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

Dipartimento di Fisica, Università Degli Studi di Trento, 38050 Povo (TN) Italia

Warszawa, 16.09.2003Warszawa, 16.09.2003

Techniques: - Doppler broadening (depth profile)- lifetime (in bulk)- coincidence (in bulk)

Samples: - Czochralski-grown silicon- He-implanted silicon

- low-k materials

- SiO2 and GeO2 conducting glasses

Positron identity

e+ is antiparticle of e- :

- 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 Dirac1932 – discovered in cosmic raysby Anderson“out of 1300 photographs of cosmic tracks, 15 were od positive particles which could nothave a mass greater as that of the proton”

1950 – Madanski-Rasetti try to moderate1951 – 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 keVspot < 1 mm

Trento Positron Annihilation Set-up

Trento-München Positron Microscope

E=500 eV – 25 keVspot = 2 μm

Positron walking

 Positron in a crystal

 

 

Positron lifetime technique

τdefect > τbulk

Doppler broadening technique

ΔE = cpz / 2ptot=pe+pp

S=(E0±0.85keV)/(E0±4.25keV)

506 507 508 509 510 511 512 513 514 515 5160

20000

40000

60000

80000

100000

A+EA+B+C+D+E

A+B+C+D+E

C

W=

S=

E

B

A

D

C

Ilość

zlic

zeń

Energia [keV]

Doppler-broadening: normalization

0 2 4 6 8 10 12 14 16 18 200.90

0.92

0.94

0.96

0.98

1.00

1.02

1.04

250020001000500200100

mean positron implantation depth [nm]

reference sample

as impl. fluence 5x1015

sample 450°C annealing

S-p

ara

mete

r

positron implantation energy [keV]

He bubbles in Si

He – implantation

n=0.5x1016cm2 NO! n=2x1016cm2 YES!

0.1 1 10 100 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

2x1016

He cm-2

as impl. 150°C 200°C 250°C

S

mean positron implantation depth [nm]

0.1 1 10 100 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

2x1016

He cm-2

250°C 300°C 350°C 400°C 450°C

S

mean positron implantation depth [nm]

He bubbles in Si

He bubbles in Si

0.1 1 10 100 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

2x1016

He cm-2

500°C 550°C 600°C 700°C

S

mean positron implantation depth [nm]

0.1 1 10 100 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

2x1016

He cm-2

700°C 750°C 800°C 850°C 900°C

S

mean positron implantation depth [nm]

He bubbles in Siquantization of S - values

0 100 200 300 400 500 600 700 800 900 10001,00

1,01

1,02

1,03

1,04

1,05

1,06

1,07

1,08

1,09

1,10

1,11

1,12

1,13

1,14

V5

V4

V3

V2

V1

próbki implantowane He o dozie

5x1015

cm-2

2x1016

cm-2

Sd

Temperatura wygrzewania (o

C)

Doppler-coincidence technique

505 510 515 520 525 530 535 540

101

102

103

104

105 low-momentum electrons

(conduction and valence bands)

high-momentum electrons(core electrons)

background in asingle-detector system

background ina coincidence system

Si coincidence Si non-coincidence

Cou

nts

Energy [keV]

0 10 20 30 40 50 60 70p

L [10

-3 m

0c]

0 10 20 30 40 501

10

100

1000

10000

100000

rys1wr2

Ni Al Ti Nb Ag Au Si

Coun

ts

pL (10

-3 m

0c)

Doppler-coincidence spectra

0 10 20 30 40 500.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

rys5wr2

Ti d2

V d3

Cr d5

Mn d5

Fe d6

Co d7

Ni d8

Cu d10

Zn d10

Rat

io t

o S

i (an

neal

ed s

ampl

es)

PL ( 10

-3 m

0c )

D-C - chemical sensitivity

0 10 20 30 40 500.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Hf d2

W d3

Pt d9

Au d10

Pb d10

Rat

io t

o S

i (an

neal

ed s

ampl

es)

PL ( 10

-3 m

0c )

D-C - chemical sensitivity

Si – Czochralski grown

cO≈ 1018 cm-3

cB≈ 1016 cm-3

Oxygen in Cz-grown silicon

“as grown”: annealed at 450°C

thermal donors

precipitates

new donors

0 5 10 15

0.9

1.0

1.1

1.2

Oxygen peak

as grown

Ra

tio to

Si

PL ( 10

-3 m

0c )

0 5 10 15

0.9

1.0

1.1

1.2

Oxygen peak

450°C

Ra

tio to

Si

PL ( 10

-3 m

0c )

0 5 10 15

0.9

1.0

1.1

1.2

Oxygen peak

450°C+650°CR

atio

to S

i

PL ( 10

-3 m

0c )

Oxygen in Cz-grown silicon

0 5 10 15

0.9

1.0

1.1

1.2

Oxygen peak

as grown

Ra

tio to

Si

PL ( 10

-3 m

0c )

