Morphology and structure of advanced oxide nanostructures using hard X-rays. Antoine Barbier
description
Transcript of Morphology and structure of advanced oxide nanostructures using hard X-rays. Antoine Barbier
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