Analysis of positron diffusion data

Huomo, H.; Soininen, E.; Vehanen, A.

doi:10.1007/bf00616989

Cited by 25 publications

(15 citation statements)

References 27 publications

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“…The difference in the diffusion length between the ϩ50 and Ϫ50 V will give an estimate of the error. Huomo et al 40 proposed another method to analyze the S and F parameters when nonthermal positrons are present. They chose a minimum implantation energy for the data analysis and assumed that S is a nearly linear function of F. The deviation from linearity is mainly associated with nonthermal positrons reaching the surface.…”

Section: Analysis Of Diffusion Datamentioning

confidence: 99%

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Positron diffusion in solid and liquid metals

et al. 1999

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We made a systematic study of the diffusion of positrons in several liquid and solid metals with a vertical positron beam. Several interesting effects have been observed by studying the line shape parameter S, the fraction of positronium formed at the surface, and the diffusion length of positrons in liquids. The S parameter and the fraction of positronium created and released at the surface ͑F parameter͒ were measured as a function of temperature in the solid and liquid phases of Ga, Bi, Na, Sn, In, and Pb. An appreciable change just below or across the melting point in the S parameter was measured in metals where positron trapping has not been observed ͑Ga, Bi, and Sn͒. In metals where positron trapping occurs in the solid phase, there is a small change or none in the S parameter ͑Pb and In͒, which indicates that there is only a small change in the nature of the traps. Positron trapping was seen in all the liquid metals, indicating that they have a high density of defectlike sites that trap positrons. The diffusion length of positrons in the liquid was extracted from the experimental data. In Ga, Bi, and Sn, there is a large drop in the diffusion length upon melting; in Pb and In, only a small change or none is seen. In all liquid metals the diffusion length increases as the temperature increases, suggesting that diffusion is related to trapping in temporary fluctuations in the liquid's structure. The positron moves from fluctuation to fluctuation. The size of the traps strongly depends on temperature, and so when it increases, the positron's hopping motion increases. We also measured the reemitted energy spectra of positrons from liquid and solid surfaces. No appreciable change was seen with increasing temperature or when the metals melted.

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Section: Analysis Of Diffusion Datamentioning

confidence: 99%

“…Because the mean free path for nonthermal positrons is short, 34 they can reach the surface only if the mean implantation depth is small. 40 Thus the number of nonthermal positrons reaching the surface decreases rapidly as the incident energy is increased. Evidence that the data in Fig.…”

Section: Measurements Of Diffusion Length In Ga Bi Sn and Namentioning

confidence: 99%

Positron diffusion in solid and liquid metals

et al. 1999

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“…Previously, S maxima at low energy were also found on foils with no anodizing treatment, 7,8,17 and were shown to be due to voids in the Al metal near the oxide/aluminum interface. 7,8 In Fig.…”

Section: S-energy Profiles-mentioning

confidence: 90%

Positron Annihilation Spectroscopy Study of Interfacial Defects Formed by Anodic Oxidation of Aluminum

Hebert

Gessmann

Lynn

et al. 2004

J. Electrochem. Soc.

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Positron annihilation spectroscopy ͑PAS͒ measurements were carried out to characterize open-volume defects associated with anodic oxidation of aluminum. The annihilation fractions with low and high momentum electrons ͑S and W spectral lineshape parameters, respectively͒ of the annihilation photopeak were determined, as a function of the positron beam energy. A subsurface defect layer, containing nanometer-scale voids in the metal near the metal/oxide film interface, was found after oxide growth, and was shown to contain new voids created by anodizing. Such interfacial voids in the metal are of interest because of their possible role as corrosion initiation sites. The S parameter characterizing the defect-containing layer (S d ) was obtained by simulation of the S-energy profiles. On samples with two different surface conditions, S d remained constant at its initial value during anodizing. Because S d is related to the void volume fraction in the interfacial metallic layer containing the voids, that result suggests that formation of metallic voids, and their subsequent incorporation into the growing oxide layer, occurred repeatedly at specific favored sites.

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“…H =(l -jfo)Fs-^(\ -F^) is a normalization factor [7]. Sps is the S parameter associated with the fraction (j /o) of positrons that annihilate after forming para-Ps (note that the fraction j/o that form ortho-Ps do not contribute to S because they undergo 3/ photon annihilation), 5ss is associated with the fraction (1 -/o) annihilating from the surface state.…”

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confidence: 99%

“…This formalism does not include nonthermal positrons, which affect S and F measurements [3,7] at low implantation energies. Huomo, Soininen, and Vehanen [7] have proposed to choose a minimum implantation energy for the data analysis.…”

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Positron diffusion in solid and liquid Ga and Bi

et al. 1991

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The diffusion length of positrons in Ga and Bi was measured using a positron beam. For Ga, there is a drop from 1200(100) to 60(5) A upon melting; this is interpreted in terms of creation of centers that trap the positron. As the temperature of the liquid is increased, the diffusion length increases, suggesting that the size of the traps changes. For Bi, the diffusion length decreases from 500(30) to 190(10) A upon melting, and increases slightly as the temperature is increased. This drop is interpreted as increased positron-ion scattering, and not positron trapping as in Ga.

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Analysis of positron diffusion data

Cited by 25 publications

References 27 publications

Positron diffusion in solid and liquid metals

Positron diffusion in solid and liquid metals

Positron Annihilation Spectroscopy Study of Interfacial Defects Formed by Anodic Oxidation of Aluminum

Positron diffusion in solid and liquid Ga and Bi

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