stanford synchrotron radiation laboratory more thin film x-ray scattering: polycrystalline films...
TRANSCRIPT
Stanford Synchrotron Radiation Laboratory
More Thin Film X-ray Scattering: Polycrystalline Films
Mike Toney, SSRL
1. Introduction (real space – reciprocal space)2. Some general aspects of thin film scattering3. Polycrystalline film (no texture) – RuPt4. Some texture film - MnPt5. Summary
• how do you get diffraction data from thin films• how to choose what to do (what beam line & scans)• what do you learn
20 nm
10x
(11L)
(02L)
(12L)
(20L)
(21L)
(13L)(22L)
(14L)
(23L)(31L)
(24L)
20 nm
10x
(11L)
(02L)
(12L)
(20L)
(21L)
(13L)(22L)
(14L)
(23L)(31L)
(24L)
Real and Reciprocal Space
epitaxialfilm
“powder” film(polycrystalline)
Arturas
Real space Reciprocal space
spots
spheres
Diffraction Pattern: Powders
“Powder”: randomorientation of many smallcrystals (crystallites)
(-2 0)
(1 1)
(1-1)
(-1 1)
(-1 -1)
(2 0)
(0 -2)
(0 -1)
(0 1)
(1 0)(-1 0)
(0 2) Q
(20)
Q
Inte
nsity
(10)
(02)
Real and Reciprocal Space
Real spaceReciprocal spacetextured film
differences in extent of texture
rings
slice gives spots
side
top
rings
textured 2D Powder:oriented normal to surfacerandom orientation of crystals in substrate plane
Qxy
(1 1)
(1-1)
(-1 1)
(-1 -1)
(-2 0)
(-1 2) (0 2) (1 2)
(2 0)
(1 -2)(-1 -2) (0 -2)
(-2 0)
(1 1)
(1-1)
(-1 1)
(-1 -1)
(2 0)
(0 -2)
(0 -1)
(0 1)
(1 0)(-1 0)
(0 2)
Textured Thin Film
Thin Film Scattering: what do I do?
•what beam line? (2-1, 7-2, 11-3)• area vs point detector, nature of sample• energy & flux
•what scans? (“where” in reciprocal space)• what do you want to learn?• what kind of sample (epitaxial, textured)? phase identification lattice parameters defects texture crystallite size atomic structure
Thin Film Scattering
Q
Two ways: Area detector & Point detector
incidentscattered
Detector
Qincident
scattered
Detector
Q
Polycrystalline (powder) film
Cu
“Powder”: randomorientation of many smallcrystals (crystallites)
Q
Inte
nsity
Q
What scans:• what Q range to scan?• what direction for Q?• rocking mode?
• avoid substrate peaks• best signal to noise• fast or accurate?
Textured Thin Films
rings
slice gives spots
(111)
(110) (220)
(111)
(200) Q
Texture: preferred orientation of crystallites
What scans:• what Q range to scan?• what direction for Q?• texture determination?
• avoid substrate peaks• Q goes through peaks• best signal to noise• fast or accurate?
