Hiroyuki Nishikawa | Shibaura Institute of Technology (original) (raw)

Papers by Hiroyuki Nishikawa

The Japan Society of Applied Physics, 2016

はじめに:MeVクラスのエネルギーを有する陽子線には、(1)高い直進性、(2)加速エネルギーの大きさで侵入深 さを制御可能、および(3)集束とその走査による直接描画が可能、といった特徴がある。こ... more はじめに:MeVクラスのエネルギーを有する陽子線には、(1)高い直進性、(2)加速エネルギーの大きさで侵入深 さを制御可能、および(3)集束とその走査による直接描画が可能、といった特徴がある。これらの特徴を活かし、 高アスペクト比を有する加工が可能となる。本研究の目的は、集束陽子線描画(Proton Beam Writing, PBW)によ る照射効果を用い P(VDF/TrFE)のウェットエッチング特性を調べることである。フッ化ビニリデン (vinylidene fluoride, VDF)とトリフルオロエチレン(trifluoroethylene, TrFE)のランダム共重合体である P(VDF/TrFE)は、高分子材料の中で最も強い圧電効果と焦電効果をもち、その圧電効果を利用して触覚セ ンサや超音波探傷の超音波トランスデューサなどに利用され 、PBWによる三次元加工により、更なる 高機能化が期待できる。 実験方法:(株)クレハ製P(VDF/TrFE)組成比(75/25)粉末をDMFへ室温環境下で溶解(10 wt%)させた。脱脂 洗浄した10 mm角Si基板へ溶液を滴下し、スピンコーターを用いて 300 rpmを5 s、500rpmを5sで回転 させ、ホットプレート上にて 40 °C、2 hの熱処理を行った。成膜したP(VDF/TrFE)膜へプロトンビームラ イター((株)神戸製鋼所MBS-S1000、加速エネルギー:1.0 MeV、ビームサイズ:1.0 μm)を用いて真空中に て集束陽子線描画を行った。照射図形は、Figure 1に示す 30 μm角パターンを照射量0.3-4.8 μC/mmの範 囲で変化させて照射した。その後、KMnO4(濃度0.25 mol/L)添加KOH水溶液(濃度9 mol/L、80 °C)で1 h の液侵によるアルカリエッチングを行い、純水洗浄、乾燥処理をした。 実験結果および考察: P(VDF/TrFE)膜のエッチング後の観察・加工深さ測定は、共焦点レーザ顕微鏡 (OLYMPUS 社製、LEXT OLS4000) を使用した。ステッチング機能による表面構造を 3D表示により観察 した結果をFigure2に示す。また測定した加工深さの照射量依存性をFigure3に示す。照射量 0.3-2.1 μC/mm の範囲での加工深さは徐々...

The Proceedings of the Symposium on Micro-Nano Science and Technology, 2013

We investigated optical properties of mono-dispersed silica with diameters of several hundred nan... more We investigated optical properties of mono-dispersed silica with diameters of several hundred nanometers. The mono-dispersed silica particles were formed by the Stober method from tetraethoxysilane (TEOS). Structures and impurities of the silica particles were studied by Fourier Transform Infrared (FT-IR) absorption. Impurities such as hydroxyls were removed by an anneal at temperatures more than 500 C. In addition, the peak position around 1100 cm-1 due to the Si-O bonds was changed to higher frequencies during the anneal. This suggests the structures such as Si-O-Si bond angles of mono-dispersed silica were modified during annealing. These silica particles were easily self-assembled on silicon substrates or glass. The states of the self-assembled structures were observed by an optical microscope, an atomic force microscope, and a scanning electron microscope. Two dimensional or three dimensional close-packed structures with were observed.

This paper reports a result carried out in order to clarify the applicability of ion irradiation ... more This paper reports a result carried out in order to clarify the applicability of ion irradiation effects to polymer materials used for optical waveguides. We irradiated 950-keV He+ ions or 1.0-MeV H+ ions to a fluorinated polyimide film to a fluence between 1 × 1014 and 7 × 1016 cm-2, and the film surface was scanned by a profilometer. The depth of a dent induced by the irradiation increases with an increase in the fluence. From the depth of the dent, the projected range of the He+ ions, and the Lorentz-Lorenz equation, the refractive index of the ion-irradiated region was found to increase by 2.9 %. This value agrees with the increment in refractive index measured by spectroscopic ellipsometry, which also increases as the fluence increases. Furthermore, the increment in refractive index, 0.21 %, induced by the irradiation of H+ ions to the fluence of 1 × 1015 cm-2 is comparable to the value, 0.35 %, observed when H+ ions of a similar fluence were irradiated to SiO2 glass. Therefore...

