Hirozumi Azuma

Stress measurements in silicon substrates with TiSi2 patterns using Raman microprobe

The horizontal and depth distributions of the stress induced in silicon substrates with titanium silicide ( TiSi2) patterns were evaluated using the Raman microprobe. Tensile stress is generated beside the TiSi2 pattern. The tensile stress reaches a maximum value of 150–350 MPa at the distance of ~0.5 µ m from the edge of the TiSi2 pattern, and the range of the tensile stress is as far as 2–4 µ m from the edge. Under the TiSi2 pattern, compressive stress is generated. The compressive stress becomes a maximum value of 25–75 MPa at the TiSi2/Si interface, and the depth of the compressive stress extends to 2–1 µ m.

Influence of bismuth as a surfactant on the growth of germanium on silicon

The influence of a Bi surfactant layer on the growth of Ge on Si(100) substrates was investigated by using a medium‐energy ion‐backscattering spectrometer and a transmission electron microscope. A monolayer of Bi predeposited on the Si substrates suppressed islanding in the subsequent molecular‐beam‐epitaxial growth of Ge. The Bi atoms moved on top of the Ge film during the growth process.

Phenomenological Studies in Laser Cladding. Part I. Time-Resolved Measurements of the Absorptivity of Metal Powder

Time-resolved measurements were introduced to study the dynamic behavior of the absorptivity of metal powder under CO2 laser irradiation conditions. The absorptivity of metal powder was more than 90% under short-term laser irradiation (6-20 ms), but it was below 30% under relatively long-term laser irradiation (50-1000 ms). The experimental results propose that the dynamic change of the absorptivity is caused by time-dependent aggregation of powder particles induced by laser irradiation.

1 Hz fast-heating fusion driver HAMA pumped by a 10 J green diode-pumped solid-state laser

A Ti : sapphire laser HAMA pumped by a diode-pumped solid-state laser (DPSSL) is developed to enable a high-repetitive inertial confinement fusion (ICF) experiment to be conducted. To demonstrate a counter-irradiation fast-heating fusion scheme, a 3.8 J, 0.4 ns amplified chirped pulse is divided into four beams: two counter-irradiate a target with intensities of 6 × 1013 W cm−2, and the remaining two are pulse-compressed to 110 fs for heating the imploded target with intensities of 2 × 1017 W cm−2. HAMA contributed to the first demonstration by showing that a 10 J class DPSSL is adaptable to ICF experiments and succeeded in DD neutron generation in the repetition mode. Based on HAMA, we can design and develop an integrated repetitive ICF experiment machine by including target injection and tracking.

Laser Annealing to Form High-Temperature Phase of FeS2

We fabricated single-phase pyrite thin films of FeS2 by laser annealing of multi-phase FeS2 films. Sputter-deposited FeS films followed by sulfurization in sulfur vapor at high temperatures were mainly composed of the high-temperature phase (pyrite) but contained a small amount of the low-temperature phase (marcasite) that likely grew when the samples were naturally cooled after the sulfurization. We applied the rapid cooling feature of laser annealing to preventing the marcasite phase formation. No trace of marcasite phase was observed in Raman spectra and X-ray diffraction patterns of the laser-annealed samples. We analyzed temporal evolution of the sample temperature during the laser-annealing processes to confirm that the laser heating induced phase change of the small amount of marcasite to pyrite and the rapid cooling prevented marcasite regrowth.

Internal Stress of CoSi2 Films Formed by Rapid Thermal Annealing

This paper presents a discussion on internal stress generation in CoSi2 films formed by rapid thermal annealing (700–900° C). The internal stress is measured by X-ray diffractometry. The internal stress is 1.1–1.3 GPa, and is almost independent of the annealing temperature. This is in contrast with the fact that the internal stress of TiSi2 films increases with the annealing temperature. This contrast is attributed to the fact that thermal stress of CoSi2 films relaxes during cooling, while in TiSi2 films the thermal stress contributes to the internal stress without relaxing.

Thermally Induced Structural Modification of Nanometer-Order Mo/Si Multilayers by the Spectral Reflectance of Laser-Plasma Soft X-Rays

Thermally induced structural modification of a nm-order multilayer of Mo/Si was investigated by spectral reflect-ance of soft X-rays from laser-produced plasma. Dependence of reflectivity of the nm-order multilayers on the incidence angle of soft X-rays indicated that some structural changes start to occur at 300°C and that the nm-order multilayer structures shrink at 500°C because of the formation of Mo-silicide. These results were found to be consistent with the cross-sectional transmission electron microscope observations. It is clearly shown that measurement of spectral reflectance of soft X-rays from laser plasma is a powerful method for analyzing nm-order structural modifications of multilayers.

New Surface Treatment of Polymers by Simultaneous Exposure to Vacuum Ultra-Violet Light and Nanometer-Sized Particles

By focusing the strong vacuum ultra-violet absorption of carbon atoms, polymer surfaces were simultaneously exposed to vacuum ultra-violet light (VUV) and nanometer-sized particles. As a result, the adhesive properties of polymer surfaces were improved. The improvement of the polymer surface is caused by the creation of the bonds between nanometer-sized particles and carbon atoms of the polymer surfaces, which is supported by the theoretical calculation of core electron bonding energy. Despite the other UV treatment, the polymers themselves were not damaged or maintained their surface activations for more than one month. This result should expand new applications of polymers, and apply to almost all polymers scientifically and industrially.

Phenomenological Studies in Laser Cladding. Part II. Thermometrical Experiments on the Melt Pool

A novel two-color pyrometer composed of a high-speed shutter TV camera and an image intensifier is employed to study the surface temperatures of the cladding layer under CO2 laser radiation. The two dimensional image of the surface temperature of the melt pool was stored in the frame memory in National Television System Committee (NTSC) formula. Also, high-speed photography was used to observe the dynamic behavior of the melt pool. The rapid motion and temperature change of the melt pool were observed and the former was greater than the laser scan (200 Hz). From these two time-resolved measurements, the laser cladding layer was found to be under the control of the dynamic behavior of the melt pool.

Multilayered polycrystallization in single-crystal YSZ by laser-shock compression

A single shot of an ultra-intense laser with 0.8 J of energy and a pulse width of 110 fs (peak intensity of W cm−2) is divided into two beams and the two beams counter-irradiated onto a 0.5 mm-thick single crystal yttria-stabilized zirconia (YSZ), changing the YSZ into a multilayered polycrystalline state. The laser-driven shock wave of the intensity 7.6 Pa penetrated the crystal as deep as 96 m, causing formation of a four-layered structure (the first layer from the surface to 12 m, the second from 12 to 28 m, the third from 28 to 96 m, and the fourth from 96 to 130 m, respectively). The grain size of the first layer was 1 m, while that of the second layer was broken into a few tens nanometers. The grain size of the third layer was a few hundred nanometers to a few ten micrometers. The area deeper than 96 m remained as a single crystal. The plasma heat wave might remelt the first layer, resulting in the grain size becoming larger than that of the second layer. The surface polycrystallization seems to maintain the residual stresses frozen in the film thickness direction. Our experimentally observed spatial profile of the grain size can be explained by this shock and heat waves model.