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Kyhm, Kwangseuk,Kim, Jihoon,Yang, Ho-Soon,Je, Koo-Chul,Murayama, Akihiro American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.3
<P>The ultrafast spin dynamics of the bright exciton in CdSe/ZnS nanocrystal quantum dots has been investigated using a circularly polarized pump-probe experiment. A remarkably fast spin flip (-500 fs) of the bright exciton was observed at 4 K, which is attributed to the anisotropic electron-hole exchange interaction and the random positioning of nanocrystal quantum dots. In the presence of an applied magnetic field (5 T), the exciton spin parallel to the external magnetic field was favored due to Zeeman splitting. We found that this imbalance can possibly be suppressed by the state-blocking and the mixing of the 1(L) and 1(U) states in asymmetric quantum dots.</P>
Jihoon Kim,Rajesh Sharma,양호순,Kwangseuk Kyhm 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.2
All-optical switching (AOS) was demonstrated utilizing spin-based dichroism in CdSe/ZnS nanocyrstal quantum dots (NQDs). The spin-degenerate ground state of 1Se-1Sh3/2 was excited selectively and resonantly with circular polarization and spectral laser tuning, respectively. Strong confinement provide a firm spin state at room temperature and an ultrafast spin-flip process, which enables a subpicosecond switching-time resolution. An origin of the AOS was identified in terms of the population difference between the spin degenerate states by using a polarization-dependent degenerate pump-probe. The AOS signal was found to be sensitive to the the deviation of the perpendicular analyzer angle and to the spatial homogeneity of NQDs. All-optical switching (AOS) was demonstrated utilizing spin-based dichroism in CdSe/ZnS nanocyrstal quantum dots (NQDs). The spin-degenerate ground state of 1Se-1Sh3/2 was excited selectively and resonantly with circular polarization and spectral laser tuning, respectively. Strong confinement provide a firm spin state at room temperature and an ultrafast spin-flip process, which enables a subpicosecond switching-time resolution. An origin of the AOS was identified in terms of the population difference between the spin degenerate states by using a polarization-dependent degenerate pump-probe. The AOS signal was found to be sensitive to the the deviation of the perpendicular analyzer angle and to the spatial homogeneity of NQDs.
Alternative Patterning Process for Realization of Large-Area, Full-Color, Active Quantum Dot Display
Park, Joon-Suh,Kyhm, Jihoon,Kim, Hong Hee,Jeong, Shinyoung,Kang, JoonHyun,Lee, Song-ee,Lee, Kyu-Tae,Park, Kisun,Barange, Nilesh,Han, JiYeong,Song, Jin Dong,Choi, Won Kook,Han, Il Ki American Chemical Society 2016 Nano letters Vol.16 No.11
<P>Although various colloidal quantum dot (QD) coating and patterning techniques have been developed to meet the demands in optoelectronic applications over the past years, each of the previously demonstrated methods has one or more limitations and trade-offs in forming multicolor, high-resolution, or large-area patterns of QDs. In this study, we present an alternative QD patterning technique using conventional photolithography combined with charge-assisted layer-by-layer (LbL) assembly to solve the trade-offs of the traditional patterning processes. From our demonstrations, we show repeatable QD patterning process that allows multicolor QD patterns in both large-area and microscale. Also, we show that the QD patterns are robust against additional photolithography processes and that the thickness of the QD patterns can be controlled at each position. To validate that this process can be applied to actual device applications as an active material, we have fabricated inverted, differently colored, active QD light-emitting device (QD-LED) on a pixelated substrate, which achieved maximum electroluminescence intensity of 23 770 cd/m(2), and discussed the results. From our findings, we believe that our process provides a solution to achieving both high-resolution and large-scale QD pattern applicable to not only display, but also to practical photonic device research and development.</P>
Ahn, Il-Ho,Kyhm, Jihoon,Lee, Juwon,Cho, Sangeun,Jo, Yongcheol,Kim, Deuk Young,Choi, Soo Ho,Yang, Woochul ELSEVIER 2019 Current Applied Physics Vol.19 No.4
<P><B>Abstract</B></P> <P>We report here a simple alternative method for measuring charge carrier drift mobilities in semiconductor devices. A typical falling photocurrent transient formula for switch-off-state was adjusted to obtain simultaneously electron and hole mobilities. For both undoped ZnO film and InAlAs/InGaAs quantum well structure, electron mobilities extracted from our model were compared with those obtained from maximum-entropy mobility-spectrum analysis method (ME-MSA). Our results demonstrated that electron mobility obtained from our photocurrent response model could serve as substitutes for a representative mobility obtained from ME-MSA.</P>
Light Controlled Optical Aharonov-Bohm Oscillations in a Single Quantum Ring
Kim, Heedae,Park, Seongho,Okuyama, Rin,Kyhm, Kwangseuk,Eto, Mikio,Taylor, Robert A.,Nogues, Gilles,Dang, Le Si,Potemski, Marek,Je, Koochul,Kim, Jongsu,Kyhm, Jihoon,Song, Jindong American Chemical Society 2018 NANO LETTERS Vol.18 No.10
<P>We found that optical Aharonov-Bohm oscillations in a single GaAs/GaAlAs quantum ring can be controlled by excitation intensity. With a weak excitation intensity of 1.2 kW cm<SUP>-2</SUP>, the optical Aharonov-Bohm oscillation period of biexcitons was observed to be half that of excitons in accordance with the period expected for a two-exciton Wigner molecule. When the excitation intensity is increased by an order of magnitude (12 kW cm<SUP>-2</SUP>), a gradual deviation of the Wigner molecule condition occurs with decreased oscillation periods and diamagnetic coefficients for both excitons and biexcitons along with a spectral shift. These results suggest that the effective orbit radii and rim widths of electrons and holes in a single quantum ring can be modified by light intensity via photoexcited carriers, which are possibly trapped at interface defects resulting in a local electric field.</P> [FIG OMISSION]</BR>