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WORKSHOP AND USERS WORKSHOP AND USERS February 2007February 2007
Lattice site location of implanted Fe in SrTiO3 and lattice damage recovery studies
A. C. Marques1,4 *, U. Wahl1,2, J. G. Correia1,2,4, E. Rita1,2, J. P. Araújo3, L. Pereira3, C. Marques2, E. Alves2, M. A. Reis2, P. C. Chaves2, M. R. Silva1, J. C.
Soares1
(1)Centro de Física Nuclear da Universidade de Lisboa, Portugal(2)Instituto Tecnológico e Nuclear, Sacavém, Portugal
(3) IFIMUP, Fac. Ciências, Porto, Portugal(4)CERN, Geneva, Switzerland
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WORKSHOP AND USERS WORKSHOP AND USERS February 2007February 2007
OutlineOutline
Materials,
• Undoped SrTiO3
• SrTiO3 pre-implanted with stable Fe
emission channeling technique,
studies
• Fe lattice site location
• lattice damage recovery
• Magnetic properties
• impurities search by means of PIXE
and conclusions.
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WORKSHOP AND USERS WORKSHOP AND USERS February 2007February 2007
Why studying SrTiOWhy studying SrTiO33??
Because …
• High bulk dielectric constant microelectronic applications (ex. high-k FET).
• interesting and complex electrical, optical and magnetic properties that can be
modified by the incorporation of dopants (ex. Fe-doped SrTiO3 has been applied in
electrochemical electrodes and resistive oxygen sensors )
• Transition metal doped SrTiO3 is a possible material for a RT ferromagnetic
semiconductor Spintronics applications
• Variety of phase transitions in the low temperature range
Besides,
• little is known on the lattice site location of implanted impurities and
remaining point defects in heir neighborhood. EC and PAC can give unique
answers in that respect!
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WORKSHOP AND USERS WORKSHOP AND USERS February 2007February 2007
Electron Emission Channeling
2D emission patterns characterizes specific
lattice sites of the emitting atoms
(accuracy up to 0.1 Ǻ)
(b) When electrons are emitted from interstitial impurities there will be channeling and blocking effects that will
decrease the anisotropy when looking along the row of atoms.
(a) When electrons are emitted from substitutional
impurities, there will be a channeling effect:
electrons ere preferentially steered along this row of
atoms, resulting in a higher anisotropy.
(a)
(b)
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WORKSHOP AND USERS WORKSHOP AND USERS February 2007February 2007
Off-line set-upOn-line set-upfor short-lived isotopes
radioisotope
parent half-life decay ratio
(%) E (keV)
low energy
conversio
nElectron emitters
73Ge 73As 80.3 days 181 10-53
119Sn119mS
n 293.1 d 192 19-66
125Te 125I 60.1 d 33.3 22-35
58Co 58mCo 9.15h 92.6 17.2-24.1
radioisotope
parent half-life E (keV) Emax
(keV)
short-lived
- emitters
27Mg 27Na 9.5 min 703 1767
61Co 61Fe 1.7 h 460 1254
65Ni 65Co 2.5 h 629 2137
69Zn 69Cu 56 min 322 906
75Ge 75Ga 1.4h 421 1177
Table: Some radioactive isotopes for possible future use with the EC technique:
Experimental set-up
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WORKSHOP AND USERS WORKSHOP AND USERS February 2007February 2007
0 10 20 30 40 50 60 70 80 90 100 110 120 130 1400.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
57Co
241Am
TbBa
Ag
Mo
Rb
SERIAL READOUT MODE
even
ts (
a. u
.)
energy (keV)
lowest detectable energy 13.4 keV
FWHM @ 17.4 keV 1.18 keV
PCB
.
.
.
Si Pad detector
Chip(Front-End) IB
InterfaceModule
USBUSBVMECard
LinuxV
ATA
-DA
Q a
s a
read
ou
t syste
m
168 k
eV
219 k
eV
242 k
eV111In
100 200 300 400 5000
5000
10000
15000
20000INTEGRAL SPECTRUM - NOT GAIN CALIBRATED!
entr
ies
adc_output
14
5 k
eV
INTEGRAL SPECTRA - NOT GAIN CALIBRATED
e-
181Hf
65
keV
- K
12
2 k
eV
- L
13
1keV
- M
• Lowest 111In electron energy
of 145 keV has an FWHM of 4.8
keV!
• Lowest energy that can be
detected with this PSD is 15
KeV!
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WORKSHOP AND USERS WORKSHOP AND USERS February 2007February 2007
EC results – 59Fe:SrTiO3
Where: ISOLDE, CERN (Geneva)
Energy: 60 keV
Dose: 2×1013 at./cm2
EC measurements: patterns were recorded along 4
directions in the as-implanted state and after
annealing at 300ºC, 600ºC, 750ºC and 900ºC.
