Publications

@article{2013tateAPB1,

title = {Fixed-distance coupling and encapsulation of heterogeneous quantum dots using phonon-assisted photo-curing},

author = {Naoya Tate and Yang Liu and Tadashi Kawazoe and Makoto Naruse and Takashi Yatsui and Motoichi Ohtsu},

doi = {10.1007/s00340-012-5249-5},

year  = {2013},

date = {2013-01-01},

journal = {Applied Physics B},

volume = {110},

number = {1},

pages = {39-45},

publisher = {Springer Nature},

abstract = {We propose a novel method of coupling heterogeneous quantum dots at fixed distances and capsulating the coupled quantum dots by utilizing nanometric local curing of a photo-curable polymer caused by multistep electronic transitions based on a phonon-assisted optical near-field process between quantum dots. Because the coupling and the capsulating processes are triggered only when heterogeneous quantum dots floating in a solution closely approach each other to induce optical near-field interactions between them, the distances between the coupled quantum dots are physically guaranteed to be equal to the scale of the optical near fields. To experimentally verify our idea, we fabricated coupled quantum dots, consisting of CdSe and ZnO quantum dots and a UV-curable polymer. We also measured the photoluminescence properties due to the quantum-dot coupling and showed that the individual photoluminescences from the CdSe and ZnO quantum dots exhibited a trade-off relationship.},

keywords = {Droplet, Nanophotonic fabrication},

pubstate = {published},

tppubtype = {article}

}

@article{Yatsui_2012,

title = {Realization of an atomically flat surface of diamond using dressed photon–phonon etching},

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

url = {https://doi.org/10.1088%2F0022-3727%2F45%2F47%2F475302},

doi = {10.1088/0022-3727/45/47/475302},

year  = {2012},

date = {2012-11-01},

journal = {Journal of Physics D: Applied Physics},

volume = {45},

number = {47},

pages = {475302},

publisher = {IOP Publishing},

abstract = {We obtained an atomically flat diamond surface following dressed photon–phonon (DPP) etching using 3.81 eV light and O2 gas. We obtained a surface roughness (Ra) of 0.154 nm for Ib-type (1 1 1) diamond and 0.096 nm for Ib-type (1 0 0) diamond. To evaluate the surface roughness, we grouped the surface into bins of width l and introduced the standard deviation of the height difference function for a given separation l, which allowed us to determine the height variation of the surface. Based on the calculation of standard deviation, the conventional adiabatic photochemical reaction did not remove the small surface features, while DPP etching decreased the surface roughness for all length scales.},

keywords = {Diamond, First, Nanophotonic fabrication, Near-field etching},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/1.4765355,

title = {Effects of laser irradiation on the self-assembly of MnAs nanoparticles in a GaAs matrix},

author = {Pham Nam Hai and Wataru Nomura and Takashi Yatsui and Motoichi Ohtsu and Masaaki Tanaka},

doi = {10.1063/1.4765355},

year  = {2012},

date = {2012-10-01},

urldate = {2012-10-01},

journal = {Applied Physics Letters},

volume = {101},

number = {19},

pages = {193102},

abstract = {We investigate the effects of laser irradiation on the self-assembly of MnAs nanoparticles during solid-phase decomposition in a GaAs matrix. It is found that laser irradiation suppresses the growth of MnAs nanoparticles from small to large size, and that the median diameter D1 in the size distribution of small MnAs nanoparticles depends on the incident photon energy E following D1 ∼ E−1/5. We explain this behavior by the desorption of Mn atoms on the MnAs nanoparticle surface due to resonant optical absorption, in which incident photons excite intersubband electronic transitions between the quantized energy levels in the MnAs nanoparticles.},

keywords = {Nanoparticle, Nanophotonic fabrication, Near-field effect},

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:10.1063/1.4725514,

title = {Superradiance from one-dimensionally aligned ZnO nanorod multiple-quantum-well structures},

author = {Takashi Yatsui and Akira Ishikawa and Kiyoshi Kobayashi and Akira Shojiguchi and Suguru Sangu and Tadashi Kawazoe and Motoichi Ohtsu and Jinkyoung Yoo and Gyu-Chul Yi},

doi = {10.1063/1.4725514},

year  = {2012},

date = {2012-05-01},

urldate = {2012-05-01},

journal = {Applied Physics Letters},

volume = {100},

number = {23},

pages = {233118},

abstract = {Using one-dimensionally aligned ZnO nanorod multiple-quantum-well structures (MQWs), we observed a superradiance, i.e., a cooperative spontaneous emission. We confirmed that the excitation power dependence of the emissions from the MQWs originated from the coherent coupling of the QWs due to the well organization at nanoscale. We identified two QWs with cooperative emission. Additionally, we evaluated the number of coherently coupled QWs sets of four that resulted in the superradiance. Our findings provide criteria for designing nanoscale synergetic devices without the use of an external cavity.},

keywords = {First, nanorod, Superradiance, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{2012yatsuiAPB,

title = {Room-temperature growth of high-quality ZnO nanocrystals using a dressed-photon-assisted near-field process},

author = {Takashi Yatsui and Kosuke Nakanishi and Kokoro Kitamura and Motoichi Ohtsu},

doi = {10.1007/s00340-012-5076-8},

year  = {2012},

date = {2012-05-01},

journal = {Applied Physics B},

volume = {107},

number = {3},

pages = {637-641},

publisher = {Springer Nature},

abstract = {Single-crystalline ZnO nanocrystals were fabricated by room-temperature photo-chemical vapor deposition (PCVD). We further enhanced the growth of high-quality single-crystalline ZnO nanocrystals using dressed photons and phonons (DPPs). This resulted in greater position control and the growth of high-quality ZnO nanocrystals. The ZnO nanocrystals produced with DPPs had excellent cathodoluminescence characteristics, indicating that the near-field PCVD process could be a promising technique for nanophotonic integrated circuit production.},

