F'Messina, M'Cannas, R'Boscaino

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Erice, June 2005
UV laser irradiation of amorphous SiO
2
generation and conversion of point defects and
post-irradiation processes

• F.Messina, M.Cannas, R.Boscaino

Dipartimento di Scienze Fisiche ed Astronomiche,
Università di Palermo, Palermo, Italy
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Silica glass
Scientific interest
1. Simple Model of amorphous insulator
3. Point defects
Are physically different from their crystalline
counterpart
Their generation (often induced by radiation)
deteriorates good macroscopic properties such
as transparency.
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Qiu et Al. NIM B (1998)
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Experiments
Experiment Irradiation (room T) with 266nm
NdYAG radiation various spectroscopic
measurements during irradiation and in the
post-irradiation stage
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Laser-induced OA
Evidence band peaked at 5.8eV
Generation of E center
Si,O atoms
1. Growth during irradiation
2. Decrease in the post-irradiation stage
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Previously measured absorption cross section
(s 6.410-17cm2)
5.8eV band peak amplitude
Concentration of E center vs time
Most of the induced defects are transient
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ESR measurements
Post-irradiation stage!
Hyperfine ESR signal of H(II) center
ESRex situ
Ge,O,H atoms
H(II) post-irradiation growth
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PL measurements
Post-irradiation stage!
Typical PL activity of twofold coordinated Ge
Ge,O atoms
Post-irradiation decrease
Note this defect is already present in the
material prior to irradiation
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Summary of experimental results
Irradiation triggers..
Generation of E and their post-irradiation decay
Post-irradiation growth of Ge-related H(II)
Post-irradiation decrease of preexisting twofold
coordinated Ge center
Si,Ge,O,H atoms
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Discussion-I
Si,O,H atoms
Breaking of diffusing H2 at E-site causes the
decay of E and makes available H0
H0 may be trapped on twofold coordinated Ge
causing its conversion in H(II)
Ge,O,H atoms
Diffusing hydrogen is made available by
radiolysis of SiH or OH impurities
Chemical reactions
1)E (?Si?) H2? ?Si-H H0 2)E (?Si?)H0 ?
?Si-H 3)GLPC (Ge??) H0 ? H(II) (Ge? -H)
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Discussion-II
Chemical rate equations fit experimental datasets
ltEagt 0.54eV FWMH(Ea) 0.11eV
Work in progress
1. Temperature dependance
2. Isotopic substitution H/D
3. Comparison with in situ kinetics under b and g
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Publications
? M.Cannas, S.Agnello, R.Boscaino, S.Costa,
F.M.Gelardi, F.Messina, Journ. Non Cryst. Solids
322 (2003) 90 ? M.Cannas, F.Messina , J.
Non-Cryst. Solids 345-346 (2004) 433 ? F.
Messina, M. Cannas, R. Boscaino, Phys. Stat. Sol.
(c) 2 (2005) 616 ? M. Cannas, F. Messina, J.
Non-Cryst. Solids in press ? F. Messina, M.
Cannas, R. Boscaino, J. Non-Cryst. Solids in
press ? F. Messina, M. Cannas, J. Phys. Cond.
Matter 17 (2005) 3837
The end