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Combined Analyses of Ion Beam Synthesized Layers in Porous Silicon

100%

Ramos A., Pászti F., Horváth Z., Vázsonyi É., Conde O., da Silva M., da Silva M., Soares J.

Acta Physica Polonica A

2001

vol. 100

issue 5

773-780

High dose ion implantation was used to form polycrystalline silicide films on porous silicon with different native concentrations of light impurities (C and O). Porous silicon layers severalμm thick were implanted with 170 keV Cr^+ ions to fluences of 3×10^{17} ions/cm^2 both at room temperature and 450^ºC. Similar samples were implanted with 100 keV Co^+ ions to fluences of 2×10^{17} ions/cm^2 at room temperature, 350ºC, and 450ºC. The formed silicide compounds were studied by Rutherford backscattering spectrometry, elastic recoil detection, glancing incidence X-ray diffraction, and four point-probe sheet resistance measurements. Selected Co implanted samples were analysed by cross-section transmission electron microscopy. Results show that the light impurities were partially expelled from the forming silicide layer. Combining cross-section transmission electron microscopy with ion beam methods it was possible to show that, in the implanted region, the porous structure collapses and densifies during implantation, but the underlying porous silicon remains intact. The layer structure, as well as the quality and type of the formed silicide, were found to depend on the original impurity level, implantation temperature, and annealing.

Positronium Trapping in Porous Solids: Means and Limitations for Structural Studies

72%

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

2005

vol. 107

issue 5

729-737

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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2 Acta Physica Polonica A

1 2005

1 2001

2 Pászti F.

1 Azenha M.

1 Beyer H.

1 Caullet P.

1 Conde O.

1 Duplâtre G.

1 Ferreira Marques M.

1 Gordo P.

1 Horváth Z.

1 Kajcsos Z.

1 Kótai E.

1 Liszkay L.

1 Lohonyai L.

1 Lopes Gil C.

1 Lázár K.

1 Patarin J.

1 Pál-Borbély G.

1 Ramos A.

1 Soares J.

1 Szilágyi E.

1 Varga L.

1 Vázsonyi É.

1 da Silva M.

1 de Lima A.

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Combined Analyses of Ion Beam Synthesized Layers in Porous Silicon

Positronium Trapping in Porous Solids: Means and Limitations for Structural Studies