Hisashi Togashi

Mesoporous low-k hydrogen-silsesquioxane films characterized by positron annihilation and other techniques

Abstract Pore characteristics of hydrogen-silsesquioxane low- k films with various porosities were studied by positron annihilation γ -ray spectroscopy and lifetime measurements. From positron annihilation γ -ray spectra, 3 γ annihilation probabilities ( I 3 γ ) of incident positrons were determined. I 3 γ due to the self-annihilation of ortho -positronium escaped out from the film increased with increasing film porosity, indicating the presence of open pores in high porosity films. Positron lifetime measurement showed that the pore is enlarged with increasing film porosity.

Formation of large carbon cluster ions at graphite (HOPG) surfaces by laser irradiation

The formation process of carbon cluster ions by the irradiation of CO2 laser and N2 laser on the different surfaces of graphite (HOPG) has been investigated. Large cluster ions Cn+ (44 ≤ n ≳ 160) were observed by the first irradiation of CO2 laser pulse on a cut surface of which normal axis is perpendicular to the c-axis of the graphite, whereas only small cluster ions were obtained by the irradiation on cleaved surfaces. The N2 laser produced only small cluster ions on the cut and cleaved surfaces. The formation mechanism of the large cluster ions is considered to be the condensation of carbon vapor in gaps between graphite crystallites being exposed at the cut surface.

Properties of laser speckle images produced from narrow elliptical illumination regions.

The properties of laser speckles formed by laser light scattered from narrow elliptical illumination regions on a rough surface are investigated. Analytical expressions are derived for the correlation between 1D pixel data arrays in single speckle images and between averaged pixel data arrays of speckle images from different illumination regions. In deriving the formulas, the phase shift of the scattered light is expressed by a function that approximates the roughness of the illuminated surface. Experimental results are interpreted by the formulas, and the parameters of the formulas are evaluated.

Effects of substrate surfaces in matrix-assisted laser desorption/ionization mass spectrometry

For matrix-assisted laser desorption/ionization (MALDI) mass spectra, undesirable ion contamination can occur due to the direct laser excitation of substrate materials (i.e., laser desorption/ionization (LDI)) if the samples do not completely cover the substrate surfaces. In this study, comparison is made of LDI processes on substrates of indium and silver, which easily emit their own ions upon laser irradiation, and conventional materials, stainless steel and gold. A simultaneous decrease of ion intensities with the number of laser pulses is observed as a common feature. By the application of an indium substrate to the MALDI mass spectrometry of alkali salts and alkylammonium salts mixed with matrices, 2,5-dihydroxybenzoic acid (DHB) or N-(4-methoxybenzylidene)-4-butylaniline (MBBA), the mixing of LDI processes can be detected by the presence of indium ions in the mass spectra. This method has also been found to be useful for investigating the intrinsic properties of the MALDI matrices: DHB samples show an increase in the abundance of fragment ions of matrix molecules and cesium ions with the number of laser pulses irradiating the same sample spot; MBBA samples reveal a decrease in the level of background noise with an increase in the thickness of the sample layer.

IONIC CLUSTERS OF TRIAZINE DERIVATIVES PRODUCED BY MATRIX-ASSISTED N 2 LASER DESORPTION AND CO 2 LASER DESORPTION

Mass spectra of ions from the pyrolytic product of cyanuric trichloride and ammonia were obtained by matrix-assisted N 2 laser desorption time of flight mass spectrometry (TOF -MS) and CO 2 laser desorption Fourier transform mass spectrometry (FT-MS). Cluster ions of which chemical formulae are expressed by C x N 2 x-y H 2 x -3 y +1 + were found and were assigned as a series of ionic clusters of triazine oligomers.