To reduce the effects of global warming, visible and near-infrared light must be used more efficiently. Deep ultraviolet light (8 eV) is required for the direct dissociation of CO2 by light; however, the introduction of a metal complex has made it possible to realize CO2 reduction with visible light. We demonstrate that the optical near field (ONF) can increase the CO2 reduction rate. For this, we used gold clusters, because they can be a suitable source for ONFs, as their size and density can be controlled by the number of gold atoms. By attaching a metal complex near gold clusters with diameters of 1.0 to 1.3 nm, we confirm that the reduction rate of CO2 to CO increased by 1.5 to 2.1 times. The gold clusters were sufficiently small; therefore, there was no plasmonic resonant peak or heat generation. Because the near-field effect is based on a photochemical reaction, it can be applied to other metal complexes used in CO2 reduction, and it has other applications such as water splitting and water purification.
An optical near field should promote phonon-assisted multiple excitation in nanoscale structures. With the phonon-assisted process, greater catalytic activity is expected without heating. To confirm this effect, photo-induced current generation using platinum black electrodes in ferricyanide solution (an absorption band-edge wavelength of 470 nm) under visible light irradiation continuous wave [(CW), λ=532 nm ] was observed. Higher order dependence of the generated current density on the incident light power was observed, indicating two-step activation of electron transfer, which originated from the phonon-assisted near-field effect on the nanostructured surface of the electrode.
Although the quality of extreme ultraviolet (EUV) mask substrates has improved by continuous refinement of the
polishing processes, the yield of defect-free blanks is still very low. Dressed-photon nanopolishing (DPNP) is a novel
vapor phase, photo-chemical, non-contact etching process that has been shown to locally smooth bumps and pits to
below 1 nm in height/depth while not affecting the surface roughness. DPNP is based on the concept of a dressed
photon, which is a quasi-particle in the optical near field of a surface that can couple with lattice phonons in nanometric
regions (< 100 nm). When illuminated with light of a suitable wavelength, such coupled states are generated on a
nanometrically rough material surface and impart sufficient energy to an etchant gas to enable its dissociation and
etching in the rough regions only. DPNP can be the last polishing step on EUV substrates to eliminate any remnant pits
and/or embedded particles on the surface to yield potentially defect-free substrates.
KEYWORDS: Nanophotonics, Holograms, Near field optics, Polarization, Nano opto mechanical systems, Near field, Nanolithography, Data processing, Holography, Prototyping
A nanophotonic 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. In principle, a structural change occurring at the
subwavelength scale does not affect the optical response functions, which are dominated by propagating light. Therefore,
the visual aspect of the hologram is not affected by such a small structural change on the surface, and retrieval in both
fields can be processed independently. 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 demonstrations of a prototype nanophotonic hierarchical hologram
with a nanophotonic code and describe its optical characterization.
Nanophotonics, a novel optical technology, utilizes the local interaction between nanometric particles via optical near
fields. The optical near fields are the elementary surface excitations on nanometric particles. Of the variety of qualitative
innovations in optical technology realized by nanophotonics, this talk focuses on fabrication. A realization of an ultra-flat
silica surface with angstrom-scale average roughness using noadiabatic optical near-field etching and repairing are
demonstrated and its origin is discussed.
"Nanophotonics" uses the local interaction between nanometric particles via optical near-fields to bring "qualitative
innovation" to the field of optical technology. Optical near-field interactions respond hierarchically at the nanometer
scale, allowing unique nanophotonic functions. We defined two kinds of hierarchical optical near-field interactions:
those between optical far- and near-fields, and those in the optical near-field only. We demonstrated these hierarchical
effects numerically and experimentally using several prototype "nanophotonic architectures." The first, a "hierarchical
hologram," operated in both the far- and near-fields with few adverse effects. We also demonstrated hierarchical effects
in the optical near-field by core-shell metal nanostructures. Hierarchical nanoscale architectures could allow single
optical devices to perform multiple functions. The practical realization of such devices could have a major impact, for
example, in the field of optical security.
To decrease the sizes of photonic devices beyond the diffraction limit of light, we propose nanophotonic devices based
on optical near-field interactions between semiconductor quantum dots (QDs). To drive such devices, an optical signal
guide whose width is less than several tens of nanometers is required. Furthermore, unidirectional signal transfer is
essential to prevent nanophotonic devices operating incorrectly due to signals reflected from the destination. For
unidirectional signal transfer at the nanometer scale, we propose a nanophotonic signal transmitter based on optical nearfield
interactions between small QDs of the same size and energy dissipation in larger QDs that have a resonant exciton
energy level with the small QDs. To confirm such unidirectional energy transfer, we used time-resolved
photoluminescence spectroscopy to observe exciton energy transfer between the small QDs via the optical near-field, and
subsequent energy dissipation in the larger QDs. We estimated that the energy transfer time between resonant CdSe/ZnS
QDs was 135 ps, which is shorter than the exciton lifetime of 2.10 ns. Furthermore, we confirmed that exciton energy did
not transfer between nonresonant QD pairs. These results indicated that the proposed nanophotonic signal transmitters
based on optical near-field interactions and energy dissipation could be used to make multiple transmitters and selfdirectional
interconnections.
