12 results on '"Kidong Park"'
Search Results
2. Phase Controlled Growth of Cd
- Author
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Kidong, Park, Minkyung, Jung, Doyeon, Kim, Janice Ruth, Bayogan, Jong Hyun, Lee, Sung Jin, An, Jungpil, Seo, Jaemin, Seo, Jae-Pyoung, Ahn, and Jeunghee, Park
- Abstract
The bottom-up synthesis process often allows the growth of metastable phase nanowires instead of the thermodynamically stable phase. Herein, we synthesized Cd
- Published
- 2020
3. Quantum Dots Formed in Three-dimensional Dirac Semimetal Cd
- Author
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Minkyung, Jung, Kenji, Yoshida, Kidong, Park, Xiao-Xiao, Zhang, Can, Yesilyurt, Zhuo Bin, Siu, Mansoor B A, Jalil, Jinwan, Park, Jeunghee, Park, Naoto, Nagaosa, Jungpil, Seo, and Kazuhiko, Hirakawa
- Abstract
We demonstrate quantum dot (QD) formation in three-dimensional Dirac semimetal Cd
- Published
- 2018
4. Reversible Halide Exchange Reaction of Organometal Trihalide Perovskite Colloidal Nanocrystals for Full-Range Band Gap Tuning
- Author
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Jeunghee Park, Jong Woon Lee, Duk Hwan Kim, Fazel Shojaei, Kidong Park, Hong Seok Kang, Jae Pyung Ahn, Jae Kyu Song, and Dong Myung Jang
- Subjects
chemistry.chemical_classification ,Band gap ,Mechanical Engineering ,Iodide ,Trihalide ,Halide ,Bioengineering ,General Chemistry ,Methylammonium lead halide ,Condensed Matter Physics ,Photochemistry ,Active layer ,chemistry.chemical_compound ,chemistry ,Nanocrystal ,General Materials Science ,Perovskite (structure) - Abstract
In recent years, methylammonium lead halide (MAPbX3, where X = Cl, Br, and I) perovskites have attracted tremendous interest caused by their outstanding photovoltaic performance. Mixed halides have been frequently used as the active layer of solar cells, as a result of their superior physical properties as compared to those of traditionally used pure iodide. Herein, we report a remarkable finding of reversible halide-exchange reactions of MAPbX3, which facilitates the synthesis of a series of mixed halide perovskites. We synthesized MAPbBr3 plate-type nanocrystals (NCs) as a starting material by a novel solution reaction using octylamine as the capping ligand. The synthesis of MAPbBr(3-x)Clx and MAPbBr(3-x)Ix NCs was achieved by the halide exchange reaction of MAPbBr3 with MACl and MAI, respectively, in an isopropyl alcohol solution, demonstrating full-range band gap tuning over a wide range (1.6-3 eV). Moreover, photodetectors were fabricated using these composition-tuned NCs; a strong correlation was observed between the photocurrent and photoluminescence decay time. Among the two mixed halide perovskite series, those with I-rich composition (x = 2), where a sole tetragonal phase exists without the incorporation of a cubic phase, exhibited the highest photoconversion efficiency. To understand the composition-dependent photoconversion efficiency, first-principles density-functional theory calculations were carried out, which predicted many plausible configurations for cubic and tetragonal phase mixed halides.
- Published
- 2015
5. In Situ Temperature-Dependent Transmission Electron Microscopy Studies of Pseudobinary mGeTe·Bi2Te3 (m = 3–8) Nanowires and First-Principles Calculations
- Author
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Jae-Pyoung Ahn, Jae Nyeong Kim, Hyungsoon Im, Jeunghee Park, Han Sung Kim, Kidong Park, Chan Su Jung, Ji Hoon Shim, Seung Jo Yoo, and Jin-Gyu Kim
- Subjects
Phase transition ,Materials science ,Mechanical Engineering ,Superlattice ,Alloy ,Nanowire ,Bioengineering ,General Chemistry ,engineering.material ,Condensed Matter Physics ,Crystallography ,Transmission electron microscopy ,Phase (matter) ,Thermal ,engineering ,General Materials Science ,Thermal stability - Abstract
Phase-change nanowires (NWs) have emerged as critical materials for fast-switching nonvolatile memory devices. In this study, we synthesized a series of mGeTe·Bi2Te3 (GBT) pseudobinary alloy NWs—Ge3Bi2Te6 (m = 3), Ge4Bi2Te7 (m = 4), Ge5Bi2Te8 (m = 5), Ge6Bi2Te9 (m = 6), and Ge8Bi2Te11 (m = 8)—and investigated their composition-dependent thermal stabilities and electrical properties. As m decreases, the phase of the NWs evolves from the cubic (C) to the hexagonal (H) phase, which produces unique superlattice structures that consist of periodic 2.2–3.8 nm slabs for m = 3–8. In situ temperature-dependent transmission electron microscopy reveals the higher thermal stability of the compositions with lower m values, and a phase transition from the H phase into the single-crystalline C phase at high temperatures (400 °C). First-principles calculations, performed for the superlattice structures (m = 1–8) of GBT and mGeTe·Sb2Te3 (GST), show an increasing stability of the H phase (versus the C phase) with decreasin...
