Morphology and structure of advancedoxide nanostructures using hard X-rays.

Antoine Barbier

C.E.A./Saclay – DSM / IRAMIS / SPCSIF-91191 Gif Sur Yvette

1. Introduction2.Grazing incidence X-ray diffraction3.Grazing incidence small angle scattering4.Scanning x-ray Diffraction Microscope5.Conclusion

1. Introduction - Context

MRAM chip (IBM)

FM1/Insulator/FM2

Generation of a spin polarized current

Array of micron sized structures obtained by lithography- High areal density- High current densities for writing

Spin-filter effectGMR, TMR…

GMR : Nobel Prize 2007 : Albert Fert and Peter Grünberg

Reciprocal spaceExample : NiO(111) type surface

CTRs relative position vs. bulk

Bulk Bragg peaks

00L

02L

20L

22L

Bulk mesh

h00

0k0

Spec

ular

In-plane diffraction Projected 2D structure

Reconstruction diffraction rods relaxation and thickness

12L

11L

10L

21L01L

(2x2) mesh

GISAXS

Magnetic Bragg peaks (Antiferromagnet)

0,0,3/2

2,2,3/2

2,2,1/2

AF mesh

Grazing incidence X-ray scattering

Complex refraction index of X-rays : n i 1 .

with

2 2

2 22 10 5e

mcZ jcell j

ZMv

f( ')

2 2

2 2 410 6e

mc jcellv

f ''

If n then nmfewaandc 5.01.02

q

q//

q

ki

kf

2

f

i

610BulkISurfaceI

Z (L)

X (h)

Y (k)

Insensitive to charge build-up – Very sensitive to surface through Insensitive to charge build-up – Very sensitive to surface through grazing incidence – Requires synchrotron radiationgrazing incidence – Requires synchrotron radiation

Real space Reciprocal space

q//

q

GIXD on MgO(111) Air 1500°C/3h annealed surface

1 2 3 4 5 6101

102

103

104

105

106

Bragg Peak

CTRp(2x2)

CTR

p(2x2)

MgO(111)-p(2x2)(H, 0, 0.05)

Coun

ts/s

H (in p(2x2) units) -80.6 -80.5 -80.4 -80.3 -80.2 -80.1 -80.0 -79.9

1000

(1,0,0.05) - Reconstruction peakWidth = 0.04°

MgO(111)-p(2x2)

Cou

nts/

s

Rocking angle (Theta)

254°CRT

GIXD, RT, 17 keV, @ ID03, ESRF

Simple monoxide without electronic correlations DFT calculations possible

R.Plass et al. PRL 81 (1998) : Cyclic Ozone• Electrostatic ???• Diverging surface energy

Es (octopole) =2.05 J/m2

Es (spinel) =4.45 J/m2 (metastable !!!)Es (1x1) =5.6 J/m2

Es (ozone)> Es (1x1) (unstable !!!)Role of oxygen potential ???

F.Finocchi, A.Barbier, J.Jupille, C.Noguera PRL 92 (2004) 136101A. Barbier et al., J. Phys.: Condens. Matter 20 (2008) 184014

GIXD on MgO(111) Air 1500°C/3h annealed surface

Reproducing the GIXD structure factors(150K - 320K)+ Satisfy the electrostatic criterion+ Minimising surface energy+ Taking into account the oxygen potential(grand canonical)

h h

k k(a) (b)

h h

k k(a) (b)

(c)

(d)

-1.5 0.0 1.5

0.00

0.15

1 4

0.1

1

F 1-1L

, F1-

2L

L [r.l.u. MgO]

F -44L

, F-4

0L

h h

k k(a) (b)

h h

k k(a) (b)

(c)

(d)

-1.5 0.0 1.5

0.00

0.15

1 4

0.1

1

F 1-1L

, F1-

2L

L [r.l.u. MgO]

F -44L

, F-4

0L

Numerical relaxation of structuresRelative fraction = Only fitting parameter

RT – 28% O-Oct

520K – 13% O-Oct

O-octopole + Mg/MgO(111)

GIXD on MgO(111) Role of oxygen chemical potential

Patterson (self-correlation) maps vs O

MgO(111) surface termination depends on chemical environement

A. Barbier et al., J. Phys.: Condens. Matter 20 (2008) 184014

@ ESRF, ID03

GIXD on -Fe2O3(0001) Role of oxygen chemical potential

A.Barbier et al. Phys. Rev. B 75 (2007) 233406

Reduction – re-oxidation cycleSurface structure changes (irreversible)

@ ANKA

Small angle X-Ray Scatteringin situ deposition

Geometry - Principle

Ag/MgO, Co/Au : G. Renaud et al., Science 300, 1416 (2003)