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

urldate = {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{2012NatPhoton,

title = {Observing the localization of light in space and time by ultrafast second-harmonic microscopy},

author = {Manfred Mascheck and Stephen Schmidt and Martin Silies and Takashi Yatsui and Kokoro Kitamura and Motoichi Ohtsu and David Leipold and Erich Runge and Christoph Lienau},

url = {https://www.altmetric.com/details/698801},

doi = {10.1038/nphoton.2012.69},

year  = {2012},

date = {2012-05-01},

journal = {Nature Photonics},

volume = {6},

number = {5},

pages = {293-298},

publisher = {Springer Nature},

abstract = {Multiple coherent scattering and the constructive interference of certain scattering paths form the common scheme of several remarkable localization phenomena of classical and quantum waves in randomly disordered media. Prominent examples are electron transport in disordered conductors, the localization of excitons in semiconductor nanostructures, surface plasmon polaritons at rough metallic films or light in disordered dielectrics and amplifying media. However, direct observation of the fundamental spatiotemporal dynamics of the localization process remains challenging. This holds true, in particular, for the localization of light occurring on exceedingly short femtosecond timescales and nanometre length scales. Here, we combine second harmonic microscopy with few-cycle time resolution to probe the spatiotemporal localization of light waves in a random dielectric medium. We find lifetimes of the photon modes of several femtoseconds and a broad distribution of the local optical density of states, revealing central hallmarks of the localization of light.},

keywords = {Near-field effect, Selected, SHG},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/1.4711808,

title = {Stochastic processes in light-assisted nanoparticle formation},

author = {Makoto Naruse and Yang Liu and Wataru Nomura and Takashi Yatsui and Masaki Aida and Laszlo B Kish and Motoichi Ohtsu},

doi = {10.1063/1.4711808},

year  = {2012},

date = {2012-04-01},

urldate = {2012-04-01},

journal = {Applied Physics Letters},

volume = {100},

number = {19},

pages = {193106},

abstract = {Recently, light-assisted nanofabrication have been introduced, such as the synthesis of quantum dots using photo-induced desorption that yields reduced size fluctuations or metal sputtering under light illumination resulting in self-organized, nanoparticle chains. The physical mechanisms have originally been attributed to material desorption or plasmon resonance effects. However, significant stochastic phenomena are also present that have not been explained yet. We introduce stochastic models taking account of the light-assisted processes that reproduce phenomenological characteristics consistent with the experimental observations.},

keywords = {Near-field effect},

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{doi:10.1063/1.3663632,

title = {Optical near-field induced visible response photoelectrochemical water splitting on nanorod TiO2},

author = {Thu Hac Huong Le and Kazuma Mawatari and Yuriy Pihosh and Tadashi Kawazoe and Takashi Yatsui and Motoichi Ohtsu and Masahiro Tosa and Takehiko Kitamori},

url = {https://doi.org/10.1063/1.3663632},

doi = {10.1063/1.3663632},

year  = {2011},

date = {2011-11-01},

urldate = {2011-11-01},

journal = {Applied Physics Letters},

volume = {99},

number = {21},

pages = {213105},

abstract = {Here we report a way to induce the visible response of non-doped TiO2 in the photocatalytic electrochemical water splitting, which is achieved by utilizing the optical near-field (ONF) generated on nanorod TiO2. The visible response is attributed to the ONF-induced phonon-assisted excitation process, in which TiO2 is excited by sub-bandgap photons via phonon energy. Our approach directly gets involved in the excitation process without chemical modification of materials; accordingly it is expected to have few drawbacks on the photocatalytic performance. This study may offer another perspective on the development of solar harvesting materials.},

keywords = {nanorod, Near-field effect, TiO2, Water splitting},

pubstate = {published},

tppubtype = {article}

}

@article{2011noruseAPB,

title = {A stochastic modeling of morphology formation by optical near-field processes},

author = {Makoto Naruse and Tadashi Kawazoe and Takashi Yatsui and Naoya Tate and Motoichi Ohtsu},

doi = {10.1007/s00340-011-4708-8},

year  = {2011},

date = {2011-11-01},

journal = {Applied Physics B},

volume = {105},

number = {4},

pages = {185-190},

publisher = {Springer Nature},

abstract = {We previously reported (S. Yukutake et al. in Appl. Phys. B 99:415, 2010) that by depositing Ag particles on the electrode of a photovoltaic device composed of poly(3-hexylthiophene) (P3HT) and ZnO under light illumination (wavelength 660 nm) while reversely biasing the P3HT/ZnO p-n junction, a unique granular Ag film was formed. The resultant device generated a photocurrent at wavelengths as long as 670 nm, which is longer than the long-wavelength cutoff (=570 nm) of P3HT. Such an effect originates from a phonon-assisted process induced by an optical near field. In this paper, we analyze the morphological character of the Ag clusters and build a stochastic model in order to understand the principles behind the self-organized pattern formation process. The modeling includes the geometrical character of the material, its associated optical near fields, and the materials that flow in and out of the system. The model demonstrates behavior consistent with that observed in the experiment. We can see these phenomena as a new kind of self-organized criticality taking account of near-field effects, which will provide an insight into the analysis and design of future nanophotonic devices.},

keywords = {Near-field effect},

pubstate = {published},

tppubtype = {article}

}

@article{Matsui:11,

title = {Optical dynamics of energy-transfer from a CdZnO quantum well to a proximal Ag nanostructure},

author = {Hiroaki Matsui and Wataru Nomura and Takashi Yatsui and Motoichi Ohtsu and Hitoshi Tabata},

