Grzegorz P Karwasz Istituto Nazionale per la Fisica

Positron identity e+ is antiparticle of e- : - mass 511. 003 ke. V/c

Positron history History of “slow” positrons 1930 – e+ postulated by Dirac 1932 –

Positron sources Radioactive nuclides Moderators W (100): ε= 4 x 10 -4 Solid Ne:

Trento Positron Annihilation Set-up E=100 e. V – 25 ke. V spot < 1

Trento-München Positron Microscope E=500 e. V – 25 ke. V spot = 2 μm

Positron lifetime technique τdefect > τbulk

Doppler broadening technique ptot=pe+pp ΔE = cpz / 2 S=(E 0± 0. 85 ke.

He bubbles in Si He – implantation n=0. 5 x 1016 cm 2 NO!

He bubbles in Si quantization of S - values

Si – Czochralski grown c. O≈ 1018 cm-3 c. B≈ 1016 cm-3

Oxygen in Cz-grown silicon thermal donors precipitates new donors “as grown”: annealed at 450°C

Conducting glasses (Si. O 2+Bi 2 O 3) a) b) AFM picture of Si-Pb

Silica based, low ε materials - structure From K. Maex et al. J. Appl.

$Intense beams ! Auger Spectroscopy Low-energy Positron Diffraction$

Acknowledgements: Uni. TN: Marco Bettonte Monica Spagolla Sebastiano Mariazzi PAP: Tomasz Wróblewski Eryk Rajch

Slides: 41

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Grzegorz P. Karwasz Istituto Nazionale per la Fisica della Materia, Università di Trento, Povo (TN), Italia and Instytut Fizyki, Pomorska Akademia Pedagogiczna, 76200 Slupsk, Polska Roberto S. Brusa, Antonio Zecca Dipartimento di Fisica, Università Degli Studi di Trento, 38050 Povo (TN) Italia Warszawa, 16. 09. 2003

Techniques: - Doppler broadening (depth profile) - lifetime (in bulk) - coincidence (in bulk) Samples: - He-implanted silicon - Czochralski-grown silicon - low-k materials - Si. O 2 and Ge. O 2 conducting glasses

Positron identity e+ is antiparticle of e- : - mass 511. 003 ke. V/c 2 - spin ½ - opposite Q - opposite μ - stable in vacuum (>2 x 1021 y) Ps is light H : - Energy E= ½ Ry - p-Ps: τ=125 ns, 2γ - o-Ps: τ=142 ns, 3γ

Positron history History of “slow” positrons 1930 – e+ postulated by Dirac 1932 – discovered in cosmic rays by Anderson “out of 1300 photographs of cosmic tracks, 15 were od positive particles which could not have a mass greater as that of the proton” 1950 – Madanski-Rasetti try to moderate 1951 – evidence of Ps atom (Deutsch) 1958 – moderated e+ , ε=3 x 10 -8 (Cherry) 1979 – single crystal moderator (Mills) 1980 – brightness enhancement (Mills)

Positron slowing down

Positron sources Radioactive nuclides Moderators W (100): ε= 4 x 10 -4 Solid Ne: ε=1% ?

Positrons in Solid State Physics

Trento Positron Annihilation Set-up E=100 e. V – 25 ke. V spot < 1 mm

Trento Positron Annihilation Set-up

Trento-München Positron Microscope E=500 e. V – 25 ke. V spot = 2 μm

Positron walking

Positron in a crystal

Positron lifetime technique τdefect > τbulk

Doppler broadening technique ptot=pe+pp ΔE = cpz / 2 S=(E 0± 0. 85 ke. V)/(E 0± 4. 25 ke. V)

Doppler-broadening: normalization

He bubbles in Si He – implantation n=0. 5 x 1016 cm 2 NO! n=2 x 1016 cm 2 YES!

He bubbles in Si

He bubbles in Si quantization of S - values

Doppler-coincidence technique

Doppler-coincidence spectra

D-C - chemical sensitivity

Si – Czochralski grown c. O≈ 1018 cm-3 c. B≈ 1016 cm-3

Oxygen in Cz-grown silicon thermal donors precipitates new donors “as grown”: annealed at 450°C

Oxygen in Cz-grown silicon

Conducting glasses (Si. O 2+Bi 2 O 3) a) b) AFM picture of Si-Pb glass; a) freshly broken; b) Annealed at 580ºC for 21 h

Conducting glasses (Si. O 2+Bi 2 O 3)

Conducting glasses (Si. O 2+Pb. O 2)

Conducting glasses (Ge. O 2+Bi 2 O 3)

Conducting glasses (Si. O 2+Bi 2 O 3)

Silica based, low ε materials - structure From K. Maex et al. J. Appl. Phys. 11, 93, 8793

low ε materials - annealing

low ε materials - ageing

$Intense beams ! Auger Spectroscopy Low-energy Positron Diffraction$

Intense beams ! Auger Spectroscopy Low-energy Positron Diffraction

Acknowledgements: Uni. TN: Marco Bettonte Monica Spagolla Sebastiano Mariazzi PAP: Tomasz Wróblewski Eryk Rajch Damian Pliszka PG: Bogusław Kusz Maria Gazda Konrad Trzebiatowski