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1

Observation of Vacancies in Ga_{1-x}Mn_xAs with Positron Annihilation Spectroscopy

100%

Tuomisto F., Slotte J., Saarinen K., Sadowski J.

Acta Physica Polonica A

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2003

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vol. 103

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issue 6

601-606

EN

Positron annihilation spectroscopy can be used to determine the role of vacancy defects in semiconductors, by identification and quantification of the vacancies and their chemical surroundings. We have studied 0.5-0.8μm thick low temperature MBE GaMnAs layers with Mn content 0.5--5% and different As_2 partial pressures at growth. The Doppler broadening results show that the Ga vacancy concentration in the layers decreases with increasing Mn content and decreasing As_2 partial pressure.

2

Stability and Performance Characteristics of a Digital Positron Lifetime Spectrometer

100%

Aavikko R., Rytsölä K., Nissilä J., Saarinen K.

Acta Physica Polonica A

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2005

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vol. 107

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issue 4

592-597

EN

We summarize the setup and performance tests of a digital positron lifetime spectrometer presently in routine use at HUT/Laboratory of Physics. The performance of the spectrometer is found to be equal to or better than that of an analog spectrometer with similar detectors. We present also results on measuring the stability of the system, which is found to be similar to that of analog spectrometers: variation in the time-zero of the spectrometer is found to be ≈10 ps/week. We suggest that the remaining instabilities of the spectrometers originate primarily from the detectors.

3

Relations Between Hole Volume and Macroscopic Volume in Various Polymers

88%

Dlubek G., Alam M., Saarinen K., Stejny J., Fretwell H.

Acta Physica Polonica A

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1999

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vol. 95

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issue 4

521-526

EN

Different definitions of the free volumes are discussed and related to the total specific volume and to the local free (hole) volume. Positron lifetime measurements are reported for polyethylene, polytetrafluoroethylene, and CR39-copolymers. Two long-lived components appear in polyethylene and polytetrafluoroethylene, which were attributed to o-Ps annihilations in crystalline regions and in holes of the amorphous phase. From a relation between the coefficients of the thermal expansion of macroscopic and hole volume, the fractional hole volume h and from this the number of holes, N, is estimated. Values of T_{g}=195 K, h_{g}=4.5% (polyethylene) and 5.7% (polytetrafluoroethylene) and N_{g}=0.73 nm^{-3} (polyethylene) and 0.36 nm^{-3} (polytetrafluoroethylene) were obtained. In semicrystalline polymers these values agree with estimates obtained from the densities of the crystalline and amorphous phases. The effect of cross-linking on the free-volume properties of CR39-copolymer networks was studied. The comparison of the hole volume with the specific volume allowed us to estimate the number density of holes to ≈1 nm^{-3}.

4

Positron Annihilation Characteristics in Zn_{1-x}Mg_{x}Se Mixed Crystals

64%

Firszt F., Szatkowski J., Męczyńska H., Łęgowski S., Saarinen K., Hautojarvi P., Plazaola A., Reniewicz H., Dobrzyński L., Chabik S.

Acta Physica Polonica A

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1998

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vol. 94

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issue 2

300-304

EN

Positron annihilation characteristics as a function of composition and annealing in zinc vapour were measured and compared with photoluminescence spectra for Zn_{1-x}Mg_{x}Se mixed crystals with 0 ≤ x ≤ 0.6. The positron annihilation data show that there is a substantial number of divacancies present in the system under study. The concentration of such defects is reduced at least by the factor of two upon annealing in zinc vapour.

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Observation of Vacancies in Ga_{1-x}Mn_xAs with Positron Annihilation Spectroscopy

Stability and Performance Characteristics of a Digital Positron Lifetime Spectrometer

Relations Between Hole Volume and Macroscopic Volume in Various Polymers

Positron Annihilation Characteristics in Zn_{1-x}Mg_{x}Se Mixed Crystals