Ion implantation doping of perovskites and related oxides

Ulrich WahlInstituto Tecnológico e Nuclear (ITN), Sacavém, Portugal

Collaborators:João Guilherme Correia (Senior Res., ITN & CERN)

Eduardo Alves (Senior Res., ITN)Ana Claudia Marques (PhD student, U Lisbon & CERN)

Carlos Pedro Marques (PhD student, U Lisbon)Karl Johnston (Post-Doc, U Saarbrücken & CERN)

João Pedro Araújo (Prof., U Porto)Lino Pereira (PhD student, U Porto)

Outline

• Motivation for implantation studies in perovskites• Objectives and work plan• Implantation damage annealing in SrTiO3:

– RBS/C, 89Sr emission channeling, PL

• Fe in SrTiO3:– emission channeling lattice location, – magnetic moments (SQUID)

• 67Cu and 111Ag emission channeling in SrTiO3

• Rare earth 169Yb in SrTiO3

• Conclusions• Outlook

What are perovskites?

Perovskites are metal oxides of the form ABO3

A forms a simple cubic latticeB forms a simple cubic latticeA and B together form a bcc latticeO occupies the faces of the cube

abcxyz

Best studied perovskite: SrTiO3

Perovskites are ionic compounds:e.g. Sr2+Ti4+O23

Perovskites and doping

• Perovskites (SrTiO3, CaTiO3, BaTiO3, KTaO3, ...) are multifunctional materials...

• ...whose electrical, magnetic and optical properties can be drastically changed by doping

• Many possible applications of perovskites rely on doping these materials.

SrTiO3: great variety of possible dopants

• Possible electrical dopantsPossible electrical dopants• Some magnetic dopantsSome magnetic dopants• Some optical dopantsSome optical dopants

But little is known about ion But little is known about ion implantation doping: implantation doping:

lattice sites ?lattice sites ?damage annealing ?damage annealing ?

Motivation: ion implantation in perovskites

Trecrystallization

Amorphization threshold temperature [K]

In short:

• perovskites are hard to amorphize and...• ...recrystallize at moderate temperatures

should be attractive systems for ion implantation

Major objectives of this project:

• investigate basic possibilities for ion implantation doping of perovskite oxides and related materials in order to modify their optical, magnetic and electrical properties

• implantation of magnetic impurities such as Fe or Mn, optically active dopants such as rare earth elements, and prospective electrically active donor and acceptor impurities

• study lattice location of impurities and annealing of implantation damage using nuclear techniques

• complementary characterization of optical, magnetic and electrical properties for certain implanted impurities

Secondary objectives:

• promoting the use of nuclear techniques in the production and characterization of novel materials in the technologically relevant fields of microelectronics, optoelectronics and spintronics

• transfer of know-how in the application of nuclear techniques to the other participants of the Coordinated Research Project

• training and formation of PhD and undergraduate students on a national level in materials science and in the application of nuclear techniques

Work plan:

• Year 1 (2005-06): lattice location and damage annealing studies in SrTiO3, first measurements of optical and magnetic properties

• Year 2 (2006-07): lattice location and damage annealing studies extended to other perovskites, e.g. KTaO3, measurements of optical and magnetic properties under optimized conditions (dose, annealing…)

• Year 3 (2007-08): set priorities for the study of those systems where, according to outcome of research in years 1+2, best results were obtained

Foreseen methods of study

• stable and radioactive ion implantation

• nuclear methods using radioactive isotopes- Emission Channeling (EC) lattice location- Perturbed Angular Correlation (PAC)- Photoluminescence (PL)

• Rutherford Backscattering / Channeling (RBS/C)• conventional Photoluminescence (PL)• macroscopic magnetic moments by means of SQUID

...work in progress, presentation includes several experiments that are not yet fully analyzed!

