Stanford Synchrotron Radiation Laboratory More Thin Film X ...
Transcript of Stanford Synchrotron Radiation Laboratory More Thin Film X ...
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Stanford Synchrotron Radiation Laboratory
More Thin Film X-ray Scattering and X-ray Reflectivity
Mike Toney, SSRL
1. Introduction (real space – reciprocal space)2. Polycrystalline film (no texture) – RuPt3. Textured film: MnPt4. X-ray Reflectivity5. Summary
• how do you get diffraction data from thin films• how to choose what to do (what beam line & scans)• what do you learn
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Real and Reciprocal Space
epitaxialfilm
“powder” film(polycrystalline)
Arturas
Real space Reciprocal space
spotsorigin
spheres
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Real and Reciprocal Space
Real space Reciprocal spacetextured film
differences in extent of texture
rings
slice gives spots
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Thin Film Scattering
What do you do?• what beam line? (2-1, 7-2, 11-3)
• area vs point detector; flux; energy• what scans? (“where” in reciprocal space)
• what do you want to learn:phase identificationlattice parametersdefectstexture crystallite sizeatomic structure
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Thin Film Scattering
2θ
Q
Two ways: Area detector & Point detector
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RuPt Thin FilmsDirect Methanol Fuel Cell (DMFC)• low operating temperature & high energy density• low power applications (cell phones, PCs,)
RuPt alloys used as catalysts for DMFCs• as nanoparticles, but also films• catalytic activity of RuPt depends on
composition and structure (hcp or fcc)
anode: CH3OH + H2O => CO2 + 6H+ + 6e-
cathode: 3/2O2 + 6H+ +6e- => 3H2O sum: CH3OH + 3/2O2 => CO2 + 2H2O
Hamnet, Catalysis Today 38, 445 (1997)Park et al., J. Phys. Chem. B 106, 1735 (2002)
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RuPt Thin Films
• T-W Kim, S-J Park, Gwangju Institute of Science & Technology, South Korea
• K-W Park, Y-E Sung, Seoul National University, South Korea
• Lindsay Jones, (SULI Internship)
SiRuPt: vary %
thin films of RuPtrf sputtered13 nm thick
Goal: Correlate crystal structure of RuPtalloys to catalytic activity
Pt is fcc; Ru is hcpfcc->hcp transition as Ru increases
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Polycrystalline (powder) film
Cu
“Powder”: randomorientation of many smallcrystals (crystallites)
QIn
tens
ity
Q
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RuPt Thin FilmsArea
Detector2θ incident
α ~ 0.1−0.2 degQ scattered
Beam line11-3 incidentscattered
Detector
Q
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RuPt Thin FilmsRu() Pt ()
fcc(111)
glitchfcc
(220)fcc
(200)
fcc(311)& (222)
Q
in-plane scan
Q
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RuPt Thin Films: diffraction
T-W. Kim et al., J. Phys. Chem. B 109, 12845 (2005)
Increasing Ru =>transition from fcc to mixed fcc/hcp to hcp
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RuPt Thin FilmsUse peak intensities to quantify phases
Thin Film Phase Diagram
Thin film different from bulk, due to sputter depositionKinetics do not allow equilibrium
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RuPt Thin Films
0 20 40 60 80 1000.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
at 0.4 V vs. Ag / AgCl
Percentage of Ru / %
C
urre
nt d
ensi
ty /
mA
cm
-2
fccfcc/hcp hcp
• composition dependent activity similar to pure fcc alloys • hcp RuPt does not adversely affect activity• may be manifestation of surface properties (similarity of fcc(111) and hcp(002)
0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.500.000
0.004
0.008
0.012
0.016
0.020
46.2% of Ru
67.0% of Ru
28.8% of Ru
Potential / V vs. Ag/AgCl
Cur
rent
den
sity
/ m
A c
m-2
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RuPt Films: Lattice Parameters
bulk alloys• Accurately determine lattice parameters• Cannot use bulk alloy lattice parameters to get composition
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Summary: polycrystallineRuPt films:
phase identification (hcp, fcc)lattice parameters (strain)no strong texturecrystallite size
• Area detector• Point detector
Scan choice straightforward
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XRD - BS• GUI for removal of background and thickness corrections
– http://www-ssrl.stanford.edu/~swebb/xrdbs.zip– http://www-ssrl.stanford.edu/~swebb/xrdbs.htm (coming soon)
SamWebb
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Thin Films for Magnetic Recording
Tsann Lin and Daniele Mauri,Hitachi Global StorageMahesh Samant, IBM
$5.2/MB $0.0003/MB
ContactHard Bias
ContactHard Bias
Read Head
Write Head
500 nm
2 μm
PinnedFerromagntic
Film
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Exchange bias (Heb)
Thin Films for Magnetic Recording
current flow
Toney, Samant, Lin, Mauri, Appl. Phys. Lett. 81, 4565 (2002)
• Understand this behavior (for MnPt)
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MnPt Films: chemical order
chemically disorderedfcc structurenot antiferromagnetic
chemically orderedL10 structure (face centered tetragonal)c/a = 0.92antiferromagnetic (TN = 700-800o C)
Cebollada, Farrow & Toney, in Magnetic Nanostructures, Nalaw, ed. 2002
Mn
Mn
Pt
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partial chemical order: S=1/2
Cebollada, Farrow & Toney, in Magnetic Nanostructures, Nalaw, ed. 2002
No chemical order: S=0 Full chemical order: S=1
S=0S=½S=1
MnPt Films: chemical order