- Published
- 2015
6. Zn3P2–Zn3As2 Solid Solution Nanowires
- Author
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Hyungsoon Im, Dong Myung Jang, Chan Su Jung, Seung Jo Yoo, Kidong Park, Jeunghee Park, and Jin-Gyu Kim
- Subjects
Materials science ,Band gap ,Mechanical Engineering ,Superlattice ,Nanowire ,chemistry.chemical_element ,Bioengineering ,Nanotechnology ,General Chemistry ,Chemical vapor deposition ,Condensed Matter Physics ,Tetragonal crystal system ,chemistry.chemical_compound ,Crystallography ,chemistry ,General Materials Science ,Indium ,Solid solution ,Zinc arsenide - Abstract
Semiconductor alloy nanowires (NWs) have recently attracted considerable attention for applications in optoelectronic nanodevices because of many notable properties, including band gap tunability. Zinc phosphide (Zn3P2) and zinc arsenide (Zn3As2) belong to a unique pseudocubic tetragonal system, but their solid solution has rarely been studied. Here In this study, we synthesized composition-tuned Zn3(P1–xAsx)2 NWs with different crystal structures by controlling the growth conditions during chemical vapor deposition. A first type of synthesized NWs were single-crystalline and grew uniformly along the [110] direction (in a cubic unit cell) over the entire compositional range (0 ≤ x ≤ 1) explored. The use of an indium source enabled the growth of a second type of NWs, with remarkable cubic-hexagonal polytypic twinned superlattice and bicrystalline structures. The growth direction of the Zn3P2 and Zn3As2 NWs was also switched to [111] and [112], respectively. These structural changes are attributable to the ...
- Published
- 2015
7. In Situ Temperature-Dependent Transmission Electron Microscopy Studies of Pseudobinary mGeTe·Bi₂Te₃ (m = 3-8) Nanowires and First-Principles Calculations
- Author
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Chan Su, Jung, Han Sung, Kim, Hyung Soon, Im, Kidong, Park, Jeunghee, Park, Jae-Pyoung, Ahn, Seung Jo, Yoo, Jin-Gyu, Kim, Jae Nyeong, Kim, and Ji Hoon, Shim
- Abstract
Phase-change nanowires (NWs) have emerged as critical materials for fast-switching nonvolatile memory devices. In this study, we synthesized a series of mGeTe·Bi2Te3 (GBT) pseudobinary alloy NWs-Ge3Bi2Te6 (m = 3), Ge4Bi2Te7 (m = 4), Ge5Bi2Te8 (m = 5), Ge6Bi2Te9 (m = 6), and Ge8Bi2Te11 (m = 8)-and investigated their composition-dependent thermal stabilities and electrical properties. As m decreases, the phase of the NWs evolves from the cubic (C) to the hexagonal (H) phase, which produces unique superlattice structures that consist of periodic 2.2-3.8 nm slabs for m = 3-8. In situ temperature-dependent transmission electron microscopy reveals the higher thermal stability of the compositions with lower m values, and a phase transition from the H phase into the single-crystalline C phase at high temperatures (400 °C). First-principles calculations, performed for the superlattice structures (m = 1-8) of GBT and mGeTe·Sb2Te3 (GST), show an increasing stability of the H phase (versus the C phase) with decreasing m; the difference in stability being more marked for GBT than for GST. The calculations explain remarkably the phase evolution of the GBT and GST NWs as well as the composition-dependent thermal stabilities. Measurement of the current-voltage curves for individual GBT NWs shows that the resistivity is in the range 3-25 mΩ·cm, and the resistivity of the H phase is lower than that of the C phase, which has been supported by the calculations.