Annealing of radiation damage: RBS/C

• SrTiO3 implanted with 56Fe at doses of 151015 cm2

• 2 MeV 4He+ RBS/C minimum yield min measured as function of TA

only for TA>1000°C remaining damage reaches values similar to a virgin crystal

0 200 400 600 800 1000 12000.00

0.05

0.10

0.15

0.20

0.75

0.80

0.85

0.90

0.95

1.00

<100> 51015 cm2 Fe <100> 11015 cm2 Fe

<110> 51015 cm2 Fe <110> 11015 cm2 Fe

<111> 51015 cm2 Fe <111> 11015 cm2 Fe

<100> virgin crystal <110> virgin crystal <111> virgin crystal

RB

S m

inim

um y

ield

m

in

annealing temperature TA [°C]

Annealing of radiation damage: 89Sr emission channeling

as was expected, 89Sr (60 keV, 81014 cm2) occupies mainly Sr sites broad damage recovery stage 2001000°C annealing probably not yet finished at 1000°C information on rms displacement of Sr atoms as function of TA could not be derived (problem of angular resolution, mosaicity of implanted sample!)

analysis of experiment still in progress!

2 1 0 -1 -2

10

5

0

-5

-10

2 1 0 -1 -2

10

5

0

-5

-10

+ M2:- M2:

cnterclwclockw

6.6E3 -- 7E3

6.2E3 -- 6.6E3

5.8E3 -- 6.2E3

5.4E3 -- 5.8E3

5E3 -- 5.4E3

4.6E3 -- 5E3

4.2E3 -- 4.6E3

3.8E3 -- 4.2E3the plot shows the crystal as

it is viewn from the detector+ z:

- z:

+ M1:

"on-line" display: template C:\ORIGIN\PADSPEC4.OTP read with script file C:\ORIGIN\CHANRED4.SCRConversion electron emission channeling with 30 mm x 30 mm Si pad4 detector:

U. Wahl, ITN

- M1:

rel.

Z-c

oord

inat

e [m

m]

rel. M1-angle [deg]

counts raw data

SSr STi

<211> following TA=1000°C

max ~ substitutional fraction

0 100 200 300 400 500 600 700 800 900 1000 11001.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

<100> <111> <110> <211> <411>

max

of e

lect

ron

ch

an

ne

ling

annealing temperature TA [°C]

Annealing of radiation damage: PL

• Sample implanted with 89Sr at a dose of ~1014 cm2

• PL with 325nm excitation (above band edge 387 nm = 3.2 eV ) measured at 1.6 K as function of TA

near-band edge luminescence restored only for TA>800°C

Motivation: SrTiO3 in the focus as...

... dilute magnetic semiconductor

(room-temperature ferromagnetism?)

Fe in SrTiO3

• As 3d transition metal element, Fe is a candidate for magnetic doping of SrTiO3 (cf Mn)

• which lattice site does Fe occupy following ion implantation?

study by means of emission channeling using the radioactive isotope 59Fe (t1/2=44 d)low dose implantations (60 keV, 51012 11013 cm2)

• What are the magnetic properties of Fe-implanted SrTiO3?

study by means of SQUIDhigh dose implantations (60 keV, 1015 1016 cm2)

Emission channeling lattice location: basic principle

The cubic perovskite lattice of SrTiO3

u1(Sr)=.077 Åu1(Ti)=.061 Åu1(Sr)=.085 Å

59Fe lattice sites in SrTiO3 as function of TA

as-implanted: octahedral interstitial I8 prominent + substitutional Ti Fe on I8 decreases fast no damage recovery stage no (or little) Fe on Sr sites Fe prefers <100> displaced Ti sites (0.4-0.8 Å) + Ti sites

emission channeling patterns, 59Fe 60 keV 1013 cm2 in SrTiO3, as-impl.

<100> displ. STi I8 sites

-2

-1

0

1

2

-2 -1 0 1 2 3

(a)

{100}

{110}

experiment

-2 -1 0 1 2 3

1.72 - 1.85 1.59 - 1.72 1.46 - 1.59 1.33 - 1.46 1.19 - 1.33 1.06 - 1.19 0.93 - 1.06 0.80 - 0.93

best fit STi + STiSO + Oi

(e) <100>

-1

0

1

2

3

{211}

{111}(b)

{110}

1.54 - 1.64 1.44 - 1.54 1.35 - 1.44 1.25 - 1.35 1.15 - 1.25 1.06 - 1.15 0.96 - 1.06 0.86 - 0.96

(f) <110>

-2

-1

0

1

2(c)

