Yoshizo Kawaguchi

Fractoluminescence Spectra in Crystalline Quartz

Fractoluminescence and charge emission upon three-point-bending fracture of synthetic and natural quartz crystals have been studied. Broad luminescence bands centered at about 2.0, 2.9, and 5.0 eV have been observed in both cases. Time-resolved luminescence measurement could be performed on the 2.0 and 2.9 eV bands. The 2.9 eV band has a maximum intensity at about 5 ms after the fracture, and this band decayed within about 13 ms. On the other hand, the decay profile of the 2.0 eV band differed between synthetic and natural crystals. The 2.9 eV band might be due to the relaxation of the oxygen vacancy on the fracture surface, as in the case of silica glass. The 2.0 eV band seems to be due to an impurity center.

Nano- and Microdot Array Formation of FeSi2 by Nanosecond Excimer Laser-Induced Forward Transfer

Fabrication of FeSi2 nano- and microdot array was performed by utilizing droplet ejection through nanosecond laser-induced forward transfer (ns-LIFT). An amorphous FeSi2 source film on a transparent support was illuminated from the support by a nanosecond excimer laser pulse patterned into migcrogrid form, resulting in size- and site-controlled deposition of microdot array onto a silicon substrate. Micro-Raman spectroscopy confirmed β-FeSi2 crystalline phase even on unheated substrates. Moreover, the dot size was successfully reduced to approximately 500 nm in diameter, smaller than any previously reported by ns-LIFT. This technique is useful for integrating functional nano- and microdots under atmospheric room-temperature conditions.

Laser-Induced Backside Wet Etching of Sapphire

Sapphire plates were etched with the approach of laser-induced backside wet etching (LIBWE) using neat toluene or saturated pyrene/acetone solutions as the etching medium. Using this approach, flexible patterns on the scale of 4-µm can be fabricated on the surface of the plates. The etching process was observed in situ by a CCD camera, which revealed the deposition of black particles and the formation thereafter of a laser-absorbing film in the etched area. By Raman spectroscopic analysis, the film was characterized to be amorphous carbon resulting from the decomposition of toluene or pyrene upon laser irradiation, which is an essential factor contributing to the etching process.

Etching a Micro-Trench with a Maximum Aspect Ratio of 60 on Silica Glass by Laser-Induced Backside Wet Etching (LIBWE)

We have successfully fabricated a deep micro-trench about 7 µm wide and 420 µm deep on silica glass with a maximum aspect ratio of 60 by laser induced backside wet etching (LIBWE) via KrF laser ablation of a saturated pyrene/acetone solution. The processing time for the microetching was as short as 5 min at a repetition rate of 80 Hz and a fluence of F = 1.0 Jcm-2pulse-1. The etch rate was calculated to be approximately 17 nmpulse-1. The LIBWE method is shown to be very useful for surface microstructuring of silica glass with high aspect ratio and high throughput.

Charged Particle Emission and Luminescence upon Bending Fracture of Granite

Charged particle emission and luminescence upon bending fracture of granite were investigated in a vacuum. In most cases, sharp peaks of charged particle emission and luminescence were observed at the very instant of final fracture, and continued for several seconds. However, it sometimes happened that the bending fracture needed about 10-20 ms, and a sharp peak of charged particle emission was also observed at the beginning of the decrease in the applied load, suggesting that initiation and propagation of microcrack induced the charged particle emission. In both cases, luminescence was observed only at the instant of final fracture. Luminescence spectra were composed of two bands centered at about 2.1 and 3.0 eV, and each band showed different decay profiles, suggesting the contribution of the different defect centers.

Room-temperature preparation of β-FeSi2 microprecipitates by the KrF excimer laser ablation of an iron disilicide alloy target

We have fabricated β-FeSi2 microprecipitates at room temperature using KrF excimer laser ablation of an α-FeSi2 alloy target. Raman spectra with a spatial resolution of 1 μm confirmed that the micron-sized droplets generated by laser ablation precipitate as the β-FeSi2 crystalline phase on a silicon substrate maintained at RT, whereas the rest of the deposited film is amorphous. It was also found that films containing a high density of β-FeSi2 precipitates exhibited 1.55 μm photoluminescence at low temperature (up to 200 K) after annealing at 800 °C for 6 h in an argon atmosphere.

A deep micro-trench on silica glass fabricated by laserinduced backside wet etching (LIBWE)

By using laser-induced backside wet etching (LIBWE), we have fabricated very deep micro-trenches in silica glass of 9-μm width and 300-μm depth (aspect ratio ≈ 33). In this paper, we present the details of fabricating the micro-trenches, and discuss why such a deep micro-trench is available by the LIBWE method.

Pulsed laser deposition of semiconductor-ITO composite films on electric-field-applied substrates

Abstract The DC electric-field effect on the crystallinity of II–VI semiconductor in composite systems has been investigated for CdS–ITO films fabricated via alternative pulsed laser deposition (PLD) of CdS and indium tin oxide (ITO) on electric-field-applied substrates. The alternative laser ablation was performed under irradiation of ArF excimer laser in mixture gas of helium and oxygen. The application of electric-field facilitated the preferential crystal-growth of CdS in nanometer scale at low pressure, whereas all the films grown without the field were amorphous. There is a large difference in the crystallization between the films grown on field-applied and heated substrates; the latter showed the crystal-growth with random orientations. This difference indicates that the existence of electric-field has an influence on the transformation from amorphous to crystalline phase of CdS. The driving force for the field-induced crystallization is also discussed in the light of the Joule heat.

Fabrication of 1 μm patterns on fused silica plates by laser-induced backside wet etching (LIBWE)

Laser-induced backside wet etching of fused silica plates using aqueous solutions of naphthalene-1,3,6-trisulfonic acid trisodium salt (Np) and pyranine (py) was performed upon KrF excimer laser irradiation at 248 nm. The two etching media show different etching behavior with changing laser fluence and medium concentrations. Well-defined line-and-space and grid micropatterns at 1 μm scale were fabricated using an aqueous solution of Np and the etched pattern was free of debris and microcracks.

Site-selective dye deposition on microstructures of fused silica fabricated using the LIBWE method

Using laser-induced backside wet etching (LIBWE) technique, microstructures were fabricated onto the surface of fused silica plates, which were pre-coated with self-assembled monolayers (SAMs). Dye molecules and proteins were alternately deposited onto the laser-irradiated or non-irradiated areas by either chemical bonding or physical adsorption.