• Journal of the Korean Chemical Society
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• v.25 no.6
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• pp.367-375
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• 1981

Single crystals of Potassium Sulfate ($K_2SO_4$) have been grown from the saturated solution by the evaporation method at the optimum conditions. Radiation damages in the crystal by ${\gamma}$-irradiation of about $12{\times}10^6$ Roentgen have given rise to paramagnetic centers or paramagnetic defects. Electron spin resonance (ESR) spectra of the centers are obtained with the X-band EPR spectrometer at room temperature. The ESR peaks of the paramagnetic species are found to be anisotropic but the peak of $SO_3-$ radical is an isotropic of Gaussian shape at g = 2.0036. A number of ESR spectra of the crystal for angular variation of the anisotropic peaks are recorded at various orientations of rotation about a, b and c crystallographic axes respectively. The g-values are calculated from the line position between anisotropic peaks and the isotropic one and then principal g-values and its direction cosines of the species are obtained by diagonalization of 9 matrix elements of the corresponding g-values. All the paramagnetic defects are identified by the characteristic principal g-values and its direction cosines.

• Korean Journal of Crystallography
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• v.8 no.1
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• pp.38-47
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• 1997

A new weighing sensor for the automatic diameter control system of the crystal growth is developed in this study. This weighing sensor measures the frequency of the vibrating element which is lineally changing with respect to weight. The signal and the power of this system are transmitted without any physical contact, so that this sensor offers high accuracy and resolution. This system consists of a string, a sinusoidal wave generator, an automatic amplification adjusting circuit, signal transformers and a PCB. 4 kinds of programs are developed for checking DAC, weight calibration and controlling growth process. The measurements of the standard deviation and the resolution show $\pm0.10g$(measured at every second) and $5{\times}10^{-5}$, respectively, This weighing sensor is effective under high pres-sure of 200 atm, high temperature and vacuum condition. The weighing system can control the temperature in the accuracy of $\pm0.025^{\circ}C$ with the 'signal divider'. The optical quality single crystals of $(YGd)_3Sc_2Ga_3O_{12},\;Er-Y_3Sc_2Al_3O_{12},\;and\;Bi_{12}GeO_{20}$ have been grown by Czo-chralski method using this auto-diameter control system.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.14-15
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• 2010

Recently there has been growing interest in topological insulators or the quantum spin Hall (QSH) phase, which are insulating materials with bulk band gaps but have metallic edge states that are formed topologically and robust against any non-magnetic impurity [1]. In a three-dimensional material, the two-dimensional surface states correspond to the edge states (topological metal) and their intriguing nature in terms of electronic and spin structures have been experimentally observed in bulk Bi1-xSbx single crystals [2,3,4]. However, if we want to know the transport properties of these topological metals, high purity samples as well as very low temperature will be needed because of the contribution from bulk states or impurity effects. In a recent report, it was also shown that an intriguing coupling between the surface and bulk states will occur [5]. A simple solution to this bothersome problem is to prepare a topological metal on an ultrathin film, in which the surface-to-bulk ratio is drastically increased. Therefore in the present study, we have investigated if there is a method to make an ultrathin Bi1-xSbx film on a semiconductor substrate. From reflection high-energy electron diffraction observation, it was found that single crystal Bi1-xSbx films (0${\sim}30\;{\AA}A$ can be prepared on Si(111)-$7{\times}7$. The transport properties of such films were characterized by in situ monolithic micro four-point probes [6]. The temperature dependence of the resistivity for the x=0.1 samples was insulating when the film thickness was $240\;{\AA}A$. However, it became metallic as the thickness was reduced down to $30\;{\AA}A$, indicating surface-state dominant electrical conduction. Figure 1 shows the Fermi surface of $40\;{\AA}A$ thick Bi0.92Sb0.08 (a) and Bi0.84Sb0.16 (b) films mapped by angle-resolved photoemission spectroscopy. The basic features of the electronic structure of these surface states were shown to be the same as those found on bulk surfaces, meaning that topological metals can be prepared at the surface of an ultrathin film. The details will be given in the presentation.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.4
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• pp.121-127
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• 2022

