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In this study, nitrogen is doped into 4H-SiC by irradiating 4H-SiC with a SiNx thin film and a KrF excimer laser. The doping depth profile, crystal structure, electrical properties, and surface roughness results are analyzed to evaluate the excimer-laser doping mechanism. High-concentration doping is possible at a fluence of 2.5 J cm−2 and 10 shots, while maintaining the 4H-SiC crystal structure via solid-phase diffusion. However, changes in the 4H-SiC crystalline state are observed upon liquid-phase diffusion at a fluence of ≥2.8 J cm−2. At a fluence of 2.5 J cm−2 and 100 shots, nitrogen can be deeply diffused via solid-phase diffusion; however, an amorphous layer is formed on the surface and there is an increase in contact resistance.

The working mechanism of the anti-parasitic-reaction (APR) catalyst of tungsten carbide (WC) coating on graphite in hydride vapor phase epitaxy GaN growth were examined. During NH3 annealing, the surface of WC is reduced as well as nitrided. The W2N topmost layer was found to work as an APR-active catalyst to suppress the formation of GaN polycrystals during high-rate HVPE-GaN growth, while the regions covered with thick pyrolytic graphite residues were catalytically inert. The formation of an additional W2C top layer on the WC underlayer was demonstrated to exhibit superior APR activity, i.e. complete suppression of GaN polycrystal formation.

In this paper, the whispering gallery mode lasing from Sm3+ doped ZnO micro-spheres operating in the visible wavelength range 550-750 nm is studied. Highly smooth and crystalline Sm3+:ZnO micro-spheres of various diameters were synthesized by simple laser ablation of sintered target in air. The dopant concentration has been restricted within the solid solubility limit of 1 mol%. The Sm3+ ion substitution in ZnO matrix results in the formation of inter-band levels by the characteristic 4f level of Sm3+ in the forbidden gap of ZnO. Thus, when the micro-spheres are excited with 488 nm, four major visible emissions associated with Sm3+ f−f transitions namely, transitions from 4G5/2 to its low-lying multiplets of 6HJ (J = 5/2, 7/2, 9/2 and 11/2), are obtained. These emissions are coupled to the WGMs of the Sm3+:ZnO micro-cavity resulting in sharp resonances in the visible region. Interestingly, the resonances are found to be lasing above lower pumping powers. The Q-factor obtained is of the order of 103 for spheres of size ranging 1.8-10.2 μm. The best Q-factor obtained is 3744 for 561.61 nm peak (FWHM 0.15 nm) from 8 μm sphere. These results would find a place in visible range lasing and sensor applications.

The material yield of Ga during GaN growth via halogen-free vapor-phase epitaxy (HF-VPE) was systematically investigated and found to be much higher than that obtained using conventional hydride VPE. This is attributed to the much lower process pressure and shorter seed-to-source distance, owing to the inherent chemical reactions and corresponding reactor design used for HF-VPE growth. Ultrahigh-yield GaN growth was demonstrated on a 4-in.-diameter sapphire seed substrate.

Vertically aligned ZnO nanowires with controllable density were successfully synthesized by nanoparticle-assisted pulsed-laser deposition (NAPLD), by which nanoparticles formed in the gas phase by the condensation of the ablated species are transported onto the substrate, and nanoparticles play an important role in density control. The effects of synthesis conditions on the density and optical properties of ZnO nanowires were investigated in detail. With the increase in repetition rate and laser energy, ZnO nanowires with a higher density can be obtained as a result of a larger quantity of nanoparticles formed in the gas phase. The density-controlled growth also depends on substrate–target distance. UV emission was observed from all the obtained nanowires at about 390 nm without visible fluorescence near 500 nm due to their excellent crystallinity and the oxygen-deficient defect.

An extremely high-resolution, nanometer-resolution, solid-surface trace element detection has been demonstrated. Nanometer-thinned pulsed laser ablation was combined with extremely sensitive laser-induced fluorescence spectroscopy, and depth resolution of 3.6 nm was experimentally demonstrated for the first time on sodium detection in polymeric samples. An extremely high absolute detection limit of 25.2 fg was also obtained, and a theoretical calculation program was also generated to analyze the results.

