Masahito Katto

Hydroxyapatite coatings deposited by laser-assisted laser ablation method

Application of a new hydroxyapatite coating method called the laser-assisted laser ablation method improves adhesion due to irradiation by an assist laser beam for optical annealing. In this study, substrate immersion in a simulated body fluid was performed to confirm the biocompatibility of the technique. The coatings contained a significant quantity of amorphous calcium phosphates. The amorphous phase was dissolved in the simulated body fluid, but coatings in the assisted area remained and grew in the solution. It is shown that the assist laser annealed the coatings and micro-crystals of hydroxyapatite were achieved.

Laser beam profiler in the vacuum ultraviolet spectral range using photostimulable phosphor

We propose and demonstrate the use of a photostimulable phosphor material, BaFBr:Eu2+, for recording two‐dimensional intensity distributions within output beams of vacuum ultraviolet lasers. The sensitivity characteristics were measured not only for nanosecond pulsed radiation from KrF, ArF, and Ar2 excimer lasers but also for quasi‐continuous‐wave synchrotron radiation. We designed and constructed a laser beam profiler to record, read, and erase images in vacuum. The intensity distribution in the output beams from an Ar2 excimer laser was measured with it, and then the threshold gas pressure for obtaining the well collimated beams was found to be 22 kg/cm2. The intensity is not uniform in the beams but stronger in the peripheral part than in the central one.

Hydroxyapatite Coating on Titanium Plate with an Ultrafine Particle Beam

A coating technology was developed to form hydroxyapatite (HAp) films on the surface of titanium (Ti) plates using an ultrafine particle (UFP) beam. The UFP beam was composed of HAp particles of submicron size. The dependence of the films formation on the beams incident angle was also investigated. A thick HAp film was produced at an incident angle of 0?, but the film did not display good adhesion to the Ti plate. At incident angles of 40? and 60?, the HAp films formed were fine, although not as thick as that formed at 0?. The adhesion strength between the HAp film and the Ti plate was found to be higher than 20 MPa in the films formed at both 40? and 60?.

Suppression of suprathermal ions from a colloidal microjet target containing SnO2 nanoparticles by using double laser pulses

We have demonstrated suppression of suprathermal ions from a colloidal microjet target plasma containing tin-dioxide (SnO2) nanoparticles irradiated by double laser pulses. We observed a significant decrease of the tin and oxygen ion signals in the charged-state-separated energy spectra when double laser pulses were irradiated. The peak energy of the singly ionized tin ions decreased from 9to3keV when a preplasma was produced. The decrease in the ion energy, considered as debris suppression, is attributed to the interaction between an expanding low-density preplasma and a main laser pulse.

Hydroxyapatite coatings using novel pulsed laser ablation methods

Abstract We developed two methods for depositing hydroxyapatite (HAp) coatings based on the pulsed laser ablation, laser irradiation and laser-assisted laser ablation (LALA) techniques. In laser irradiation, the HAp coatings were deposited in air. LALA involves both laser ablation and laser annealing using two laser beams. The assisting laser beam helped crystallize and anneal the deposited HAp layer. HAp coatings deposited using LALA remained intact during the Scotch ® tape test and grew in the simulated body fluid.

Deposited debris characteristics and its reduction of a laser-produced plasma extreme ultraviolet source using a colloidal tin dioxide jet target

Debris characteristics and their reduction have been investigated for a laser-produced plasma extreme ultraviolet source by using a colloidal jet target containing tin dioxide nanoparticles. The amounts of deposited debris on a witness plate were determined by total laser energy irradiated onto a target. In situ low-temperature (100°C) heating of a plate was effective to reduce the amounts of deposited debris, since colloidal debris was easily vaporized by the heat.

Silicon Nitride Film Deposition by Photochemical Vapor Deposition Using an Argon Excimer Lamp

In this paper, we report the deposition of silicon nitride (SiNx) films for the production of semiconductor devices and flat panel displays, by chemical vapor deposition with vacuum ultraviolet excimer lamps (VUV-CVD) using SiH4 and NH3 as raw materials. An Ar2* excimer lamp (λ=126 nm, hν=9.8 eV) with a high photon energy was used to directly excite and dissociate SiH4 through a photochemical reaction. SiNx films were successfully formed at a low temperature of 100 °C with the Ar2* excimer lamp. Although the Si-rich films were obtained using an Ar2* lamp, they showed a quality almost similar to that of films obtained by conventional plasma-CVD at 400 °C.

Radiation effects of vacuum ultraviolet lasers in amorphous Si3N4 films

Abstract The effects of irradiation of silicon nitride films with an argon excimer laser having a capability of emitting 126 nm photons of a fluence of 1014 per cm2 per pulse have been studied. We found that laser irradiation induces crystalline silicon precipitation accompanied with nitrogen desorption within thin surface layers of silicon nitride films. We showed that laser-induced electronic excitation played a crucial role in the process and further that the amount of precipitated silicon depends on the film surface temperature.

Subpicosecond vacuum ultraviolet laser system for advanced materials processing

We have been developing the vacuum ultraviolet (VUV) light sources and novel applications using such short wavelength emission sources. High quality amorphous Si thin films were successfully produced at room temperature as a result of photo-dissociation of SiH4 gas by using an Ar2* excimer lamp irradiation at 126 nm. To enhance such novel VUV processing applications, a compact VUV amplifier at 126 nm was developed by use of the optical-field-ionization (OFI) electrons. The gain-length product around 5 was obtained as a result of the optical feedback by using a VUV mirror. This amplifier was operated in a table-top size with a high repetition rate up to several kHz, which should be appropriate for any process applications. We also describe the schematic concept of the ultrashort pulse high-intensity VUV laser system at 126 nm with a pulse width of 100 fs.

Growth of silicon microcrystals in thin surface layers of quartz glass with vacuum ultraviolet laser processing

Abstract Silicon precipitates in surface layers as thin as 50 nm of quartz glass plates where 9.8 eV photons from an argon excimer laser are irradiated. The surfaces have many protrusions having a spherical shape with submicrometer diameter. Raman spectra indicates that they are made of crystalline silicon. Such a phenomenon has not been observed by 8.5 eV photons from a krypton excimer laser. VUV laser material processing offers a novel way to produce directly polycrystalline silicon circuits in thin surface layers of quartz glass plates.