β-Gallium oxide (Ga₂O₃), an ultra-wide bandgap semiconductor, has attracted great attention due to its promising applications for high voltage power devices. The most stable phase among five different polytypes, β-Ga₂O₃ has the wider bandgap of 4.9 eV and higher breakdown electric field of 8 MV/cm. Furthermore, it can be grown from melt source, implying higher growth rate and lower fabrication cost than other wide bandgap semiconductors such as SiC, GaN and diamond for the power device applications. In this study, β-Ga₂O₃ bulk crystals were grown by the edge-defined film-fed growth (EFG) process. The growth direction and the principal surface were set to be the [010] direction and the (100) plane of the β-Ga₂O₃ crystal, respectively. The spectra measured by Raman an alysis could exhibit the crystal phase an d impurity dopin g in the β-Ga₂O₃ ingot, and the crystallinity quality and crystal direction were analyzed using high-resolution X-ray diffraction (HRXRD). The crystal quality and various properties of as-grown β-Ga₂O₃ ribbon was systematically analyzed in order to investigate the spatial variation in entire crystal grown by EFG method.

• Journal of the Korean Chemical Society
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• v.29 no.2
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• pp.73-79
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• 1985

The crystal and molecular structure of acetone 4-benzylthiosemicarbazone, $C_{11}H_{15}N_3S$, has been determined by the single crystal X-ray diffraction methods. The crystals are monoclinic, space group $P2_1/c$ with unit cell dimensions, a = 10.249(7), b = 11.403(9), c = 10.149(7)TEX>${\AA}$, ${\beta}$ = 90.9$(1)^0$ and z = 4. The intensities were collected on an automatic four-circle diffractometer with graphite-monochromated Mo-$K_{\alpha}$ radiation. The structure was solved by direct methods and refined by full matrix least-squares methods. The final R was 0.045 for 1554 observed reflections. S-C(8)-N(2)-N(3)-C(9)-C(10) atoms make a zigzag planar chain. There are no unusual bond lengths and angles. There are two independent hydrogen bonds in the crystal structure. One is N-H${\cdots}$S intermolecular hydrogen bond with the length of 3.555${\AA}$ and makes dimer-like units. The other is N-H${\cdots}$N intramolecular hydrogen bond with the length of 2.568${\AA}$. The structure was compared with those of other thiosemicarbazone derivatives.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.4
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• pp.135-139
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• 2014

The hydride vapor phase epitaxy (HVPE) grown GaN samples to precisely measure the surface characteristics was applied to a molten KOH/NaOH wet chemical etching. The etching rate by molten KOH/NaOH wet chemical etching method was slower than that by conventional etching methods, such as phosphoric and sulfuric acid etching, which may be due to the formation of insoluble coating layer. Therefore, the molten KOH/NaOH wet chemical etching is a better efficient method for the evaluation of etch pits density. The grown GaN single crystals were characterized by using X-ray diffraction (XRD) and X-ray rocking curve (XRC). The etching characteristics and surface morphologies were studied by scanning electron microscopy (SEM). From etching results, the optimum etching condition that the etch pits were well independently separated in space and clearly showed their shape, was $410^{\circ}C$ and 25 min. The etch pits density obtained by molten KOH/NaOH wet chemical etching under optimum etching condition was around $2.45{\times}10^6cm^{-2}$, which is commercially an available materials.

• Journal of the Mineralogical Society of Korea
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• v.28 no.1
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• pp.9-16
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• 2015

A mineralogical analysis on the factors affecting the luster of pearls was carried out using gravity measurement, optical microscope observation, X-ray diffraction analysis, and scanning electron microscopy. We divided the seawater cultured pearls from Tongyeong into the following four types based on luster and shape; good luster and round (LR), lackluster and round (LLR), lackluster and baroque (LLB), and lackluster and two nucleus (LTN) pearls. Pearls with high-quality luster had slightly lower specific gravity as compared to pearls with low-quality luster, but both these types of pearls are within the specific gravity range of commercial pearls. Regarding the cross-sectional thickness of the mother-of-pearl layer, LR pearls showed a uniform thickness of about 0.3 mm in average. On the other hand, LLR pearls were characterized by relatively thinner, but uniform thickness. LTN and LLB pearls showed a tendency of significantly large variation in thickness even within a single pearl. For the surface of pearls, pearls with high-quality luster showed narrower and clearer growth lines of aragonite crystals as compared to pearls with low-quality luster. Pearls with high-quality luster were characterized by fewer aragonite crystal lattice defects as compared to pearls with low-quality luster, and the former showed parallel arrangement, thinner thickness, and less difference in thickness on the surface and inside. If a pearl has a prismatic layer, it is composed of aragonite with calcite in the prismatic and nacreous layer, and calcite content is very high in the lackluster pearl. Pearls without a prismatic layer were devoid of calcite irrespective of their quality of luster, and were composed of aragonite.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.1
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• pp.83-91
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• 1994

