• Journal of the Korean Vacuum Society
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• v.8 no.2
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• pp.102-110
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• 1999

The LIGA X-ray exposure step was modelled into three inequalities, by assuming that the X-ray energy attenuated within a resist is deposited only in the localized range of the resist. From these inequalities, equations for the minimum and maximum exposure times required for a good quality microstructure were obtained. Also, an equation for the thickness of an X-ray mask absorber was obtained from the exposure requirement of threshold dose deposition. The calculation method of the synchrotron radiation power from a synchrotron radiation source was introduced and applied to an X-ray exposure step. A power from a synchrotron radiation source was introduced and applied to an X-ray exposure step/ A power function of photon energy, approximating the attenuation length of the representative LIGA resist, PMMA, and the mean photon energy of the XZ-rays incident upon an X-ray mask absorber were applied to the above mentioned equations. Consequently, the tendencies of the minimum and maximum exposure and with respect to mean photon energy and thick ness of PMMA was obtained. Additionally, the tendencies of the necessary thickness of PMMA and photon energy of the X-ray mask absorber with respect to thickness of PMMA and photon energy of the X-rays incident upon an X-ray mask absorber were examined. The minimum exposure time increases monotonically with increasing mean photon energy for the same total power density and is not a function of the thickness of resist. The minimum exposure time increases with increasing mean photon energy for the same total power density in the case of the general LIGA process, where the thickness of PMMA is thinner than the attenuation length of PMMA. Additionally, the minimum exposure time increases monotonically with increasing thickness of PMMA. The maximally exposable thickness of resist is proportional to the attenuation length of the resist at the mean photon energy with its proportional constant of ln $(Dd_m/D_{dv})$. The necessary thickness of a gold X-ray mask absorber due to absorption edges of gold, increases smoothly with increasing PMMA thickness ratio, and is independent of the total power density itself. The simplicity of the derived equations has made clearly understandable the X-ray exposure phenomenon and the correlation among the exposure times, the attenuation coefficient and the thickness of an X-ray mask absorber, the attenuation coefficient and the thickness of the resist, and the synchrotron radiation power density.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.4
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• pp.1-7
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• 2015

In the present study, copper micromolds with a microhole array were precisely manufactured by a synchrotron LIGA process. Like in the traditional LIGA process, a deep X-ray lithography based on a synchrotron radiation was employed as the first manufacturing step. Due to the excellent optical performance of the synchrotron X-ray used, cylindrical micropillar arrays with high aspect ratio could be efficiently obtained. The fabricated microfeatures were then used as a master of the subsequent copper electroforming process, thereby resulting in copper micromolds with a microhole array. Thermoplastic hot embossing experiments with the copper micromolds were carried out for imprinting cylindrical microfeatures onto a polystyrene sheet. Through the hot embossing, the effect of embossing temperature and usefulness of the present manufacturing method could be verified.

• Journal of Magnetics
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• v.7 no.2
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• pp.51-54
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• 2002

The crystallization of amorphous Ba-ferrite/sapphire(001) thin films was studied in real-time synchrotron x-ray scattering experiments. In the sputter-grown amorphous films, we found the existence of epitaxial $Fe_3O_4$ interfacial crystallites (50-${\AA}$-thick), well aligned $[0.03^circ$full-width at half-maximum (FWHM)] to the sapphire [001] direction. The amorphous precursor was crystallized to epitaxial Ba-ferrite and \alpha-Fe_2O_3$grains in two steps; i) the nucleation of crystalline \alpha-Fe_2O_3$ phase started at $300^circ{C}$ together with the transformation of the $Fe_3O_4$ crystallites to the \alpha-Fe_2O_3$ crystallites, ii) the nucleation of Ba-ferrite phase occurred at temperature above $600^circ{C}$. In the crystallized films irrespective of the film thickness, the crystal domain size of the \alpha-Fe_2O_3$grains was about 250 ${\AA}$ in the film plane, similar to that of the Ba-ferrite grains.

• Journal of the Korean Society of Visualization
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• v.8 no.2
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• pp.45-50
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• 2010

The objective of this study is to elucidate the feasibility of synchrotron X-ray micro CT as a non-destructive imaging method to visualize the three-dimensional morphological structures of biological and non-biological samples. The experiments were conducted in 7B2 X-ray micro CT beamline in Pohang Accelerate Laboratory (PAL). A rotational 3-axis stage was specially designed for $0^{\circ}-180^{\circ}$ scanning of test samples. Preliminary tests were performed for opaque samples including a mosquito head, a plant seed and gas diffusion layer (GDL) of polymer electrolyte fuel cell to verify the feasibility of the X-ray micro CT. It visualized clearly the internal structure of all the test samples, supporting its usefulness.