- Published
- 2015
8. Zn₃P₂-Zn₃As₂ solid solution nanowires
- Author
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Hyung Soon, Im, Kidong, Park, Dong Myung, Jang, Chan Su, Jung, Jeunghee, Park, Seung Jo, Yoo, and Jin-Gyu, Kim
- Abstract
Semiconductor alloy nanowires (NWs) have recently attracted considerable attention for applications in optoelectronic nanodevices because of many notable properties, including band gap tunability. Zinc phosphide (Zn3P2) and zinc arsenide (Zn3As2) belong to a unique pseudocubic tetragonal system, but their solid solution has rarely been studied. Here In this study, we synthesized composition-tuned Zn3(P1-xAsx)2 NWs with different crystal structures by controlling the growth conditions during chemical vapor deposition. A first type of synthesized NWs were single-crystalline and grew uniformly along the [110] direction (in a cubic unit cell) over the entire compositional range (0 ≤ x ≤ 1) explored. The use of an indium source enabled the growth of a second type of NWs, with remarkable cubic-hexagonal polytypic twinned superlattice and bicrystalline structures. The growth direction of the Zn3P2 and Zn3As2 NWs was also switched to [111] and [112], respectively. These structural changes are attributable to the Zn-depleted indium catalytic nanoparticles which favor the growth of hexagonal phases. The formation of a solid solution at all compositions allowed the continuous tuning of the band gap (1.0-1.5 eV). Photocurrent measurements were performed on individual NWs by fabricating photodetector devices; the single-crystalline NWs with [110] growth direction exhibit a higher photoconversion efficiency compared to the twinned crystalline NWs with [111] or [112] growth direction.
- Published
- 2015
9. GaP-ZnS pseudobinary alloy nanowires
- Author
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Kidong Park, Han Sung Kim, Jung Ah Lee, Chan Su Jung, Chang-Lyoul Lee, Jeunghee Park, and Hyungsoon Im
- Subjects
Photocurrent ,Photoluminescence ,Materials science ,business.industry ,Band gap ,Mechanical Engineering ,Alloy ,Nanowire ,Bioengineering ,Heterojunction ,General Chemistry ,engineering.material ,Condensed Matter Physics ,Phase (matter) ,engineering ,Optoelectronics ,General Materials Science ,business ,Electronic band structure - Abstract
Multicomponent nanowires (NWs) are of great interest for integrated nanoscale optoelectronic devices owing to their widely tunable band gaps. In this study, we synthesize a series of (GaP)(1-x)(ZnS)(x) (0 ≤ x ≤ 1) pseudobinary alloy NWs using the vapor transport method. Compositional tuning results in the phase evolution from the zinc blende (ZB) (x0.4) to the wurtzite (WZ) phase (x0.7). A coexistence of ZB and WZ phases (x = 0.4-0.7) is also observed. In the intermediate phase coexistence range, a core-shell structure is produced with a composition of x = 0.4 and 0.7 for the core and shell, respectively. The band gap (2.4-3.7 eV) increases nonlinearly with increasing x, showing a significant bowing phenomenon. The phase evolution leads to enhanced photoluminescence emission. Strikingly, the photoluminescence spectrum shows a blue-shift (70 meV for x = 0.9) with increasing excitation power, and a wavelength-dependent decay time. Based on the photoluminescence data, we propose a type-II pseudobinary heterojunction band structure for the single-crystalline WZ phase ZnS-rich NWs. The slight incorporation of GaP into the ZnS induces a higher photocurrent and excellent photocurrent stability, which opens up a new strategy for enhancing the performance of photodetectors.
