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Nobuyuki Koguchi 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
Recent progress on the direct formation of GaAs/AlGaAs and InGaAs/GaAs QDs systems by droplet epitaxy are reviewed. The droplet epitaxy is promising for the fabrication of compound semiconductor quantum dots not only in a lattice-mismatched system but also in a lattice-matched system. By using this method, QDs samples without wetting layers are realized. We also review our recent progress toward the fabrication of site-controlled QDs by using droplet epitaxy on GaAs (001) with well-aligned nano-holes developed by combination of Atomic Force Microscopy (AFM) tip-induced oxidation and atomic hydrogen etching technique.en
Conductive hybrid crystal composed of polyoxovanadate and deprotonatable ionic-liquid surfactant
Misawa, Toshiyuki,Koguchi, Shinichi,Niwa, Kanae,Kinoshita, Yuki,Uchida, Sayaka,Ito, Takeru Elsevier 2018 Inorganic chemistry communications Vol.96 No.-
<P><B>Abstract</B></P> <P>Deprotonatable ionic-liquid surfactant cation of 1-dodecylimidazolium (C<SUB>12</SUB>im) was successfully hybridized with polyoxovanadate anion to obtain conductive inorganic-organic hybrid crystal. Single crystal X-ray analysis revealed that the hybrid crystal contained the alternate stacking of decavanadate (V<SUB>10</SUB>) layers and interdigitated C<SUB>12</SUB>im layers. Four C<SUB>12</SUB>im cations were associated with one diprotonated V<SUB>10</SUB> anion, and the two diprotonated V<SUB>10</SUB> anions formed a dimer species. Anhydrous proton conductivity derived from the dissociative protons of the hybrid crystal was estimated to be 4.6 × 10<SUP>−5</SUP> S cm<SUP>−1</SUP> at 373 K by alternating current (AC) impedance spectroscopy.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Polyoxovanadate-surfactant hybrid crystal was synthesized as single crystals. </LI> <LI> Long-tailed ionic-liquid was employed as cationic surfactant. </LI> <LI> The hybrid crystal consisted of decavanadate and ionic-liquid layers. </LI> <LI> Dissociative protons were successfully introduced into the hybrid crystals. </LI> <LI> The hybrid crystal exhibited moderate anhydrous proton conductivity. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kim, Dmitriy Spartakovich,Murayama, Kentaro,Nurtazin, Yernat,Koguchi, Yasuhiro,Kenzhin, Yergazy,Kawamura, Hiroshi The Korean Association for Radiation Protection 2019 방사선방어학회지 Vol.44 No.2
Background: The main goal of experiments is to compare various operational and technical characteristics of D-Shuttle semiconductor personal dosimeters of the Japanese company "Chiyoda Technol Corporation" and Harshaw thermoluminescent dosimeters (TLD) manufactured by "Thermo Fisher Scientific" and DTL-02 of the Russian Research and Production Enterprise (RPE) "Doza" by their occupational and calibration exposure at various dose equivalents from 0.5 to 20 mSv of gamma-radiation. Materials and Methods: Besides dosimeters DTL-02, D-Shuttle and Harshaw TLD, there were also used: (1) the primary reference radionuclide source Hopewell Designs IAEA: G10-1-12 with $^{137}Cs$ isotope (an error is not more than 6% and activity is 20 Ci), and (2) the verification device UPGD-2M of RPE "Doza" and installed in the National Center for Expertise and Certification of the Republic of Kazakhstan (Kapchagai, the National Center for Expertise and Certification). Results and Discussion: The main results of researches are the following: (1) TLDs for Harshaw 6600 and DVG-02TM have an approximately equal measurement accuracy of the individual dose equivalents in the range from 0.5 to 20 mSv of gamma-radiation. (2) Advantages of dosimeters for Harshaw 6600 are due to the high measurement productivity and opportunity to indicate the dose on the skin $H_p$(0.07). Advantages of DVG-02TM consist of operation simplicity and lower cost than of Harshaw 6600. (3) D-Shuttles are convenient for use in the current and the operational monitoring of ionizing radiation. Measurement accuracy and 10% linearity of measurements are ensured when D-Shuttle is irradiated with dose equivalents below 1 mSv at the equivalent dose rate not higher than $3mSv{\cdot}hr^{-1}$. This allows using D-Shuttle at a routine technological activity. Conclusion: The obtained results of experiments demonstrate advantages and disadvantages of D-Shuttle semiconductor dosimeters in comparison with two TLD systems of DVG-02TM and Harshaw 6600.
