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

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

Positron identity e + is antiparticle of e - : - mass keV/c 2 - spin ½ - opposite Q - opposite μ - stable in vacuum (>2x10 21 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=3x10 -8 (Cherry) 1979 – single crystal moderator (Mills) 1980 – brightness enhancement (Mills )

Positron slowing down

Positron sources Radioactive nuclides Moderators W (100): ε= 4x10 -4 Solid Ne: ε=1% ?

Positrons in Solid State Physics

Trento Positron Annihilation Set-up E=100 eV – 25 keV spot < 1 mm

Trento Positron Annihilation Set-up

Trento-München Positron Microscope E=500 eV – 25 keV spot = 2 μm

Positron walking

Positron in a crystal

Positron lifetime technique τ defect > τ bulk

Doppler broadening technique ΔE = cp z / 2 p tot =p e +p p S=(E 0 ±0.85keV)/(E 0 ±4.25keV)

Doppler-broadening: normalization

He bubbles in Si He – implantation n=0.5x10 16 cm 2 NO!n=2x10 16 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

Core electrons momenta

Si – Czochralski grown c O cm -3 c B cm -3

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

Oxygen in Cz-grown silicon

AFM picture of Si-Pb glass; a) freshly broken; b) Annealed at 580ºC for 21h a) b) Conducting glasses (SiO2+Bi2O3)

Conducting glasses (SiO 2 +PbO 2 )

Conducting glasses (GeO 2 +Bi 2 O 3 )

Conducting glasses (SiO 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

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