{210}

{110}

1.30 - 1.37 1.23 - 1.30 1.16 - 1.23 1.10 - 1.16 1.03 - 1.10 0.96 - 1.03 0.89 - 0.96 0.82 - 0.89

(g) <211>

[deg]-2 -1 0 1 2

-2

-1

0

1

2

{211}

(d)

{110}

-2 -1 0 1 2

(h) <111> 1.21 - 1.25 1.16 - 1.21 1.12 - 1.16 1.08 - 1.12 1.04 - 1.08 1.00 - 1.04 0.95 - 1.00 0.91 - 0.95

-2 -1 0 1 2simulation SSr sites

1.18 - 1.25 1.12 - 1.18 1.05 - 1.12 0.98 - 1.05 0.91 - 0.98 0.85 - 0.91 0.78 - 0.85 0.71 - 0.78

(a) <100>-2 -1 0 1 2

2.63 - 2.90 2.37 - 2.63 2.10 - 2.37 1.83 - 2.10 1.56 - 1.83 1.30 - 1.56 1.03 - 1.30 0.76 - 1.03

simulation Oi sites

(e) <100>

1.20 - 1.27 1.14 - 1.20 1.08 - 1.14 1.01 - 1.08 0.95 - 1.01 0.88 - 0.95 0.82 - 0.88 0.75 - 0.82

(b) <110> 1.55 - 1.65 1.44 - 1.55 1.34 - 1.44 1.24 - 1.34 1.14 - 1.24 1.03 - 1.14 0.93 - 1.03 0.83 - 0.93

(f) <110>

2.08 - 2.26 1.90 - 2.08 1.72 - 1.90 1.54 - 1.72 1.36 - 1.54 1.18 - 1.36 1.00 - 1.18 0.82 - 1.00

(c) <211> 1.25 - 1.31 1.18 - 1.25 1.12 - 1.18 1.05 - 1.12 0.99 - 1.05 0.92 - 0.99 0.86 - 0.92 0.79 - 0.86

(g) <211>

[deg]-2 -1 0 1 2

(h) <111>(d) <111> 1.09 - 1.13 1.05 - 1.09 1.00 - 1.05 0.96 - 1.00 0.92 - 0.96 0.88 - 0.92 0.83 - 0.88 0.79 - 0.83

-2 -1 0 1 2

1.20 - 1.24 1.15 - 1.20 1.11 - 1.15 1.06 - 1.11 1.02 - 1.06 0.97 - 1.02 0.93 - 0.97 0.88 - 0.93

-2 -1 0 1 2simulation STi sites

1.53 - 1.64 1.42 - 1.53 1.31 - 1.42 1.19 - 1.31 1.08 - 1.19 0.97 - 1.08 0.86 - 0.97 0.75 - 0.86

(a) <100>-2 -1 0 1 2

1.34 - 1.42 1.27 - 1.34 1.19 - 1.27 1.12 - 1.19 1.04 - 1.12 0.96 - 1.04 0.89 - 0.96 0.81 - 0.89

simulation STiSO sites

(e) <100>

2.81 - 3.10 2.52 - 2.81 2.23 - 2.52 1.93 - 2.23 1.64 - 1.93 1.35 - 1.64 1.06 - 1.35 0.77 - 1.06

(b) <110> 1.24 - 1.29 1.18 - 1.24 1.13 - 1.18 1.08 - 1.13 1.02 - 1.08 0.97 - 1.02 0.91 - 0.97 0.86 - 0.91

(f) <110>

1.93 - 2.10 1.77 - 1.93 1.60 - 1.77 1.43 - 1.60 1.27 - 1.43 1.10 - 1.27 0.94 - 1.10 0.77 - 0.94

(c) <211> 1.14 - 1.19 1.10 - 1.14 1.05 - 1.10 1.00 - 1.05 0.96 - 1.00 0.91 - 0.96 0.87 - 0.91 0.82 - 0.87

(g) <211>

[deg]-2 -1 0 1 2

(h) <111>(d) <111> 1.09 - 1.13 1.05 - 1.09 1.00 - 1.05 0.96 - 1.00 0.92 - 0.96 0.88 - 0.92 0.83 - 0.88 0.79 - 0.83