doi = {10.1364/OL.36.003735},

year  = {2011},

date = {2011-10-01},

journal = {Optics Letters},

volume = {36},

number = {19},

pages = {3735--3737},

publisher = {OSA},

abstract = {We studied photoluminescence (PL) and energy-transfer dynamics in a hybrid structure comprising a Cd0.08Zn0.92O quantum well (QW) and an Ag nanostructure. The observed PL quenching was dependent on the electronic states in the QW. Quenching occurred at low temperature where excited carriers recombined radiatively because of excitonic localization, which disappeared with increasing temperature due to delocalization of excitons. Furthermore, nanostructured Ag surfaces produced local surface plasmon (LSP) absorption that was resonant with the PL peak energy of the QW emission. These results indicate that the recombination energy of excitons transfers nonradiatively to induce LSP excitation, which was revealed using time-resolved PL measurements.},

keywords = {Energy-transfer, Plasmon, QW},

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{2011yatsuiAPBNFE,

title = {Self-organized near-field etching of the sidewalls of glass corrugations},

author = {Takashi Yatsui and Kazuya Hirata and Yoshinori Tabata and Yumiko Miyake and Yasuyuki Akita and Mamoru Yoshimoto and Wataru Nomura and Tadashi Kawazoe and Makoto Naruse and Motoichi Ohtsu},

doi = {10.1007/s00340-011-4569-1},

year  = {2011},

date = {2011-06-01},

journal = {Applied Physics B},

volume = {103},

number = {3},

pages = {527-530},

publisher = {Springer Nature},

abstract = {Using soda-lime glass with a nano-stripe pattern as a test specimen, we demonstrated self-organized near-field etching with a continuum-wave laser (wavelength of 532 nm) light source. Atomic force microscopy confirmed that near-field etching decreases the flank roughness of the corrugations as well as the roughness of the flat surface.},

keywords = {First, Nanophotonic fabrication, Near-field etching},

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{Schmidt:10,

title = {Distinguishing between ultrafast optical harmonic generation and multi-photon-induced luminescence from ZnO thin films by frequency-resolved interferometric autocorrelation microscopy},

author = {Stephen Schmidt and Manfred Mascheck and Martin Silies and Takashi Yatsui and Kokoro Kitamura and Motoichi Ohtsu and Christoph Lienau},

doi = {10.1364/OE.18.025016},

year  = {2010},

date = {2010-11-01},

journal = {Optics Express},

volume = {18},

number = {24},

pages = {25016--25028},

publisher = {OSA},

abstract = {The nonlinear optical properties of thin ZnO film are studied using interferometric autocorrelation (IFRAC) microscopy. Ultrafast, below-bandgap excitation with 6-fs laser pulses at 800 nm focused to a spot size of 1 textmum results in two emission bands in the blue and blue-green spectral region with distinctly different coherence properties. We show that an analysis of the wavelength-dependence of the interference fringes in the IFRAC signal allows for an unambiguous assignment of these bands as coherent second harmonic emission and incoherent, multiphoton-induced photoluminescence, respectively. More generally our analysis shows that IFRAC allows for a complete characterization of the coherence properties of the nonlinear optical emission from nanostructures in a single-beam experiment. Since this technique combines a very high temporal and spatial resolution we anticipate broad applications in nonlinear nano-optics.},

keywords = {SHG, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{Yatsuii_2010,

title = {In situ real-time monitoring of changes in the surface roughness during nonadiabatic optical near-field etching},

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

doi = {10.1088/0957-4484/21/35/355303},

year  = {2010},

date = {2010-08-01},

journal = {Nanotechnology},

volume = {21},

number = {35},

pages = {355303},

publisher = {IOP Publishing},

abstract = {We performed in situ real-time monitoring of the change in surface roughness during 

self-organized optical near-field etching. During near-field etching of a silica substrate, we detected the scattered light intensity from a continuum wave (CW) laser (λ = 633 nm) in addition to the etching CW laser (λ = 532 nm) light source. We discovered that near-field etching not only decreases surface 

roughness, but also increases the number of scatterers, as was confirmed by analyzing the 

AFM image. These approaches provide optimization criteria for the etching parameter and 

hence for further decreases in surface roughness.},

keywords = {First, Nanophotonic fabrication, Near-field etching},

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{Kitamura_2010,

title = {Site-selective deposition of gold nanoparticles using non-adiabatic reaction induced by optical near-fields},

author = {Kokoro Kitamura and Takashi Yatsui and Tadashi Kawazoe and Masakazu Sugiyama and Motoichi Ohtsu},

doi = {10.1088/0957-4484/21/28/285302},

year  = {2010},

date = {2010-06-01},

journal = {Nanotechnology},

volume = {21},

number = {28},

pages = {285302},

publisher = {IOP Publishing},

abstract = {In this paper, we report on site-selective deposition of metal nanoparticles 

using a non-adiabatic photochemical reaction. Photoreduction of gold 

was performed in a silica gel membrane containing tetrachloroaurate (AuCl4 − ) ions, using ZnO nanorods as the sources of optical near-field light, resulting in deposition 

of gold nanoparticles with an average diameter of 17.7 nm. The distribution of 

distances between the gold nanoparticles and nanorod traces revealed that the gold 

nanoparticles were deposited adjacent to the ZnO nanorods, reflecting the attenuation of 

the optical near-fields in the vicinity of the ZnO nanorods. We found that the 

emission wavelength from the ZnO nanorods was longer than the absorption edge 

wavelength of the tetrachloroaurate. Additionally, from the intensity distribution 

obtained by a finite-difference time-domain method, the gold deposited around the 