NiO/Cu(111) : A. Barbier et al., Phys. Rev. B 68 (2003) 245418

CNTs : J. Mane-Mane et al., PSSRRL 1(2007)122 & PSS(a) 204(2007)4209

Co/Au(111)

Self-organized

Ag/MgO(001)

Coalescence

GISAXS – ModelisationSelf-patterning : NiO/Cu(111)

0.3, 5.4, 8.3, 9.0, 9.8, and 10.8 Å

Self-organization above 6 Å

Reactive interface => islands + hole creation due to Ni-Cu corrals

NiO/Cu(111)

80nm x 80 nm

A. Barbier et al., Phys. Rev. B 68 (2003) 245418

GISAXS – Island shape investigationsRh/MgO(001)

From P. Nolte et al., Science 321, 1654 -1658 (2008)

Islands shape changes can be recorded upon oxidation / reduction cycles=> Catalytic activity cannot be extrapolated from UHV observations only

Principle of a “Scanning x-ray Diffraction Microscope“

(i = )samplenormal[001]

X-ray scattered beam

(2)

Sample_y

Sample_x

12Setup available @ ID01 (ESRF)

C. Mocuta et al., Phys. Rev. B 77, 245425 (2008)

Compound Refractive Lenses (CRL)

13

variable number of lenses

variable number of lenses::NN==110 -300 0 -300

single lenslens

stack of lenses:stack of lenses:compound refractive lens (CRL)compound refractive lens (CRL)

F(1 lens, 10 keV) = 29.3 mGain ~ 30

R = 200 m2R0 ~ 1 mmd ~ 5 m

NRF

2

F(50 lenses, 10 keV) = 0.6 mGain ~ 3×104

Snigirev et al, 1996

Here :E=7 keV, 18 CRL, F = 800 mmSpot size of about 69 m² (HV)

MBE growth of Pt/CoFe2O4/Al2O3/Co MTJs

14α-Al2O3 (0001)

CoFe2O4 (111)

Co (0001)

In situ RHEED characterizationReflection high energy electron diffraction

(0,1)

(0,2) (1,1)

a*b*

D2

D1

(1/2, 1/2)

Fe3O4 (111) orCoFe2O4 (111)a-Al2O3 (0001)

Reciprocal lattices

Fe + Co

Oxygen

Knudsen cell

Plasma source

(111) Growth on α-

Al2O3(0001) substrate

Oxygen plasma-assisted molecular beam epitaxy

Pt (111)

-Al2O3 (111)Pt

CoFe2O4

-Al2O3

Co

SamplesLithography CNRS/Thales

15

Full lithography with contacts Partial lithography with junctions of variable shapes

Spin filter Al2O3(0001)/Pt(10nm)/CoFe2O4(5 nm)/-Al2O3(1.5 nm)/Co(15 nm) /Au(15 nm)

MTJ Al2O3(0001)/Pt(10nm)/Fe3O4(25nm)/-Al2O3(3nm)/Co(15nm)/Au(15nm)

Lithography of structures alone

Sample crystalline structure

16

Epitaxial + Single crystalline growthContinuous layers (incl. barrier) For each layer a given /2 setting

layer selective analysis

40 45 50 55 60 65 70

CoF

e2O

4(22

2)

CoF

e2O

4(33

3)

Co(

111)

Al 2O

3(00

6)

Pt(1

11)

Au(

111)

Inte

nsity

(arb

. uni

ts)

2 (o)

detector

Sample with junction

40 45 50 55 60 65 70

CoF

e2O

4(22

2)

CoF

e2O

4(33

3)

Co(

111)

Al 2O

3(00

6)

Pt(1

11)

Au(

111)

Inte

nsity

(arb

. uni

ts)

2 (o)

detector

Sample with junction

Co(

0002

)

Specular Intensity Mapping @ Bragg peaks

17

Al2O3 substrate

Pt buffer

CoFe2O4

Co

Au

Co

CoFe2O4

Pt

Scanning probe microscope

Au

Measure of the intensitiesThe layer structure is resolved

C.Mocuta et al., Appl. Phys. Lett. 91, 241917 (2007)

Bragg peak position mapping

18-25 -20 -15 -10 -5 0 5 10 15 20 25

2.4

3.0

3.6

0

10000024.0

24.1

24.2

24.3

24.4

24.5

fwhm

Hx (microns)

Area

Int.

