Publications

@article{2014NomuraY,

title = {Demonstration of Controlling the Spatiotemporal Dynamics of Optical Near-Field Excitation Transfer in Y-Junction Structure Consisting of Randomly Distributed Quantum Dots},

author = {Wataru Nomura and Makoto Naruse and Masashi Aono and Song-Ju Kim and Tadashi Kawazoe and Takashi Yatsui and Motoichi Ohtsu},

doi = {10.1155/2014/569684},

year  = {2014},

date = {2014-02-01},

journal = {Advances in Optical Technologies},

volume = {2014},

pages = {569684},

abstract = {Solution searching devices that operate on the basis of controlling the spatiotemporal dynamics of excitation transfer via dressed photon interactions between quantum dots have been proposed. Long-range excitation transfer based on dressed photon interactions between randomly distributed quantum dots is considered to be effective in realizing such devices. Here, we successfully controlled the spatiotemporal dynamics of excitation transfer using a Y-junction structure consisting of randomly dispersed CdSe/ZnS core-shell quantum dots. This Y-junction structure has two “output ends” and one “tap end.” By exciting one output end with control light, we observed increased excitation transfer to the other output end via a state-filling effect. Conversely, we observed reduced excitation transfer to the output ends by irradiating the tap end with control light, due to excitation of defect levels in the tap end. These results show the possibility of controlling the optical excitation transfer dynamics between multiple quantum dots.},

keywords = {Nanophotonic device, Near-field effect, QD},

pubstate = {published},

tppubtype = {article}

}

@article{2012liuAPB,

title = {Controlling the sizes of ZnO quantum dots by using dressed photon-phonon assisted sol-gel method},

author = {Yang Liu and Takashi Yatsui and Motoichi Ohtsu},

doi = {10.1007/s00340-012-5151-1},

year  = {2012},

date = {2012-09-01},

journal = {Applied Physics B},

volume = {108},

number = {4},

pages = {707-711},

publisher = {Springer Nature},

abstract = {We developed a sol-gel method using the dressed photon-phonon (DPP) process. DPPs are selectively exited in nanoscale structures at photon energies that are lower than the bandgap energy, which allows one to increase the growth rate of smaller ZnO quantum dots (QDs). Thus, we obtained a smaller size variance of ZnO QDs. The growth rate was proportional to the power of the light used for DPP excitation. The results were confirmed using a rate equation that accounted for the concentration of the sol-gel solution.},

keywords = {Nanophotonic fabrication, Near-field effect, QD, Sol-gel, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/1.4723574,

title = {Emission from a dipole-forbidden energy state in a ZnO quantum dot induced by a near-field interaction with a fiber probe},

author = {Takashi Yatsui and Masahiro Tsuji and Yang Liu and Tadashi Kawazoe and Motoichi Ohtsu},

doi = {10.1063/1.4723574},

year  = {2012},

date = {2012-05-01},

journal = {Applied Physics Letters},

volume = {100},

number = {22},

pages = {223110},

abstract = {The emission intensity from the dipole-forbidden state in a spherical quantum dot (QD) was enhanced by introducing an aperture fiber probe close to the ZnO QD to induce a near-field interaction between the probe tip and the QD. The cross-sectional profiles of the photoluminescence intensities of the ground exciton state and the excited exciton states varied spatially in an anti-correlated manner.},

keywords = {First, Near-field effect, QD, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{2012nomuraAPB,

title = {Direct observation of optical excitation transfer based on resonant optical near-field interaction},

author = {Wataru Nomura and Takashi Yatsui and Tadashi Kawazoe and Makoto Naruse and Erich Runge and Christoph Lienau and Motoichi Ohtsu},

doi = {10.1007/s00340-012-5009-6},

year  = {2012},

date = {2012-04-01},

journal = {Applied Physics B},

volume = {107},

number = {2},

pages = {257-262},

publisher = {Springer Nature},

abstract = {This article reports the direct observation of long-distance optical excitation transfer based on resonant optical near-field interactions in randomly distributed quantum dots (QDs). We fabricated optical excitation transfer paths based on randomly distributed QDs by using CdSe/ZnS core-shell QDs and succeeded for the first time in obtaining output signals resulting from a unidirectional optical excitation transfer length of 2.4 ƒÊm. Furthermore, we demonstrate that the optical excitation transfer occurs via the resonant excited levels of the QDs with a comparative experiment using non-resonant QDs. This excitation-transfer mechanism allows for intersecting, non-interacting nano-optical wires.},