KEYWORDS: Near field, Zinc oxide, Excitons, Quantum wells, Nanophotonics, Near field optics, Energy transfer, Time resolved spectroscopy, Picosecond phenomena, Nanorods
We review recent progress in the development of nanophotonic devices using the optical near-field interaction. ZnO
nanocrystallites are potentially ideal components for realizing room-temperature operation of such devices due to their
high exciton-binding energy and great oscillator strength. To confirm this promising optical property of ZnO, we
examined the near-field time-resolved spectroscopy of ZnO nanorod double-quantum-well structures (DQWs). First, we
observed the nutation of the population between the resonantly coupled exciton states of DQWs, in which the coupling
strength of the near-field interaction was found to decrease exponentially as the separation increased. Furthermore, we
successfully demonstrated the AND-gate operation by controlling a dipole-forbidden optical energy transfer among
resonant exciton states. Our results provide criteria for designing nanophotonic devices. The success of time-resolved
near-field spectroscopy of isolated DQWs described here is a promising step toward realizing a practical nanometerscale
photonic switch and related devices.
KEYWORDS: Energy transfer, Excitons, Quantum dots, Near field optics, Nanophotonics, Picosecond phenomena, Time resolved spectroscopy, Photography, Luminescence, Spectroscopes
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: Quantum wells, Zinc oxide, Near field, Nanophotonics, Excitons, Near field optics, Switching, Energy transfer, Picosecond phenomena, Nanorods
We review recent progress in the development of nanophotonic devices using the optical near-field interaction. ZnO nanocrystallites are potentially ideal components for realizing room-temperature operation of such devices due to their high exciton-binding energy and great oscillator strength. To confirm this promising optical property of ZnO, we examined the near-field time-resolved spectroscopy of ZnO nanorod double-quantum-well structures (DQWs). First, we
observed the nutation of the population between the resonantly coupled exciton states of DQWs, in which the coupling
strength of the near-field interaction was found to decrease exponentially as the separation increased. Furthermore, we
successfully demonstrated the switching dynamics of a
dipole-forbidden optical energy transfer among resonant exciton
states. Our results provide criteria for designing nanophotonic devices. The success of time-resolved near-field
spectroscopy of isolated DQWs described here is a promising step toward realizing a practical nanometer-scale photonic
switch and related devices.
KEYWORDS: Silicon, Near field, Near field optics, Polarization, Luminescence, Molecules, Optical storage, Aluminum, Mass attenuation coefficient, Finite-difference time-domain method
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: Silicon, Nanocrystals, Near field, Luminescence, Near field optics, Nanostructures, Optical spectroscopy, Near field scanning optical microscopy, Visible radiation, Nanophotonics
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.
To realize the optical devices required by future systems, we have proposed nanometer-scale photonic integrated circuits (i.e., nanophotonic ICs). These devices consist of nanometer-scale dots, and an optical near field is used as the signal carrier. Since an optical near field is free from the diffraction of light due to its size-dependent localization and resonance features, nanophotonics enables the fabrication, operation, and integration of nanometric devices. To drive a nanophotonic device with an external conventional diffraction-limited photonic device, a far/near-field conversion device is required. Here, we review the use of a nanometer-scale waveguide as such a conversion device for nanophotonic ICs. Furthermore, the fabrication of a nanophotonic device using an optical near-field is introduced.
We report on photoluminescent properties of ultrafine ZnO nanorods and ZnO/Zn0.8Mg0.2O nanorod quantum-well structures. The catalyst-free metalorganic chemical vapor deposition (MOCVD) technique enables control of ZnO nanorod diameters in the range of 5 to 150 nm. From the PL spectra of ultrafine ZnO nanorods with a mean diameter smaller than 10 nm, a systematic blue-shift in their PL peak position was observed by decreasing their diameter, presumably due to the quantum confinement effect along the radial direction in ZnO nanorods. In addition, we obtained time-integrated and time-resolved PL spectra of ZnO/Zn0.8Mg0.2O nanorod single-quantum-well structures (SQWs) in the temperature range of 10 K to 300 K. The nanorod SQWs also showed a PL blue-shift and the energy shift was dependent on ZnO well layer width. The PL peak position shift originates from the quantum confinement effect of carriers in nanorod quantum structures. Furthermore, we investigated spatially-resolved PL spectra of individual nanorod SQWs using scanning near-field optical microscopy.
