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 scattering 3.Polycrystalline film (no texture) – RuPt 4.Some texture film - MnPt 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

Real and Reciprocal Space epitaxial film “powder” film (polycrystalline) Arturas Real space Reciprocal space spots spheres

Diffraction Pattern: Powders “Powder”: random orientation of many small crystals (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 Intensity (10) (02)

Real and Reciprocal Space Real space Reciprocal space textured film differences in extent of texture rings slice gives spots side top

rings textured 2D Powder: oriented normal to surface random 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

Polycrystalline (powder) film Cu “Powder”: random orientation of many small crystals (crystallites) Q Intensity 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 Films Direct 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: CH 3 OH + H 2 O => CO 2 + 6H + + 6e - cathode: 3/2O 2 + 6H + +6e - => 3H 2 O sum: CH 3 OH + 3/2O 2 => CO 2 + 2H 2 O 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) Si RuPt: vary % thin films of RuPt rf sputtered 13 nm thick Goal: Correlate crystal structure of RuPt alloys to catalytic activity Pt is fcc; Ru is hcp fcc->hcp transition as Ru increases

Polycrystalline (powder) film “Powder”: random orientation of many small crystals (crystallites) Q Intensity 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 Area Detector  incident  ~  deg Q scattered Area detector Si RuPt Grazing incidence: limits penetration in substrate (avoids substrate peaks) fast

RuPt Thin Films Area detector on beam line 11-3 incident scattered Detector Q Area Detector  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 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, (2005) accurate, but slow increasing Ru => transition from fcc to mixed fcc/hcp to hcp

RuPt Thin Films: diffraction Fit peaks to get: peak positions => lattice parameters peak widths => grain (particle) size integrated intensities => phase fraction (hcp vs fcc)

RuPt Thin Films Use peak intensities to quantify phases Thin Film Phase Diagram Thin film different from bulk, due to sputter deposition Kinetics do not allow equilibrium

RuPt Films: Lattice Parameters bulk alloys Accurately determine lattice parameters Cannot use bulk alloy lattice parameters to get composition

Summary: polycrystalline RuPt 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 Storage Mahesh Samant, IBM $5.2/MB $0.0003/MB Read Head Write Head 500 nm 2  m Pinned Ferromagntic Film

Exchange bias (H eb ) 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 disordered fcc structure not antiferromagnetic chemically ordered L1 0 structure (face centered tetragonal) c/a = 0.92 antiferromagnetic (T N = o C) Cebollada, Farrow & Toney, in Magnetic Nanostructures, Nalaw, ed Mn Pt

partial chemical order: S=1/2 Cebollada, Farrow & Toney, in Magnetic Nanostructures, Nalaw, ed No chemical order: S=0 Full chemical order: S=1 S=0 S=½ S=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)

2θ is scattering angle α = incidence angle β = 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

increased thickness: the superlattice (001) and (110) peaks increase => more chemical ordering coexistence of fcc and L1 0 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)/(f Pt -f Mn ) 2 ]/[I(220)/(f Pt +f Mn ) 2 ] I = integrated intensity of peaks A = Q dependent term f = atomic form factor S=1/2 Calculate fcc & L1 0 fraction form fcc(220) and L1 0 (220)/(202): fcc fraction = B*I(fcc)/[I(fcc) + I(L1 0 )] 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 L1 0 MnPt (inhomogeneous) complete chemical order for highest H eb MnPt Film Structure

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 annealing effect thickness effect (111) (110) (111) Q width ca 5-10 degs

MnPt Thin Films: Summary MnPt films:  phase identification (L1 0, 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 bias  coexistence between fcc and L1 0 (inhomogeneous)  need complete L1 0 order to get highest exchange  grain growth and change in preferred orientation with development of chemical order => L1 0 forms by nucleation & growth

Summary what beam line? (2-1, 7-2, 11-3) what scans? (“where” in reciprocal space) what do you want to learn?  phase identification  lattice parameters  defects  texture  crystallite size  atomic structure what kind of sample (epitaxial, textured)?