Results
-2
-1
0
1
2
-2 -1 0 1 2
(a)
experiment-2 -1 0 1 2
1.50 -- 1.60 1.40 -- 1.50 1.30 -- 1.40 1.20 -- 1.30 1.10 -- 1.20 1.00 -- 1.10 0.900 -- 1.00 0.800 -- 0.900
simulation
(e) <100>
-2
-1
0
1
2(b) 1.24 -- 1.30 1.17 -- 1.24 1.11 -- 1.17 1.05 -- 1.11 0.988 -- 1.05 0.925 -- 0.988 0.863 -- 0.925 0.800 -- 0.863
(f) <111>
-2
-1
0
1
2
(d)
(c) 1.32 -- 1.40 1.25 -- 1.32 1.17 -- 1.25 1.10 -- 1.17 1.02 -- 1.10 0.950 -- 1.02 0.875 -- 0.950 0.800 -- 0.875
(g) <211>
[deg]-2 -1 0 1 2
-2
-1
0
1
2
-2 -1 0 1 2
(h) <110> 1.32 -- 1.40 1.25 -- 1.32 1.17 -- 1.25 1.10 -- 1.17 1.02 -- 1.10 0.950 -- 1.02 0.875 -- 0.950 0.800 -- 0.875
<110>
<001>
Ti ro
w
<110>
octahedral interstitial site
<111>
mixed
<001>
Sr
row
An
gu
lar
dis
trib
uti
on
s “
@” 9
00
ºCUndoped sample ion implantation details
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WORKSHOP AND USERS WORKSHOP AND USERS February 2007February 2007
Crystalline quality for
<100>:
Virgin samp. 1.9%
STO+1x1015 Fe at.cm2 8.5%
STO+5x1015 Fe at.cm2 9%
SrTiO3 lattice characterization by RBS/Channeling
-1 0 1 20.0
0.5
1.0
1.5
2.0 STO+1x1015 Fe at./cm2
Yiel
d (c
ount
s/10
00)
-2 -1 0 1 20.0
0.5
1.0
1.5
2.0 STO+5x1015 Fe at./cm2
Yiel
d (c
ount
s/10
00)
a
b
c
xy
z
<100>
a
b
c
xy
z
<111>
a b
cx y
z
<110>
Crystalline directions under
study:
<111>random<100>
<110>
After 900ºC
annealing
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WORKSHOP AND USERS WORKSHOP AND USERS February 2007February 2007
Automated control of temperature, magnetic field Automated control of temperature, magnetic field and helium liquefaction and helium liquefaction
Magnetic measurements performed with a SQUID
MPMS EverCool System
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WORKSHOP AND USERS WORKSHOP AND USERS February 2007February 2007
10 K
is normalized to the mass sample
Magnetic measurements performed with a SQUID
Magnetic measurements were
performed in two SrTiO3 samples
pre-implanted with stable Fe at
ITN-Portugal and after 900ºC
vacuum annealing.
Low dose sample 1.69x1015
at./cm2
High dose sample 5.26 x1015
at./cm2
Undoped sample as sensitized Fe 2.2 B
Fe2+ 6 B
Fe3+ 5 B
1.69x1015 Fe at./cm2
5.26x1015 Fe at./cm25.5 T
M = 8,8 B/Fe
M is considerably higher!!Why?? … we still don’t know!
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WORKSHOP AND USERS WORKSHOP AND USERS February 2007February 2007
2.500 6.500 10.500 14.500 18.500 22.5001
10
100
1000
10000
100000
1000000
Ep= 2.150 MeV
Si(Li) detector
Cou
nts
Energy (keV)
Fe - K and K lines
Sum peaksCu-K
Escape peaks
Sum peaks
Sr - K and K lines
STO with 5x1015 Fe at./cm2
Ti - K and K lines
Impurities search in SrTiO3 by means of PIXE
Zoom
PIXE analysis revealed the following: CuCu
paramagnetiparamagneti
c impurityc impurity
(Cu(Cu2+2+)/ion = )/ion =
1.7 1.7 BB
Low dose sample
High dose sample
[Stable 56Fe] (at./cm2)
1.69 1015 5.26 1015
[Cu impurity] (at./cm2)
2.05 1015 1.99 1015 Absence of Cu impurities in
the Virgin sample
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WORKSHOP AND USERS WORKSHOP AND USERS February 2007February 2007
• Emission Channeling
• up to 900ºC 59Fe atoms preferentially go to Ti-near sites (86%).
• RBS/Channeling Spectroscopy
• Good crystalline quality samples
• after Fe-doping and 900ºC post-annealing there are still remaining defects in the sample.
• SQUID Measurements
• The magnetic properties are modified by the introduction of Fe dopant to different doses.
• Magnetization increases with Fe concentration but to a value bigger than what would be
expected.
Why? We still don’t know but the following questions comes up:
What is the Fe atoms valence in the crystal?
Are the remaining defects playing a role? Or clusters have been formed after the annealing?
FUTURE WORK: Future work at ISOLDE will be to study 65Ni (2.5 h) and 61Co (1.5 h) lattice site location in SrTiO3 and other oxides.
Summary / Future work