- Published
- 2014
10. Polymorphism of GeSbTe superlattice nanowires
- Author
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Yong Jae Cho, Hyungsoon Im, Seung Hyuk Back, Han Sung Kim, Jeunghee Park, Kidong Park, Chang Hyun Kim, Young Seok Seo, Jae-Pyoung Ahn, and Chan Su Jung
- Subjects
Materials science ,business.industry ,Mechanical Engineering ,Superlattice ,Nanowire ,Bioengineering ,Nanotechnology ,General Chemistry ,GeSbTe ,Condensed Matter Physics ,Non-volatile memory ,Phase change ,chemistry.chemical_compound ,Polymorphism (materials science) ,chemistry ,Vacancy defect ,Optoelectronics ,General Materials Science ,business ,Nanoscopic scale - Abstract
Scaling-down of phase change materials to a nanowire (NW) geometry is critical to a fast switching speed of nonvolatile memory devices. Herein, we report novel composition-phase-tuned GeSbTe NWs, synthesized by a chemical vapor transport method, which guarantees promising applications in the field of nanoscale electric devices. As the Sb content increased, they showed a distinctive rhombohedral-cubic-rhombohedral phase evolution. Remarkable superlattice structures were identified for the Ge(8)Sb(2)Te(11), Ge(3)Sb(2)Te(6), Ge(3)Sb(8)Te(6), and Ge(2)Sb(7)Te(4) NWs. The coexisting cubic-rhombohedral phase Ge(3)Sb(2)Te(6) NWs exhibited an exclusively uniform superlattice structure consisting of 2.2 nm period slabs. The rhombohedral phase Ge(3)Sb(8)Te(6) and Ge(2)Sb(7)Te(4) NWs adopted an innovative structure; 3Sb(2) layers intercalated the Ge(3)Sb(2)Te(6) and Ge(2)Sb(1)Te(4) domains, respectively, producing 3.4 and 2.7 nm period slabs. The current-voltage measurement of the individual NW revealed that the vacancy layers of Ge(8)Sb(2)Te(11) and Ge(3)Sb(2)Te(6) decreased the electrical conductivity.
- Published
- 2013
11. Reversible Halide Exchange Reaction of OrganometalTrihalide Perovskite Colloidal Nanocrystals for Full-Range Band GapTuning.
- Author
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Dong Myung Jang, Kidong Park, Duk Hwan Kim, Jeunghee Park, Fazel Shojaei, Hong Seok Kang, Jae-Pyung Ahn, Jong Woon Lee, and Jae Kyu Song
- Subjects
- *
PEROVSKITE , *OXIDE minerals , *BAND gaps , *HALIDES , *ALLYL halides , *EXCHANGE reactions - Abstract
Inrecent years, methylammonium lead halide (MAPbX3, whereX = Cl, Br, and I) perovskites have attracted tremendous interestcaused by their outstanding photovoltaic performance. Mixed halideshave been frequently used as the active layer of solar cells, as aresult of their superior physical properties as compared to thoseof traditionally used pure iodide. Herein, we report a remarkablefinding of reversible halide-exchange reactions of MAPbX3, which facilitates the synthesis of a series of mixed halide perovskites.We synthesized MAPbBr3plate-type nanocrystals (NCs) asa starting material by a novel solution reaction using octylamineas the capping ligand. The synthesis of MAPbBr3–xClxand MAPbBr3–xIxNCs was achieved bythe halide exchange reaction of MAPbBr3with MACl and MAI,respectively, in an isopropyl alcohol solution, demonstrating full-range band gaptuning over a wide range (1.6–3 eV). Moreover, photodetectorswere fabricated using these composition-tuned NCs; a strong correlationwas observed between the photocurrent and photoluminescence decaytime. Among the two mixed halide perovskite series, those with I-richcomposition (x= 2), where a sole tetragonal phaseexists without the incorporation of a cubic phase, exhibited the highestphotoconversion efficiency. To understand the composition-dependentphotoconversion efficiency, first-principles density-functional theorycalculations were carried out, which predicted many plausible configurationsfor cubic and tetragonal phase mixed halides. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
12. In SituTemperature-Dependent TransmissionElectron Microscopy Studies of Pseudobinary mGeTe·Bi2Te3(m= 3–8) Nanowiresand First-Principles Calculations.
- Author
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Chan Su Jung, Han Sung Kim, Hyung Soon Im, Kidong Park, Jeunghee Park, Jae-Pyoung Ahn, Seung Jo Yoo, Jin-Gyu Kim, Jae Nyeong Kim, and Ji Hoon Shim
- Published
- 2015
- Full Text
- View/download PDF
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