• Applied Microscopy
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• v.40 no.4
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• pp.177-183
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• 2010

A focused ion beam (FIB) system produces a beam of positive ions (usually gallium) which are heavier than electrons and can be focused by electrostatic lenses into a spot on the specimen. With its ability milling of the specimen material by 10 to 100 nm with each pass of the beam, FIB is widely adopted in materials science, semiconductor industry, and ceramics research. Recently, FIB has been increasingly employed in the field of biomedical sciences. Here we provide a brief introduction to FIB and its applications for a wide variety of biomedical research. The surface of specimen can be in situ processed and quasi-real time visualized by two beam combination of FIB and field emission scanning electron microscope (FESEM). Due to its milling process, internal structures can be exposed and analyzed: yeast cells, fungus-inoculated wheat leaf, mannitol particles in inhalation aerosols, and oyster shell. Serial blockface tomography with the system kindles 3-dimensional reconstruction researches in the realm of nervous system and life sciences. Two-beam system of FIB/FESEM is a versatile tool to be utilized in the biomedical sciences, especially in 3-dimensional reconstruction studies.

• The Korean Journal of Nuclear Medicine
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• v.28 no.3
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• pp.377-383
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• 1994

Objective : We retrospectively analysed $^{99m}Tc$-MDP bone and $^{67}Ga$ scans to evaluate therapeutic response of bone lymphoma among patients with complete remission. Subjects and Methods : We reviewed 35 cases with an increased uptake finding $^{99m}Tc$-MDP bone scans and 16 $^{67}Ga$ scans that were follow-up studies during and after therapy. The $^{99m}Tc$-MDP bone and $^{67}Ga$ scans were graded visually from 1 to 4 in which grade 3 means same uptake density as that of normal sacroiliac articulation in bone scan and normal liver in $^{67}Ga$ scan, respectively. Results: The improvement findings during and after therapy were found in 66.0% (19/ 29) and 72.7% (24/33) with $^{99m}Tc$-MDP bone scan, 84.6% (l1/13) and 86.7% (13/15) with $^{67}Ga$ scan, respectively. The mean grades of the uptake density in $^{99m}Tc$-MDP bone scan were 3.06 before, 2.34 during, 1.75 after therapy. Those in the $^{67}Ga$ scan were 3.22 before, 1.42 during 1.30 after therapy. Conclusion. $^{67}Ga$ scans appeared more sensitive than bone scans in evaluating therapeutic response of bone lymphoma.

• Journal of the Korean Vacuum Society
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• v.19 no.5
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• pp.371-376
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• 2010

The GaAs epitaxial layers were grown on Si(100) substrates by molecular beam epitaxy (MBE) using the two-step method. The Si(100) substrates were cleaned with three different surface cleaning methods of vacuum heating, As-beam exposure, and Ga-beam deposition at the substrate temperature of $800^{\circ}C$ in the MBE growth chamber. Growth temperature and thickness of the GaAs epitaxial layer were $800^{\circ}C$ and $1{\mu}m$, respectively. The surface structure and properties were investigated by reflection high-energy electron diffraction (RHEED), AFM (Atomic force microscope), DXRD (Double crystal x-ray diffraction), PL (Photoluminescence), and PR (Photoreflectance). From RHEED, the surface structure of GaAs epitaxial layer grown on Si(100) substrate with Ga-beam deposition is ($2{\times}4$). The GaAs epitaxial layer grown on Si(100) substrate with Ga-beam deposition has a high quality.

• Journal of the Korean Vacuum Society
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• v.22 no.1
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• pp.37-44
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• 2013

In order to investigate an influence of carrier trap by quantum dots (QDs) on the solar parameters, in this study, the $p^+-QD-n/n^+$ solar cells with InAs/GaAs QD active layers are fabricated, and their characteristics are investigated and compared with those of a GaAs matrix solar cell (MSC). Two different types of QD structures, the Stranski-Krastanow (SK) QD and the quasi-monolayer (QML) QD, have been introduced for the QD solar cells, and the parameters (open-circuit voltage ($V_{OC}$), short-cirucuit current ($I_{SC}$), fill factor (FF), conversion efficiency (CE)) are determined from the current-voltage characteristic curves under a standard solar illumination (AM1.5). In SK-QSC, while FF of 80.0% is similar to that of MSC (80.3%), $V_{OC}$ and $J_{SC}$ are reduced by 0.03 V and $2.6mA/cm^2$, respectively. CE is lowered by 2.6% as results of reduced $V_{OC}$ and $J_{SC}$, which is due to a carrier trap into QDs. Though another alternative structure of QML-QD to be expected to relieve the carrier trap have been firstly tried for QSC in this study, it shows negative results contrary to our expectations.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.266-267
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• 2011