-2 -1 0 1 2

1.18 - 1.22 1.14 - 1.18 1.10 - 1.14 1.06 - 1.10 1.02 - 1.06 0.98 - 1.02 0.94 - 0.98 0.90 - 0.94

emission channeling patterns, 59Fe 60 keV 1013 cm2 in SrTiO3, TA=900°C

<100> displ. STi ideal STi sites

-2 -1 0 1 2simulation STi sites

1.53 - 1.64 1.42 - 1.53 1.31 - 1.42 1.19 - 1.31 1.08 - 1.19 0.97 - 1.08 0.86 - 0.97 0.75 - 0.86

(a) <100>-2 -1 0 1 2

1.34 - 1.42 1.27 - 1.34 1.19 - 1.27 1.12 - 1.19 1.04 - 1.12 0.96 - 1.04 0.89 - 0.96 0.81 - 0.89

simulation STiSO sites

(e) <100>

2.81 - 3.10 2.52 - 2.81 2.23 - 2.52 1.93 - 2.23 1.64 - 1.93 1.35 - 1.64 1.06 - 1.35 0.77 - 1.06

(b) <110> 1.24 - 1.29 1.18 - 1.24 1.13 - 1.18 1.08 - 1.13 1.02 - 1.08 0.97 - 1.02 0.91 - 0.97 0.86 - 0.91

(f) <110>

1.93 - 2.10 1.77 - 1.93 1.60 - 1.77 1.43 - 1.60 1.27 - 1.43 1.10 - 1.27 0.94 - 1.10 0.77 - 0.94

(c) <211> 1.14 - 1.19 1.10 - 1.14 1.05 - 1.10 1.00 - 1.05 0.96 - 1.00 0.91 - 0.96 0.87 - 0.91 0.82 - 0.87

(g) <211>

[deg]-2 -1 0 1 2

(h) <111>(d) <111> 1.09 - 1.13 1.05 - 1.09 1.00 - 1.05 0.96 - 1.00 0.92 - 0.96 0.88 - 0.92 0.83 - 0.88 0.79 - 0.83

-2 -1 0 1 2

1.18 - 1.22 1.14 - 1.18 1.10 - 1.14 1.06 - 1.10 1.02 - 1.06 0.98 - 1.02 0.94 - 0.98 0.90 - 0.94

-2 -1 0 1 2simulation STi sites

1.53 - 1.64 1.42 - 1.53 1.31 - 1.42 1.19 - 1.31 1.08 - 1.19 0.97 - 1.08 0.86 - 0.97 0.75 - 0.86

(a) <100>-2 -1 0 1 2

1.34 - 1.42 1.27 - 1.34 1.19 - 1.27 1.12 - 1.19 1.04 - 1.12 0.96 - 1.04 0.89 - 0.96 0.81 - 0.89

simulation STiSO sites

(e) <100>

2.81 - 3.10 2.52 - 2.81 2.23 - 2.52 1.93 - 2.23 1.64 - 1.93 1.35 - 1.64 1.06 - 1.35 0.77 - 1.06

(b) <110> 1.24 - 1.29 1.18 - 1.24 1.13 - 1.18 1.08 - 1.13 1.02 - 1.08 0.97 - 1.02 0.91 - 0.97 0.86 - 0.91

(f) <110>

1.93 - 2.10 1.77 - 1.93 1.60 - 1.77 1.43 - 1.60 1.27 - 1.43 1.10 - 1.27 0.94 - 1.10 0.77 - 0.94

(c) <211> 1.14 - 1.19 1.10 - 1.14 1.05 - 1.10 1.00 - 1.05 0.96 - 1.00 0.91 - 0.96 0.87 - 0.91 0.82 - 0.87

(g) <211>

[deg]-2 -1 0 1 2

(h) <111>(d) <111> 1.09 - 1.13 1.05 - 1.09 1.00 - 1.05 0.96 - 1.00 0.92 - 0.96 0.88 - 0.92 0.83 - 0.88 0.79 - 0.83

-2 -1 0 1 2

1.18 - 1.22 1.14 - 1.18 1.10 - 1.14 1.06 - 1.10 1.02 - 1.06 0.98 - 1.02 0.94 - 0.98 0.90 - 0.94

