Bachelor-Themen im Positronenlabor Themen im

Bachelor-Themen im Positronenlabor Themen im

Bachelor--Themen im Positronenlabor
Bachelor
R Krause
R.
Krause-Rehberg
Rehberg
reinhard.krause rehberg@physik.uni halle.de
reinhard.krause-rehberg@physik.uni-halle.de
http://positron.physik.uni-halle.de
1
RK
R
The positron lifetime spectroscopy
22Na
14:26
•
positron wave-function can
be localized in the
attractive
tt
ti potential
t ti l of
fa
defect
•
annihilation parameters
change in the localized state
•
e.g.
g positron
p
lifetime
increases in a vacancy
•
lifetime is measured as time
difference between
appearance of 1.27 (start)
and 0.51
0 51 MeV (stop) quanta
•
defect identification and
quantification possible
2
Digital lifetime measurement
14:26
3
screenshot of two digitized anode pulses
time difference = 2.65471 samples = 663.67 ps
14:26
4
Defects in electronelectron-irradiated Ge
• Electron irradiation (2 MeV @ 4K) induces Frenkel pairs (vacancy - interstitial pairs)
• steep annealing stage at 200 K
• at high irradiation dose: divacancies are formed (thermally more stable)
G
Ge
e- irr. at 4K
14:26
(Polity et al., 1997)
5
Defects in CIGS photovoltaic layers
• positron beam measurements at POSSY system in Halle (TGZIII)
• S parameter reflects open-volume point
defects such as vacancies, vacancy
clusters, voids
6
Porosimetry with positronium
14:26
•
Positronium can be
formed in dielectric
media
•
is bound state of electron
and positron
•
lifetime is function of
pore size 0.5
0 5 ns ... 142 ns
•
closed pore systems can
be measure
7



14:26
we measured porous
glass in a broad pore
size
i range
pore size obtained by
N2-adsorption
p
method
calibration curve for
the correlation of o-Ps
lif tim and
lifetime
d pore si
size
8
Loading
g of Mesopores
p
by
y Drugs
g




CPG membranes have been loading with
Acetaminophen (C8H9NO2) – also known
as Paracetamol
different p
pore sizes were studied
filling by dropping membrane in hot
melt of drug
degree of filling can be studied with
positrons
Loading
g of Mesopores
p
by
y Drugs
g



Example: membrane with
2.2 nm pore
distribution of pore sizes is
shifted to smaller values
30.7 ns corresponds to 2.2
nm and 19.7
19 7 ns ->> 1.5
1 5 nm
Mögliche BachelorBachelor-Themen 2014/15
Thema 1: Untersuchung von Nanoporen dielektrischen Low-K-Schichten
•
•
K
Kooperation
ti mit F
Fraunhofer-Institut
h f I stit t ENAS in
i Ch
Chemnitz
m it
für GlobalFoundries (ehemals AMD Dresden)
Thema 2: Defekte in photovoltaischen CIGS-Schichten
•
Kooperation mit AG Prof. Scheer
Thema 3: Untersuchung an Porensystemen für technische Anwendungen aus Glas
•
•
Porendurchmesser 1…100 nm
Kooperation
p
mit Univ. Leipzig
p g – Prof. Enke
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