질화갈륨(GaN)은 높은 전자이동도 및 높은 항복전계를 가지며 낮은 온저항으로 인하여 에너지효율이 우수하기 때문에 고출력 전력소자 분야에서 많은 관심을 받고 있다. GaN을 이용한 고출력 전력소자의 경우 상용화 수준에 근접할 만한 기술적 진보가 있었으나, 페르미 레벨 고정(Fermi-level pinning) 현상, 소자의 누설전류 등 아직 해결되어야 할 문제를 갖고 있다. 본 연구에서는 실리콘 기판 위에 성장된 GaN 에피탁시를 활용한 고출력 전력소자의 누설전류를 억제시키기 위해 오믹 접합 중 Au의 상호확산을 억제하는 중간층 금속(Mo or Ni)을 변화시켰으며 오믹 열처리 온도에 따른 특성을 비교 연구하였다. $Cl_2$와 $BCl_3$를 이용하여 0.6 ${\mu}m$ 깊이의 메사 구조가 활성영역을 형성하였고, Si 도핑된 n-GaN 위에 Ti/Al/Mo/Au (20/100/25/200 nm) 와 Ti/Al/Ni/Au (20/100/25/200 nm) 오믹 접합을 각각 설계, 제작하였다. 오믹 열처리시의 GaN 표면오염을 방지하기 위해 $SiO_2$ 희생층을 증착하였다. 오믹 접합 형성을 위해 각 750$^{\circ}C$, 800$^{\circ}C$, 850$^{\circ}C$에서 30초간 열처리를 진행 하였으며, 이후 6 : 1 BOE 용액으로 $SiO_2$ 희생층을 제거하였다. 750, 800, 850$^{\circ}C$에서 Ti/Al/Mo/Au 구조의 오믹 접합 저항은 각 2.56, 2.34, 2.22 ${\Omega}$-mm 이었으며, Ti/Al/Ni/Au 구조의 오믹 접합 저항은 각 43.72, 2.64, 1.86 ${\Omega}$-mm이었다. Isolation 누설전류를 측정하기 위해서 두 개의 오믹 접합 사이에 메사 구조가 있는 테스트 구조를 제안하였다. Isolation 누설전류는 Ti/Al/Mo/Au 구조에서 두 오믹 접합 사이의 거리가 25 ${\mu}m$이고 100 V일 때 750, 800, 850 $^{\circ}C$의 열처리 온도에서 각 1.25 nA/${\mu}m$, 2.48 nA/${\mu}m$, 8.76 nA/${\mu}m$이었으며, Ti/Al/Ni/Au 구조에서는 각 1.58 nA/${\mu}m$, 2.13 nA/${\mu}m$, 96.36 nA/${\mu}m$이었다. 열처리 온도가 증가하며 오믹 접합 저항은 감소하였으나 isolation 누설전류는 증가하였다. 750$^{\circ}C$ 열처리에서 오믹 접합 저항은Ti/Al/Mo/Au 구조가 Ti/Al/Ni/Au 구조보다 약 17배 우수하였고, 850$^{\circ}C$ 고온의 열처리 경우 Ti/Al/Mo/Au 구조의 isolation 누설전류는 8.76 nA/${\mu}m$로 Ti/Al/Ni/Au의 누설전류 96.36 nA/${\mu}m$보다 약 11배 우수하였다. Ti/Al/Mo/Au가 Ti/Al/Ni/Au 보다 오믹 접합 저항과 isolation 누설전류 측면에서 전력용 GaN 소자에 적합함을 확인하였다.

• Korean Journal of Materials Research
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• v.3 no.5
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• pp.443-450
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• 1993

Self-alignment gatc Schottky contact structure on Si- implanted GaAs was formed by plasma enhanced chemical vapor dcposirion. Tungsten nitride thin films (ahclut 1600$\AA$) \vcre dopositcd on GaAs at $350^{\circ}C$ in order to fahricarc GaAs 1Cs and ttwn rapidly annealed at $750^{\circ}C$ to $900^{\circ}C$. Thermal charac tcristics of PECVD)-$W_{67}N_{43}$/GaAs structure were investigated by X-ray diffraction, photolumintesccnce. and optical deep level transient specrroscopy. Results revealed that $W_{67}N_{33}$ gate was more thermally sta ble with GaAs substrate than W gate and Si atoms implanted In $W_{67}N_{33}$/GaAs structure became morr active than those In W/GaAs after annealing. I-V characteristics of $W_{67}N_{33}$/GaAs diod c exhibired a nearly ideal diode behavior. The termal stability of $W_{67}N_{33}$/GaAs diode was better than that of W/GaAs diode with the post annealing at temperatures from 800 to $900^{\circ}C$ for 20s without As overpressure.