Auger processes in InGaAs QDs grown by droplet method
이주인,Il Ki Han,F. Minami,Nobuyuki Koguchi,T. Kuroda 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.43 No.42
We present the carrier dynamics of InGaAs quantum dots with and without cladding layers grown by heterogeneous droplet epitaxy. Time-resolved photoluminescence spectroscopy showed double exponential decays for the rst excited states, including an initial fast decay, of highly excited quantum dots with cladding layers in contrast to the single exponential decay in quantum dots without cladding layers. Moreover, the GaAs barriers had slow rise times of about 220 ps, which corresponded to the initial fast decay time of the rst excited states of quantum dots. These results provide evidence of Auger processes between the carriers in the GaAs barriers and those in the rst-excited states of quantum dots.
The Japan Health Physics Society Guideline on Dose Monitoring for the Lens of the Eye
Yokoyama Sumi,Tsujimura Norio,Hashimoto Makoto,Yoshitomi Hiroshi,Kato Masahiro,Kurosawa Tadahiro,Tatsuzaki Hideo,Sekiguchi Hiroshi,Koguchi Yasuhiro,Ono Koji,Akiyoshi Masahumi,Kunugita Naoki,Natsuhori 대한방사선방어학회 2022 방사선방어학회지 Vol.47 No.1
Background: In Japan, new regulations that revise the dose limit for the lens of the eye (hereafter the lens), operational quantities, and measurement positions for the lens dose were enforced in April 2021. Based on the international safety standards, national guidelines, the results of the Radiation Safety Research Promotion Fund of the Nuclear Regulation Authority, and other studies, the Working Group of Radiation Protection Standardization Committee, the Japan Health Physics Society (JHPS) developed a guideline for radiation dose monitoring for the lens.Materials and Methods: The Working Group of the JHPS discussed the criteria of non-uniform exposure and the management criteria set not to exceed the dose limit for the lens.Results and Discussion: In July 2020, the JHPS guideline was published. The guideline consists of three parts: main text, explanations, and 26 examples. In the questions, the corresponding answers were prepared, and specific examples were provided to enable similar cases to be addressed.Conclusion: With the development of the guideline on radiation dose monitoring of the lens, radiation managers and workers will be able to smoothly comply with revised regulations and optimize radiation protection.
Optical Properties of GaAs/AlGaAs Quantum Dots Grown by Droplet Epitaxy with Post-Growth Annealing
Chang Myung Lee,Joo In Lee,Dong-Han Lee,Jae-Young Leem,한일기,Nobuyuki Koguchi 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.43 No.42
We have studied the post-annealing eects on the optical properties and the spectral homogeneous broadening of GaAs/AlGaAs quantum dots (QDs) fabricated by modied droplet epitaxy. The photoluminescence (PL) intensity of the QDs increased drastically and the peak energy shifted toward high energy, by about 69 meV, after annealing. These eects may be caused by the improved crystallinity of the QD systems, the size reduction of the QDs, and/or composition changes in the QDs by post-annealing. From precise examination of the micro-PL spectra under weak excitation conditions, the minimal homogeneous linewidth of the QDs was estimated to be 1.45 1.6 meV at 77 K.
종수 김,D. Y. Lee,Gu-Hyun Kim,H. K. Choi,I. H. Bae,J. I. Lee,Jae-Young Leem,Jin Soo Kim,Minhyon Jeon,Nobuyuki Koguchi,S. H. Lee,S. I. Ban,S. K. Kang 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.III
The structural and optical properties of non-wetting layer InAs quantum dots (QDs) have been investigated by transmission electron microscopy (TEM), photoreflectance (PR) and photoluminescence (PL). By alternate depositing 0.83 $\sim$ 1.2 ML InAs and 1.2 $\sim$ 1.5 ML Ga(Al)As with different period on GaAs surface, the wetting layer of InAs QDs was controlled. TEM images clearly show the formation of QDs by using quasi monolayer (QML) deposition and non-wetting layer of InAs QDs. The QDs formed by using QML could not be grown by Stranski-Krastanov (S-K) growth. In PR measurement, the wetting layer transition is not observed for all the QML QDs. These QML QDs growth mechanisms are explained by adatom migration effect due to surface chemical potential.