keywords = {Nanophotonic device, Near-field effect, QD},

pubstate = {published},

tppubtype = {article}

}

@article{Tate:11,

title = {Demonstration of modulatable optical near-field interactions between dispersed resonant quantum dots},

author = {Naoya Tate and Makoto Naruse and Wataru Nomura and Tadashi Kawazoe and Takashi Yatsui and Morihisa Hoga and Yasuyuki Ohyagi and Yoko Sekine and Hiroshi Fujita and Motoichi Ohtsu},

doi = {10.1364/OE.19.018260},

year  = {2011},

date = {2011-09-12},

journal = {Optics Express},

volume = {19},

number = {19},

pages = {18260-18271},

publisher = {OSA},

abstract = {We experimentally demonstrated the basic concept of modulatable optical near-field interactions by utilizing energy transfer between closely positioned resonant CdSe/ZnS quantum dot (QD) pairs dispersed on a flexible substrate. Modulation by physical flexion of the substrate changes the distances between quantum dots to control the magnitude of the coupling strength. The modulation capability was qualitatively confirmed as a change of the emission spectrum. We defined two kinds of modulatability for quantitative evaluation of the capability, and an evident difference was revealed between resonant and non-resonant QDs.},

keywords = {Near-field effect, QD},

pubstate = {published},

tppubtype = {article}

}

@article{Akahane_2011,

title = {Energy Transfer in Multi-Stacked InAs Quantum Dots},

author = {Kouichi Akahane and Naokatsu Yamamoto and Makoto Naruse and Tadashi Kawazoe and Takashi Yatsui and Motoichi Ohtsu},

doi = {10.1143/jjap.50.04dh05},

year  = {2011},

date = {2011-04-01},

journal = {Japanese Journal of Applied Physics},

volume = {50},

number = {4},

pages = {04DH05},

publisher = {IOP Publishing},

abstract = {We fabricated a modulated stacked quantum dot (QD) structure to investigate energy transfer among QDs using a strain compensation technique that allowed us to fabricate a vertically aligned, highly stacked structure without any degradation in crystal quality. Enhanced photoluminescence (PL) intensity for the ground state of large QDs was clearly observed in a sample where the ground state of small QDs was resonant to the first excited state of large QDs, indicating energy transfer from small QDs to large QDs. Long-range energy transfer reached approximately 200 nm and can be considered from the measurement of N dependence of PL intensity.},

keywords = {Energy-transfer, Nanophotonic device, QD},

pubstate = {published},

tppubtype = {article}

}

@article{Liu_2011,

title = {Size control of sol–gel-synthesized ZnO quantum dots using photo-induced desorption},

author = {Yang Liu and Tetsu Morishima and Takashi Yatsui and Tadashi Kawazoe and Motoichi Ohtsu},

doi = {10.1088/0957-4484/22/21/215605},

year  = {2011},

date = {2011-03-01},

journal = {Nanotechnology},

volume = {22},

number = {21},

pages = {215605},

publisher = {IOP Publishing},

abstract = {We developed a sol–gel method using photo-induced desorption for size-controlled ZnO quantum dots (QDs). This method successfully controlled the size and size variance of ZnO QDs, and size fluctuations decreased from 23% to 18% depending on the illuminated light intensity. The sol–gel synthesis effectively reduced the number of defect levels that originated from oxygen defects.},

keywords = {Nanophotonic fabrication, QD, Sol-gel},

pubstate = {published},

tppubtype = {article}

}

@article{2010nomuraAPB,

title = {Structural dependency of optical excitation transfer via optical near-field interactions between semiconductor quantum dots},

author = {Wataru Nomura and Takashi Yatsui and Tadashi Kawazoe and Makoto Naruse and Motoichi Ohtsu},