(cps

)

max

Co (111 - hx scan - E1)

0.6°

0.2°

Co(002) // hx

(i = )samplenormal[001]

X-ray scattered beam

(2)

hz

hx

h

(i = )samplenormal[001]

X-ray scattered beam

(2)

hz

hx

h

CoFe2O4 (20 x 20 m²)CoFe2O4 (20 x 20 m²) – Rocking scans depending on positionCoFe2O4 (20 x 20 m²)

Bragg peak max moveswhen scanning ║ beam

Fwhm constantNo effect beam

Lattice deformation

-25 -20 -15 -10 -5 0 5 10 15 20 25

2.4

3.0

3.6

0

100000

23.423.623.824.024.224.424.624.825.025.225.4

fwhm

Hz corr (microns)

Area

Int.

(cps

)

max

Co (111 - hz scan - E1)

1.6°

0.6°

Co(002) // hz

hz

C.Mocuta et al., Eur. Phys. J. Special Topics 168, 53–58 (2009)

Square CoFe2O4 MTJ

19

Measure the tilt of the crystalline planes function of the lateral position in the junction(x) = Bragg(x) – Bragg(center)

Layer deformation is maximal for intermediate sized junctions like 20x20m² Effect decreases for the smallest junctions (0.3° for 10x10 m² junctions) : size effect

-30 -20 -10 0 10 20 30

0.00.20.40.60.81.0

I (ar

b. u

nits

)

distance from the center of the junction (m)

-0.8

-0.4

0.0

0.4

0.8 50 m junction 20 m junction 10 m junction

(o )

Al2O3 substrate

Pt buffer

CoFe2O4

Co

-Al2O3

~0.9o

~0.2o

~0.0o

Displacement from the centerof the junction

Co(0002)

50x50m

Fe3O4 based TMJ (Disk 50m)

20

Fe3O4(333)

-50 -40 -30 -20 -10 0 10 20 30 40 50

0.6

0.8

1.0

1.2

1.40

2000

32.6

32.8

33.0

fwhm

Hx (microns)

Aera

Int.

(cps

)

max

Fe3O4(333) - hz- scan (J3)

-45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 451.21.41.61.82.02.22.4

0

2000

4000

6000

800059.6

59.8

60.0

60.2

60.4

fwhm

Hx (microns)

Aera

Int.

(cps

)

max

Co (004) - hz- scan (J3, 50um)

Co(004)

Al2O3 substrate

Pt buffer

Fe3O4

Co

0.15o

Au

Al2O3

50m

Co electrode is more affected Similar lattice deformation Reversed effect on max

Different layer relaxation

0.3o

Co(004)

0.6°

Fe3O4(333)

0.3°

Shape effect - Fe3O4 MTJs

21

Al2O3 substrate

Pt buffer

Fe3O4

Co

Au

The deformation is shape dependent for a given materialCircular objects experience less deformation (~1 order of magnitude !!!)

Al2O3

0.9o

3o

-80 -60 -40 -20 0 20 40 60 800.00

0.25

0.50

0.75

1.00

Co(004), 2B=120.6o

120x40m =50 m

peak

are

a(a

rb.u

nits

)position from junction's center (Ty, m)

-3-2-10123

angu

lar s

hift

(deg

)

x8

Lattice Parameter Evolution

22

Latti

cem

isfit

(%)

Deposition time (min)

Lattice Parameters followed in situ by RHEED

-Al2O3

Fe3O4

Sample (CoFe2O4):Al2O3 not relaxed larger effect after lithographycontraction ?

Sample (Fe3O4):Al2O3 is relaxedsmaller effect after lithography

Tentatively it is likely that lithography promotes structural relaxationA. Bataille, PhD Thesis (2005)

ConclusionsHard X-rays methods vs oxide nanostructures

• Advantages :– No charge build-up problems– Investigation of real samples possible– Investigation under different sample environments– Non – destructive investigations– Large variety of methods available

• Surface structure investigations• Island morphology and/or reactivity• Nanostructure structural relaxation, shape and size effects

• Drawbacks– Synchrotron radiation often mandatory– Good crystalline structural required– Sometimes high photon density and /or focalization needed

Thanks for your attention

Coworkers

24

Scanning x-ray diffraction microscopeC. Mocuta, A.V. Ramos, M.-J. Guittet, J.-B. Moussy, S. Stanescu, R. Mattana, C.

Deranlot, F. Petroff

Polar oxides and MgO(111) Surface diffractionF.Finocchi, J.Jupille, C.Noguera, K. Peters, H. Kuhlenbeck, B. Richter, A. Stierle, N.

Kasper, C.Mocuta

GISAXSG.Renaud, O. Ulrich, O. Fruchart, S. Stanescu, J. Mane-Mane, R. Lazarri, J. Jupille, F.

Leroy, Yves Borensztein, C. R. Henry, J.-P. Deville, F. Scheurer, C. Boeglin