ZnO nanorods was found to be due to a non-adiabatic photochemical reaction.},

keywords = {Nanophotonic fabrication, nanorod, Near-field effect, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{2010yukutakeAPB,

title = {Selective photocurrent generation in the transparent wavelength range of a semiconductor photovoltaic device using a phonon-assisted optical near-field process},

author = {Sotaro Yukutake and Tadashi Kawazoe and Takashi Yatsui and Wataru Nomura and Kokoro Kitamura and Motoichi Ohtsu},

doi = {10.1007/s00340-010-3999-5},

year  = {2010},

date = {2010-05-01},

journal = {Applied Physics B},

volume = {99},

number = {3},

pages = {415-422},

publisher = {Springer Nature},

abstract = {In this paper, we propose a novel photovoltaic device using P3HT and ZnO as test materials for the ptype and n-type semiconductors, respectively. To fabricate an electrode of this device, Ag was deposited on a P3HT film by RF-sputtering under light illumination (wavelength λ0 = 660 nm) while reversely biasing the P3HT/ZnO pnjunction. As a result, a unique granular Ag film was formed, which originated from a phonon-assisted process induced by an optical near-field in a self-organized manner. The fabricated device generated a photocurrent even though the incident light wavelength was as long as 670 nm, which is longer than the long-wavelength cutoff λc (= 570 nm) of the P3HT. The photocurrent was generated in a wavelength-selective manner, showing a maximum at the incident light wavelength of 620 nm, which was shorter than λ0 because of the Stark effect brought about by the reverse bias DC electric field applied during the Ag deposition.},

keywords = {Nanophotonic fabrication, Near-field effect, Self-assembly},

pubstate = {published},

tppubtype = {article}

}

@article{2010nomuraAPBrepair,

title = {Repairing nanoscale scratched grooves on polycrystalline ceramics using optical near-field assisted sputtering},

author = {Wataru Nomura and Takashi Yatsui and Yoshihata Yanase and Kenji Suzuki and Mitsuhiro Fujita and Atsushi Kamata and Makoto Naruse and Motoichi Ohtsu},

doi = {10.1007/s00340-009-3797-0},

year  = {2010},

date = {2010-04-01},

journal = {Applied Physics B},

volume = {99},

number = {1-2},

pages = {75-78},

publisher = {Springer Nature},

abstract = {We propose an optical near-field assisted sputtering method for repairing scratches on the surface of polycrystalline ceramics in a self-assembling manner. An Al2O3 source was sputtered on substrates with laser radiation of wavelength 473 nm. The average depth of the scratched grooves on polycrystalline Al2O3 ceramic substrate decreased from 3.2 nm to 0.79 nm. Using a Hough transform, we also confirmed the selective repair of scratches.},

keywords = {Nanophotonic fabrication, Near-field effect},

pubstate = {published},

tppubtype = {article}

}

@article{Tate:10,

title = {Nanophotonic code embedded in embossed hologram for hierarchical information retrieval},

author = {Naoya Tate and Makoto Naruse and Takashi Yatsui and Tadashi Kawazoe and Morihisa Hoga and Yasuyuki Ohyagi and Tokuhiro Fukuyama and Mitsuru Kitamura and Motoichi Ohtsu},

doi = {10.1364/OE.18.007497},

year  = {2010},

date = {2010-03-01},

urldate = {2010-03-01},

journal = {Opt. Express},

volume = {18},

number = {7},

pages = {7497-7505},

publisher = {OSA},

abstract = {A hierarchical hologram works in both optical far-fields and near-fields, the former being associated with conventional holographic images, and the latter being associated with the optical intensity distribution based on a nanometric structure that is accessible only via optical near-fields. We propose embedding a nanophotonic code, which is retrievable via optical near-field interactions involving nanometric structures, within an embossed hologram. Due to the one-dimensional grid structure of the hologram, evident polarization dependence appears in retrieving the code. Here we describe the basic concepts, numerical simulations, and experimental results in fabrication of a prototype hierarchical hologram and describe its optical characterization.},

keywords = {Holography},

pubstate = {published},

tppubtype = {article}

}

@article{2010tateAPB,

title = {Transcription of optical near-fields by photoinduced structural change in single crystal metal complexes for parallel nanophotonic processing},

author = {Naoya Tate and Hiroki Tokoro and Keiji Takeda and Wataru Nomura and Takashi Yatsui and Tadashi Kawazoe and Makoto Naruse and Shin-ichi Ohkoshi and Motoichi Ohtsu},

doi = {10.1007/s00340-009-3772-9},

year  = {2010},

date = {2010-03-01},

journal = {Applied Physics B},

volume = {98},

number = {4},

pages = {685-689},

publisher = {Springer Nature},

abstract = {Exploiting the unique attributes of nanometer-scaled optical near-field interactions in a completely parallel manner is important for nanophotonics for enhancing the throughput in obtaining two-dimensional information on the nanometer scale, as well as for developing more practical and easy characterization or utilization of optical near-fields. In this paper, we propose transcription of optical near-fields, whereby their effects are spatially magnified so as to be detected in optical far fields. By utilizing cyano-bridged metal complexes that exhibit photoinduced structural changes, transcription at the nanometric scale can be realized. We synthesized single crystals of such metal complexes and observed their photoinduced phase changes. We experimentally achieved photoinduced structural changes via optical near-fields, which is the fundamental process in their transcription.},

keywords = {Nanophotonic fabrication, Near-field effect},

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},

urldate = {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{10.1007/978-4-431-53868-4_34,

title = {Parallel Retrieval of Nanometer-Scale Light-Matter Interactions for Nanophotonic Systems},

