Grzegorz P. Karwasz

One century of experiments on electron-atom and molecule scattering: A critical review of integral cross-sections

p. 267. Iga I., Perreira M. E., Lee M. T., Nogueira J. C. and Miglio H. C., International Symposium on Electron-Molecule Collisions and Swarms, Tokyo, edited by Y. Hatano et al. (Tokyo) 1999, Abstract, p. 123. Itikawa Y., Phys. Rep., 46 (1978) 117. Ito Y., Fujimaki A., Kobayashi K. and Tokue I., Chem. Phys., 105 (1986) 417. Karwasz G. P., Brusa R. S., Piazza A. and Zecca A., Phys. Rev. A, 59 (1999) 1341. Kasai T., Matsunami T., Fukawa T., Ohoyama H. and Kuwata K., Phys. Rev. Lett., 70 (1993) 3864. Keller O., Mang C., Nikola M. and Schulz G., Z. Phys. D, 37 (1996) 315. Keller O., Mang C., Nikola M. and Schulz G., Eur. Phys. J. D, 4 (1998) 309. Krishnakumar E. and Nagesha K., XVII International Conference on Physics of Electronic and Atomic Collisions, Aarhus, edited by T. Andersen et al. (Aarhus University) 1993, Abstract, p. 343. Krzysztofowicz A. M. and Szmytkowski Cz., Chem. Phys. Lett., 219 (1994) 86. Krzysztofowicz A. M. and Szmytkowski Cz., J. Phys. B, 28 (1995) 1593. Kusakabe M., Ito Y. and Tokue I., Chem. Phys., 170 (1993) 243. Ling X., Smith K. A. and Dunning F. B., Phys. Rev. A, 47 (1993) R1. Martinez R., Terron J., Merelas I., Rayo M. N. S. and Castano F., J. Phys. B, 31

Absolute electron-scattering total cross section measurements for noble gas atoms and diatomic molecules

Absolute electron-scattering total cross sections for noble gas atoms (He, Ne, Ar, Kr, and Xe) and H,, N, , CO, NO, and 0, molecules have been measured at impact energies between 0.5 and 250eV by the linear transmission method with the same experimental set-up for all the investigated targets. Generally, our total cross sections have been found to be in good agreement with other data with respect to shape. Some systematic discrepancies in magnitude still exist between results of different groups, especially at the lowest applied energies and in the energy range where the cross sections peak. At these energies, new measurements should be carried out before establishing a reference set of data.

Doppler-broadening measurements of positron annihilation with high-momentum electrons in pure elements

Doppler-broadening measurements of the electron–positron annihilation line in twenty-seven single-element samples are presented. A coincidence technique has been used to suppress the background and to evidence the contribution of positron annihilation with core electrons. Systematic dependences on the atomic number of the target material are found in ratio curves obtained dividing the measured spectra by the spectrum of a reference material. The positron lifetime technique has been used to detect the presence of positron traps in all the samples. The change in the highmomentum part of the annihilation line due to positron trapping is illustrated. The measured data are in a good qualitative agreement with recent theoretical calculation and constitute the most complete measurement series, up to now, to establish a future data-base for positron annihilation spectroscopy. 2002 Elsevier Science B.V. All rights reserved.

HELIUM-IMPLANTED SILICON : A STUDY OF BUBBLE PRECURSORS

The interaction of helium atoms with the radiation damage imparted to (100) silicon single crystal by He+ implantation at 5×1015 cm−2, 20 keV, and liquid–nitrogen temperature is investigated by means of various complementary techniques during and after thermal treatments. Thermal programmed desorption was used to study the dissociation kinetics of helium from the defects and to plan suitable heat treatments for the other techniques. The helium profiles were determined by 8 MeV 15N2+ elastic recoil detection, quantitative data on damage were obtained by channeling Rutherford backscattering spectrometry, double crystal x-ray diffraction, and positron annihilation spectroscopy. Isothermal treatments at 250 °C produce first helium redistribution and trapping in vacancy-like defects, rather than helium desorption from traps. The process is thermally activated with an effective activation energy, dispersed in a band from 1.1 to about 1.7 eV. For higher temperature treatments (2 h at 500 °C) the traps are almost...