A contactless measurement system of electrical conductivity was developed for application under pulsed high magnetic fields over 100 T by using a self-resonant-type, high-frequency circuit. Electromagnetic fields in the circuit were numerically analysed by the finite element method, to show how the resonant power spectra of the circuit depends on the electrical conductivity of a sample set on the probe-coil. The performance was examined using a high-temperature cuprate superconductor, Lalsubg2-ligxl/igl/subgSrlsubgligxl/igl/subgCuOlsubg4l/subg, in magnetic fields up to 102 T with a high frequency of close to 800 MHz. As a result, the upper critical field could be determined with a good signal-to-noise ratio.

The GaN growth rate during halogen-free vapor phase epitaxy (HF-VPE) is significantly increased by the use of an evaporator made of a porosity-controlled TaC ceramic. A fin-shaped evaporator, which is immersed in a molten Ga source at temperatures above 1373 K, effectively pumps molten Ga by capillary action and provides a fivefold increase in the surface area of the source. This results in a 3–5 times increase in both the Ga supply rate and the GaN growth rate.

Here, we propose a halogen-free vapor phase epitaxy (HF-VPE) technique to grow bulk GaN single crystals. This technique employs the simplest reaction for GaN synthesis (reaction of Ga vapor with NH3) and can potentially achieve a high growth rate, a prolonged growth duration, a high crystal quality, and a low cost. The analyses of thick HF-VPE-GaN layers grown under optimized growth conditions revealed that high-quality crystals, both in terms of dislocation density and impurity concentration, are obtained at high growth rates of over 100 µm/h.

Here we report the influence of substrate temperature (300-500 °C) on the deposition and growth of ZnO over a Flexible polyimide film. Owing to its simplicity, large area deposition capability and Cost effectivity Spray Pyrolysis technique was used. We have modified the conventional process of Spray pyrolysis by spraying for shorter durations and repeating the process which in turn reduced the Island formation of ZnO. Moreover, this technique helped in maintaining the constant temperature and uniformity during the deposition as prolonged spraying reduces the temperature of the heating plate drastically. Photoluminescence (PL) reveals that at 350 and 400° C the defect have reduced. XRD reveals the crystallinity and Impurities present. FE-SEM reveals the structure morphology changes with the change in the substrate temperature. TGA was done to ensure that substrate does not undergoes dissociation at high temperature. It was observed at the film deposited at 400 °C was found to be more uniform, defect free and crystalline. Hence, IV characterization of the film deposited at 400 °C was done which showed good rectification behaviour of the Schottky diodes.

Newly developed highly reliable low-cost TaC-coated graphite materials prepared by a wet ceramic process were applied to SiC sublimation growth. We demonstrated an increased long-duration growth rate and a resultant increase in crystal size by a factor of ∼1.2 (experimental value) after 24 h of growth [and ∼1.5 (extrapolated value) after the optimum duration of 53.1 h] by simply and quickly replacing graphite crucibles with TaC-coated graphite crucibles. Growth with the TaC-coated graphite crucibles reduced source gas leakage and increased the material yield for single crystals because the TaC layers were gas-tight and had a low emissivity.

Catalyst-free growth of one-dimensional zinc oxide (ZnO) nanowires is reported. ZnO nanowires were synthesized on ZnO buffer layers deposited on various-oriented sapphire substrates. Syntheses of ZnO buffer layers and nanowires were performed by ultraviolet pulsed-laser deposition. ZnO nanowire's number density was the lowest in the case of using m-cut sapphire substrates. ZnO nanowires grown on a-cut sapphire substrates had vertical alignment with distances of tens to hundreds of nanometers. On the other hand, ZnO nanowires grown on c-cut sapphire substrates had the biggest nucleation rate. The dependence of crystalline orientation of ZnO buffer layers on the orientation of sapphire substrates were investigated by electron back scatter diffraction measurement. From their results, the growth models of ZnO buffer layers were suggested and the variations in morphological properties of ZnO nanowires were discussed.

We have succeeded in controlling the growth density of ZnO nanowires synthesized by nanoparticle-assisted pulsed laser deposition (NAPLD) using a ZnO buffer layer and laser irradiation. The density of the nanowires decreased with increasing thickness of the buffer layer. In addition, the nanowire density also decreased by laser irradiation to the buffer layer. Patterned growth of ZnO nanowalls using NAPLD was successfully achieved with the help of the buffer layer patterned by interfering laser beams.

