Takashi Yatsui

Fabrication of vertically aligned ultrafine ZnO nanorods using metal?organic vapor phase epitaxy with a two-temperature growth method

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 17.7xa0nm 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.

Evaluation of the discrete energy levels of individual ZnO nanorodsingle-quantum-well structures using near-field ultraviolet photoluminescence spectroscopy

Spatially and spectrally resolved photoluminescence imaging of individual ZnO∕ZnMgO nanorod single-quantum-well structures (SQWs) with a spatial resolution of 55nm was performed using the optical near-field technique with a metallized UV fiber probe. Using excitation power density-dependent photoluminescence spectra of a ZnO∕ZnMgO SQW nanorod, we observed the discrete energy levels in a ZnO quantum-well layer.

Low-temperature (∼270 °C) growth of vertically aligned ZnO nanorods using photoinduced metal organic vapour phase epitaxy

We successfully produced a drastic decrease in the required growth temperature of single-crystalline ZnO nanorods, and enabled successful growth of vertically aligned ZnO nanorods on a Si(100) substrate using photoinduced metal organic vapour phase epitaxy (MOVPE). We introduced 325 nm light during the MOVPE growth, and achieved vertical growth of single-crystalline ZnO nanorods with a hexagonal crystal structure on Si(100) at a growth temperature of 270 °C. The successful low-temperature growth of ZnO nanorods on the Si(100) substrate described here is a promising step toward designing nanoscale photonic and electronic devices required by future systems.

Nanophotonic switch using one-dimensional ZnO double-quantum-well structures

We observed spectral switching and evaluated its dynamics by controlling the dipole- forbidden optical near-field energy transfer among resonant exciton states using lD-ZnO nanorod double-quantum-well structures.

Photoluminescent characteristics of ZnO nanorods and ZnO/ZnMgO nanorod heterostructures

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.

Observation of an optical near-field energy transfer in closely spaced ZnO/ZnMgO multiple-quantum-well nanorods for nanophotonic devices

We observed an anti-correlation feature in the photoluminescence intensity distribution of ZnO/ZnMgO multiple-quantum-well nanorods. This is attributed to the optical near-field energy transfer between resonant energy levels in closely spaced pairs of ZnO/ZnMgO multiple-quantum-well nanorods.The optical properties of ZnO/ZnMgO multiple-quantum-well (MQW) nanorods were investigated by the optical near-field technique. Using a thin metal coated UV fiber probe, we performed spatially- and spectrally-resolved photoluminescence imaging of individual ZnO/ZnMgO MQW with a spatial resolution of 40 nm. Furthermore, we observed an anti-correlation feature in the PL intensity distributions. This is attributed to an optical near-field energy transfer in closely spaced pairs of ZnO/ZnMgO MQW nanorods.

Observation of size-dependent features in the photoluminescence of ZnO nanocrystallites by near-field UV spectroscopy

Summary from only given. To evaluate the optical properties and crystallinity of ZnO nanocrystallites, the optical properties must be measured with nanometer-scale resolution. Using a UV optical near-field technique, we observed size-dependent features of individual ZnO nanocrystallites. We show a far-field photoluminescence spectrum at room temperature. The emission peak energy corresponds to spontaneous emission from the free exciton in high-quality ZnO nanocrystallites.

A slit-type near-field optical detector for neutral atoms with high sensitivity and nanometric resolution

Summary form only given. We have proposed deflection by an optical near field on a fiber probe to control atoms with high spatial accuracy. In this case, the deflection angle is estimated to be 0.1 degree for a Rb atom with an incident velocity of 10 m/s. It leads to the deviation of 10 /spl mu/m from the incident axis at 1 cm. in the downstream. To detect the deflected atoms with an accuracy of 1%, we need the spatial resolution of 100 nm. However, a commercial detector such as MCP has a low resolution of 50 /spl mu/m at most and the highest resolution that has been reported is 1 /spl mu/m to our knowledge. In addition, these are applied to metastable atoms and have less detection efficiency for the ground state atoms we manipulate. For drastic improvement, we present here a slit-type atom detector with a nanometric lateral resolution. Since the number of atoms deflected by the optical near field is very small, it is important to detect atoms with high efficiency. For this purpose, we use photoionization with two-color optical near fields.

High throughput capability of a microfabricated hollow probe for near field microscopy in ultraviolet region

Summary form only given. For realizing high sensitivity in high spatially resolved spectroscopy in ultraviolet (UV) region, we demonstrate here high throughput capability of a hollow probe fabricated by the transfer mold technique in a pyramidal silicon groove. In comparison with the conventional fiber probe, the advantages of such a probe are: 1. Hollow structure leads to no optical absorption in the UV region inside the probe, which results in high throughput. 2. Hollow structure leads to no luminescence in the UV region inside the probe, which results in high signal to noise ratio in the illumination-mode near field spectroscopy.

A pyramidal silicon probe with an extremely high throughput and resolution for optical near field technology

Summary form only given. For improvement in the performances of spatially resolved spectroscopy, optical data storage, and so on, we demonstrate here an extremely high throughput and resolution capability of a pyramidal silicon probe for near-field optical microscopy. Since the high refractive index of the silicon (n=3.67, @ /spl lambda/=830 nm) leads to a short effective wavelength inside the probe, which results in high throughput and spatial resolution compared to conventional fiber probes.