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Digitale Medien

Phase transformations and vacancy formation energies of transition metals by positron annihilation (1979)

Matter, H. ; Winter, J. ; Triftshäuser, W.

Springer

Applied physics 20 (1979), S. 135-140

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ISSN: 1432-0630

Schlagwort(e): 78.70 ; 71.60 ; 61.70

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract The technique of the coincidence count rate at the peak of the angular correlation curve (CCR) in positron annihilation has been applied to the investigation of vacancy formation energies in thermal equilibrium in nickel, cobalt, and iron. The monovacancy formation energyE 1v/F has been determined to (1.55±0.05) eV and (1.34±0.07) eV for nickel and cobalt, and (1.60±0.10) eV for α-iron, and (1.40±0.15) eV for γ-iron, respectively. The structural phase transformations in cobalt (693 K) and iron (1183 K, 1663 K) are exhibited by discontinuities of the CCR. In the case of cobalt the CCR follows exactly the change of the thermal expansion at the transition temperature. The temperature dependence of the CCR in the prevacancy region is found to be proportional to the thermal expansion for all metals investigated.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00885934

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Digitale Medien

Vacancy-impurity interaction in dilute iron alloys by positron annihilation (1982)

Triftshäuser, W. ; Matter, H. ; Winter, J.

Springer

Applied physics 28 (1982), S. 179-187

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ISSN: 1432-0630

Schlagwort(e): 78.70 ; 61.70

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract Positron annihilation measurements of the coincidence count rate at the peak of the angular correlation curve (CCR) have been performed as a function of temperature for the alloy systemFeTi in a concentration range up to about 1.3 at. %. The concentration dependence of the effective vacancy formation enthalpy (H 1V F )eff suggests the existence of an attractive interaction between vacancies and the impurity atoms. It will be shown that the description of the vacancy concentration in an alloy according to the Lomer model is not valid in this case, because it neglects binding of vacancies to solute atom pairs and to higher agglomerates. The application of a model proposed by Dorn and Mitchell gives evidence that beyond the binding of a vacancy to a single solute atom in the concentration range investigated also aggregates of a vacancy bound to two and three foreign atoms must be taken into account. The analysis of the measurements according to the method of Hehenkamp and Sander gives values for the respective vacancy-solute-atom(s) binding enthalpies H 1 B =0.25eV, H 2 B =0.53eV and H 3 B =0.91eV. The discussion of the temperature and solute-atoms concentration dependence of the vacancy concentration suggests a much more complicated behaviour than for pure metals even at low solute-atom concentrations.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00617984

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Digitale Medien

Investigations of positron lifetimes in InP with a pulsed positron beam (1995)

Willutzki, P. ; Störmer, J. ; Britton, D. T. ; [weitere]

Springer

Applied physics 61 (1995), S. 321-324

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ISSN: 1432-0630

Schlagwort(e): 78.70 ; 68.55 ; 61.70

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract Indium Phosphide layers grown by gas source Molecular Beam Epitaxy, (MBE) have been studied by positron lifetime spectroscopy using the recently modified pulsed positron beam in Munich. The as-grown samples are known to be phosphorous rich and contain a high concentration of vacancy-type defects. On annealing, phosphorous precipitates are formed and the concentration of free volume defects increases. Positron lifetime spectroscopy has identified the grown in defects to be indium vacancies at a concentration around 1018cm−3. The dominant defects after annealing exhibit a positron lifetime characteristic of divacancies and are present at concentrations in excess of 5×1019cm−3.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01538197

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On the sensitivity of positrons to electric fields and defects in MBE-grown silicon structures (1994)

Britton, D. T. ; Willutzki, P. ; Triftshäuser, W. ; [weitere]

Springer

Applied physics 58 (1994), S. 389-393

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ISSN: 1432-0630

Schlagwort(e): 71.65 ; 73.40.Lq ; 73.60.Fw ; 78.70.Bj

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract The sensitivity of the positron to the internal electric fields in good quality thin (≈100 nm) Molecular Beam Epitaxy (MBE)-grown layers is experimentally demonstrated. Both a thin intrinsic layer grown on a p-type substrate and a highly n-doped δ profile buried in intrinsic silicon form effective barriers to positron diffusion although no defects can be detected. We also extract, from a full treatment of the positron diffusion, a quantitative estimate of the concentration, below the detection limits of other methods, of large vacancy clusters in a thick (680 nm) film.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00323615

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