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The successful growth of 2-in. β-Ga2O3 crystals by the edge-defined, film fed growth (EFG) method was demonstrated. The optimization of growth conditions for larger single crystalline β-Ga2O3 is discussed in detail. The seeding conditions of temperature and neck width were found to be the most important factors to grow single crystals. X-ray rocking curve measurements of β-Ga2O3 crystals were conducted to estimate the dislocation densities of the grown crystals. Etch pit densities (EPDs) of the β-Ga2O3 crystals were also measured using KOH solution to measure the dislocation densities. The results were discussed combining with crystal growth parameters such as neck width to clarify the mechanisms of propagation and the origin of dislocations in crystals from phenomenological and crystallographic points of view.

The time-lapse observation of the electrodeposition of copper in copper sulfate solution was performed by imaging X-ray fluorescence from the copper deposition. The X-ray fluorescence was directly imaged with a full-field Wolter mirror microscope, which was constructed at the Photon Factory. Controlling the electric current in the solution from 0 to 71.7 µA, the deposition of copper on a Pt cathode was directly observed by imaging its X-ray fluorescence. One exposure time for obtaining an X-ray fluorescence image was 80 s. Then, it was 17 min later from the beginning of the electrolysis when the X-ray fluorescence image of the electrodeposition is observed for the first time. At this exposure time, the detection limit of the mass of copper was estimated to be 0.60 pg/image, which was calculated using test samples of 1.00×10-3–1.00 mol/l copper sulfate solutions.

This paper reports a new technique of micro-resolution particle image velocimetry (PIV). To investigate transient phenomena in a microfluidic device, a high-speed micro-PIV technique was developed by combining a high-speed camera and a continuous wave (CW) laser. The technique was applied to a micro counter-current flow, consisting of water and butyl acetate. The velocity fields of water in the micro counter-current flow were visualized for a time resolution of 500 µs and a spatial resolution of 2.2 × 2.2 µm2. Using the micro-PIV technique, the vortex-like motions of fluorescent particles around the water–butyl acetate interface were captured clearly.

A low-density solid xenon (Xe) target has been developed as laser-produced plasma (LPP) extreme ultraviolet (EUV) source. Xe gas was cooled to below the condensation temperature, and liquid Xe was sprayed from a swirl atomizer into a low-pressure atmosphere. Microparticles of liquid Xe were rapidly cooled by their own latent heat of evaporation, and became a solid micrometer-sized powder. The most frequent particle diameter under an atomizing pressure of 0.3 MPa was 114 µm, and the apparent density was 0.2 g/cm3, 1/13 of the density of conventional solid Xe. The apparent production rate of the powder was 2.2 cm3/s.

Hot ions with a strongly anisotropic distribution are created by radio-frequency waves and are sustained in the GAMMA 10 tandem mirror. The main power drain from the hot ions is accounted for by classical transport processes. The dominant loss is electron drag, which is confirmed in auxiliary electron heating experiments. The anisotropic distribution of hot ions is also examined in terms of neutron yield from D - D fusion reactions. The ion pressure and the anisotropy drive unstable waves near the ion cyclotron frequency. A dispersion relation and spatial distributions of the unstable waves are examined by use of magnetic probes and reflectometry cross-polarization scattering measurements. The hot-ion plasma contains a multi-shell structure of impurities creating concentric layers of pressure-driven azimuthal velocity with strong shears.

We demonstrate microscopic observations of recently discovered efficient upconversion (anti-Stokes) photoluminescence (UCPL) [Nat. Commun. 6, 8920 (2015)] of single-walled carbon nanotubes (SWNTs). UCPL images and spectra of the identical isolated SWNTs were obtained. Unlike previous observations on the SWNT ensemble, some individual SWNTs exhibit UCPL spectra coincident with Stokes PL spectra. The excitation polarization dependence of UCPL intensity indicates that the intermediate states in the upconversion process are extrinsic. These observations are likely to facilitate a comprehensive understanding of the UCPL mechanism towards the realization of highly efficient UCPL of SWNTs.

White polarized light emitting devices are produced by combining oriented β-phase polyfluorene (PFO) films with α-sexithiophene (6T) on top. Highly oriented PFO films are fabricated with the friction transfer method and exposed to toluene to partially change their conformation to the metastable β-phase PFO without loss of orientation. Orange emitting 6T is then deposited by the conventional vacuum deposition method on top of the blue emitting oriented PFO films. We studied the effects of 6T thickness on the emission color and the results indicated that whitening is possible by depositing 6T at a thickness of 1.5 nm on β-phase PFO. High polarization of both PFO and 6T emitting regions in the electroluminescence spectra suggested that 6T molecules are oriented parallel to the PFO molecules.