SPIE Proceedings, 1989

Title: Role of nonstoichiometry on UV absorption and luminescence in high-purity silica. Authors:... more Title: Role of nonstoichiometry on UV absorption and luminescence in high-purity silica. Authors: Nishikawa, Hiroyuki; Tohmon, Ryoichi; Nagasawa, Kaya; Ohki, Yoshimichi; Hama, Yoshimasa. Affiliation: AA(Waseda Univ), AB(Sagami Institute of Technology), AC(Waseda Univ). ...

Key Engineering Materials, 2011

Proton beam writing (PBW) has attracted much attention recently as a next-generation micro-fabric... more Proton beam writing (PBW) has attracted much attention recently as a next-generation micro-fabrication technology. It is a direct-drawing technique and does not need any masks to transfer micro-patterns to sample surfaces. In addition, the refractive index of a poly (methyl methacrylate) (PMMA) can be increased by proton-beam irradiation. In this study, we fabricated the first 1.5-μm-band single-mode, straight-line waveguides and Y-junction waveguides consisting of PMMA layers using the PBW technique.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006

High-purity silica glass was irradiated by a focused 15-MeV O 4+ microbeam with diameter of 1 lm ... more High-purity silica glass was irradiated by a focused 15-MeV O 4+ microbeam with diameter of 1 lm up to a fluence of 1.0 • 10 14 ions/cm 2. Spatial distribution of irradiation effects by the O 4+ microbeam on silica glass was investigated by optical microscopy, microphotoluminescence (PL)/Raman spectroscopy and atomic force microscopy (AFM). Distribution of refractive index change and defect formation was visualized by optical microscopy and PL mapping, indicating the structural changes of silica glass along the ion track up to the depth of 10 lm. In addition, we observed deformed side surface with a groove by AFM along the track suggesting the internal compaction in silica glass. This is accompanied by increased threefold rings of SiO 2 network detected by Raman scattering. We also discuss technological implications of these results on the applications of microbeam irradiation effects to the fabrication of microoptical elements.

Journal of Applied Physics, 1991

The intensity change in optical absorption at 3.8, 5.0, and 5.8 eV was measured for thermal treat... more The intensity change in optical absorption at 3.8, 5.0, and 5.8 eV was measured for thermal treatment up to 1000 °C done on silica glass samples manufactured by various methods. It was found that these absorption bands change differently with heat, depending on the synthesis process of the sample. The 3.8-eV absorption band due to peroxy linkage is found to increase with high-temperature treatment when the sample contains dissolved oxygen molecules within the sample. For the sample with no oxygen molecules, high-temperaturetreatment does not alter the absorption intensity at 3.8 eV. The 5.0-eV absorption band is found to decrease by high-temperature treatment. In the case of an oxygen-containingsample, the reaction of oxygen molecules with oxygen vacancy sites is a cause of this decrease. The 5.1-eV band, which was thought to have no temperature dependence, is found to be annealed at a temperature region around 950 °C.

Journal of Applied Physics, 1991

Mechanical stress is applied to high-purity amorphous SiO2 samples by means of fracturing. The el... more Mechanical stress is applied to high-purity amorphous SiO2 samples by means of fracturing. The electron-spin-resonance spectra suggest that the formation of a majority of paramagnetic defects is from cleavage of Si—O—Si bridges in the glass network, but there are some sample-to-sample variances in fracture-induced paramagnetic defects, suggesting cleavage of differing chemical bonding states in the samples. Nonstoichiometric bonds, ≡Si—Si≡ and ≡Si—O—O—Si≡, are assumed to be one reason for the sample dependency. Formation of Si—O—Si strained bonds from mechanical fracturing is confirmed from sequential γ-ray irradiation and heat annealing experiments. The Si—O—Si strained bond is approximately annealed at about 300 °C. By comparing the fracture-induced defects for glass preforms and optical fibers, the change in chemical bonding state can be analyzed. Analysis of mechanical-fracture-induced defects is a strong technique for elucidation of the chemical bonding state of silica glass.