doi = {10.1007/s00340-010-3977-y},

year  = {2010},

date = {2010-07-01},

journal = {Applied Physics B},

volume = {100},

number = {1},

pages = {181-187},

publisher = {Springer Nature},

abstract = {The distribution dependency of quantum dots was theoretically and experimentally investigated with respect to the basic properties optical excitation transfer via optical near-field interactions between quantum dots. The effects of three-dimensional structure and arraying precision of quantum dots on the signal transfer performance were analyzed. In addition, the quantum dot distribution dependency of the signal transfer performance was experimentally evaluated by using stacked CdSe quantum dots and an optical near-field fiber probe tip laminated with quantum dots serving as an output terminal, showing good agreement with theory. These results demonstrate the basic properties of signal transfer via optical near-field interactions and serve as guidelines for a nanostructure design optimized to attain the desired signal transfer performances.},

keywords = {Energy-transfer, Nanophotonic device, QD},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/1.3372639,

title = {Self-assembly method of linearly aligning ZnO quantum dots for a nanophotonic signal transmission device},

author = {Takashi Yatsui and Yang Ryu and Tetsu Morishima and Wataru Nomura and Tadashi Kawazoe and Tetsu Yonezawa and Masao Washizu and Hiroyuki Fujita and Motoichi Ohtsu},

url = {https://doi.org/10.1063/1.3372639},

doi = {10.1063/1.3372639},

year  = {2010},

date = {2010-01-01},

journal = {Applied Physics Letters},

volume = {96},

number = {13},

pages = {133106},

abstract = {We report a self-assembly method that aligns nanometer-sized quantum dots (QDs) into a straight line along which photonic signals can be transmitted by optically near-field effects. ZnO QDs were bound electrostatically to DNA to form a one-dimensional QD chain. The photoluminescence intensity under parallel polarization excitation along the QDs chain was much greater than under perpendicular polarization excitation, indicating an efficient signal transmission along the QD chain. As optical near-field energy can transmit through the resonant energy level, nanophotonic signal transmission devices have a number of potential applications, such as wavelength division multiplexing using QDs of different sizes.},

keywords = {First, Nanophotonic device, QD, Self-assembly, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{2008yatsuiAPBZnO,

title = {Controlling the energy transfer between near-field optically coupled ZnO quantum dots},

author = {Takashi Yatsui and Hyung Su Jeong and Motoichi Ohtsu},

doi = {10.1007/s00340-008-3154-8},

year  = {2008},

date = {2008-10-01},

journal = {Applied Physics B},

volume = {93},

number = {1},

pages = {199-202},

publisher = {Springer Nature},

abstract = {We performed time-resolved spectroscopy of ZnO quantum dots (QD), and observed exciton energy transfer and dissipation between QD via an optical near-field interaction. Two different sizes of ZnO QD with resonant energy levels were mixed to test the energy transfer and dissipation using time-resolved photoluminescence spectroscopy. The estimated energy transfer time was 144 ps. Furthermore, we demonstrated that the ratio of energy transfer between the resonant energy states could be controlled.},

keywords = {Electrodes, First, QD, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{10.1117/1.2817657,

title = {Observation of dissipated optical energy transfer between CdSe quantum dots},

author = {Wataru Nomura and Takashi Yatsui and Tadashi Kawazoe and Motoichi Ohtsu},

doi = {10.1117/1.2817657},

year  = {2007},

date = {2007-11-01},

journal = {Journal of Nanophotonics},

volume = {1},

number = {1},

pages = {011591},

publisher = {SPIE},

abstract = {Exciton energy transfer between quantum dots via an optical near-field and subsequent dissipation was observed. Two sizes of CdSe/ZnS quantum dots with resonant energy levels were mixed to confirm the energy transfer and dissipation using time-resolved photoluminescence spectroscopy. It was estimated that the energy transfer time was 135 ps, which is shorter than the exciton lifetime of 2.10 ns. This indicates that CdSe quantum dots are promising material for nanophotonic devices.},

keywords = {dissipation, Excitons, Nanophotonic device, Near-field effect, QD},

pubstate = {published},

tppubtype = {article}

}