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)
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 RuPt alloys to catalytic activity
Pt is fcc; Ru is hcpfcc->hcp transition as Ru increases
Polycrystalline (powder) film
“Powder”: randomorientation of many smallcrystals (crystallites)
Q
Inte
nsity
Q
what do you want to learn? phase identification lattice parameters defects crystallite size
choose scans to:• avoid substrate peaks• best signal to noise
RuPt Thin Films
AreaDetector incident
~ degQ scattered
Area detector
Si
RuPt
Grazing incidence:• limits penetration in substrate
(avoids substrate peaks)• fast
RuPt Thin Films
Area detector onbeam line 11-3
incidentscattered
Detector
Q
AreaDetector incident
small Q scattered
RuPt Thin Films
Ru(72) Pt (28)
fcc(111)
glitch
fcc(220)
fcc(200)
fcc(311)& (222)
Q
in-plane scan
Q
use fit2d (or other) to integrate
GIXS Thin Films
Si
RuPt
2
Grazing incidence:• planes parallel to surface• limits penetration in substrate
Q = k’ – k ;parallel to surface
RuPt Thin Films: diffraction
T-W. Kim et al., J. Phys. Chem. B 109, 12845 (2005)
• accurate, but slow• increasing Ru =>transition from fcc to mixed fcc/hcp to hcp
RuPt Thin Films: diffractionFit peaks to get:• peak positions => lattice parameters• peak widths => grain (particle) size• integrated intensities => phase fraction (hcp vs fcc)
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
RuPt Films: Lattice Parameters
bulk alloys• Accurately determine lattice parameters• Cannot use bulk alloy lattice parameters to get composition
Summary: polycrystallineRuPt films: phase identification (hcp, fcc) correlate structure to activity (hcp
RuPt does not adversely affect activity) lattice parameters (strain) no strong texture crystallite size
Thin Films for Magnetic Recording
Tsann Lin and Daniele Mauri,Hitachi Global StorageMahesh Samant, IBM
$5.2/MB $0.0003/MB
C ontac t
Hard Bias
C ontac tHard Bias
Read Head
Write Head
500 nm
2m
PinnedFerromagntic
Film
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)
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
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=0 S=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)
Textured Thin Films
sputter deposition annealed at 280C for 2 hours
Q
What to:• avoid substrate peaks• best signal to noise
What scans? What do you want to learn?
phase identification crystallite size texture
(111)
(110) (220)
(111)
(200)
2
2θ is scattering angleα = incidence angleβ = exit angle
Si
MnPt
MnPt Films: diffraction
Grazing incidence:• planes parallel to surface• limits penetration in substrate
Q = k’ – k ;parallel to surface
(110) (220)
(111)
Q
fc c (2 2 0 )
(2 2 0 )
(2 0 2 )(11 0 )
(0 0 1 )
(111 )
(11 0 )(2 0 0 )
(0 0 2 )
• 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
MnPt Films: chemical order
Mn
S = extent of chemical order
Calculate S from (110)/(220)intensity ratio:S = A[I(110)/(fPt-fMn)2]/[I(220)/(fPt+fMn)2]I = integrated intensity of peaksA = Q dependent termf = atomic form factor
fc c (2 2 0 )
(2 2 0 )
(2 0 2 )(11 0 )
(0 0 1 )
(111 )
(11 0 )(2 0 0 )
(0 0 2 )
S=1/2
Calculate fcc & L10 fraction form fcc(220) and L10 (220)/(202):fcc fraction = B*I(fcc)/[I(fcc) + I(L10)]B is Q dependent term close to 1.0
S=0 S=1
Cebollada, Farrow & Toney, in Magnetic Nanostructures, Nalaw, ed. 2002
• coexistence of fcc and L10 MnPt (inhomogeneous)• complete chemical order for highest Heb
MnPt Film Structure
M nP t (111)
as depositedannealed
as deposited
annealed
N iFe, C u (111)
MnPt Films: crystallite size
(110) (220)
(111) Q
more chemically ordered MnPt -> larger grains NiFe & Cu do not change much with annealing
diameter = 2π*0.86/fwhm(Q)
Texture in Thin Films
• Pole figure measures orientation distribution of diffracting planes
• Ψ = 0 deg planes along substrate
• Ψ = 90 deg planes ┴ to substrate
MnPt Films: Texture
20 nm M nP t annealed
annealed
as deposited
M n P t(111 )
10 nm
N iF e , C u (111 ) N iF e , C u (111 )
M n P t(111 )20 nm
5 nm
1 2 x
1 2 x
annealing effect thickness effect
(111)
(110)
(111)
Q
width ca 5-10 degs
MnPt Thin Films: Summary
MnPt films: phase identification (L10, fcc) crystallite size texture determination
• Scan choice requires knowledge of reciprocal space & what you want to learn
(111)
(110) (220)
(111)
(200)
thin MnPt remains fcc => not antiferromagnetic and no exchange biascoexistence between fcc and L10 (inhomogeneous) need complete L10 order to get highest exchange grain growth and change in preferred orientation with development of chemical order
=> L10 forms by nucleation & growth
Summary
hcpfcc
• what beam line? (2-1, 7-2, 11-3)• what scans? (“where” in reciprocal space)
• what do you want to learn? phase identificationlattice parameters defects texture crystallite size atomic structure
•what kind of sample (epitaxial, textured)?
