Lattice site location of implanted Fe in SrTiO 3 and lattice damage recovery studies

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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

* [email protected]

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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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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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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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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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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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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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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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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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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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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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• 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

Lattice site location of implanted Fe in SrTiO 3 and lattice damage recovery studies

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