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1
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Study on the Structure of Defects in a-Si:H Films by Positron Annihilation and Micro-Raman Spectroscopy

100%
Gordo P., de Lima A., Ferreira Marques M., Kajcsos Z.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1373-1378
EN
Thin films of hydrogenated amorphous silicon deposited on glass and crystalline silicon substrates by rf plasma enhanced chemical vapor deposition at different rf power were studied using slow positron beam and the Raman scattering spectroscopy in order to verify the influence of that deposition parameter on the film defect structure and on the degree of disorder. By positron annihilation spectroscopy, it was found that there are mainly two types of defects in the films: large vacancy clusters or voids and small vacancy type defects. By micro-Raman spectroscopy it was observed that the degree of structural disorder is lower for the film with large vacancy clusters and this finding was related to structural relaxation process. Light soaking induced changes attributed to major atomic rearrangements were also observed.
2
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Studies of the Cu-Mn System

100%
Nicht E.-M., Brauer G., Kajcsos Z., Molnar B.
Acta Physica Polonica A
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1995
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vol. 88
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issue 1
205-210
EN
The superstructures Cu_{3}Mn and Cu_{5}Mn have been characterized for the first time by X-ray and differential scanning calorimetry measurements. In addition, positron lifetime measurements are presented in order to show the defect structure of these alloys. It turned out that the annealing behaviour is equal for the two different alloys and the two different deforming processes. An annealing temperature of 300°C is not sufficient to obtain a defect free state.
3
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Free-Volume Studies in Polycaprolactone/Poly(propylene oxide) Urethane/Urea Membranes by Positron Lifetime Spectroscopy

76%
Ferreira Marques M., Gordo P., de Lima A., Queiroz D., Norberta de Pinho M., Major P., Kajcsos Z.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1359-1364
EN
Positron annihilation lifetime spectroscopy was used to study the free volume parameters in polypropylene oxide-based tri-isocyanate terminated prepolymer/polycaprolactone diol bi-soft urethane/urea membranes (PU/PCL) with PCL content from 5 up to 25 wt%. Positron annihilation lifetime spectroscopy measurements carried out in the temperature range 298-324 K mirrored the phase separation of the various soft and hard segments present in the membranes. The size and amount of free volume holes determined by positron annihilation lifetime spectroscopy appear to be correlated with the CO_2 gas permeability through the membranes.
4
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Positrons and Positroniu m in Grainy and Porous Solids

64%
Kajcsos Z., Liszkay L., Duplâtre G., Varga L., Lázár K., Pál-Borbély G., Beyer H., Lohonyai L., Caullet P., Patarin J.
Acta Physica Polonica A
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2001
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vol. 99
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issue 3-4
399-406
EN
Systematic investigations have been performed using positron annihilation techniques on micrograins of crystalline powders (e.g., MgO, Al_2O_3, SiO_2) and on various zeolites (e.g., silicalite 1, Na-X, Na-Y, ZSM-5, mordenite) aiming at a better under standing of the formation and decay of the long-lived ortho-positronium states. The techniques were lifetime spectroscopy, Doppler-effect measurements and the recording of the full energy distribution of the annihilation radiation. The influences of heat treatment, sample evacuation and presence of gases were investigated. Lifetimes over 130 ns and o-Ps fractions of about 30% were found. A strong correlation of positron annihilation technique data with a water content of the samples was evidenced. Possible pictures of the formation and decay of ortho-positronium in porous media are discussed.
5
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Positron and Positronium Trapping in Heat Treated Zeolites (Ceramics), the Effect of Swift Heavy Ion Irradiation

52%
Major P., Kajcsos Z., Liszkay L., Zalán P., Kosanović C., Bosnar S., Subotić B., Lázár K., Skuratov V., Havancsák K., Gordo P., Ferreira Marques M.
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EN
A systematic study of zeolite precursor gels, zeolites, and products of their recrystallization to ceramics was carried out in presence of various alkali ions. The investigation of radiation damage induced by high-energy ion beam irradiation with swift heavy ions (Bi ions at 670 MeV energy with 4×10^{12} ion/cm^2 fluence) was also included. The shortening of lifetimes found after irradiation in ceramics might probably be ascribed to interactions of o-Ps with free radicals and other quenching agents created through the ion irradiation. These lifetime-shortening interactions probably partly hide the o-Ps trapping in free volume sites.
6
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Positronium Trapping in Porous Solids: Means and Limitations for Structural Studies

46%
Kajcsos Z., Liszkay L., Duplâtre G., Varga L., Lohonyai L., Pászti F., Szilágyi E., Lázár K., Kótai E., Pál-Borbély G., Beyer H., Caullet P., Patarin J., Azenha M., Gordo P., Lopes Gil C., de Lima A., Ferreira Marques M.
Acta Physica Polonica A
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2005
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vol. 107
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issue 5
729-737
EN
Positron annihilation techniques are used for the structural investigation of solids but the interpretation of results in grainy and porous media is still unclear. A unique picture can be obtained assuming that the dominant process is Ps trapping in competing "extended free volume" sites. In samples with a large amount of free volumes near-saturation Ps trapping will rule the lifetime pattern, and very long lifetimes of over 100 ns might arise from o-Ps trapped in mesopores. It is shown that lifetime parameters must be corrected for the 3γ/2γ counting efficiency ratio. The results demonstrate the high sensitivity of Ps to mesopores in zeolites but also that Ps-trapping poses limitations on the applicability of lifetime to structural investigation in porous systems. The evolution of the lifetime spectra upon changes in the sample and measuring conditions should be considered in a complex way, observing not only changes in some selected components but in the whole lifetime pattern simultaneously.
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