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

doi = {10.1007/978-4-431-53868-4_34},

isbn = {978-4-431-53868-4},

year  = {2010},

date = {2010-01-01},

booktitle = {Natural Computing},

journal = {Natural Computing },

pages = {298-307},

publisher = {Springer Japan},

address = {Tokyo},

abstract = {Exploiting the unique attributes of nanometer-scale optical near-field interactions in a completely parallel manner is important for innovative nanometric optical processing systems. In this paper, we propose the basic concepts necessary for parallel retrieval of light--matter interactions on the nanometer-scale instead of the conventional one-dimensional scanning method. One is the macro-scale observation of optical near-fields, and the other is the transcription of optical near-fields. The former converts effects occurring locally on the nanometer scale involving optical near-field interactions to propagating light radiation, and the latter magnifies the distributions of optical near-fields from the nanometer scale to the sub-micrometer one. Those techniques allow us to observe optical far-field signals that originate from the effects occurring at the nanometer scale. We numerically verified the concepts and principles using electromagnetic simulations.},

keywords = {Near-field effect},

pubstate = {published},

tppubtype = {article}

}

@article{2009kitamuraAPB,

title = {Observation of quantum confinement in ZnO nanorods fabricated using a two-temperature growth method},

author = {Kokoro Kitamura and Takashi Yatsui and Motoichi Ohtsu},

doi = {10.1007/s00340-009-3654-1},

year  = {2009},

date = {2009-12-01},

journal = {Applied Physics B},

volume = {97},

number = {4},

pages = {825-828},

publisher = {Springer Nature},

abstract = {We observed a quantum confinement effect in vertically well-aligned ultrafine ZnO nanorods using polarized excitation photoluminescence measurements. Room-temperature and low-temperature photoluminescence spectra revealed that free excitons were confined in the nanorods. The magnitude of the energy shift due to the quantum confinement in the ultrafine ZnO nanorods was 6 meV at room temperature, which corresponded to the luminescence from ZnO nanorods 12.8 nm in diameter. The diameter estimated from the spectra was comparable to the value measured from SEM images.},

keywords = {nanorod, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{2009yatsuiGaNAPB,

title = {Increased spatial homogeneity in a light-emitting InGaN thin film using optical near-field desorption},

author = {Takashi Yatsui and Shunsuke Yamazaki and Keiichi Ito and Hiroshi Kawamura and Michinobu Mizumura and Tadashi Kawazoe and Motoichi Ohtsu},

doi = {10.1007/s00340-009-3757-8},

year  = {2009},

date = {2009-10-01},

journal = {Applied Physics B},

volume = {97},

number = {2},

pages = {375-378},

publisher = {Springer Nature},

abstract = {We report a self-assembly method that produces greater spatial uniformity in InGaN thin films using optical near-field desorption. Spatial homogeneity in the In fraction was reduced by introducing additional light during the photo-enhanced chemical vapor deposition of InGaN. Near-field desorption of InGaN nanoparticles, upon addition depended on the In content of the film, and the photon energy of the illumination source determined the energy of the emitted photons. Since this deposition method is based on a photo-desorption reaction, it can easily be applied to other deposition techniques and used with other semiconductor systems.},

keywords = {First, GaN, Nanophotonic fabrication, Near-field effect, Self-assembly},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/1.3193536,

title = {Production of size-controlled Si nanocrystals using self-organized optical near-field chemical etching},

author = {Takashi Yatsui and Motoichi Ohtsu},

doi = {10.1063/1.3193536},

year  = {2009},

date = {2009-07-24},

urldate = {2009-07-24},

journal = {Applied Physics Letters},

volume = {95},

number = {4},

pages = {043104},

abstract = {We demonstrate the selective photochemical etching of Si in a self-organized manner, which strongly depends on the distribution of the optical near field. This dependence was described by the virtual exciton-phonon-polariton model. The photoluminescence (PL) spectra from the etched Si exhibited a blueshifted PL peak at 1.8 eV, corresponding to Si nanocrystals of 2.8 nm diameter.},

keywords = {First, Nanophotonic fabrication, Near-field effect, Self-assembly, Si},

pubstate = {published},

tppubtype = {article}

}

@article{Kobayashi_2009,

title = {New Aspects in Nanofabrication Using Near-Field Photo-Chemical Vapor Deposition},

author = {Kiyoshi Kobayashi and Arata Sato and Takashi Yatsui and Tadashi Kawazoe and Motoichi Ohtsu},

doi = {10.1143/apex.2.075504},

year  = {2009},

date = {2009-07-01},

journal = {Applied Physics Express},

volume = {2},

number = {7},

pages = {075504},

publisher = {IOP Publishing},

abstract = {On the basis of the dressing nature of optical near fields and the important role of optically forbidden molecular vibrational excitations, a simple model is proposed to describe atom or atom cluster desorption due to optical near fields from a nanodot deposited on a substrate. Assuming an anharmonic potential for each atomic binding, we evaluate an effective atom–nanodot potential to determine the desorption energy and stabilized dot size. The model describes the reported experimental data reasonably well, and shows that optically forbidden molecular vibrational excitations play an important role in optical near-field processes, which could potentially leads to a new fabrication method in addition to the controlling the size and position of nanostructures.},

keywords = {Nanophotonic fabrication, Near-field effect},

pubstate = {published},

tppubtype = {article}

}

@article{2009tateAPB,

title = {Hierarchy in optical near-fields based on compositions of nanomaterials},

author = {Naoya Tate and Wataru Nomura and Takashi Yatsui and Makoto Naruse and Motoichi Ohtsu},

doi = {10.1007/s00340-008-3354-2},

year  = {2009},

date = {2009-07-01},

journal = {Applied Physics B},

volume = {96},

number = {1},

pages = {1-4},

publisher = {Springer Nature},

abstract = {Optical near-field interactions exhibit hierarchical responses in the nanometer scale allowing unique functions in nanophotonic systems. Such hierarchical properties in optical near-fields originate various physical entities in the nanometer scale. Engineering nanomaterial compositions, while maintaining geometrically equivalent conditions, leads to characteristic hierarchical responses. We experimentally demonstrate such material-dependent optical near-field hierarchy using core-shell-type nanostructures composed of gold and silver.},

keywords = {Near-field effect},

pubstate = {published},

tppubtype = {article}

}

@article{Tate:09,

title = {Quadrupole-Dipole Transform based on Optical Near-Field Interactions in Engineered Nanostructures},