We have been studying oriented thin films of polymers fabricated by the friction transfer method, which allows a variety of conjugated polymers to be aligned into highly oriented films. However, with this method it is difficult to prepare oriented films from a mixture. In this work we prepared oriented thin films of a mixture of regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which is a promising combination for application in organic solar cells. We obtained oriented blend films of P3HT and PCBM by the friction transfer method from a solid block prepared from a mixed solution with a weight ratio of 1 : 1. Atomic force microscopy shows that microscale phase separation took place in the blend films. Polarized UV–visible spectra show that the P3HT chains were aligned parallel to the friction direction in the blend films. X-ray diffraction studies suggested that the preferred orientation of P3HT crystallites was the “face-on” orientation in the blend film.

Plasmonic chips, which are grating replicas coated with thin metal layers and overlayers such as ZnO, were applied in immunosensors to improve their detection sensitivity. Fluorescence from labeled antibodies bound to plasmonic chips can be enhanced on the basis of a grating-coupled surface plasmon resonance (GC-SPR) field. In this study, as one of the representative candidate protein markers for brain disorders, the brain-derived neurotrophic factor (BDNF) was quantitatively measured by sandwich assay on a plasmonic chip and detected on our plasmonic chip in the concentration of 5–7 ng/mL within 40 min. Furthermore, BDNF was detected in the blood sera from three types of mice: wild-type mice and two types of mutant mice. This technique is promising as a new clinical diagnosis tool for brain disorders based on scientific evidence such as blood test results.

High-quality thick GaN layers were directly grown by hydride vapor phase epitaxy on sapphire substrates preliminary processed by a laser beam focused within the substrate. The critical thickness for crack generation was improved drastically from 10–20 µm for regular substrates to 220–250 µm by using the laser processed sapphire substrates. Layers of 200 µm thickness grown on the laser processed sapphire substrates exhibited a crack-free surface over the entire 2-in. area and a threading dislocation density as low as 1×107 cm-2, which is one order of magnitude lower than that achievable with a regular sapphire substrate.

A plasmonic chip with a periodic structure coated with thin metal films was fabricated and applied to bioimaging under a fluorescence microscope. By using the enhanced electric field of surface plasmon resonance excited on the chip, an enhanced fluorescence of samples was observed by conventional fluorescence microscopy. In this study, neurons were cultured on a plasmonic chip, which was used instead of a glass-bottomed dish or cover glass; the received fluorescence images of neuron dendrites were more than four times brighter than those obtained from similar specimens cultured on a glass-bottomed dish and observed using an upright fluorescence microscope.

The importance of the atomically well-controlled surface of sapphire substrate with slight misorientation and ideally minimized surface roughness for III–nitride epitaxy is discussed in detail. An atomically controlled surface of sapphire substrate with slight misorientation angle is modeled and an almost ideal level of atomic surface roughness of sapphire substrate is found to be obtained by a chemical mechanical polishing (CMP) with colloidal silica. Cathodoluminescence (CL) imaging indicated the complete absence of subsurface damage induced by mechanical polishing. GaN and AlN thin films are grown on misoriented sapphire substrate with an atomically controlled surface by the CMP to investigate the misorientation angle of both sapphire and grown GaN and AlN thin films. An interface model is proposed to explain the difference in misorientation angle between sapphire and III–nitride thin films, providing strong evidence of the necessity of atomically controlled surface of sapphire substrate for III–nitride epitaxy.

Reduction of the bowing of GaN-on-sapphire and GaN-on-silicon substrates was demonstrated with an internally focused laser processing. Stress implantation was successfully achieved inside the sapphire and silicon substrates by the internally focused laser process to compensate for the strain generated by the GaN/sapphire and GaN/Si systems which resulted in substrate bow reduction. This new approach gives us a larger flexibility in the design engineering of epitaxial and device fabrication processes and thus accelerates the realization of a larger diameter device process with GaN-on-sapphire and GaN-on silicon.

In the development of a high power EUV source used in the EUV lithography system, it is important to understand basic physics of EUV plasma and to optimize laser and target conditions. We have been constructed EUV database of laser-produced tin plasma by the theoretical and experimental studies. On the basis of our understanding, the optimum conditions of lasers and plasmas were clarified, and we proposed the guidelines of laser plasma to obtain clean, efficient and high power EUV source for the practical EUV lithography system. In parallel to such studies, novel targets and high power laser system to generate the optimized EUV source plasma have been developed. Recent progresses of our program are presented.