-2

-1

0

1

2

-2 -1 0 1 2

(a)

{100}

{110}

experiment

-2 -1 0 1 2

1.30 - 1.37 1.24 - 1.30 1.17 - 1.24 1.10 - 1.17 1.03 - 1.10 0.97 - 1.03 0.90 - 0.97 0.83 - 0.90

best fit STi + STiSO

(e) <100>

-2

-1

0

1

2

{211}

{111}(b)

{110}

1.64 - 1.75 1.53 - 1.64 1.42 - 1.53 1.32 - 1.42 1.21 - 1.32 1.10 - 1.21 0.99 - 1.10 0.88 - 0.99

(f) <110>

-2

-1

0

1

2(c)

{210}

{110}

1.29 - 1.36 1.23 - 1.29 1.16 - 1.23 1.10 - 1.16 1.03 - 1.10 0.97 - 1.03 0.91 - 0.97 0.84 - 0.91

(g) <211>

[deg]-2 -1 0 1 2

-2

-1

0

1

2

{211}

(d)

{110}

-2 -1 0 1 2

(h) <111> 1.16 - 1.20 1.12 - 1.16 1.08 - 1.12 1.04 - 1.08 0.99 - 1.04 0.95 - 0.99 0.91 - 0.95 0.87 - 0.91

emission channeling patterns, 59Fe 60 keV 1013 cm2 in SrTiO3, TA=900°C

<100> displ. STi ideal STi

-2 -1 0 1 2simulation STi sites

1.53 - 1.64 1.42 - 1.53 1.31 - 1.42 1.19 - 1.31 1.08 - 1.19 0.97 - 1.08 0.86 - 0.97 0.75 - 0.86

(a) <100>-2 -1 0 1 2

1.34 - 1.42 1.27 - 1.34 1.19 - 1.27 1.12 - 1.19 1.04 - 1.12 0.96 - 1.04 0.89 - 0.96 0.81 - 0.89

simulation STiSO sites

(e) <100>

2.81 - 3.10 2.52 - 2.81 2.23 - 2.52 1.93 - 2.23 1.64 - 1.93 1.35 - 1.64 1.06 - 1.35 0.77 - 1.06

(b) <110> 1.24 - 1.29 1.18 - 1.24 1.13 - 1.18 1.08 - 1.13 1.02 - 1.08 0.97 - 1.02 0.91 - 0.97 0.86 - 0.91

(f) <110>

1.93 - 2.10 1.77 - 1.93 1.60 - 1.77 1.43 - 1.60 1.27 - 1.43 1.10 - 1.27 0.94 - 1.10 0.77 - 0.94

(c) <211> 1.14 - 1.19 1.10 - 1.14 1.05 - 1.10 1.00 - 1.05 0.96 - 1.00 0.91 - 0.96 0.87 - 0.91 0.82 - 0.87

(g) <211>

[deg]-2 -1 0 1 2

(h) <111>(d) <111> 1.09 - 1.13 1.05 - 1.09 1.00 - 1.05 0.96 - 1.00 0.92 - 0.96 0.88 - 0.92 0.83 - 0.88 0.79 - 0.83

-2 -1 0 1 2

1.18 - 1.22 1.14 - 1.18 1.10 - 1.14 1.06 - 1.10 1.02 - 1.06 0.98 - 1.02 0.94 - 0.98 0.90 - 0.94

-2 -1 0 1 2simulation STi sites

1.53 - 1.64 1.42 - 1.53 1.31 - 1.42 1.19 - 1.31 1.08 - 1.19 0.97 - 1.08 0.86 - 0.97 0.75 - 0.86

(a) <100>-2 -1 0 1 2

1.34 - 1.42 1.27 - 1.34 1.19 - 1.27 1.12 - 1.19 1.04 - 1.12 0.96 - 1.04 0.89 - 0.96 0.81 - 0.89

simulation STiSO sites

(e) <100>

2.81 - 3.10 2.52 - 2.81 2.23 - 2.52 1.93 - 2.23 1.64 - 1.93 1.35 - 1.64 1.06 - 1.35 0.77 - 1.06