Japanese Journal of Applied Physics, 1995

The intrinsic breakdown strength of thin SiO2 films formed by plasma-enhanced chemical vapor depo... more The intrinsic breakdown strength of thin SiO2 films formed by plasma-enhanced chemical vapor deposition of tetraethoxysilane was measured using a self-healing technique by applying short-duration voltage pulses. Point defects in the films and other film qualities were examined by instrumental analyses and by optical absorption and luminescence using synchrotron radiation. The intrinsic breakdown strength decreases when the deposition temperature becomes higher than 400° C, in spite of the fact that the optical gap and the density increase and the impurity content decreases. Based on the fact that the film deposited at high temperatures shows absorption at 7.6-eV and luminescence at 4.4-eV, the existence of oxygen vacancies ( ≡Si-Si≡) is suggested. The intrinsic breakdown strength is increased by decreasing oxygen vacancies through oxygen treatment. From these results, it is considered that oxygen vacancies play a crucial role in lowering the breakdown strength. Three possible mechan...

Proton beam writing (PBW) has attracted much attention recently as a technology. We next generati... more Proton beam writing (PBW) has attracted much attention recently as a technology. We next generation micro-fabricatio n fabricated the first single-mode, straight-line waveguides and Y -junction waveguides for A=l.55 flm consisting of PMMA films using the PBW technique.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2019

Defects in buried oxide ͑BOX͒ in Si prepared from the separation by implantation of oxygen ͑SIMOX... more Defects in buried oxide ͑BOX͒ in Si prepared from the separation by implantation of oxygen ͑SIMOX͒ technique under various preparation conditions such as doses of oxygen ͓(0.39-1.9)ϫ10 18 cm Ϫ2 ͔ and anneal temperatures ͑1310-1350°C͒ were investigated by a photoluminescence technique using synchrotron radiation as a light source. Under excitation at 5.0 eV at room temperature, all the SIMOX BOX samples typically exhibit a broad photoluminescence ͑PL͒ band in the range of 2-3 eV, which can be deconvoluted into three Gaussian components at 3.1, 2.6-2.8, and 2.4 eV. The 3.1-and 2.6-2.8-eV bands have lifetimes of about 2-45 ns, while the 2.4-eV band has a much longer lifetime. In addition, some high-dose SIMOX BOX's prepared with multiple oxygen implant steps show a 4.4-eV PL band with a lifetime of about 4 ns associated with a form of oxygen-deficient centers ͑ODC's͒ called ODC͑II͒ in a-SiO 2 , which were suppressed by a supplemental oxygen implantation. The behavior of the short-lived 2-3-eV PL components was sensitive to the oxygen doses and anneal temperatures, and conditions that tended to increase the 2-3-eV PL tended to decrease the 4.4-eV band. Etchback experiments of the BOX layer show that the defects responsible for the 2-3-eV band were located at the BOX close to the superficial Si/BOX interface, while those for the 4.4-eV band exist throughout the whole BOX layer. Comparison with high-temperature oxide grown on Si at 1350°C suggests that the postimplantation, high-temperature anneal results in the generation of defects responsible for the short-lived 2-3-eV bands. Based on the similarities with the PL bands in Si clusters in SiO 2 , we conclude that the 2-3-eV bands in the BOX's are associated with Si clusters in SiO 2. ͓S0163-1829͑99͒03247-6͔

Applied Physics Letters, 1999

Defects in as-grown thermal oxide were investigated by photoluminescence (PL) spectroscopy using ... more Defects in as-grown thermal oxide were investigated by photoluminescence (PL) spectroscopy using synchrotron radiation as a light source. A PL band at 3.3 eV was observed under excitation at 5 eV for dry thermal oxide at room temperature. The PL band was also observed for forming-gas annealed oxide, in which the 3.3 eV PL was either enhanced by subsequent vacuum

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2015

A focused 750 keV proton microbeam was used to fabricate an embedded Mach-Zehnder (MZ) optical wa... more A focused 750 keV proton microbeam was used to fabricate an embedded Mach-Zehnder (MZ) optical waveguide in a polydimethylsiloxane (PDMS) film for interferometer application. The sample position was precisely controlled by a mechanical stage together with scanning microbeam to form an embedded MZ waveguide structure within an area of 0.3 mm  40 mm. The MZ waveguides with core size of 8 lm was successfully embedded in PDMS film at a depth of 18 lm by 750 keV proton microbeam with fluences from 10 to 100 nC/mm 2. The MZ waveguides were coupled with an IR fiber-laser with a center wavelength of 1550 nm and evaluated by using the transmitted intensity images from an IR vidicon camera. The results indicate that the embedded MZ waveguide structure in PDMS achieved single spot light propagation, which is necessary for building optical switching circuits based on polymer MZ waveguides.