EUV emission from spherical and planer targets were precisely characterized as an experimental database for use in EUV source generation at high repetition rates. In the single-shot base experiments, conversion efficiency as high as those for the plasma geometry has been demonstrated. The integrated experiment was made with 10 Hz plasma generation, obtained conversion efficiency is low mainly due to unstable positioning of the droplets.

The optimum plasma conditions of extreme ultraviolet (EUV) light source for lithography were experimentally clarified that is optically thin and minimum mass Sn plasma generated from a limited size target. Sn plasma is quite opaque for EUV light of 13.5 nm in wavelength, therefore 13.5 nm light emitted from deep within a Sn plasma is strongly absorbed, thus optically thin plasma production is essential for efficient EUV generation. Contamination of EUV optics caused by debris emanated from laser irradiated Sn targets is a serious problem in the Sn based EUV source system. Target residue around the laser spot is the dominant source of neutral debris, which can be reduced with supplying the minimum mass target containing the minimum number of Sn atoms required for sufficient EUV generation. Spectral purity of generated EUV light is an important requirement to expose clear mask image on a photo-resist film without chromatism. Out-of-band radiation in the vacuum ultraviolet range is dominantly radiated from the laser spot peripheral. Target size must be equal to the laser spot size to suppress the out-of-band radiation.

We investigated dislocation motions in C 60 crystals after indentation, by x-ray topography and etching method. A rosette pattern was observed around an indentation after etching. The dislocations in the rosette were moved by thermal annealing and the positions in the dislocations were measured before and after annealing by the double etching method. The annealing temperature dependence of dislocation motions was measured in the temperature range 490-610 K. The characteristics of dislocation motion showed dislocation locking due to impurity atmosphere. It was concluded that oxygen and oxide of C 60 molecules could lock the dislocations. Moreover, a pair of pits in the rosette pattern were observed after annealing. It corresponded to a pair of Shockley's partial dislocations.

The effect of the initial density of xenon (Xe) targets on extreme ultraviolet (EUV) emission has been investigated. With decreasing initial density, it was found that the spectral width around 11 nm becomes broad, and the intensity of 13.5 nm emission increases. The maximum conversion efficiency (CE) for solid Xe targets is approximately 0.6% at a 2×1011 W/cm2 of laser intensity, whereas that for the low-density targets is approximately 0.7% at a 4×1011 W/cm2. The spectral broadening with decreasing initial density can be attributed to the change in optical thickness of laser-produced plasmas. The enhancement of CE is attributed to optically thick plasma formation.

We have investigated the surface acoustic wave (SAW) properties of atomically flat-surface (0001)aluminum nitride on a (0001)sapphire (AlN/α-Al2O3) combination. SAW propagated along [1210]AlN/[1100]α-Al2O3 and [1010]AlN/[1120]α-Al2O3. SAW velocity was measured to be approximately 1.0% higher than that of a conventionally calculated curve. The dispersion of SAW velocity as a function of normalized thickness (kH) was as low as 1.3%. The measured temperature coefficient of delay was 9 ppm/°C at kH values of 5.9 and 9.9. The propagation loss in the case of using an atomically flat-surface AlN film was lower by one order of magnitude than that using a conventional AlN film. The propagation loss at 5.172 GHz was measured to be 0.0053 dB/λ.

An ultraviolet (UV) short-pulse intensity diagnostic method using atmosphere as a nonlinear medium was developed. This diagnostic method is based on evaluating the ion charge of the two-photon ionization of atmospheric oxygen upon irradiation with a UV (238–299 nm) short-pulse laser. The observed ion signal increased proportionally to the input intensity to the power of ∼2.2, during the two-photon ionization of atmospheric oxygen. An autocorrelator was constructed and used to successfully measure a UV laser pulse of ∼400 fs duration. Since this diagnostic system is used in the open-air under windowless conditions, it can be set along the beam path and used as a UV intensity monitor.

A high c-axis-oriented and atomically flat-surface aluminum nitride (AlN) film has been successfully deposited on a (0001)sapphire substrate by metalorganic chemical vapor deposition. We evaluated the dependences of surface roughness, tilted mosaicity and twisted mosaicity on the conditions of AlN deposition. It was found that the atomically flat-surface AlN film was deposited under the diffusion-limited area with suppression of vapor phase reaction at a substrate temperature of 1200°C and a V/III ratio of 800. It was also recognized that surface roughness was controlled by gas flow velocity, which is determined by both gas flow rate and pressure in reactor. Mean surface roughness (R a) of the deposited AlN films was approximately 1 Å. The full width at half maximum of X-ray rocking curve for (0002) and (1012)AlN were approximately 100 and 2300 arcsec, respectively.