Porosity in Silicon and Silica Thin Films Monitored by Positrons and Positronium

Veen, A. van; Galindo, R. Escobar; Eijt, S.W.H.; Schüt, H.; Gog, Heleen van; Balkenende, A.R.; Theije, F.K. de

doi:10.4028/www.scientific.net/msf.445-446.254

Cited by 3 publications

(4 citation statements)

References 9 publications

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“…Also, from the reports of Van Veen et al, we find there is ample possibility of observing p-Ps component in the various silica gel samples. It is shown in the concerned reference 21 that in silica gel samples with smaller pore size there is considerable increase in shorter component intensities with temperature as there the volume of surface layer is considerably large compared to void volume.…”

Section: Discussionsupporting

confidence: 60%

“…If an unpaired electron (local paramagnetic center) exists (6) at the activated surface as a defect or the strained surface groups (Si-O • ), 22 created due to irradiation with about 10-15 µCi positron source under high vacuum (∼10 -6 Torr), a lifetime quenching effect can be observed. 21,23 Also, from the reports of Van Veen et al, 8 we find there is ample possibility of observing p-Ps component in the various silica gel samples. It is shown in the concerned reference 21 that in silica gel samples with smaller pore size there is considerable increase in shorter component intensities with temperature as there the volume of surface layer is considerably large compared to void volume.…”

Section: Discussionmentioning

confidence: 82%

“…The growing interest in the recent years in the positron annihilation studies on amorphous silica or silica gel material (not only bulk but also thin films) [1][2][3][4][5][6][7] revealed that positronium (Ps) formation occurs with high efficiency in intrinsic microvoids of molecular network which was confirmed with several experimental techniques like positron annihilation lifetime spectroscopy (PALS), 2 angular correlation of annihilation radiation (ACAR), 8 and age-momentum correlation spectroscopy (AMOC). 9 Now that to these events the stimulating and contemplated effect of coherent emission of γ-rays via Bose-Einstein condensation 10 has been added with a further motivation, which in fact beckons more intense investigations in the field.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Temperature on Positronium Annihilation in Silica Gel

Dutta¹,

Ganguly²,

Chatterjee³

et al. 2005

J. Phys. Chem. B

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A systematic temperature-dependent study of positronium annihilation rate within the void spaces (micro- and mesopores) of silica gel material has been performed through positronium annihilation spectroscopy. The results find their plausible interpretation through a novel theoretical explanation based on vibrational interaction of thermally energized atoms on the surface layer of the pores with positronium, which in fact justifies the observed increase in the annihilation rate of the latter, with the increase in temperature.

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Section: Discussionsupporting

confidence: 60%

Section: Discussionmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of Temperature on Positronium Annihilation in Silica Gel

Dutta¹,

Ganguly²,

Chatterjee³

et al. 2005

J. Phys. Chem. B

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“…Surface interaction also could be responsible for quenching of the lifetime or inhibition/enhancement of intensities, 11,26 and in a different context, the effusion of parapositronium has been shown from the internal surface of pores in silica which is ultimately degraded in energy due to collision interactions with the atoms of the pore. 29 This in fact stimulates further enhanced activities on porosity and organized pore structures in siliceous materials.…”

Section: Comparison Of the Methods For Determining The Pore Size: mentioning

confidence: 99%

Structural aspects of synthetic zeolite: A comparative assay through positron annihilation and gas adsorption methods

Dutta

Chatterjee

Ganguly

et al. 2005

Journal of Applied Physics

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Structural arrangement in alumino-silicate compounds (synthetic zeolite species), which encompasses large cavities and channels, have been discussed on the basis of their molecular organization and is further illustrated with the help of micrographs as perceived through transmission electron microscopic studies. The crystallinity aspects and structural defects were investigated through line broadening in x-ray diffraction and the grain sizes through the Debye-Scherrer method. Further, assays of the void size (micro- as well as mesopores) have been performed through positronium annihilation lifetime spectroscopy (PALS) and Brunauer-Emmett-Teller adsorption-desorption isotherm and compared. Despite of some of the limitations of the latter, the final results are in close agreement. The utility of PALS as a microprobe is illustrated through our models. Finally, it has been justified that PALS not only probes the subnanometer micropore sizes efficiently but it also senses the mesopores.

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The lives and deaths of positrons in the interstellar medium

Guessoum

Jean

Gillard

2005

A&A

178

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Abstract. We reexamine in detail the various processes undergone by positrons in the interstellar medium (ISM) from their birth to their annihilation using the most recent results of positron interaction cross sections with atomic and molecular hydrogen, as well as helium. The positrons' lives are divided into two phases: the "in-flight" phase (between ≈1 MeV and tens of eV) and the thermal phase. The first phase is treated with a Monte Carlo simulation that allows us to determine the fraction of positrons that form positronium and annihilate as well as the characteristics of the annihilation emission as a function of the medium conditions. The second phase is treated with a binary reaction rate approach, with cross sections adopted from experimental measurement or theoretical calculations. An extensive search and update of the knowledge of positron processes was thus undertaken. New reaction rates and line widths have been obtained. We investigate the treatment of the complicated interactions between positrons and interstellar dust grains. Fully relevant data were not always available, but we were nonetheless able to reach satisfactory understanding of positron annihilation on grains, both qualitatively and quantitatively. All factors of the problem have been considered, including the grain size distribution and composition, the electric charge of the grains, the backscattering, positronium formation and ejection from the grain, the pick-off annihilation inside them and the partial destruction of dust in the hot regions of the ISM. New reaction rates and widths of the line resulting from the annihilation inside and outside of the grain have been obtained. The final results of our calculations (reaction rates and spectra) showed that dust is only important in the hot phase of the ISM, where it dominates all other processes. Combining the new calculations, we have constructed annihilation spectra for each phase of the ISM, considering various grain contents, as well as an overall combined spectrum for the ISM as a whole.

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Porosity in Silicon and Silica Thin Films Monitored by Positrons and Positronium

Cited by 3 publications

References 9 publications

Effect of Temperature on Positronium Annihilation in Silica Gel

Effect of Temperature on Positronium Annihilation in Silica Gel

Structural aspects of synthetic zeolite: A comparative assay through positron annihilation and gas adsorption methods

The lives and deaths of positrons in the interstellar medium

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