Physical Review B, 1996

The generation mechanism of the absorption changes, which cause a photorefractive change through ... more The generation mechanism of the absorption changes, which cause a photorefractive change through the Kramers-Kronig relation in Ge-doped SiO 2 glass, has not been clarified yet. In the present paper, we examined the laser-power dependence of the absorption changes around 5 eV, induced by a KrF excimer laser. The induced absorption around 5 eV is composed of three different components, centering at 4.50, 5.08, and 5.80 eV. The increasing behavior of each absorption component depends strongly on the energy density. The three absorption components reach different saturation levels, depending on the energy density. Furthermore, the absorption induced by a high-power KrF excimer laser is bleached by a laser, the energy density of which is about one-twentieth of the inducing laser. Combining the results of mathematical analysis, it was found that a two-photon process and a one-photon process are, respectively, involved with the induction and the bleach of each absorption. It was also found that the precursor defect, which causes the absorption change, is of an oxygen-deficient type.

Physical Review B, 1992

An electron-spin-resonance (ESR) study was made on the defect centers induced by vacuumultraviole... more An electron-spin-resonance (ESR) study was made on the defect centers induced by vacuumultraviolet (vuv) laser (7.9-eV) irradiation in high-purity silica glasses. %e observed two types of ESR spectra, each consisting of a concentric pair of four-line peaks, in low-OH oxygen-surplus silica produced with plasma methods. Spin-Hamiltonian parameters determined by computer simulation of the experimental ESR line shapes are consistent with oxy-radicals of chlorine. The observed C10"(x=2, 3) radicals are considered to be due to the reaction between chlorine and oxygen, which were both produced by vuv-laser irradiation. I. INrRODUCTION Impurities in silica glass such as transition-metal ions and hydroxyls afFect the optical transmission of the material. ' Thorough elimination of hydroxyl has been found to be critical in the fina development of low-loss optica1 fiber with 0.2 dB/km absorption loss at the wavelength of 1.55 tMm. High-purity silica is generally produced by flame hydrolysis (type III) or plasma oxidation (type IV) of SiC14. In the VAD (vapor-phase axial deposition} process, SOC12 and Clz gases are used as a dehydration reagent. ' Therefore, chlorine is a common impurity abundant (about ten to several thousands ppm} even in the so-called "high-purity" silica. Recently, high-purity silica glass also attracts much attention as a material for ultraviolet (uv}-grade optics for excimer-laser applications. Several reports showed that irradiation with intense uv light from excimer lasers results in the activation of defect precursors or the bond breaking of normal Si-0-Si networks. A nitrogen center was observed in some types of commercially available silica (Suprasil 1 or 2) irradiated with 7.9-eV excimer laser or x-ray. A reaction of hydroxyls has been reported to lead to the production of nonbridging-oxygen hole centers (NBOHC's, =Si-O) and atomic hydrogens (H) in a high-OH silica irradiated with 6.4-eV laser: = Si-OH-+ = Si-0-+H Here, the symbol = and the dot denote a bonding with three separate oxygens and an unpaired spin, respectively. Despite fairly large concentrations

Physical Review B, 1990

High-purity silicas synthesized by various manufacturing methods were studied by electron-spin re... more High-purity silicas synthesized by various manufacturing methods were studied by electron-spin resonance after being irradiated by Arp excimer laser (6.4 eV) at room temperature. E' centers (= Si) are induced in all samples, while nonbridging oxygen hole centers (-=Si-0) appear only in oxygen-surplus silicas and in a sample which has an absorption band at 5.1 eV. The concentration of E' centers varies from sample to sample, ranging between 10' and 10' spins/cm' for the exposure at the average power density of 28 mJ/cm per pulse at 15 Hz for 1 h. The sample dependence regarding the species and concentrations of photoinduced defects is well explained in terms of transformation of preexisting precursors to paramagnetic defects through a two-photon-absorption process.

