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) – RuPt 3. Textured film: MnPt 4. X-ray Reflectivity 5. 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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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
Real and Reciprocal Space
epitaxialfilm
“powder” film(polycrystalline)
Arturas
Real space Reciprocal space
spotsorigin
spheres
Real and Reciprocal Space
Real space Reciprocal spacetextured film
differences in extent of texture
rings
slice gives spots
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
Thin Film Scattering
2θ
Q
Two ways: Area detector & Point detector
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
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 RuPtalloys to catalytic activity
Pt is fcc; Ru is hcpfcc->hcp transition as Ru increases
Polycrystalline (powder) film
Cu
“Powder”: randomorientation of many smallcrystals (crystallites)
QIn
tens
ity
Q
RuPt Thin FilmsArea
Detector2θ incident
α ~ 0.1−0.2 degQ scattered
Beam line11-3 incidentscattered
Detector
Q
RuPt Thin FilmsRu() Pt ()
fcc(111)
glitchfcc
(220)fcc
(200)
fcc(311)& (222)
Q
in-plane scan
Q
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
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 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
RuPt Films: Lattice Parameters
bulk alloys• Accurately determine lattice parameters• Cannot use bulk alloy lattice parameters to get composition