Here we show our architectural approaches to nanophotonics to benefit from unique physical properties obtained by local interactions between nanometric elements, such as quantum dots, via optical near fields, that provide ultra high-density integration capability beyond the diffraction limit of light. We discuss a memory-based architecture and a simple hierarchical architecture. By using resonant energy levels between quantum dots and inter-dot interactions, nanometric data summation and broadcast architectures are demonstrated including their proof-of-principle experimental verifications using CuCl quantum dots. Through such architectural and physical insights, we are seeking nanophotonic information systems for solving the integration density limited by diffraction limit of light and providing ultra low-power operations as well as unique functionalities which are only achievable using optical near-field interactions.
Particles several tens of nanometers in size were aligned in the desired positions in a controlled manner by using capillary force interaction and suspension flow. Latex beads 40-nm in diameter were aligned linearly around a 10-μm-hole template fabricated by lithography. Further control of their position and separation was realized using colloidal gold nanoparticles by controlling the particle-substrate and particle-particle interactions using an optical near field generated on the edge of a Si wedge, in which the separation of the colloidal gold nanoparticles was controlled by the direction of polarization.
KEYWORDS: Gold, Nanoparticles, Near field optics, Near field, Energy transfer, Nanophotonics, Waveguides, Nano opto mechanical systems, Plasmons, Light scattering
To realize a nanometer-scale optical waveguide for far-/near-field conversion, we proposed a nanodot coupler which is the linear array of closely spaced metallic nanoprticles in order to transmit the optical signal to a nanophotonic device. In comparison with metallic core waveguide, the use of nano-dot coupler is expected to realize lower energy loss due to the resonant in the metallic nanoparticles. First, to optimize the efficiency in the nanodot coupler, we checked whether the single Au nanoparticles led to efficient scattering. The Au nanoparticles on the glass substrate were fabricated by the focused ion beam milling technique. The optical near-field intensity for the Au nanoparticles in diameter range from 100 to 300nm with constant height of 50nm were observed by the collection mode near-field optical microscope (NOM) at λ = 785nm. Near-field intensity took the maximum for the Au nanoparticle with 200nm in diameter, and this result is in good agreement with the calculated value of plasmon resonance by Mie's theory for an Au prolate spheroid. Next, we examined the plasmon-polariton transfer of nanodot couplers whose diameter range from 150 to 300nm by the collection mode NOM. The efficient energy transfer was observed only in the nanodot coupler with 200nm in diameter. This result agreed well with that of single Au nanoparticles. From these results, efficient energy transfer along nanodot coupler was confirmed by the near-field coupling between plasmon-polariton in the nanoparticles.
We propose and demonstrate a new optical near-field slider with a planar apertured probe array for optical memory. The slider was fabricated by utilizing anisotropical etching of a silicon membrane and anodic bonding of a silicon membrane and glass substrate. We also present for the first time a subwavelength-sized phase-change recording/reading by using the planar apertured probe array. Apertures were fabricated at the bottom end of the pyramidal grooves. A SiO2/AgInTe2/glass substrate was used as the recording medium. By scanning the planar apertured probe array, we obtained resolved images with line width of 250 nm.
We applied a super-wavelength apertured fiber probe to phase-change recording/readout. Though the fiber probe had a super-wavelength aperture, the spot size at the aperture was as small as 150 nm (< λ/5). An as-deposited SiO2/AgInTe2/glass substrate was used as a recording medium. For recording, a laser diode with a pulsewidth of 2 μs (λ=850 nm) was used. By scanning the probe for reading, we obtained resolved images of the recorded dot with a width of 250 nm.
We proposed and demonstrated a novel silicon planar apertured probe array as a near-field optical head for optical memory. In comparison with the conventional fiber probe, the apertured probe array has durability, higher read-out data transmission rate and it allows us to overcome difficulty of precise mechanical tracking of the single fiber probe because it can be used for reading data as a surface information. The probe array was fabricated by utilizing wet etching technique of a silicon wafer. Inverted pyramids were formed on the silicon plate, and apertures were fabricated at the tops of the inverted pyramids. An aperture with a size less than 100nm was realized. By scanning the probe array we obtained resolved images of the lines in corrugation which was made on a metal thin film. The observed line width was 250 nm. Furthermore, we put spherical lens inside the inverted pyramids to focus the propagating light at the apertures automatically. The near- field intensity at an aperture was 16 times larger than that without a spherical lens.
KEYWORDS: Near field optics, Wet etching, Near field, Optical fibers, Ion beams, Metals, Cladding, Near field scanning optical microscopy, Imaging spectroscopy, Fiber coupled lasers
We have successfully fabricated an extremely high throughput probe for near-field optics introducing a triple-tapered structure to reduce the loss in a tapered core, to focus the light, and to excite effectively the HE11 mode. A focused ion beam and selective chemical etching were used for fabrication. Over 100 times increase in the throughput of the triple-tapered probe with the aperture diameter D < 100 nm was realized in comparison with the conventional single-tapered probe. Furthermore, due to the third taper with a small cone angle, the localized optical near-field on the triple-tapered probe with D equals 60 nm has been confirmed.
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