• Korean Journal of Materials Research
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• v.13 no.6
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• pp.347-351
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• 2003

II-Ⅵ ZnO compound semiconductor thin films were grown on $\alpha$-Al$_2$O$_3$(0001) single crystal substrate by radical beam assisted molecular beam epitaxy and the optical properties were investigated. Zn(6N) was evaporated using Knudsen cell and O radical was assisted at the partial pressure of 1$\times$10$^{4}$ Torr and radical beam source of 250-450 W RF power. In $\theta$-2$\theta$ x-ray diffraction analysis, ZnO thin film with 500 nm thickness showed only ZnO(0002)and ZnO(0004) peaks is believed to be well grown along c-axis orientation. Photoluminescence (PL) measurement using He-Cd ($\lambda$=325 nm) laser is obtained in the temperature range of 9 K-300 K. At 9 K and 300 K, only near band edge (NBE) is observed and the FWHM's of PL peak of the ZnO deposited at 450 RF power are 45 meV and 145 meV respectively. From no observation of any weak deep level peak even at room temperature PL, the ZnO grains are regarded to contain very low defect density and impurity to cause the deep-level defects. The peak position of free exciton showed slightly red-shift as temperature was increased, and from this result the binding energy of free exciton can be experimentally determined as much as $58\pm$0.5 meV, which is very closed to that of ZnO bulk. By van der Pauw 4-point probe measurement, the grown ZnO is proved to be n-type with the electron concentration($n_{e}$ ) $1.69$\times$10^{18}$$cm^3$, mobility($\mu$) $-12.3\textrm{cm}^2$/Vㆍs, and resistivity($\rho$) 0.30 $\Omega$$\cdot$cm.

• Proceedings of the Optical Society of Korea Conference
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• 2008.02a
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• pp.281-282
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• 2008

The glancing angle deposition (GLAD) technique was used to fabricate $ZrO_2$ thin films by electron-beam evaporation. The crystal structure, cross-sectional structure, surface morphology and optical properties are characterized by X-ray diffraction meter (XRD, Rigaku, Cu $K{\alpha}$ - radiation), scanning electron microscope (SEM), and spectrophotometer, respectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.885-886
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• 2010

• Journal of Radiation Protection and Research
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• v.23 no.1
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• pp.33-47
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• 1998

Using a combination of an X-ray generator Installed in radiation calibration laboratory of Korea Atomic Energy Research Institute (KAERI) and a series of 8 radiators and filters described in ISO-4037, monoenergetic fluorescent X-rays from 8.6 keV to 75 keV were produced. This fluorescent X-rays generated by primary X-rays from radiator were discriminated $K_{\beta}$ lines with the aid of filter material and the only $K_{\alpha}$ X-rays were analyzed with the high purity Ge detector and portable MCA. The air kerma rates were measured with the 35 co ionization chamber and compared with the calculational results, and the beam uniformity and the scattered effects of radiation fields were also measured. The beam purities were more than 90 % for the energy range of 8.6 keV to 75 keV and the air kerma rates were from 1.91 mGy/h (radiator : Au, filter : W) to 54.2 mGy (radiator : Mo, filter : Zr) at 43 cm from center of the radiator. The effective area of beam at the measurement point of air kerma rates was 12 cm ${\times}$ 12 cm and the influence of scattered radiation was less than 3 %. The fluorescent X-rays established in this study could be used for the determination of energy response of the radiation measurement devices and the personal dosemeters in low photon energy regions.

• Journal of Radiation Protection and Research
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• v.21 no.2
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• pp.125-129
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• 1996

The energy response of HPGe detector for low energy Photons was determined by using three Monte Carlo codes. MCNP4A. EGS4, and CYLTRAN in ITS3. In this study. bare HPGe detector$(100 mm^2{\times}10mm)$ was used and a pencil beam was incident perpendicularly on the center of the detector surface. The photopeak efficiency, $K_{\alpha}$ and $K_{\beta}$ escape fractions were calculated as a function of incident X-ray energies ranging from 12 to 60 keV in 2-keV increments. Since the Compton. elastic. ana penetration fraction were negligible in this energy range. they were ignored in the calculation. Although MCNP. EGS, and CYLTRAN codes calculated slightly different energy response of HPGe detector for low energy Photons, it appears that the three Monte Carlo codes can Predict the low energy Photon scattering Processes accurately. The MCNP results, which are generally known as to be less accurate at low energy ranges than the EGS and ITS results. are comparable to the results of EGS and ITS and are applicable to the calculation of the low energy response data of a detector.

