Hidetoshi Nojiri

Formation of Transparent SiO2 Protective Layer on Polycarbonate by 157 nm F2 Laser for Lightweight Automobile Window

A transparent, hard silica glass (SiO2) layer was formed on a conventional protective coat made of silicone ([SiO(CH3)2]n) on a polycarbonate plate by the 157 nm F2 laser-induced photochemical modification of silicone into SiO2. An optimum laser irradiation time of the F2 laser was found to form a crack-free SiO2 layer. The high optical transparency of the samples in the visible light region remained unchanged after the F2 laser irradiation. In the Taber abrasion test, the SiO2 layer markedly reduced the number of scratches, resulting in a low haze value. The haze values of the samples also depend on the thickness of the silicone protective coat underneath the SiO2 protective layer. As a result, the difference of haze value (δHz) was successfully reduced to 3.6%, compared with these of the nonirradiated sample and a bare polycarbonate plate of approximately 11.3 and 41.3%, respectively, which is comparable to the case of a bare silica glass of approximately 1.6%. In addition, the thickness of the SiO2 protective layer was estimated to be approximately 0.44 µm for the 30-s laser irradiation by immersing the samples in 1 wt % hydrogen fluoride aqueous solution and measuring the depth using a surface profilometer.

Surface and Interface Modifications of Aluminum Thin Films on Silica Glass Substrate Using 157 nm F2 Laser for Selective Metallization

A 157 nm F2 laser induced strong oxidation of an Al thin film surface, allowing it to show chemical resistance to KOH aqueous solution used for selective metallization on silica glass or native oxide Si substrate. The strong oxidation reactions on the surface and in the depth direction were confirmed by X-ray photoelectron spectroscopy. A high adhesion strength of 663 kgf/cm2 between Al and silica glass was also obtained for the F2-laser-irradiated sample, compared with that of the nonirradiated sample, 16 kgf/cm2. The suitable thickness of Al thin films for the F2-laser-irradiated surface and interface modifications was examined to be approximately 20 nm. The mechanism of the F2-laser-induced interface modification was discussed regarding the dependence of substrate material and the analyses of the chemical bonding state of silica glass underneath Al thin films.

Laser Wavelength Dependence on Photochemical Surface and Interface Modifications of Aluminum Thin Films on Silica Glass

Photochemical surface and interface modifications of Al thin films on silica glass were successfully carried out using a 157 nm F2 laser for micropatterning. The surface modification phenomenon was discussed in relation to by changing the laser wavelength using a 193 nm ArF laser or a 266 nm neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. The ArF laser could induce the surface modification of Al thin films to form a protective Al2O3 layer resistant to KOH aqueous solution, similarly to the F2 laser. However, the mechanical hardness of the ArF-laser-irradiated sample was clearly lower than that of the F2-laser-irradiated sample. The origin of the surface modification was examined by irradiating the F2 laser in vacuum. The interface modification phenomenon was analyzed by X-ray photoelectron spectroscopy in the three cases. The adhesion strengths of the samples were also compared. The 266 nm Nd:YAG laser was not effective for the present photochemical modifications.

F2-Laser-Induced Modification of Aluminum Thin Films into Transparent Aluminum Oxide

A vacuum–UV F2 laser of 157 nm wavelength induced strong oxidation of 10-nm-thick Al thin films, forming transparent Al2O3 on silica glass. The laser-induced modification occurred at the surface of Al thin films; consequently, the thickness of the formed Al2O3 thin films increased linearly with increasing number of F2 laser photons. The formation of equivalent-phase Al2O3 thin films was confirmed by X-ray photoelectron spectroscopy. The oxidation reaction in the laser-induced modification of 10-nm-thick Al thin films was slower than that for 20- and 60-nm-thick Al thin films. Morphological changes leading to the crystallization of the Al2O3 thin films were also observed when the thickness of Al thin films increased from 10 to 20 and 60 nm.

