Stanford Synchrotron Radiation Laboratory More Thin Film X-ray Scattering: Polycrystalline Films...

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)?