The Japan Society of Applied Physics, 2016

はじめに:MeVクラスのエネルギーを有する陽子線には、(1)高い直進性、(2)加速エネルギーの大きさで侵入深 さを制御可能、および(3)集束とその走査による直接描画が可能、といった特徴がある。こ... more はじめに:MeVクラスのエネルギーを有する陽子線には、(1)高い直進性、(2)加速エネルギーの大きさで侵入深 さを制御可能、および(3)集束とその走査による直接描画が可能、といった特徴がある。これらの特徴を活かし、 高アスペクト比を有する加工が可能となる。本研究の目的は、集束陽子線描画(Proton Beam Writing, PBW)によ る照射効果を用い P(VDF/TrFE)のウェットエッチング特性を調べることである。フッ化ビニリデン (vinylidene fluoride, VDF)とトリフルオロエチレン(trifluoroethylene, TrFE)のランダム共重合体である P(VDF/TrFE)は、高分子材料の中で最も強い圧電効果と焦電効果をもち、その圧電効果を利用して触覚セ ンサや超音波探傷の超音波トランスデューサなどに利用され 、PBWによる三次元加工により、更なる 高機能化が期待できる。 実験方法:(株)クレハ製P(VDF/TrFE)組成比(75/25)粉末をDMFへ室温環境下で溶解(10 wt%)させた。脱脂 洗浄した10 mm角Si基板へ溶液を滴下し、スピンコーターを用いて 300 rpmを5 s、500rpmを5sで回転 させ、ホットプレート上にて 40 °C、2 hの熱処理を行った。成膜したP(VDF/TrFE)膜へプロトンビームラ イター((株)神戸製鋼所MBS-S1000、加速エネルギー:1.0 MeV、ビームサイズ:1.0 μm)を用いて真空中に て集束陽子線描画を行った。照射図形は、Figure 1に示す 30 μm角パターンを照射量0.3-4.8 μC/mmの範 囲で変化させて照射した。その後、KMnO4(濃度0.25 mol/L)添加KOH水溶液(濃度9 mol/L、80 °C)で1 h の液侵によるアルカリエッチングを行い、純水洗浄、乾燥処理をした。 実験結果および考察: P(VDF/TrFE)膜のエッチング後の観察・加工深さ測定は、共焦点レーザ顕微鏡 (OLYMPUS 社製、LEXT OLS4000) を使用した。ステッチング機能による表面構造を 3D表示により観察 した結果をFigure2に示す。また測定した加工深さの照射量依存性をFigure3に示す。照射量 0.3-2.1 μC/mm の範囲での加工深さは徐々...

The Proceedings of the Symposium on Micro-Nano Science and Technology, 2013

We investigated optical properties of mono-dispersed silica with diameters of several hundred nan... more We investigated optical properties of mono-dispersed silica with diameters of several hundred nanometers. The mono-dispersed silica particles were formed by the Stober method from tetraethoxysilane (TEOS). Structures and impurities of the silica particles were studied by Fourier Transform Infrared (FT-IR) absorption. Impurities such as hydroxyls were removed by an anneal at temperatures more than 500 C. In addition, the peak position around 1100 cm-1 due to the Si-O bonds was changed to higher frequencies during the anneal. This suggests the structures such as Si-O-Si bond angles of mono-dispersed silica were modified during annealing. These silica particles were easily self-assembled on silicon substrates or glass. The states of the self-assembled structures were observed by an optical microscope, an atomic force microscope, and a scanning electron microscope. Two dimensional or three dimensional close-packed structures with were observed.

This paper reports a result carried out in order to clarify the applicability of ion irradiation ... more This paper reports a result carried out in order to clarify the applicability of ion irradiation effects to polymer materials used for optical waveguides. We irradiated 950-keV He+ ions or 1.0-MeV H+ ions to a fluorinated polyimide film to a fluence between 1 × 1014 and 7 × 1016 cm-2, and the film surface was scanned by a profilometer. The depth of a dent induced by the irradiation increases with an increase in the fluence. From the depth of the dent, the projected range of the He+ ions, and the Lorentz-Lorenz equation, the refractive index of the ion-irradiated region was found to increase by 2.9 %. This value agrees with the increment in refractive index measured by spectroscopic ellipsometry, which also increases as the fluence increases. Furthermore, the increment in refractive index, 0.21 %, induced by the irradiation of H+ ions to the fluence of 1 × 1015 cm-2 is comparable to the value, 0.35 %, observed when H+ ions of a similar fluence were irradiated to SiO2 glass. Therefore...