(b) <110> 1.24 - 1.29 1.18 - 1.24 1.13 - 1.18 1.08 - 1.13 1.02 - 1.08 0.97 - 1.02 0.91 - 0.97 0.86 - 0.91

(f) <110>

1.93 - 2.10 1.77 - 1.93 1.60 - 1.77 1.43 - 1.60 1.27 - 1.43 1.10 - 1.27 0.94 - 1.10 0.77 - 0.94

(c) <211> 1.14 - 1.19 1.10 - 1.14 1.05 - 1.10 1.00 - 1.05 0.96 - 1.00 0.91 - 0.96 0.87 - 0.91 0.82 - 0.87

(g) <211>

[deg]-2 -1 0 1 2

(h) <111>(d) <111> 1.09 - 1.13 1.05 - 1.09 1.00 - 1.05 0.96 - 1.00 0.92 - 0.96 0.88 - 0.92 0.83 - 0.88 0.79 - 0.83

-2 -1 0 1 2

1.18 - 1.22 1.14 - 1.18 1.10 - 1.14 1.06 - 1.10 1.02 - 1.06 0.98 - 1.02 0.94 - 0.98 0.90 - 0.94

-2

-1

0

1

2

-2 -1 0 1 2

(a)

{100}

{110}

experiment

-2 -1 0 1 2

1.30 - 1.37 1.24 - 1.30 1.17 - 1.24 1.10 - 1.17 1.03 - 1.10 0.97 - 1.03 0.90 - 0.97 0.83 - 0.90

best fit STi + STiSO

(e) <100>

-2

-1

0

1

2

{211}

{111}(b)

{110}

1.64 - 1.75 1.53 - 1.64 1.42 - 1.53 1.32 - 1.42 1.21 - 1.32 1.10 - 1.21 0.99 - 1.10 0.88 - 0.99

(f) <110>

-2

-1

0

1

2(c)

{210}

{110}

1.29 - 1.36 1.23 - 1.29 1.16 - 1.23 1.10 - 1.16 1.03 - 1.10 0.97 - 1.03 0.91 - 0.97 0.84 - 0.91

(g) <211>

[deg]-2 -1 0 1 2

-2

-1

0

1

2

{211}

(d)

{110}

-2 -1 0 1 2

(h) <111> 1.16 - 1.20 1.12 - 1.16 1.08 - 1.12 1.04 - 1.08 0.99 - 1.04 0.95 - 0.99 0.91 - 0.95 0.87 - 0.91

-2 -1 0 1 2simulation SSr sites

1.18 - 1.25 1.12 - 1.18 1.05 - 1.12 0.98 - 1.05 0.91 - 0.98 0.85 - 0.91 0.78 - 0.85 0.71 - 0.78

(a) <100>-2 -1 0 1 2

2.63 - 2.90 2.37 - 2.63 2.10 - 2.37 1.83 - 2.10 1.56 - 1.83 1.30 - 1.56 1.03 - 1.30 0.76 - 1.03

simulation Oi sites

(e) <100>

1.20 - 1.27 1.14 - 1.20 1.08 - 1.14 1.01 - 1.08 0.95 - 1.01 0.88 - 0.95 0.82 - 0.88 0.75 - 0.82

(b) <110> 1.55 - 1.65 1.44 - 1.55 1.34 - 1.44 1.24 - 1.34 1.14 - 1.24 1.03 - 1.14 0.93 - 1.03 0.83 - 0.93

(f) <110>

2.08 - 2.26 1.90 - 2.08 1.72 - 1.90 1.54 - 1.72 1.36 - 1.54 1.18 - 1.36 1.00 - 1.18 0.82 - 1.00

(c) <211> 1.25 - 1.31 1.18 - 1.25 1.12 - 1.18 1.05 - 1.12 0.99 - 1.05 0.92 - 0.99 0.86 - 0.92 0.79 - 0.86

(g) <211>

[deg]-2 -1 0 1 2

(h) <111>(d) <111> 1.09 - 1.13 1.05 - 1.09 1.00 - 1.05 0.96 - 1.00 0.92 - 0.96 0.88 - 0.92 0.83 - 0.88 0.79 - 0.83