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

doi = {10.1364/OE.17.011113},

year  = {2009},

date = {2009-06-01},

urldate = {2009-06-01},

journal = {Optics Express},

volume = {17},

number = {13},

pages = {11113-11121},

publisher = {OSA},

abstract = {Nanophotonics has the potential to provide novel devices and systems with unique functions based on optical near-field interactions. Here we experimentally demonstrate, for the first time, what we call a quadrupole-dipole transform achieved by optical near-field interactions between engineered nanostructures. We describe its principles, the nanostructure design, fabrication of one- and two-layer gold nanostructures, an experimental demonstration, and optical characterization and analysis.},

keywords = {Near-field effect},

pubstate = {published},

tppubtype = {article}

}

@article{Yamazaki_2009,

title = {Room-Temperature Growth of UV-Emitting Dendritic GaN Fractal Nanostructures Using Photochemical Vapor Deposition},

author = {Shunsuke Yamazaki and Takashi Yatsui and Motoichi Ohtsu},

doi = {10.1143/apex.2.031004},

year  = {2009},

date = {2009-03-01},

journal = {Applied Physics Express},

volume = {2},

number = {3},

pages = {031004},

publisher = {IOP Publishing},

abstract = {A dendritic gallium nitride (GaN) structure was grown at room temperature using photochemical vapor deposition with trimethylgallium and ammonia as the source materials. The sample was investigated by a scanning electron microscope and photoluminescence (PL). Its morphology was evaluated using fractal analysis. The surface morphology of the deposited film had dendritic nanostructures similar in morphology to the diffusion-limited aggregation. Dendritic GaN had a strong PL spectrum with a peak energy of 3.55 eV at 5 K, indicating the quantum size effect. Using the box-counting method, the fractal dimension of the dendritic GaN nanostructure was calculated to be approximately 1.7.},

note = {The paper was highlighted in Nature Photonics Vol.3, 252 (2009)},

keywords = {Fractal, GaN, Nanophotonic fabrication},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/1.3095467,

title = {Analysis of surface roughness of optical elements planarized by nonadiabatic optical near-field etching},

author = {Makoto Naruse and Takashi Yatsui and Wataru Nomura and Kazuya Hirata and Yoshinori Tabata and Motoichi Ohtsu},

url = {https://doi.org/10.1063/1.3095467},

doi = {10.1063/1.3095467},

year  = {2009},

date = {2009-03-01},

urldate = {2009-03-01},

journal = {Journal of Applied Physics},

volume = {105},

number = {6},

pages = {063516},

abstract = {Nonadiabatic optical near-field etching is a novel way of polishing surfaces of optical elements without any mechanical contact processes. It selectively induces photochemical reactions on the surface in regions where optical near fields are excited, namely, in the vicinity of portions having fine-scale rough structures, which leads to reduced surface roughness. In this paper, we analyze the surface roughness of optical elements planarized by nonadiabatic optical near-field etching based on power spectrum-based methods. Our analysis clearly reveals the effects of the near-field etching which are otherwise concealed when using conventional roughness measures such as the roughness average (Ra). We also investigate the effect of planarization via numerical simulations using surface profiles obtained experimentally before and after the near-field etching.},

keywords = {Near-field etching},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/1.3090491,

title = {Nanophotonic energy up conversion using ZnO nanorod double-quantum-well structures},

author = {Takashi Yatsui and Suguru Sangu and Kiyoshi Kobayashi and Tadashi Kawazoe and Motoichi Ohtsu and Jinkyoung Yoo and Gyu-Chul Yi},

url = {https://doi.org/10.1063/1.3090491},

doi = {10.1063/1.3090491},

year  = {2009},

date = {2009-02-01},

urldate = {2009-02-01},

journal = {Applied Physics Letters},

volume = {94},

number = {8},

pages = {083113},

abstract = {We report on near-field spectroscopy of ZnO/ZnMgO nanorod double-quantum-well structures (DQWs) for a nanometer-scale photonic device. We observed energy up conversion assisted by the absorption of phonons generated in the ZnO nanorod DQWs. Theoretical calculation of the coherent excitonic excitation of the population with incoherent phonon coupling agrees well with the obtained experimental power dependence of the up conversion efficiency. It should result in an increase in the efficiency of devices, such as photodetectors, solar cells, and so on.},

keywords = {First, nanorod, Non-uniform optical near field, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{2008IEEE,

title = {Nanophotonics: Application of Dressed Photons to Novel Photonic Devices and Systems},

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

doi = {10.1109/JSTQE.2008.918110},

year  = {2008},

date = {2008-11-01},

journal = {IEEE Journal on Selected Topics in Quantum Electronics},

volume = {14},

number = {6},

pages = {1404-1417},

publisher = {IEEE},

abstract = {This paper reviews recent progress in nanophotonics, a novel optical technology proposed by one of the authors (M. Ohtsu). Nanophotonics utilizes the local interaction between nanometric particles via optical near fields. The optical near fields are the elementary surface excitations on nanometric particles, that is, dressed photons that carry the material energy. Of the variety of qualitative innovations in optical technology realized by nanophotonics, this paper focuses on devices and systems. The principles of device operation are reviewed considering the excitation energy transfer via the optical near-field interaction and subsequent dissipation. As representative examples, the principles of a nanophotonic and gate, not gate, and optical nanofountain are described. Experimental results for operating devices using CuCl quantum dots (QDs), InAlAs QDs, and nanorod ZnO double quantum wells are described. Using a systems-perspective approach, the principles of content-addressable memory based on nanophotonic device operations and experimental results are reviewed. The hierarchy of optical near-field interactions is discussed, and its application to a multilayer memory retrieval system is demonstrated.},

note = {review article},

keywords = {Nanophotonic fabrication, Near-field effect, Review},

pubstate = {published},

tppubtype = {article}

}

@article{Naruse_2008,

title = {Nanophotonic Matching by Optical Near-Fields between Shape-Engineered Nanostructures},