We have constructed a vertical gradient freeze (VGF) grower for GaAs single crystals 2 inch in diameter and have grown semi-insulating GaAs co-doped with Cr and In. For the co-doped crystal, the segregation coefficients of the dopants remain unchanged when compared to those doped with only Cr or In. The concentration of Cr and in atoms range from about $2{\Times}10_{16} to 3{imes}10^{17} cm^{-3}$ and $2{\Times}10^{19} to 3{\Times}10^{20} cm^{-3}$ at the seed to the tail part of the grown crystal, respectively. The averaged dislocation etch pit density is found to be less than $8000 cm^{-2}$ throughout the ingot. It is also found that there is some evidence of lattice hardening for the crystal in which the dislocation density is decreased to less than $1000 cm^{-2}$ as In concentration increases. The resistivity increases abruptly from $10^{-2}$ up to $10^8$ Ohm-cm, while the carrier concentration decreases from $10^{16}$ to $10^8 cm^{-3}$ along the growth direction of the GaAs crystal. Semi-insulating properties can be obtained above a critical concentration of Cr of about $6{\Times}10{^16} cm^{-3}$ in the crystal. The main deep levels existing in the GaAs: Cr,In sample are two electron traps at $E_C-0.81eV, E_C-0.35eV$, and two hole traps at $E_V+0.89eV, E_V+0.65eV$.

• The Journal of the Petrological Society of Korea
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• v.20 no.4
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• pp.191-206
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• 2011

The emplacement ages, whole-rock geochemistry and Sr-Nd isotopic compositions of granitoid rocks from Cheongju area, South Korea, were investigated for delineating their petrogenetic link to the Jurassic Daebo granitoid rocks. Zircon crystals were collected from the diorite, biotite granite and acidic dyke samples in a single outcrop. Cross-cutting relationships show that the emplacement of diorite was postdated by the intrusion of biotite granite. Both rocks have been subsequently intruded by acidic dyke. The U-Pb isotopic compositions of zircon from the diorite, biotite granite, and acidic dyke were measured using a SHRIMP-II ion microprobe, yielding the crystallization ages of $174{\pm}2Ma$, $170{\pm}2Ma$, and $170{\pm}5Ma$, respectively, with 95% confidence limits ($t{\sigma}$). The emplacement ages are consistent with those determined from the above relative ages. The major and trace element patterns of the rocks are consistent with those of the Jurassic Daebo granitoid rocks, possibly suggesting a subduction-related I-type granite. The geochemical signature is, however, betrayed by the Sr and Nd isotopic compositions of these rocks. The isotopic signatures suggest that the rocks were produced either by the partial melting of lower-crust or by the mantle-derived magma contaminated by the basement rocks during its ascent and/or emplacement. In addition, the inherited ages of zircons of the rocks (ca. 2.1, 1.8, 0.8 and 0.4 Ga) suggest a possible assimilation with crustal rocks from the Gyeonggi massif and Ogcheon metamorphic belt.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.51-57
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• 2008

we have demonstrated structural evolution and optical properties of Si-nanowires (NWs) synthesized on Si (111) substrates with nanoscale Au-Si islands by rapid thermal chemical vapor deposition (RTCVD). The Au-Si nano-islands (10-50nm in diameter) were employed as a liquid-droplet catalysis to grow Si-NWs via vapor-liquid-solid mechanism. The Si-NWs were grown by a mixture gas of SiH4 and H2 at a pressure of 1.0 Torr and temperatures of $500{\sim}600^{\circ}C$. Scanning electron microscopy measurements showed that the Si-NWs are uniformly sized and vertically well-aligned along <111> direction on Si (111) surfaces. The resulting NWs are ${\sim}60nm$ in average diameter and ${\sim}5um$ in average length. High resolution transmission microscopy measurements indicated that the NWs are single crystals covered with amorphous SiOx layers of ${\sim}3nm$ thickness. In addition, the optical properties of the NWs were investigated by micro-Raman spectroscopy. The downshift and asymmetric broadening of the Si main optical phonon peak were observed in Raman spectra of Si-NWs, which indicates a minute stress effects on Raman spectra due to a slight lattice distortion led by lattice expansion of Si-NW structures.