We report on the growth of ZnO nanowires on a p-type diamond substrate using nanoparticle-assisted pulsed laser deposition technique. Microstructural analysis on different growth stages reveals that the self-assembled 1D ZnO nanowires emerge on well-formed 2D hexagonal base with spiral-like structures. We explain the formation of screw-dislocation-driven spiral-like-hexagons invoking crystal growth velocities at different regions of the hexagons. High-resolution transmission electron microscopy and selective area electron diffraction studies show that the nanowires are single crystalline in nature and grow along 0 0 0 1 direction of the wurtzite hexagonal structure. Room temperature photoluminescence spectrum of the ZnO nanowire shows a strong near band edge emission at 3.2 eV with a linewidth of 136 meV. � 2014 IOP Publishing Ltd.

We have investigated direct etching of poly(methyl methacrylate) (PMMA) using laser plasma soft X-rays. We focused soft X-rays of 6–25 nm on PMMA sheets efficiently using an Au coated ellipsoidal mirror. 7×10-2% of laser energy is estimated to be converted to soft X-rays that was incident to the PMMA sheets. We found that PMMA surfaces are etched beyond a threshold power density. The energy density of absorbed soft X-rays at the threshold is 7 kJ/cm3. The results suggest that etching is governed by decomposition into fragments.

We report the growth and low-temperature photoluminescent characteristics of well-aligned Ni-doped ZnO nanoneedles and V-doped ZnO nanostructured thin film grown by a modified pulsed laser deposition technique. Low-temperature photoluminescence spectra of the as-grown films show the presence of free excitonic as well as bound excitonic transitions, whose relative intensity changes with increasing temperature. Ni-doped ZnO films show a characteristic fine structure in the visible range (2.6?2.9?meV) attributed to either exciton?polariton longitudinal?transverse splitting or the splitting caused by electron?hole exchange interaction. The excitonic and visible region emission can be clearly seen as can the phonon replicas produced from longitudinal optical phonons. Different possible attributions of the various peaks in the emission band at low temperature have been discussed. The as-grown nanostructures of Ni- and V-doped ZnO thin films also clearly show the effect of doping on the microstructure of ZnO.

The ablation dynamics of a tin (Sn) micro-droplet by double pulse laser irradiation for the development of an extreme ultraviolet lithography source was investigated. The solid state Sn droplet target with a diameter of 30 µm was irradiated by double laser pulses from a Q-switched Nd : YAG laser and a CO2 laser, and the kinetic behaviour of debris such as Sn atoms, ions and of the dense particles from the droplet was investigated by the laser-induced fluorescence imaging method, Faraday cups and high-speed imaging, respectively. After the pre-pulse irradiation of the Nd : YAG laser, the ions were emitted towards the laser incident direction with an average kinetic energy of 3–6 keV and the dense particle cloud moved in the direction opposite to the laser incident direction with expansion by a reaction force due to the plasma expansion at a speed of approximately 500 m s−1. On the other hand, the Sn atoms were ejected in all directions from the target with a speed as fast as 20 km s−1. The expanding target was subsequently irradiated by the main pulse of the CO2 laser with a delay of 800 ns and the dense cloud almost disappeared due to main-pulse irradiation.

The emission characteristics of debris from laser-produced tin plasma were investigated for an extreme ultraviolet lithography (EUV) light source. The ions and droplets emitted from tin plasma produced by a CO2 laser or an Nd: YAG laser were detected with Faraday cups and quartz crystal micro-balance (QCM) detectors, respectively. A higher ion kinetic energy and a lower droplet emission were observed in the case of CO2 laser in compared with Nd: YAG laser for the same laser energy (50 mJ). The reason comes from the interaction of the laser pulse with the plasma. CO2 laser is absorbed in superficial region of the plasma due to the long wavelength, in contrast, Nd: YAG laser penetrates deeply into the plasma. Therefore, the absorbed energy density of CO2 laser will be much larger than that of Nd: YAG laser for the same laser energy. This causes the higher ion energy and complete vaporizing the target material.

The many-electron eigenstates of anisotropic parabolic quantum dots with cylindrical symmetry are investigated using an unrestricted Hartree-Fock method, in a magnetic field parallel to the cylindrical z-axis. The many-electron eigenstates are assigned by two quantum numbers, L z and S z, the z-components of the total orbital angular momentum and the total spin, respectively. The many-electron ground states exhibit sequential transitions via three stages with increasing magnetic field. At the transition magnetic fields, the ground state energy crosses that of the first-excited state with different values of (L z, S z) and they replace each other. The phase diagram of the ground state is obtained in a space of the magnetic field and the electron number. The phase diagram is greatly affected by the lateral extent of quantum dots, but the effect of the vertical extent is small for quasi-two-dimensional quantum dots. In these magnetic field induced transitions, the Hartree interaction plays a dominant role.