author = {Makoto Naruse and Takashi Yatsui and Tadashi Kawazoe and Naoya Tate and Hiroki Sugiyama and Motoichi Ohtsu},

doi = {10.1143/apex.1.112101},

year  = {2008},

date = {2008-10-01},

journal = {Applied Physics Express},

volume = {1},

number = {11},

pages = {112101},

publisher = {IOP Publishing},

abstract = {Engineering light-matter near-field interactions on the nanometer scale offers the possibility of devices with unique functions. Here we show that two metal nanostructures can be designed to exhibit far-field radiation only when their shapes are appropriately configured and when they are closely stacked. Such functionality is useful in ensuring product authentication or certification, where a system should work only when the two nanostructures match, just like a lock and key. We describe its operating principle by observing induced electric currents and their associated optical near-fields, and we show example nanostructures designed by numerical simulations.},

keywords = {Near-field effect},

pubstate = {published},

tppubtype = {article}

}

@article{2008yatsuiAPBNFE,

title = {Realization of an ultra-flat silica surface with angstrom-scale average roughness using nonadiabatic optical near-field etching},

author = {Takashi Yatsui and Kazuya Hirata and Wataru Nomura and Yoshinori Tabata and Motoichi Ohtsu},

doi = {10.1007/s00340-008-3142-z},

year  = {2008},

date = {2008-10-01},

journal = {Applied Physics B},

volume = {93},

number = {1},

pages = {55-57},

publisher = {Springer Nature},

abstract = {We propose a new method of optical near-field etching where a nonadiabatic process is applied to a synthetic silica substrate using a continuum wave laser (λ=532 nm) with a Cl2 gas source. Because the absorption band edge energy of Cl2 is higher than the photon energy of the light source, we preclude the conventional adiabatic photochemical reaction. An optical near field, generated on the nanometrically rough substrate, induces the nonadiabatic chemical reaction to the Cl2 molecules and thereby selectively etches away the roughness, leaving an ultra-flat synthetic silica surface with a minimum average surface roughness R a of 1.37 A.},

keywords = {First, Nanophotonic fabrication, Near-field etching, Selected},

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{Kitamura_2008,

title = {Optical and Structural Properties of ZnO Nanorods Grown on Polyimide Films},

author = {Kokoro Kitamura and Takashi Yatsui and Motoichi Ohtsu},

doi = {10.1143/apex.1.081202},

year  = {2008},

date = {2008-08-01},

journal = {Applied Physics Express},

volume = {1},

number = {8},

pages = {081202},

publisher = {IOP Publishing},

abstract = {We report the direct growth of vertically well-aligned single-crystal ZnO nanorods on a polyimide film by low-temperature catalyst-free metal organic chemical vapor deposition at 450 °C. The polyimide film maintained its flexibility after the nanorods were grown. The growth direction of the nanorods was along the c-axis. They exhibited excellent photoluminescence characteristics. The spectral full-width at half-maximum measured at room temperature was found to be comparable to that of ZnO nanorods grown on sapphire substrate.},

keywords = {nanorod, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/1.2937081,

title = {Polarization in optical near and far fields and its relation to shape and layout of nanostructures},

author = {Makoto Naruse and Takashi Yatsui and Hirokazu Hori and Masaaki Yasui and Motoichi Ohtsu},

doi = {10.1063/1.2937081},

year  = {2008},

date = {2008-06-01},

urldate = {2008-06-01},

journal = {Journal of Applied Physics},

volume = {103},

number = {11},

pages = {113525},

abstract = {We discuss the polarization control in optical near fields and far fields by engineering nanostructures, focusing on the individual shapes of elemental structures and their arrangement, called elemental-shape and layout factors, respectively. These factors are physically related to electrical currents induced within elemental shapes and optical near fields between elemental shapes, respectively, which are then associated with polarization properties in a unified manner by using the concept of flow vectors. The proposed scheme explains polarizations in optical near and far fields in an intuitive manner, such as in analyzing layout dependence or symmetry of shapes. Together with the hierarchical properties of optical near fields, it also aids in the design of complex structures, such as three-dimensional multilayer nanostructures for polarization control devices.},

keywords = {Near-field effect},

pubstate = {published},

tppubtype = {article}

}

@article{Yamazaki_2008,

title = {Room-Temperature Growth of UV-Emitting GaN with a Hexagonal Crystal-Structure Using Photochemical Vapor Deposition},

author = {Shunsuke Yamazaki and Takashi Yatsui and Motoichi Ohtsu},

doi = {10.1143/apex.1.061102},

year  = {2008},

date = {2008-06-01},

journal = {Applied Physics Express},

volume = {1},

number = {6},

pages = {061102},

publisher = {IOP Publishing},

abstract = {The room-temperature (RT) growth of ultraviolet-emitting hexagonal gallium nitride (h-GaN) on a sapphire substrate using photochemical vapor deposition (PCVD) has been demonstrated. A high photoluminescence (PL) peak at 3.47 eV was observed at 5 K, indicating a high-quality crystalline structure for h-GaN. A RT PL energy peak of 3.40 eV indicated the reduction of thermal residual stresses in GaN. In addition, the RT growth resulted in the formation of dendrite-like GaN, which originated from the low kinetic energy of the precursors for migration. A high PL peak at 3.55 eV observed at 5 K in the dendrite-like GaN indicated the quantum size effect.},

keywords = {GaN},

pubstate = {published},

tppubtype = {article}

}

@article{Naruse_2008b,

title = {Hierarchy in Optical Near-fields by Nano-scale Shape Engineering and its Application to Traceable Memory},

author = {Makoto Naruse and Takashi Yatsui and Jun Hyoung Kim and Motoichi Ohtsu},