• Journal of the Korean Chemical Society
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• v.35 no.4
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• pp.301-307
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• 1991

The solubilities of the n-propyl iodide in nitrobenzene and m-xylene have been measured at 8$^{\circ}$, 15$^{\circ}$ and 25$^{\circ}C$ in the presence and the absence of gallium iodide. When gallium iodide does not exist in the system, the solubility of n-propyl iodide in m-xylene is greater than in nitrobenzene, indicating a stronger interaction of n-propyl iodide with m-xylene than that with nitrobenzene. It could be thought that n-propyl iodide forms unstable complex with gallium iodide in the presence of gaillium iodide in the system. This complex has been assumed in various ways and evaluated, that instability constant (K value) is relatively certain under the assumption of 1:1 complex, n-C$_3H_7I{\cdot}GaI_3$. Therefore, the complex would form the following equilibrium in the solution: n-C$_3H_7{\cdot}GaI _3{\rightleftharpoons}n-C_3H_7I+1/2Ga_2I_6$ the instability of the complex of n-propyl iodide with gallium iodide is compared with similar complexes of gallium iodide with methyl iodide. The changes of enthalpy, free energy and entropy for the dissociation of the complex are also calculated.

• Journal of the Korean Society of Food Science and Nutrition
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• v.46 no.10
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• pp.1195-1204
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• 2017

This study was designed to determine the effects of three cooking methods, boiling, microwave, and steaming, on elemental compositions of green pumpkin, zucchini, and sweet and ripened pumpkin. The cooking methods were carried out at 3, 5, and 10 min. The samples were then dried, crushed, and decomposed by microwave-assisted digestion method. Macro elements were analyzed by Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES), whereas ICP-Mass Spectrometer (ICP-MS) was used for micro elements determination. From the results, macro elements were present in the order of K, P, Ca, Mg, S, Fe, Zn, and Na in all analyzed pumpkins. Among micro elements, Mn, Cu, Rb, and Ba, were present at high levels. For the effects of cooking methods, boiling significantly reduced the concentrations of elements. Cooking time affected concentrations of elements in the same manner with large differences between elemental contents in samples cooked for 5 and 10 min. Regarding micro elements contents, both effects were not significant. Similar elemental compositions with different concentration levels in all pumpkin types were observed. Green pumpkin and ripened pumpkin showed high retention rates of inorganic components upon steaming, and zucchini and sweet pumpkin showed high retention rates upon microwave cooking. Conclusively, cooking method and time affect amounts of residual inorganic ingredients in pumpkin.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.6
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• pp.274-278
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• 2012

$TiO_2$ can be used optically and is applied on many areas such as gas sensor, solar cell and photocatalysis. Electrospun nanofibers have received great interest for development and utilization in some novel applications, such as chemical sensors, dye-sensitized solar cell and photo catalysis. In this study, pure $TiO_2$ and Ga-doped $TiO_2$ nanofibers synthesized by a modified electrospinning method. The Ga doped $TiO_2$ solution is prepared by mixing poly vinyl pyrrolidone, ethyl alcohol, and titanium (IV) isopropoxide. By electrospinning these sols, nanofibers were fabricated. These fibers are heat-treated at $800^{\circ}C$ in air. The prepared pure $TiO_2$ and Ga-doped $TiO_2$ nanofibers samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy.

• Korean Journal of Optics and Photonics
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• v.24 no.4
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• pp.176-183
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• 2013

In this paper, we report the design, fabrication and characterization of the 3-Dimensional optical receiver for a Laser Detection And Ranging (LADAR) system. The optical receiver is composed of three parts; $16{\pm}16$ Geiger Mode InGaAs Avalanche Photodiode (APD) array device operated at 1560 nm wavelength, Read Out Integrated Circuit (ROIC) measuring the Time-Of-Flight (TOF) of the return signal reflected from target objects, a package and cooler maintaining the proper operational condition of the detector and control electronics. We can confirm that the LADAR system can detect the signal from a target up to 1.2 km away, and it showed low Dark Count Rate (DCR) of less than 140 kHz, and higher than 28%-Photon Detection Efficiency (PDE). This is considered to be the best performance of the $16{\pm}16$ FPA APD optical receiver for a LADAR system.