• Proceedings of the Korean Vacuum Society Conference
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• 1995.02a
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• pp.36-36
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• 1995

The cubic (zinc blende) CdSe eppilayers were grown on GaAs(100) substrates by electron beam (e-beam) evapporation technique. X-ray scans with copper $K\alpha$ radiation indicate that the CdSe eppilayers are zinc blende. The lattice pparameter obtained from the (400) reflection is 6.077$\AA$, which is in excellent agreement with the value repported in the literature for zinc blende CdSe. The orientation of as-grown CdSe eppilayer is determined by electron channeling ppatterns(ECpp). The crystallinity of heteroeppitaxial CdSe layers were investigated based on the double crystal x-ray rocking curve(DCRC). The deppendence of the rocking curve width on layer thickness was studied. The FWHM(full width at half maximum) of CdSe eppilayers grown on GaAs(100) substrates is decreasing with increasing eppilayer thickness. The carrier concentration and mobility of the as-grown eppilayers deduced Hall data by van der ppauw method, are about 7$\times$1017 cm-3 and 2$\times$102 $\textrm{cm}^2$ / sec at room tempperature, resppectively. The energy gapp was determinded from the pphotocurrent sppectrum. In pphotocurrent sppectrum of a 1-${\mu}{\textrm}{m}$-thick CdSe eppilayer at 30K, the ppeak at 1.746 eV is due to the free exciton of cubic CdSe. In summary, We have shown that eppilayers of zinc blende CdSe can be grown on GaAs(100) substrates by e-beam, desppite the large mismatch between eppilayer and substrate, as well as the natural ppreference for CdSe to form in the wurtzite structure.

• Journal of Powder Materials
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• v.25 no.4
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• pp.340-345
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• 2018

Additive manufacturing by electron beam melting is an affordable process for fabricating near net shaped parts of titanium and its alloys. 3D additive-manufactured parts have various kinds of voids, lack of fusion, etc., and they may affect crack initiation and propagation. Post process is necessary to eliminate or minimize these defects. Hot isostatic pressing (HIP) is the main method, which is expensive. The objective of this paper is to achieve an optimum and simple post heat treatment process without the HIP process. Various post heat treatments are conducted for the 3D-printed Ti-6Al-4V specimen below and above the beta transus temperature ($996^{\circ}C$). The as-fabricated EBM Ti-6Al-4V alloy has an ${\alpha}^{\prime}$-martensite structure and transforms into the ${\alpha}+{\beta}$ duplex phase during the post heat treatment. The fatigue strength of the as-fabricated specimen is 400 MPa. The post heat treatment at $1000^{\circ}C/30min/AC$ increases the fatigue strength to 420 MPa. By post heat treatment, the interior pore size and the pore volume fraction are reduced and this can increase the fatigue limit.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.1
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• pp.123-134
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• 2019

This paper proposed a new design equation for the inelastic lateral torsional buckling (LTB) of singly symmetric stepped I-beams with non-compact flange sections. The proposed equation was generated using a finite element program, ABAQUS, and a statistical program, MINITAB. The parameters used were the stepped beams parameters; ${\alpha}$, ${\beta}$, and ${\gamma}$ and the length-to-height ratio ($L_b/h$) of the beam. The proposed equation was further validated by means of experimental test, where beams were subjected to four-point bending and supported by roller and lateral braces near the end supports. In addition, finite element models were simulated using the same parameters used in the experimental test to verify the results of the test conducted. It was proved that LTB capacity calculated from the proposed equation is accurate and conservative in comparison with the yielded values from the FEM and actual test, making it a reliable and safe approach in calculating the buckling capacities of singly symmetric stepped beams with non-compact flange sections.

• Journal of Applied Biological Chemistry
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• v.55 no.4
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• pp.267-272
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• 2012

We investigated that electron beam irradiation is the effective method to control the sprouting of sweetpotato roots without changing of food quality characteristics. In 12 and $25^{\circ}C$ storage after electron beam irradiation, all control samples were sprouted from 6 and 4 weeks after storage, respectively. The sprouting rate of control increased with time and the rate reached to 11.2-12.4 and 70.5-74.2% at 8 weeks after 12 and $25^{\circ}C$ storage. Also, the sprouting of middle and below positioning sweetpotato roots at 12 and $25^{\circ}C$ storage after irradiation reached to 8.6-11.3 and 42.7-48.7% after a storage period of 8 weeks, respectively. However, the sprouting of all sweetpotato roots stored at $4^{\circ}C$ and upper (0-7 cm) positioning samples of box stored at 12 and $25^{\circ}C$ with electron beam was completely inhibited due to increase peroxidase and indole acetic acid (IAA) oxidase activity. Also, all samples with electron beam such as hardness, pH, sugar content, weight loss, and vitamin C and dacarotene content did not differ from that of the control. Therefore, if electron beam will be irradiated to sweetpotato roots above 0.1 kGy before packing, it will effectively inhibit their sprouting stored at $25^{\circ}C$ without the change of food quality characteristics.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.59-68
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• 2005

This paper as Part II of the present study deals with the verification of the new truss model that has been conceptually derived and formulated in Part I. Since the model includes the arch coefficient-$\alpha$, the characteristics of this coefficient are examined, and it appears that the coefficient-$\alpha$ is a function of a/d, $\rho$ and $\rho_v$ After transforming the model Into a sectional approach, the formula for predicting the stirrup stress, the longitudinal steel force, and ultimate shear strength are derived. Then, the equations are applied to the test specimens available in literatures, and the predicted values are shown to be in excellent agreement with the experimental results.