SPIE Proceedings, 1989

Title: Role of nonstoichiometry on UV absorption and luminescence in high-purity silica. Authors:... more Title: Role of nonstoichiometry on UV absorption and luminescence in high-purity silica. Authors: Nishikawa, Hiroyuki; Tohmon, Ryoichi; Nagasawa, Kaya; Ohki, Yoshimichi; Hama, Yoshimasa. Affiliation: AA(Waseda Univ), AB(Sagami Institute of Technology), AC(Waseda Univ). ...

Key Engineering Materials, 2011

Proton beam writing (PBW) has attracted much attention recently as a next-generation micro-fabric... more Proton beam writing (PBW) has attracted much attention recently as a next-generation micro-fabrication technology. It is a direct-drawing technique and does not need any masks to transfer micro-patterns to sample surfaces. In addition, the refractive index of a poly (methyl methacrylate) (PMMA) can be increased by proton-beam irradiation. In this study, we fabricated the first 1.5-μm-band single-mode, straight-line waveguides and Y-junction waveguides consisting of PMMA layers using the PBW technique.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006

High-purity silica glass was irradiated by a focused 15-MeV O 4+ microbeam with diameter of 1 lm ... more High-purity silica glass was irradiated by a focused 15-MeV O 4+ microbeam with diameter of 1 lm up to a fluence of 1.0 • 10 14 ions/cm 2. Spatial distribution of irradiation effects by the O 4+ microbeam on silica glass was investigated by optical microscopy, microphotoluminescence (PL)/Raman spectroscopy and atomic force microscopy (AFM). Distribution of refractive index change and defect formation was visualized by optical microscopy and PL mapping, indicating the structural changes of silica glass along the ion track up to the depth of 10 lm. In addition, we observed deformed side surface with a groove by AFM along the track suggesting the internal compaction in silica glass. This is accompanied by increased threefold rings of SiO 2 network detected by Raman scattering. We also discuss technological implications of these results on the applications of microbeam irradiation effects to the fabrication of microoptical elements.

Journal of Applied Physics, 1991

The intensity change in optical absorption at 3.8, 5.0, and 5.8 eV was measured for thermal treat... more The intensity change in optical absorption at 3.8, 5.0, and 5.8 eV was measured for thermal treatment up to 1000 °C done on silica glass samples manufactured by various methods. It was found that these absorption bands change differently with heat, depending on the synthesis process of the sample. The 3.8-eV absorption band due to peroxy linkage is found to increase with high-temperature treatment when the sample contains dissolved oxygen molecules within the sample. For the sample with no oxygen molecules, high-temperaturetreatment does not alter the absorption intensity at 3.8 eV. The 5.0-eV absorption band is found to decrease by high-temperature treatment. In the case of an oxygen-containingsample, the reaction of oxygen molecules with oxygen vacancy sites is a cause of this decrease. The 5.1-eV band, which was thought to have no temperature dependence, is found to be annealed at a temperature region around 950 °C.

Journal of Applied Physics, 1991

Mechanical stress is applied to high-purity amorphous SiO2 samples by means of fracturing. The el... more Mechanical stress is applied to high-purity amorphous SiO2 samples by means of fracturing. The electron-spin-resonance spectra suggest that the formation of a majority of paramagnetic defects is from cleavage of Si—O—Si bridges in the glass network, but there are some sample-to-sample variances in fracture-induced paramagnetic defects, suggesting cleavage of differing chemical bonding states in the samples. Nonstoichiometric bonds, ≡Si—Si≡ and ≡Si—O—O—Si≡, are assumed to be one reason for the sample dependency. Formation of Si—O—Si strained bonds from mechanical fracturing is confirmed from sequential γ-ray irradiation and heat annealing experiments. The Si—O—Si strained bond is approximately annealed at about 300 °C. By comparing the fracture-induced defects for glass preforms and optical fibers, the change in chemical bonding state can be analyzed. Analysis of mechanical-fracture-induced defects is a strong technique for elucidation of the chemical bonding state of silica glass.

