Formation of periodic structures by the space-selective precipitation of Ge nanoparticles in channel waveguides

Thermally stabilized channel waveguides with Bragg gratings were fabricated by the space-selective precipitation technique of crystalline Ge nanoparticles using KrF excimer laser irradiation. The periodic structures consisting of Ge nanoparticles were formed in Ge-B-SiO₂ thin glass films after exposure to an interference pattern of the laser followed by annealing at 600 °C. The channel waveguides with the periodic structures were fabricated by the cladding of the patterned Cr layers on the films. The diffraction peak for the TE-like mode of 11.8 dB depth was observed clearly at a wavelength of 1526.4 nm, indicating that the periodic structure also served as the optical band-pass filter in optical communication wavelength. The spectral shape, diffraction efficiency, and diffraction wavelength remained unchanged even after annealing at 400 °C. Furthermore, a low temperature dependence of the diffraction wavelength - as low as 8.1 pm/°C - was achieved. The diffraction efficiency was further enhanced after subsequent annealing at 600 °C. The space-selective precipitation technique is expected to be useful for the fabrication of highly reliable optical filters or durable sensing devices operating at high temperature.     

Laser desorption/ionization on porous silicon mass spectrometry for accurately determining the molecular weight distribution of polymers evaluated using a certified polystyrene standard.

Desorption/ionization on porous silicon-mass spectrometry (DIOS-MS) is a novel soft ionization MS technique that does not require any matrix reagent, ideally resulting in fewer obstructive peaks in the lower mass region. In this study, the etching conditions of porous silicon spots as an ionization platform of DIOS-MS were investigated for determining the molecular weight distribution (MWD) of polymers. To evaluate the accuracy of DIOS mass spectra observed using porous silicon spots prepared under various etching conditions, a certified polystyrene (PS) standard sample with an average molecular weight of ca. 2400 was used as a model sample. By optimizing the etching conditions, the MWD of the PS sample could be accurately observed by DIOS-MS using both p-type and n-type porous silicon spots. Especially, in the case of a suitable n-type spot, an accurate peak distribution with very fewer obstructive background peaks could be observed using the minimum laser power, comparable to the conventional matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS).     

Fluorescence analysis of p-hydroxymethamphetamine in urine by thin-layer chromatography.

A highly-sensitive analytical method for the detection of p-hydroxymethamphetamine (pOHMA) in urine is presented. The proposed method combines liquid-liquid extraction with acetonitrile and solid-phase extraction by thin-layer chromatography (TLC) with oxidation using potassium hexacyanoferrate(III) and sodium hydroxide to detect the fluorophor of pOHMA. The detection limit for pOHMA is 10 ng (n = 3). The analysis of pOHMA in forensic samples is successfully performed, without interference from endogenous fluorophors, yielding concentrations in the appropriate range for methamphetamine abusers.     

Photochemistry and photocuring properties of thiol‐substituted α‐aminoalkylphenone as radical photoinitiator

Thiol‐substituted α‐aminoalkylphenone was newly developed as a radical photoinitiator. Introduction of the thiol group drastically improved photosensitivity in an alkaline developable resist formulation composed of a prepolymer and a multifunctional acrylate monomer. The improvement in the photocuring speed was explained by a mechanism based on chain transfer reaction of the thiol group. Time‐resolved electron spin resonance (ESR) spectroscopy indicated that the thiol group attached to the chromophore does not influence the photochemical process to generate primary radicals. The photoinitiation of α‐aminoalkylphenone can be spectrally sensitized by 2,4‐diethylthioxanthone (DETX). However, thiol‐substituted α‐aminoalkylphenone showed smaller spectral sensitization than the corresponding compound without a thiol group. Time resolved laser flash photolysis indicated that the rate constant of the quenching of the triplet state of DETX by thiol‐substituted α‐aminoalkylphenone is twice as large as that by the corresponding one without a thiol group. This suggests that, besides energy transfer from DETX in the excited triplet state to the α‐aminoalkylphenone, the thiol group quenches the excited triplet state of DETX via charge transfer and/or hydrogen transfer, as supported by the ESR analysis using a spin trapping technique, and lowers the efficiency of the spectral sensitization effect. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1684–1695, 2005     

Self homotopy groups with large nilpotency classes

We demonstrate that for any n>0 there exists a compact connected Lie group G such that the self homotopy group [G,G] has the nilpotency class greater than n, where [G,G] is a nilpotent group for a compact connected Lie group G.     

Determination of bisphenol A and 4-nonylphenol in human milk using alkaline digestion and cleanup by solid-phase extraction.

A highly sensitive and selective method based on alkaline digestion for the simultaneous determination of bisphenol A (BPA) and 4-nonylphenol (NP) was developed. The method consists of digestion of the matrix with ethanolic KOH, extraction with diethyl ether under a mild alkaline condition, cleaning with successive aminopropyl (NH2) cartridges and derivatization followed by a GC-MS analysis. The assay accuracies, expressed as recoveries, were 82 - 113% for BPA and 89 - 97% for NP. The limits of detection of BPA and NP were 0.09 ng/g and 0.50 ng/g, respectively. The procedure will be reliable for the trace analysis of BPA and NP in human milk, since alkaline digestion can diminish their documented association with protein.     

Piano-Convex Solid Immersion Mirror with a Small Aperture for Near-field Optical Data Storage

We proposed and developed a new solid immersion mirror (SIM) for near-field optical data storage. The SIM has some advantages, especially in manufacturing, because its shape is similar to a general plano-convex lens. Making an aperture of about 130 nm in diameter just on the focus area of the SIM, a bit-data recording onto a photochromic thin film was carried out. Minimum diameter of the written marks was estimated to be 180nm. We also demonstrated readout experiments where a recorded medium was rotating and a gap between the SIM and the disk was controlled with capacitance sensing. This is the first result of reading with a rotating disk using an SIM containing a small aperture.This paper was originally presented at the 10th Optical Near Field Workshop, which was held on June 27-28, 2001 at Osaka University, organized by the Optical Near Field Group, the Optical Society of Japan, an affiliate of the Japan Society of Applied Physics.