Mn
chemical order parameter (S): extent of chemical order
a
determine S from peak intensities(110)/(220) ratio
(111)(200)
(220)
(111) (200)
(220)(202)
(002)(110)
(001)
(111)(200)
(220) (202)
(002)(110)(001)
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Highly Textured Thin Films
rings
slice gives spots
sputteredannealed at 280C
for 2 hours(111)
(110) (220)
(111)
(200) Q
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2θα
β
2θ is scattering angleQ = scattering vectorQ = (4π/λ) sin θα = incidence angleβ = exit angle
Si
MnPt
MnPt Films: diffraction
(111)
(110) (220)
(111)
(200)
Q
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fcc(220)
(220)
(202)(110)
(001)
(111)
(110)(200)
(002)
• increased thickness: the superlattice (001) and (110) peaks increase => more chemical ordering
• coexistence of fcc and L10 Toney, Samant, Lin, Mauri, Appl. Phys. Lett. 81, 4565 (2002)
MnPt Films: diffraction
(110) (220)
(111)
Q
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• coexistence of fcc and L10 MnPt (inhomogeneous)• complete chemical order for highest Heb
MnPt Film Structure
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MnPt (111)
as depositedannealed
as deposited
annealed
NiFe, Cu (111)
more chemically ordered MnPt -> larger grains
NiFe & Cu do not change much with annealing
MnPt Films: crystallite size
(110) (220)(111) Q
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L1 (202)0
L1 (220)0
fcc(220)fcc(220)
L1 (220)0
L1 (202)0
fcc(220)
(220)
(202)(110)
(001)
(111)
(110)(200)
(002)
MnPt Films: crystallite size
datafit
resolvedpeaks
L10 (transformed) regions have larger crystallite than fcc regions
fcc regions close to unanneled crystallite size
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Texture in Thin Films• Pole figure measures orientation distribution of diffracting planes
• Ψ = 0 deg planes along substrate
• Ψ = 90 deg planes ┴ to substrate
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MnPt Films: Texture
20 nm MnPt annealed
annealed
as deposited
MnPt(111)
10 nm
NiFe, Cu (111) NiFe, Cu (111)
MnPt(111)20 nm
5 nm
12x
12x
annealing effect thickness effect
(111)
(110)
(111)
Q
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MnPt Films
fcc MnPt L1 phase MnPt0
as depositedseed layer induces (111) growth in
NiFe & Cu [(00.2) in hcp Co & CoFe] and columnar morphology
MnPt follows (111) growth
annealedNiFe & Cu maintain (111)
orientation [(00.2) in Co & CoFe]fcc MnPt keeps (111) orientation L10 MnPt:
some keeps (111) orientation some becomes nearly isotropicgrain growth
=> L10 MnPt forms by nucleation and growth
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MnPt Films: Summarythin MnPt remains fcc => not antiferromagnetic and no
exchange bias coexistence between fcc and L10(inhomogeneous)
need complete L10 order to get highest exchangeno (<0.5 nm) fcc layer near interfacegrain growth and change in preferred orientation with
development of chemical order
=> L10 forms by nucleation & growth
fcc(220)
(220)
(202)(110)
(001)
(111)
(110)(200)
(002)
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MnPt Thin Films: SummaryMnPt films:
phase identification (L10, fcc)lattice parameters (strain)texturecrystallite size
• Area detector• Point detector
(111)
(110) (220)
(111)
(200)
Q
• Scan choice requires knowledge of reciprocal space & what you want to learn
• Same is true for pentacene
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X-ray ReflectivityQ = (4π/λ) sin θ
Q < Qc : R ≈ 1Q >> Qc: R ≈ (Qc/Q)4
R= reflectivityQc ≈ √ρe- , electron density
R ≈ | r1 + r2 exp (iQD)|2
incident reflectedQ
D
θ θ
• Lu, Lee, Thomas, Acta Cryst. A52, 11-41 (1996).• Tolan, “X-ray Scattering from Soft-Matter: Materials
Science and Basic Research”, Springer (1998).
Qc
2π/D
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Lubricant Films
How thick is the lubricant?
CR
F
F
C
F
F
O C
F
F
O R
n m
CR =
F
F
C
H
H
OH 4700 g/mol
CR =
F
F
F 4600 g/mol
Z-Dol
random co-polymer
Z
What we did:use reflectivity to measure various thicknessescompare with ‘established’ methods
FomblinDisk Lubricants:
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Lubricant Films: Thickness
film thickness (accurate!)film densityfilm roughness
What can you learn?
• Toney, Mate, Pocker, IEEE Trans. Magn. 34, 1774 (1998)• Toney, Mate, Leach, Pocker, J. Coll. Inter. Sci. 225, 119 (2000)
hydrocarbons
2π/D R ≈ | r1 + r2 exp (iQD)|2
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Lubricant Films: Thickness
organics
ellipsometry and ESCA can provide accurate thickness
organicslubricant
Slope = 1.0
ellipsometry ≡ 0
• Toney, Mate, Pocker, IEEE Trans. Magn. 34, 1774 (1998)• Toney, Mate, Leach, Pocker, J. Coll. Inter. Sci. 225, 119 (2000)
ellipsometry
reflectivity
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Lubricant Films: Roughness
Toney, Mate, Leach, Appl. Phys Lett. 77, 3296 (2000)
• lubricant smoothes carbon surface
• for thick films, roughness approaches limit due to molecular nature of lubricant molecule
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X-ray Reflectivity: Summary
What you can learn:accurate film thickness
(Å resolution)film densityfilm roughnesssurface morphology
single and multiple layers
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Summary
hcpfcc
what do you want to learn:phase identificationlattice parametersdefectstexture crystallite sizeatomic structure
What do you do?• what beam line? (2-1, 7-2, 11-3)
• area vs point detector; flux; energy• what scans? (“where” in reciprocal space)