Japanese Journal of Applied Physics, 1995

The intrinsic breakdown strength of thin SiO2 films formed by plasma-enhanced chemical vapor depo... more The intrinsic breakdown strength of thin SiO2 films formed by plasma-enhanced chemical vapor deposition of tetraethoxysilane was measured using a self-healing technique by applying short-duration voltage pulses. Point defects in the films and other film qualities were examined by instrumental analyses and by optical absorption and luminescence using synchrotron radiation. The intrinsic breakdown strength decreases when the deposition temperature becomes higher than 400° C, in spite of the fact that the optical gap and the density increase and the impurity content decreases. Based on the fact that the film deposited at high temperatures shows absorption at 7.6-eV and luminescence at 4.4-eV, the existence of oxygen vacancies ( ≡Si-Si≡) is suggested. The intrinsic breakdown strength is increased by decreasing oxygen vacancies through oxygen treatment. From these results, it is considered that oxygen vacancies play a crucial role in lowering the breakdown strength. Three possible mechan...

Proton beam writing (PBW) has attracted much attention recently as a technology. We next generati... more Proton beam writing (PBW) has attracted much attention recently as a technology. We next generation micro-fabricatio n fabricated the first single-mode, straight-line waveguides and Y -junction waveguides for A=l.55 flm consisting of PMMA films using the PBW technique.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2019

Defects in buried oxide ͑BOX͒ in Si prepared from the separation by implantation of oxygen ͑SIMOX... more Defects in buried oxide ͑BOX͒ in Si prepared from the separation by implantation of oxygen ͑SIMOX͒ technique under various preparation conditions such as doses of oxygen ͓(0.39-1.9)ϫ10 18 cm Ϫ2 ͔ and anneal temperatures ͑1310-1350°C͒ were investigated by a photoluminescence technique using synchrotron radiation as a light source. Under excitation at 5.0 eV at room temperature, all the SIMOX BOX samples typically exhibit a broad photoluminescence ͑PL͒ band in the range of 2-3 eV, which can be deconvoluted into three Gaussian components at 3.1, 2.6-2.8, and 2.4 eV. The 3.1-and 2.6-2.8-eV bands have lifetimes of about 2-45 ns, while the 2.4-eV band has a much longer lifetime. In addition, some high-dose SIMOX BOX's prepared with multiple oxygen implant steps show a 4.4-eV PL band with a lifetime of about 4 ns associated with a form of oxygen-deficient centers ͑ODC's͒ called ODC͑II͒ in a-SiO 2 , which were suppressed by a supplemental oxygen implantation. The behavior of the short-lived 2-3-eV PL components was sensitive to the oxygen doses and anneal temperatures, and conditions that tended to increase the 2-3-eV PL tended to decrease the 4.4-eV band. Etchback experiments of the BOX layer show that the defects responsible for the 2-3-eV band were located at the BOX close to the superficial Si/BOX interface, while those for the 4.4-eV band exist throughout the whole BOX layer. Comparison with high-temperature oxide grown on Si at 1350°C suggests that the postimplantation, high-temperature anneal results in the generation of defects responsible for the short-lived 2-3-eV bands. Based on the similarities with the PL bands in Si clusters in SiO 2 , we conclude that the 2-3-eV bands in the BOX's are associated with Si clusters in SiO 2. ͓S0163-1829͑99͒03247-6͔

Applied Physics Letters, 1999

Defects in as-grown thermal oxide were investigated by photoluminescence (PL) spectroscopy using ... more Defects in as-grown thermal oxide were investigated by photoluminescence (PL) spectroscopy using synchrotron radiation as a light source. A PL band at 3.3 eV was observed under excitation at 5 eV for dry thermal oxide at room temperature. The PL band was also observed for forming-gas annealed oxide, in which the 3.3 eV PL was either enhanced by subsequent vacuum

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2015

A focused 750 keV proton microbeam was used to fabricate an embedded Mach-Zehnder (MZ) optical wa... more A focused 750 keV proton microbeam was used to fabricate an embedded Mach-Zehnder (MZ) optical waveguide in a polydimethylsiloxane (PDMS) film for interferometer application. The sample position was precisely controlled by a mechanical stage together with scanning microbeam to form an embedded MZ waveguide structure within an area of 0.3 mm  40 mm. The MZ waveguides with core size of 8 lm was successfully embedded in PDMS film at a depth of 18 lm by 750 keV proton microbeam with fluences from 10 to 100 nC/mm 2. The MZ waveguides were coupled with an IR fiber-laser with a center wavelength of 1550 nm and evaluated by using the transmitted intensity images from an IR vidicon camera. The results indicate that the embedded MZ waveguide structure in PDMS achieved single spot light propagation, which is necessary for building optical switching circuits based on polymer MZ waveguides.