0 5 10 15

0.9

1.0

1.1

1.2

Oxygen peak

450°C

Ra

tio to

Si

PL ( 10

-3 m

0c )

0 5 10 15

0.9

1.0

1.1

1.2

Oxygen peak

450°C+650°CR

atio

to S

i

PL ( 10

-3 m

0c )

0 5 10 15

0.9

1.0

1.1

1.2

Oxygen peak

-- + 900°CR

atio

to S

i

PL ( 10

-3 m

0c )

0 5 10 15

0.9

1.0

1.1

1.2

Oxygen peak

-- + 1050°C

Ra

tio to

Si

PL ( 10

-3 m

0c )

Oxygen in Cz-grown silicon

975oC/5h/100bar

975oC/5h/100bar

0 5 10 15

0.9

1.0

1.1

1.2

Oxygen peak

as grown

Ra

tio to

Si

PL ( 10

-3 m

0c )

0 5 10 15

0.9

1.0

1.1

1.2

Oxygen peak

450°C

Ra

tio to

Si

PL ( 10

-3 m

0c )

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)

-100 0 100 200 300 400 500 600-0,3

-0,2

-0,1

0,0

0,1

0,2

0,3

270.6oC

231.5oC179oC

(485.2oC)0.3Bi2O30.7SiO2

CB

A

as obtained

reduced at 300oC

reduced at 300oC

and annealed at 400oC

DS

C [m

W/m

g]

T [oC]

Conducting glasses (SiO2+Bi2O3)

0 2 4 6 8 10 12 14 16 18 20 220.48

0.49

0.50

0.51

0.52

0.53

0.54

0.55

IIIIII

250 500 100050Mean positron implantation depth [nm]

91h25h3h20minas-grown

S-p

ara

met

er

Positron implantation energy [keV]

Conducting glasses (SiO2+Bi2O3)

Conducting glasses (SiO2+PbO2)

Conducting glasses (GeO2+Bi2O3)

0.1 1 10

0.47

0.48

0.49

0.50

0.51

0.52

0.53

Mean positron implantation depth (nm)

G0 G1 G2 G3

Pa

ram

ete

r S

Positron Energy (keV)

0.1 1 10 100 1000

Conducting glasses (SiO2+Bi2O3)

0.1 1 100.47

0.48

0.49

0.50

0.51

0.52

0.53

0.54

B0 B1 B2 B3 B4

Par

amet

er S

Energy (keV)

0.1 1 10 100 1000Mean implantation depth (nm)

Silica based, low ε materials - structure

From K.Maex et al. J. Appl. Phys. 11, 93, 8793

low ε materials - annealing

0.1 1 10 100 10000.90

0.92

0.94

0.96

0.98

1.00

1.02

1.04

1.06

1.08

1.10

1.12

Sn21ad Sn21a(400°C) Sn21b(450°C) Sn21c(500°C) Sn21d(600°C) Sn21e(700°C) Sn21f(800°C) Sn21g(900°C)

Sn

(ann

ihila

tion

with

low

mom

ent

ele

ctro

ns)

depth[nm]

low ε materials - annealing

0.1 1 10 100 10000.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28 PVmad21 PVm21a(400°C) PVm21b(450°C) PVm21c(500°C) PVm21d(600°C) PVm21e(700°C) PVm21f(800°C) PVm21g(900°C)

PV

(3

/2 r

atio

: O

Ps

form

atio

n)

depth[nm]

511 keV

Energia [keV]

obszar anihilacji 3Powierzchnia całkowita

Ilo

ść z

licze

ń

low ε materials - ageing

0.1 1 100.90

0.92

0.94

0.96

0.98

1.00

1.02

1.04

1.06

1.08

1.10

1.12

Sn

Energy[keV]

0.1 1 100.90

0.92

0.94

0.96

0.98

1.00

1.02

1.04

1.06

1.08

1.10

1.12

Sn

Energy[keV]

0.1 1 100.90

0.92

0.94

0.96

0.98

1.00

1.02

1.04

1.06

1.08

1.10

1.12

Sn

Energy[keV]

0.1 1 10

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

PV

(3

/2 r

atio

: o-P

s fo

rma

tion

)

Energy[keV]

0.1 1 10

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

PV

(3

/2 r

atio

: o-P

s fo

rma

tion

)

Energy[keV]

0.1 1 10

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

PV

(3

/2 r

atio

: o-P

s fo

rma

tion

)

Energy[keV]

Intense beams !

Auger Spectroscopy

Low-energy Positron Diffraction

Acknowledgements:

UniTN: Marco BettonteMonica SpagollaSebastiano Mariazzi

PAP: Tomasz WróblewskiEryk RajchDamian Pliszka

PG: Bogusław KuszMaria GazdaKonrad Trzebiatowski