doi = {10.1143/apex.1.062004},

year  = {2008},

date = {2008-06-01},

journal = {Applied Physics Express},

volume = {1},

number = {6},

pages = {062004},

publisher = {IOP Publishing},

abstract = {Optical near-fields have a hierarchical nature, meaning that they exhibit different behavior at different scales of observation. This is one notable feature in nanometer-scale light-matter interactions, besides the ability to break through the diffraction limit of light. We studied such hierarchy in optical near-fields by engineering the shape of metal nanostructures. We numerically and experimentally demonstrated a hierarchical optical response from triangular-shaped metal nanostructures. Strong localized electric fields were excited on a smaller scale, whereas two different states were excited on a larger scale. Combined with localized energy-dissipation on the smaller-scale, this hierarchy should enable novel functionality, such as traceability of optical memories.},

keywords = {Near-field effect},

pubstate = {published},

tppubtype = {article}

}

@article{Kitamura_2008b,

title = {Fabrication of vertically aligned ultrafine ZnO nanorods using metal–organic vapor phase epitaxy with a two-temperature growth method},

author = {Kokoro Kitamura and Takashi Yatsui and Motoichi Ohtsu and Gyu-Chul Yi},

doi = {10.1088/0957-4484/19/17/175305},

year  = {2008},

date = {2008-03-01},

journal = {Nanotechnology},

volume = {19},

number = {17},

pages = {175305},

publisher = {IOP Publishing},

abstract = {We report the fabrication of vertically aligned ultrafine ZnO nanorods using metal–organic 

vapor phase epitaxy and applying a two-temperature growth method. First, thick nanorods 

were grown vertically on the substrate at a lower temperature. Then, ultrafine ZnO 

nanorods with an average diameter of 17.7 nm were grown from the tips of the thick 

nanorods at a higher temperature. The direction of the ultrafine ZnO nanorods followed 

that of the preformed vertically aligned thick nanorods. Electron microscopy revealed that 

the ultrafine nanorods were single crystals and the growth direction was along the 

c 

axis. Excellent photoluminescence characteristics of the nanorods were confirmed.},

keywords = {nanorod, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{Tate:s,

title = {Hierarchical Hologram based on Optical Near- and Far-Field Responses},

author = {Naoya Tate and Wataru Nomura and Takashi Yatsui and Makoto Naruse and Motoichi Ohtsu},

doi = {10.1364/OE.16.000607},

year  = {2008},

date = {2008-01-01},

urldate = {2008-01-01},

journal = {Optics Express},

volume = {16},

number = {2},

pages = {607-612},

publisher = {OSA},

abstract = {A ``hierarchical hologram'' and experiments using it are described. This type of hologram works both in optical far-fields and near-fields. We exploit the physical difference between the propagating light and optical near-field, where the former is associated with conventional holographic patterns obtained in optical far-fields, whereas the latter is associated with nanometric structure accessible only via optical near-fields. We also describe an experimental demonstration of the basic principles with our prototype optical elements.},

keywords = {Near-field effect},

pubstate = {published},

tppubtype = {article}

}

@article{2008naruseIEEE,

title = {Design and simulation a nanophotonic traceable memory using localized energy dissipation and hierarchy of optical near-field interactions},

author = {Makoto Naruse and Takashi Yatsui and Tadashi Kawazoe and Yoshinori Akao and Motoichi Ohtsu},

doi = {10.1109/TNANO.2007.910335},

year  = {2008},

date = {2008-01-01},

journal = {Applied Physics B},

volume = {7},

number = {1},

pages = {1404-1417},

publisher = {IEEE},

abstract = {Optical near-field interactions allow energy localization at scales smaller than the diffraction limit of light. They also show intrinsic hierarchical responses, meaning that optical near-fields exhibit different physical behavior at different scales. In this paper, by combining the localized energy dissipation and hierarchy properties, we present an architecture for a novel traceable optical memory that records memory access events to each bit, which is useful in applications such as high-security information transfer. The basic principles are demonstrated by numerical simulations using a metal nanostructure.},

keywords = {Near-field effect},

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}

}

@article{10.1117/1.2794355,

title = {Near-field components and evaluation of photoluminescence in silicon nanostructures},

author = {Takashi Yatsui and Tadashi Kawazoe and Kiyoshi Kobayashi and Motoichi Ohtsu},

doi = {10.1117/1.2794355},

year  = {2007},

date = {2007-09-01},

journal = {Journal of Nanophotonics},

volume = {1},

number = {1},

pages = {011570},

publisher = {SPIE},

abstract = {Using illumination-collection mode optical near-field spectroscopy, a a spectral shift of photoluminescence of silicon (Si) nanocrystals compared with the far-field measurement was observed, due to the near-field coupling of the Si nanocrystals and the probe.},

keywords = {First, Non-uniform optical near field, Si, silicon},

pubstate = {published},

tppubtype = {article}

}

@article{10.1117/1.2794357,

title = {Metallized slit-shaped pyramidal Si probe with extremely high resolution for 1.5-Tbit/in2 density near-field optical storage},

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

url = {https://doi.org/10.1117/1.2794357},

doi = {10.1117/1.2794357},

year  = {2007},

date = {2007-09-01},

journal = {Journal of Nanophotonics},

volume = {1},

number = {1},

pages = {011550},

publisher = {SPIE},

abstract = {We have developed a near-field optical probe by introducing the metallized pyramidal structure of a Si probe with a slit-shaped tip for high-density optical storage. Numerical analysis using the finite-difference time-domain method showed that the optical spot generated at the aperture measured 13×30 nm. We fabricated a slit-type Si probe and evaluated the spot size using fluorescence imaging of a single dye molecule. The full-width at half maximum of the signal profiles was 16 nm×26 nm, which corresponds to a data density of 1.5 Tbit/in2. Furthermore, a large extinction coefficient depending on the polarization was confirmed.},

keywords = {First, near-field optical recording, Optical storage, Si},

pubstate = {published},

tppubtype = {article}

}