Physical Review B, 1996

The generation mechanism of the absorption changes, which cause a photorefractive change through ... more The generation mechanism of the absorption changes, which cause a photorefractive change through the Kramers-Kronig relation in Ge-doped SiO 2 glass, has not been clarified yet. In the present paper, we examined the laser-power dependence of the absorption changes around 5 eV, induced by a KrF excimer laser. The induced absorption around 5 eV is composed of three different components, centering at 4.50, 5.08, and 5.80 eV. The increasing behavior of each absorption component depends strongly on the energy density. The three absorption components reach different saturation levels, depending on the energy density. Furthermore, the absorption induced by a high-power KrF excimer laser is bleached by a laser, the energy density of which is about one-twentieth of the inducing laser. Combining the results of mathematical analysis, it was found that a two-photon process and a one-photon process are, respectively, involved with the induction and the bleach of each absorption. It was also found that the precursor defect, which causes the absorption change, is of an oxygen-deficient type.

Physical Review B, 1992

An electron-spin-resonance (ESR) study was made on the defect centers induced by vacuumultraviole... more An electron-spin-resonance (ESR) study was made on the defect centers induced by vacuumultraviolet (vuv) laser (7.9-eV) irradiation in high-purity silica glasses. %e observed two types of ESR spectra, each consisting of a concentric pair of four-line peaks, in low-OH oxygen-surplus silica produced with plasma methods. Spin-Hamiltonian parameters determined by computer simulation of the experimental ESR line shapes are consistent with oxy-radicals of chlorine. The observed C10"(x=2, 3) radicals are considered to be due to the reaction between chlorine and oxygen, which were both produced by vuv-laser irradiation. I. INrRODUCTION Impurities in silica glass such as transition-metal ions and hydroxyls afFect the optical transmission of the material. ' Thorough elimination of hydroxyl has been found to be critical in the fina development of low-loss optica1 fiber with 0.2 dB/km absorption loss at the wavelength of 1.55 tMm. High-purity silica is generally produced by flame hydrolysis (type III) or plasma oxidation (type IV) of SiC14. In the VAD (vapor-phase axial deposition} process, SOC12 and Clz gases are used as a dehydration reagent. ' Therefore, chlorine is a common impurity abundant (about ten to several thousands ppm} even in the so-called "high-purity" silica. Recently, high-purity silica glass also attracts much attention as a material for ultraviolet (uv}-grade optics for excimer-laser applications. Several reports showed that irradiation with intense uv light from excimer lasers results in the activation of defect precursors or the bond breaking of normal Si-0-Si networks. A nitrogen center was observed in some types of commercially available silica (Suprasil 1 or 2) irradiated with 7.9-eV excimer laser or x-ray. A reaction of hydroxyls has been reported to lead to the production of nonbridging-oxygen hole centers (NBOHC's, =Si-O) and atomic hydrogens (H) in a high-OH silica irradiated with 6.4-eV laser: = Si-OH-+ = Si-0-+H Here, the symbol = and the dot denote a bonding with three separate oxygens and an unpaired spin, respectively. Despite fairly large concentrations

Physical Review B, 1990

High-purity silicas synthesized by various manufacturing methods were studied by electron-spin re... more High-purity silicas synthesized by various manufacturing methods were studied by electron-spin resonance after being irradiated by Arp excimer laser (6.4 eV) at room temperature. E' centers (= Si) are induced in all samples, while nonbridging oxygen hole centers (-=Si-0) appear only in oxygen-surplus silicas and in a sample which has an absorption band at 5.1 eV. The concentration of E' centers varies from sample to sample, ranging between 10' and 10' spins/cm' for the exposure at the average power density of 28 mJ/cm per pulse at 15 Hz for 1 h. The sample dependence regarding the species and concentrations of photoinduced defects is well explained in terms of transformation of preexisting precursors to paramagnetic defects through a two-photon-absorption process.