-2 -1 0 1 2

1.20 - 1.24 1.15 - 1.20 1.11 - 1.15 1.06 - 1.11 1.02 - 1.06 0.97 - 1.02 0.93 - 0.97 0.88 - 0.93

ideal SSr

SQUID magnetic moment of SrTiO3:Fe (H)

• 56Fe 60 keV 51015 cm2, TA=900°C, SQUID measurement at 10 K• Diamagnetism of SrTiODiamagnetism of SrTiO33 substrate substrate• Weak paramagnetism of implanted Fe and contaminants (0.5 ppm Cu2+?)• Ferromagnetism of implanted Fe

SQUID magnetic moment of SrTiO3:Fe (T)

• Paramagnetic component becomes obvious from temperature dependence:

1/T Brillouin paramagnetic vs constant diamagnetic + ferromagnetic

-1000 -500 0 500 1000

-0.0002

0.0000

0.0002

-1 x1 04

-5 x1 03 0 5 x1 0

31 x1 0

4

-2 x1 0-3

-1 x1 0-3

0

1 x1 0-3

2 x1 0-3

/m

[em

u g

-1]

S T O _ 2 5 6 (51 015

)

S T O _ 2 5 7 (11 015

) S T O _ v irg in

H[Oe]

small ferromagnetic signals from virgin SrTiO3 11015 cm2 Fe implanted

magnetization of 51015 cm2 Fe implanted SrTiO3

7.5 B

ferromagnetic signature

SQUID results for different Fe fluences

Note: 60 keV 11015 cm2 corresponds to [Fe]max = 1.8% /unit cell

implanted Fe exhibits ferromagnetism in SrTiO3

Sources of magnetism in Fe-implanted SrTiO3

Cu and Ag in SrTiO3

• As group Ib elements, Cu and Ag on Sr sites are candidates for p-type (acceptor) doping of SrTiO3

• which lattice site do they occupy following ion implantation?

study by means of emission channeling using the radioactive isotopes 67Cu (t1/2=63 h) and 111Ag (7.5 d)

• Note: low dose implantations (60 keV, 51012 11013 cm2)

0 200 400 600 800 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0 sum of all fractions f(I8) octahedral interst.

f(Sr) f(Ti)

67C

u fr

actio

ns f

annealing temperature TA [°C]

67Cu and 111Ag lattice sites in SrTiO3 as function of TA

as-implanted: substitutional + octahedral interstitial I8 sites Cu and Ag on I8 disappears fast broad recovery stage of damage 300-900°C, Cu and Ag are both amphoteric (found on both Sr and Ti sites) Cu prefers Ti sites while Ag prefers Sr sites!

Possible explanation: ionic radiiSr2+ 1.13 Å Cu1+ 0.96 Å Ag1+ 1.26 Å Ti4+ 0.68 Å Cu2+ 0.69 Å Ag2+ 1.08 Å

67Cu

111Ag

Motivation: SrTiO3 in the focus as...

... red phosphor material flat panel displays

emission channeling patterns, 169Yb 1014 cm2 in SrTiO3, TA=900°C

SSr STi

-2

-1

0

1

2

-2 -1 0 1 2

(b)

(a)

{100}

{110}

experiment

-2 -1 0 1 2 1.67 - 1.83 1.52 - 1.67 1.36 - 1.52 1.21 - 1.36 1.05 - 1.21 0.89 - 1.05 0.74 - 0.89 0.58 - 0.74

simulation best fit

(f) <100>

-2

-1

0

1

2

{110}

2.09 - 2.28 1.90 - 2.09 1.71 - 1.90 1.52 - 1.71 1.33 - 1.52 1.14 - 1.33 0.95 - 1.14 0.76 - 0.95

(g) <110>

-2

-1

0

1

2

{110}

(c) 2.06 - 2.25 1.86 - 2.06 1.67 - 1.86 1.48 - 1.67 1.28 - 1.48 1.09 - 1.28 0.89 - 1.09 0.70 - 0.89

(h) <211>

[deg]

-2

-1

0

1

2(d)

