E center in amorphous silicon dioxide: a potential probe for embedded silicon nanostructures

1
E? center in amorphous silicon dioxide a
potential probe for embedded silicon
nanostructures
G. Buscarino, S. Agnello , F. M. Gelardi
Department of Physical and Astronomical Sciences,
University of Palermo, Via Archirafi 36, 90123
Palermo, Italy buscarin_at_fisica.unipa.it
EURODIM 2006 10th europhysical conference on
defects in insulating materials, MILANO (Italy)
july 10-14, 2006
2
Outline
Introduction
Experimental details
Results and discussion
Conclusions
3
IntroductionElectron paramagnetic resonance
features of the E? center
Main resonance line
Hyperfine structure
4
IntroductionProposed microscopic structures for
the E? center
Hole capture
2-Si model
Tohmon et al., Phys. Rev, B 41, 7258 (1990)
Hole capture
Zhang and Leisure, J. Appl. Phys. 8, 3744 (1996)
4-Si model
Hole capture
1-Si model
Vanheusden and Stesmans, J. Appl. Phys. 74, 275
(1993)
4-Si model
Hole capture
5
IntroductionIntensity ratio between the 10 mT
hyperfine doublet and the main resonance line
NOTE The natural abundance of O atoms with non
zero nuclear spin is very low (0.038 ) and will
not be considered.
where 0.047 is the natural abundance of 29Si
nuclei.
The probability to observe the E? main EPR line
is
The probability to observe the 10 mT hyperfine
doublet is
Then the expected intensity ratio between the 10
mT doublet and the main resonance line of the
E? center is
It depend on the number of Si atoms over which
the unpaired elevtron is delocalized !!!
6
Outline
Introduction
Experimental details
Results and discussion
Conclusions
7
Experimental detailsMaterials, treatments and
measurements
Materials
All the materials considered are commercial
a-SiO2 i) QC (fused quartz) ii) Pursil
453 (fused quartz) iii) KUVI (synthesized by
vapour axial deposition technique) The optical
absorption spectra of these materials show an
intense band peaked at 7.6 eV of amplitude of
?20 cm-1 for KUVI, and larger than 100 cm-1 for
Pursil 453 and QC, characterizing them as
oxygen-deficient silicon dioxide. All these
materials have an Al atoms content higher than
1017 cm-3.
?-ray irradiation
?-ray irradiation has been carried out with a
60Co source at room temperature and with dose
rate ?7 kGy/hr.
Thermal treatments
Many ?-ray irradiated samples of each material
were subjected to isochronal and isothermal
treatments.
Measurements
EPR measurements were carried out at room
temperature with a Bruker EMX spectrometer
working at frequency ? ? 9.8 GHz (X-band) and
with magnetic-field modulation frequency of
100 kHz. The spectra were acquired in the
first-harmonic unsaturated mode (FH-EPR) or in
the high-power second-harmonic mode (SH-EPR).
8
Outline
Introduction
Experimental details
Results and discussion
Conclusions
9
Results and discussion?-ray irradiation and
thermal treatment effects
First-harmonic EPR spectrum
Isochronal thermal treatment of a ?-ray
irradiated sample of Pursil 453
An hole-transfer could occur from the AlO40
centers to the sites precursors of the E centers
10
Results and discussion?-ray irradiation and
thermal treatment effects
Second-harmonic EPR spectrum
First-harmonic EPR spectrum
11
Results and discussionCorrelation between the 10
mT doublet and the E? center
The EPR signal intensity of the 10 mT doublet and
that of the E? center main resonance are
strictly correlated, confirming the attribution
of the 10 mT dobulet to the hyperfine structure
of the E? center .
12
Results and discussionEstimation of the
intensity ratio of the 10 mT doublet with respect
to the E? center
Second-harmonic EPR spectrum
First-harmonic EPR spectrum
13
Results and discussionEstimation of the
intensity ratio between the 10 mT doublet and the
E? center
By a fit procedure we obtained ?experimental
0.180.03 (E? )
14
Results and discussionEstimation of the
intensity ratio between the 42 mT doublet and the
E? center
Main resonance line
Right component of the 42 mT hyperfine doublet
By a fit procedure we obtained ?experimental
0.050.01 (E? )
15
Results and discussionDiscussion of the
microscopic models proposed for the E? center
?experimental 0.180.03 (E? )
Hole capture
2-Si model
Tohmon et al., Phys. Rev, B 41, 7258 (1990)
?(n2)0.099
Hole capture
Zhang and Leisure, J. Appl. Phys. 8, 3744 (1996)
4-Si model
?(n4)0.197
Hole capture
1-Si model
Vanheusden and Stesmans, J. Appl. Phys. 74, 275
(1993)
?(n1)0.049
4-Si model
Hole capture
?(n4)0.197
16
Outline
Introduction
Experimental details
Results and discussion
Conclusions
17
Conclusions
i) We have found evidences that in a-SiO2 a
thermally induced hole-tranfer process from the
AlO40 centers to the sites precursors of the E
centers occurs.
ii) We have confirmed the attribution of the 10
mT doublet to the 29Si hyperfine structure of
the E? .
iii) We have estimated the intensity ratio
between the 10 mT doublet and the main resonance
line of the E? center to be ?0.180.03,
indicating that the unpaired electron of this
defect is delocalized over four nearly equivalent
Si atoms.
18
Outline
Introduction
SiO2 group in Palermo (Italy)
Thank you
Experimental details
Results and discussion
Conclusions
Related papers
G. Buscarino, S. Agnello and F. M. Gelardi, Phys.
Rev. Lett. 94, 125501 (2005)
G. Buscarino, S. Agnello and F. M. Gelardi, Phys.
Rev. B 73, 45208 (2006)
G. Buscarino, S. Agnello and F. M. Gelardi, Mod.
Phys. lett. B 20, 451 (2006)
G. Buscarino, S. Agnello and F. M. Gelardi, J.
Phys. Condens. Matter 18, 5213 (2006)