Patterning of aluminum thin films by 157nm F 2 laser

A 157 nm F2 laser was used for the surface and interface modifications of Al thin films on silica glass substrate for fabricating a pattern of Al thin films. The F2-laser irradiated surface swelled remarkably by inducing the strong oxidation reaction of Al thin films to form Al2O3 protective layer. High adhesion strength of 663 kgf/cm2 between Al and silica glass was also obtained for the F2-laser-irradiated sample, compared with the cases in the ArF-laser irradiated, fourth harmonic of Nd:YAG-laser irradiated and nonirradiated samples of 326, 19 and 16 kgf/cm2, respectively. Thus, the F2- laser irradiated sample showed high abrasion resistance for embossing a fine pattern of Al thin films on silica glass. Mechanism of the F2-laser-induced surface and interface modifications was discussed, comparing with the cases in the ArF laser and fourth harmonic of Nd:YAG laser.

Crack suppression of SiO2 thin film formed by 157 nm F2 laser induced photochemical surface modification of hard silicone coating film on polycarbonate(Conference Presentation)

Light-weighting of vehicle is now strongly required for reducing gasoline consumption and CO2 emission. In this study, F2 laser was irradiated to the surface of hard silicone resin, coated by dip coating method onto the film of acrylic resin on a polycarbonate substrate. The surface part of the silicone resin was photo-chemically modified into SiO2. One of two types of aperture mask, 3×3 mm2 and 50×50 μm2, was set on the sample surface. The single pulse fluence was varied from 4 to 14 mJ/cm2, pulse repetition frequency was set to 10 Hz, and irradiation time was changed from 30 to 120 s. N2 gas was induced around the surface of the sample. After modification, SiO2 modified layer was etched by HF 1% diluted solution, and the etched depth was measured by a stylus-type surface profilometer. As a result of experiments, stress in the SiO2 modified layer increased by increasing of F2 laser irradiation time. In case of using aperture mask of 3×3 mm2, cracks were generated only on the irradiated area for longer irradiation time than 60 s. It is considered that the tensile stress in the modified layer exceeded the tensile fracture strength of 48 MPa of typical SiO2. When a mesh mask of 50×50 μm2 aperture was used, no crack generated even for a long irradiation of 200 s. We found, the tensile stress in SiO2 modified film can be reduced remarkably with using smaller aperture size of mesh mask, and it is very effective to prevent cracking.

Crack suppression of silica glass formed by zoned F2 laser-induced photochemical surface modification of hard silicone thin film coating on polycarbonate

The surface layer of a hard silicone thin film coating on polycarbonate was modified to silica glass (SiO2) through F2-laser-induced photochemical reactions. To obtain samples with higher abrasion resistances, SiO2 films of 1 ?m thickness and over were successfully formed without cracking, by zoning the laser-irradiated area of micrometer order. With the conversion of silicone to SiO2, the volumetric shrinkage of the sample was induced, which simply depended on the number of photons, by varying the single-pulse fluence and irradiation time of a F2 laser. The ratio of volumetric shrinkage to the original silicone was estimated to be approximately 0.85, generating tensile stress in SiO2. The stress could be suppressed to be lower than 48 MPa for typical SiO2 by reducing the laser-irradiated area to be of micrometer order. Also, when the length of one side of the irradiated area is 1 mm, the thickness of the SiO2 film is expected to increase to approximately 5 ?m.

F2 laser formation of SiO2 protective layer onto polycarbonate for lightweight vehicle window

Silicone-coated polycarbonate (PC) through an acrylic primer was photochemically modified into silica (SiO2) by 157 nm F2 laser. The photomodified surface showed high scratch resistance comparable to the case in a bulk silica. Corresponding to the conversion of silicone into silica on PC, the photomodified surface was found to be shrunk, measured by a surface profilometer. For instance, the coated silicone on PC reduced the thickness of approximately 15 % when the F2 laser modified silicone into silica 0.59 μin thickness. An excess irradiation of F2 laser for the photochemical modification induced the degradation of acrylic primer underneath silicone.