Aplicaciones: Defectos en semiconductores Sustitución catiónica en polvos nanocristalinos

t(ns)

Aplicaciones: Volúmenes libres en polímeros Polivinilsiloxanos (PVS) POSITRONFIT CONTIN Alessandrini, SLAP 2004, Spain

Aplicaciones: Volúmenes libres en polímeros Polímeros de Poli(Acrilato de Etilo) Se determinó el tamaño de los huecos: R~2.5 Å M.A.Hernández-Fenollosa, APHYS 2003, Spain

Aplicaciones: Volúmenes libres en polímeros Estructuras CB[n] to-Ps en función del tamaño del hueco en las CB[n] Variación de tave con el llenado de las cavidades para CB[7]

Application of positron annihilation techniques for semiconductor studies Techniques: - Doppler broadening (depth profile) - lifetime (in bulk) - coincidence (in bulk) Samples: - He-implanted silicon - Czochralski-grown silicon low-k materials - SiO2 and GeO2 conducting glasses

Positron identity e+ is antiparticle of e- : Ps is light H : mass 511.003 keV/c2 spin ½ opposite Q opposite μ stable in vacuum (>2x1021y) 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 Moderators Radioactive nuclides W (100): ε= 4x10-4 Solid Ne: ε=1% ?

Positrons in Solid State Physics

Trento Positron Annihilation Set-up

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

Positron walking

   Positron in a crystal  

Espectroscopía de aniquilación de positrones

Positron lifetime technique τdefect > τbulk

Doppler broadening technique ptot=pe+pp ΔE = cpz / 2 S=(E0±0.85keV)/(E0±4.25keV)

Doppler-broadening: normalization

He bubbles in Si He – implantation n=0.5x1016cm2 NO! n=2x1016cm2 YES!

He bubbles in Si

He bubbles in Si

He bubbles in Si quantization of S - values

Doppler-coincidence technique

Doppler-coincidence spectra

D-C - chemical sensitivity

D-C - chemical sensitivity

Si – Czochralski grown cO≈ 1018 cm-3 cB≈ 1016 cm-3

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

Oxygen in Cz-grown silicon

Oxygen in Cz-grown silicon

Oxygen in Cz-grown silicon

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

Conducting glasses (SiO2+Bi2O3)

Conducting glasses (SiO2+Bi2O3)

Conducting glasses (SiO2+PbO2)

Conducting glasses (GeO2+Bi2O3)

Conducting glasses (SiO2+Bi2O3)

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

low ε materials - annealing

low ε materials - annealing

low ε materials - ageing

Positron Spectroscopy in Solid State Physics Intense beams ! Future ? Auger Spectroscopy Low-energy Positron Diffraction

Positron Spectroscopy in Solid State Physics Intense beams ! Future ? Auger Spectroscopy Low-energy Positron Diffraction