [1,2]. PVO thin films were grown on LaAlO3 (001) substrates under reduction atmosphere from a stable Pb2V2O7 sintered target using pulsed laser deposition method. Epitaxial growth of the PVO films is possible only under Ar atmospheren with no oxygen partial pressure. X-ray diffraction was used to investigate the phase formation and texture of the films. We confirmed epitaxial growth of the PVO films with crystalline relationship of PbVO3[001]//LaAlO3[001] and PbVO3[100]//LaAlO3[100]. In addition, surface morphology of the films displays drastic changes in accordance with the growth conditions. Elongated PVO grains are related to the Pb2V2O7 pyrochlore structure. The relation between structural deformation and ferroelectricity in the PVO films was examined by local measurement of piezoresponse force microscopy.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.2
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• pp.181-186
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• 2000

The setup of the moir$\acute{e}$ deflectometry using the virtual grating was done, so the convergence and divergence of a pencil of ray was determined. The light source was He-Ne laser(3mW). The focal length of the first lens, the second lens being 18 mm, 250 mm respectively was used for the setup of the beam expander. The optics of the moir$\acute{e}$ deflectometry determining the vergence was used a diffraction grating(pitch = $1.6{\mu}m/line$) and a front flat reflection mirror. The effective focal length of the trial lens set was measured and compared with the theoretical value.

• Journal of the Korean institute of surface engineering
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• v.29 no.5
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• pp.437-442
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• 1996

High quality $YBa_2Cu_3O_y$(YBCO) thin films for directly coupled dc superconducting quantum interference device (SQUID) were fabricated by pulsed laser deposition. Several critical parameters have been optimized through systematic studies. Thus, the films showing the $T_c$ of above 91K and $J_c$ of above$2\times10^6A/cm^2$ at 77K were routinely obtained. Extensive AFM and X-ray diffraction studies have been conducted for morphological and structural analyses. The directly coupled DC-SQUIDs were fabricated from the YBCO thin films deposited on $SrTiO_3$ bicrystals under the optimized conditions. The measurement on $2I_c$ and swing voltage give 200$\mu$A and 17$\mu$V at 77K, respectively.

• Korean Journal of Materials Research
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• v.33 no.6
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• pp.229-235
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• 2023

An all-perovskite oxide heterostructure composed of SrSnO₃/Nb-doped SrTiO₃ was fabricated using the pulsed laser deposition method. In-plane and out-of-plane structural characterization of the fabricated films were analyzed by x-ray diffraction with θ-2θ scans and φ scans. X-ray photoelectron spectroscopy measurement was performed to check the film's composition. The electrical transport characteristic of the heterostructure was determined by applying a pulsed dc bias across the interface. Unusual transport properties of the interface between the SrSnO₃ and Nb-doped SrTiO₃ were investigated at temperatures from 100 to 300 K. A diodelike rectifying behavior was observed in the temperature-dependent current-voltage (IV) measurements. The forward current showed the typical IV characteristics of p-n junctions or Schottky diodes, and were perfectly fitted using the thermionic emission model. Two regions with different transport mechanism were detected, and the boundary curve was expressed by ln I = -1.28V - 13. Under reverse bias, however, the temperature- dependent IV curves revealed an unusual increase in the reverse-bias current with decreasing temperature, indicating tunneling effects at the interface. The Poole-Frenkel emission was used to explain this electrical transport mechanism under the reverse voltages.

• Journal of ILASS-Korea
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• v.20 no.2
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• pp.82-87
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• 2015

A nozzle with vortex generator was used to develop the low pressure nozzle with high atomization performance and the nozzle atomized the liquid by centrifugal shear forces. In order to analyze the atomization characteristics, a shadowgraphy method was used and the measurement of droplet size was performed by using laser diffraction analyzer. The liquid injection pressure was fixed as 0.03 bar which is very low pressure and the gas injection pressures were changed from 0 bar to 2.0 bar. As a result, the breakup was achieved at the air injection pressure of 0.25 bar and over. The nozzle with the orifice diameter of 0.4 mm and the orifice gap of 0.25 mm presented small droplet diameters under 50 at the air injection pressure of 0.75 bar.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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• pp.132-139
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• 1997

Spray characteristics of external mixing sonic twin-fluid atomization nozzles are investigated experimentally. Particle sizes are measured by the Fraunhofer diffraction method using the Malvern particle analyzer, and their radial distributions are obtained using the tomographical transformation technique. The spatial distribution of SMD shows that the drop size increases in the radial direction at a fixed liquid flow rate, and the distribution is getting uniform rapidly as the atomizing gas pressure increases. The SMD decreases as the liquid flow rate increases at a fixed GLR. It is found that the atomization efficiency of the flush type sonic nozzle is superior to that of protrusion type. The effect of laser beam diameter of the particle analyzer on the spatial SMD distribution is minor at present experimental conditions.

• Journal of ILASS-Korea
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• v.16 no.4
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• pp.210-214
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• 2011

This paper presents the spray characteristics of the gun type burner nozzle with bio-diesel blending rate. The burner nozzle used in this experiment is a pressure swirl type nozzle. For the spray characteristics, visualization of spray was conducted to obtain the spray angle, and laser diffraction spectroscope (LDS) was used for the measurement of the droplet diameters. The results showed that the $D_{max}$, SMD and spray angle were decreased with increasing the bio-diesel blending rate and BD30 (30% bio-diesel blending rate) could be found to be the maximum blending rate for using without any modification of the gun type burner of the homesize kerosene fuel boiler.