• Progress in Medical Physics
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• v.22 no.3
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• pp.117-123
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• 2011

Synchrotron radiation (SR) imaging enables us to observe internal structures of biologic samples without staining. In this study, we obtained X-ray microscopic images of human breast tissues with 11.1 KeV hard X-ray microscope of the Pohang light source and used zone plates and phase-contrast technique to get high resolution X-ray images. Hard X-ray microscopic images of fibrocystic change and breast cancer tissues with a spatial resolution of 60 nm were obtained and from these images, we could observe the micro-structures of human breast tissue. Also we analyzed and compared these images, which revealed distinct features of each condition. In conclusion, SR imaging with phase-contrast hard X-ray microscope for medical application, especially in breast disease can give some useful information for clinical research.

• Macromolecular Research
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• v.14 no.2
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• pp.166-172
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• 2006

This is a short review article of our recent studies on the ATP-induced, allosteric conformational transition of the chaperonin GroEL complex by solution X-ray scattering. We used synchrotron X-ray scattering with a two-dimensional, charge-coupled, device-based X-ray detector to study (1) the specificity of the chaperonin GroEL for its ligand that induced the allosteric transition, and (2) the identification of the allosteric transition of GroEL in its complicated kinetics induced by ATP. Due to the dramatically increased sensitivity of the X-ray scattering technique based on the use of the two dimensional X-ray detector and synchrotron radiation, different allosteric conformational states of GroEL populated under different conditions were clearly distinguished from each other. It was concluded that solution X-ray scattering is an extremely powerful tool for investigating the equilibrium and kinetics of cooperative conformational transitions of oligomeric protein complex, especially when combined with other spectroscopic techniques such as fluorescence spectroscopy.

• Journal of the Korean Physical Society
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• v.73 no.12
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• pp.1834-1839
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• 2018

A tabletop ultrafast soft x-ray has been generated from the laser-produce plasma with a femtosecond pulsed Ti:Sapphire laser. The estimated total flux of Al $K{\alpha}$ is of $2.2{\times}10^9photons/sec$ in $4{\pi}$ radian and the parameters related to the optical performance were obtained. The tungsten/silicon multilayer, flat quartz and bent thallium acid phthalate (TLAP) crystal were used for monochromatization of soft x-ray to refine the aluminum $K{\alpha}$ radiation and compared the respective value of $E/{\Delta}E$. To estimate the size of the x-ray source beam generated by a fs laser, the approximation using the FWHM obtained from the x-ray beam scan near the focal point was discussed, and the size of the diameter was about $9.76{\mu}m$.

• Journal of the Korean Society of Radiology
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• v.2 no.2
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• pp.23-30
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• 2008

X-ray microscopy with synchrotron radiation(SR) might be a useful tool for novel x-ray imaging in the clinical and laboratory settings. Microscopically, it enables us to observe detailed structure of animal organs samples with a great magnification power and an excellent resolution. The phase contrast mechanisms in image by X-ray are described. The phase-contrast X-ray imaging with SR from in-vivo and in-vitro mouse tail, rat nerve and rat lung were obtained with an 8 KeV monochromatic beam. The visual image was magnified using 10x microscope objective lens and captured using an digital CCD camera. The results showed more structural details and high resolution images with SR imaging system than conventional X-ray radiography system. The SR imaging system may have a potential for imaging in biological researches, material applications and clinical radiography.

• Current Applied Physics
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• v.18 no.11
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• pp.1205-1211
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• 2018

The frustrated magnet has been regarded as a system that could be a promising host material for the quantum spin liquid (QSL). However, it is difficult to determine the spin configuration and the corresponding mechanism in this system, because of its geometrical frustration (i.e., crystal structure and symmetry). Herein, we systematically investigate one of the geometrically frustrated magnets, the $TbB_4$ compound. Using resonant soft x-ray scattering (RSXS), we explored its spin configuration, as well as Tb's quadrupole. Comprehensive evaluations of the temperature and photon energy/polarization dependences of the RSXS signals reveal the mechanism of spin reorientation upon cooling down, which is the sophisticated interplay between the Tb spin and the crystal symmetry rather than its orbit (quadrupole). Our results and their implications would further shed a light on the search for possible realization of QSL.

• Journal of the Korean Vacuum Society
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• v.8 no.1
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• pp.13-19
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• 1999

Total reflection X-ray fluorescence spectroscopy using synchrotron radiation source called as TRSFA was explored to achieve high sensitivities to impurity metals on Si wafer surface. It consists of monochromating part to select a specific wavelength, slit part to shield direct beam and to control monochromated beam, and main chamber to dectect fluorescent X-ray counts of impurities on si wafer. Monochromated X-ray of 10.90 KeV was selected and the optimum total reflection condition on silicon wafer was obtained through tuning the dead time and fluorescent X-ray count of Si and Fe. TRSFA system could increase the sensitivity as high as 50 times in comparision with TRXFA using normal X-ray source. But the trend was varied since the surface conditions of Si wafers and, therefore, the reflectivities were different. Furthemore, there seems to be a promising path to reaching a detection limit useful to the next generation metal impurities control, because Fe impurity below to the $5\times10^{9}\textrm{atomas/cm}^2$ can be detectable through the developed TRSFA system.