{110}

(i) <411> 1.79 - 1.94 1.63 - 1.79 1.48 - 1.63 1.33 - 1.48 1.17 - 1.33 1.02 - 1.17 0.86 - 1.02 0.71 - 0.86

-2 -1 0 1 2

-2

-1

0

1

2(e)

{110}

-2 -1 0 1 2

(j) <111> 1.30 - 1.39 1.21 - 1.30 1.12 - 1.21 1.03 - 1.12 0.94 - 1.03 0.85 - 0.94 0.76 - 0.85 0.67 - 0.76

-2

-1

0

1

2

-2 -1 0 1 2

1.41 - 1.53 1.30 - 1.41 1.18 - 1.30 1.07 - 1.18 0.95 - 1.07 0.83 - 0.95 0.72 - 0.83 0.60 - 0.72

(b) <110>

(a) <100>

Sr sites-2 -1 0 1 2

1.87 - 2.05 1.68 - 1.87 1.50 - 1.68 1.32 - 1.50 1.14 - 1.32 0.96 - 1.14 0.77 - 0.96 0.59 - 0.77

Ti sites

(e) <100>

-2

-1

0

1

2 1.31 - 1.40 1.22 - 1.31 1.12 - 1.22 1.03 - 1.12 0.94 - 1.03 0.85 - 0.94 0.75 - 0.85 0.66 - 0.75

3.40 - 3.80 3.00 - 3.40 2.60 - 3.00 2.19 - 2.60 1.79 - 2.19 1.39 - 1.79 0.99 - 1.39 0.59 - 0.99

(f) <110>

-2

-1

0

1

2 2.94 - 3.27 2.62 - 2.94 2.29 - 2.62 1.97 - 2.29 1.64 - 1.97 1.31 - 1.64 0.99 - 1.31 0.66 - 0.99

(c) <211> 2.89 - 3.21 2.56 - 2.89 2.24 - 2.56 1.92 - 2.24 1.59 - 1.92 1.27 - 1.59 0.94 - 1.27 0.62 - 0.94

(g) <211>

[deg]-3 -2 -1 0 1

-2

-1

0

1

2 2.06 - 2.26 1.86 - 2.06 1.66 - 1.86 1.47 - 1.66 1.27 - 1.47 1.07 - 1.27 0.87 - 1.07 0.67 - 0.87

(d) <411>

-3 -2 -1 0 1

(h) <411> 2.16 - 2.38 1.93 - 2.16 1.71 - 1.93 1.49 - 1.71 1.26 - 1.49 1.04 - 1.26 0.81 - 1.04 0.59 - 0.81

169Yb lattice sites in SrTiO3 as function of TA

no octahedral interstitial I8 sites (in contrast to TMs Fe, Cu, Ag) also broad recovery stage of damage 300-900°C, Yb is also amphoteric (found on both Sr and Ti sites) Yb prefers Ti sites

Overview: SrTiO3 emission channeling lattice location experiments

• Electrical dopantsElectrical dopants• Magnetic dopantsMagnetic dopants• Optical dopantsOptical dopants

Emission channeling lattice location Emission channeling lattice location experiments undertaken so far experiments undertaken so far Experiments foreseen or possibleExperiments foreseen or possible Experiments attemptedExperiments attempted

Conclusions

SrTiO3 relatively resistant against implantation damage

damage annealing starts above 200-300°C...• but is only complete at ~1000-1100°C annealing is less efficient than expected• lattice location experiments in SrTiO3 difficult to

analyze:– Cu, Ag, Yb are amphoteric impurities: multiple sites– Fe also shows site distribution: <100> diplaced Ti + Ti

generally doping is complicated by amphoteric nature

• Ag more promising Sr-site acceptor than Cu,• Fe was shown to act as ferromagnetic dopant

Performance against original work plan:

Year 1 (2005-06): lattice location and damage annealing studies in SrTiO3, first measurements of optical and magnetic properties

• Year 2 (2006-07): lattice location and damage annealing studies extended to other perovskites, e.g. KTaO3 (samples have now been bought), measurements of optical and magnetic properties under optimized conditions (dose, annealing…)

• Year 3 (2007-08): set priorities for the study of those systems where, according to outcome of research in years 1+2, best results were obtained