Porosity in low dielectric constant SiOCH films depth profiled by positron annihilation spectroscopy

The 3γ annihilation of orthopositronium and the Doppler broadening of the positron annihilation line have been measured by implanting low energy positrons in low dielectric constant (low-k) SiOCH films. The evolution and stability of film porosity with thermal treatments in the 400–900 °C temperature range has been studied. The films have been produced by plasma enhanced chemical vapor deposition and after annealing in N2 atmospheres at 480 °C have been treated in N2+He plasma. The minimum free volume of the pores in the as-produced samples has been estimated to correspond to that of a sphere with radius r=0.6 nm. The treatment in the N2 plasma was found to seal the pores up to 45 nm depth. Both the composition of the films (as obtained by Rutherford backscattering spectroscopy and elastic recoil detection analysis) and the chemical environment of the pores probed by positrons were found to be very stable up to 600 °C thermal treatment. Above such a temperature a reduction of the hydrogen content accompan...

A new electrostatic positron beam for surface studies

A new electrostatic positron beam has been constructed and tested. The energy range spans more than three decades, from less than 50 eV to more than 50 keV. The machine can operate in a low-energy mode (50 eV to 2 keV) with a beam diameter (FWHM) from 2.9 to 1.7 mm or in a high-energy mode (1 keV to 50 keV) with a FWHM from 1.4 to 1.0 mm. The transverse spot position on the target is very stable, with wandering being much smaller than the beam diameter. The apparatus transmission function is very flat, with an intensity change of only 30% when going from 10 eV to 50 keV. The product of moderation and optical transmission efficiency is , corresponding to 800-1000 with a 1 mCi source. The apparatus shows low noise in S-parameter measurements. The background of the high-energy wing of the annihilation line is also one of the best reported. Optical and constructional details are given.

Absolute total cross sections for electron scattering on CH4 molecules in the 1-4000 eV energy range

Absolute total cross sections for electron-methane scattering have been measured in the energy range from 0.9 to 4000eV in two separate experiments. The present results, the first available above 500 eV, are in good agreement with other recent experimental and theoretical data. The law energy scattering is dominated by a shape resonance; a broad hump has been detected centred around 100eV. A short critical review of previous measurements is given.

Low energy electron driven reactions in single formic acid molecules (HCOOH) and their homogeneous clusters

Low energy (0-3 eV) electron attachment to single formic acid (FA) and FA clusters is studied in crossed electron/molecular beam experiments. Single FA molecules undergo hydrogen abstraction via dissociative electron attachment (DEA) thereby forming HCOO(-) within a low energy resonance peaking at 1.25 eV. Experiments on the isotopomers HCOOD and DCOOH demonstrate that H/D abstraction occurs at the O-H/O-D site. In clusters, electron attachment is strongly enhanced leading to a variety of negatively charged complexes with the dimer M2(-) (M[triple bond]HCOOH) and its dehydrogenated form M (M-H)(-) as the most abundant ones. Apart from the homologous series containing the non-dissociated (Mn(-)) and dehydrogenated complexes (M(n-1) (M-H)(-), n > or = 1) further products are observed indicating that electron attachment at sub-excitation energies (approximately 1 eV) can trigger a variety of chemical reactions. Among these we detect the complex H2O (M-H)(-) which is interpreted to arise from a reaction initiated in the cyclic hydrogen bonded dimer target. In competition to hydrogen abstraction yielding the dehydrogenated complex M (M-H)(-) the abstracted hydrogen atom can react with the opposite FA molecule forming H2O and HCO with the polar water molecule attached to the closed shell HCOO(-) ion. The FA dimer can thus be used as a model system to study the response of a hydrogen bridge towards dehydrogenation in DEA.

Positron annihilation study of vacancy-like defects related to oxygen precipitates in Czochralski-type Si

We report the direct measurement of vacancy-like defects related to oxygen in the oxygen precipitation process in Czochralski Si. The vacancy-like defects were detected by measuring the positron lifetime and narrowing of the positron–electron annihilation momentum distribution. Oxygen atoms surrounding the vacancy-like defects were detected by analyzing the high-momentum part of the positron–electron momentum distribution measured by a Doppler broadening coincidence technique. It was found that the majority of the defects associated with oxygen have an effective open volume smaller than that of a silicon monovacancy.

Absolute total cross section measurements for electron scattering on benzene molecules

The absolute total cross section for electron scattering on C,H, molecules has been measured in two distinct electron-transmission experiments for impact energies between 0.6 eV and 3.5 keV. The present results are compared with other total cross section experimental data.