Diffrazione da nano-particelle con luce di sincrotrone

Transcription

1 Diffrazione da nano-particelle con luce di sincrotrone Dr Carlo Meneghini Dip. Di Fisica, Università di Roma Tre, Roma OGG-INFM GILDA c/o ESRF Grenoble, France Powder-XRD e nano-particelle: generalità Luce di sincrotrone: sorgenti e apparati sperimentali Esempi: Leghe nano-granulari e magnetoresistenza gigante Nanoparticelle e catalisi Materiali vetroceramici biomateriali

2 X-ray Powder Diffraction Particle size and defects Peak shapes Peak positions Background θ Peak relative intensities Atomic distribution in the unit cell c b a Unit cell Symmetry and size Diffuse scattering, sample holder, matrix, amorphous phases, etc...

3 Powder diffraction patterns k = k q=sin(θ) 4πλ 1 (exchanged momentum vector) q k Bragg law 2d hkl sin(2θ) = nλ k d hkl Peak intensity I hkl ~ F hkl 2 F hkl = structure factor F hkl = Σ f n e ik. r n Structural Disorder effects: f n = f no e -q2 u 2 e -q2 u 2 = Debye Waller factor u = mean square displacement u=<r n -r o >

4 Line shape breath anisotropy Crystallite defects Crystallite size Sherrer Law β τ =D-d

5 XRD from Nano-sized particles Broad lines (small crystallites and strain) + Weak peaks (disorder and defects) + Intense background (matrix, amorphous phases, supports, etc..) Poor diffraction patterns Signal Background

6 Reliable structural refinement requires -High count statistics -High reproductibility / long term stability- - Complementary patterns - (low energy + high energy) -Independent patterns - (anomalous scattering) -Complementary techniques (ND, XAS,...) Synchrotron Radiation provides intense, stable energy tunable and versatile x-ray sources

7 Synchrotron Radiation properties EM field S.R. spectrum a flux vs. years S.R. X-ray tube spectrum

8 Synchrotron Radiation properties High intensity Collimated flux Small (ultra small) spot size (mm-µm) Widely Tunable energy ( ev) High energy resolution ( E/E~ ) Time Pulsed structure Polarized radiation (linear/circular) High count statistics, short collection time Parallel beam geometry (high resolution) (Ultra-) High resolution, µm probe Optimal wavelength choice, independent measurements (anomalous dispersion) Clean XRD patterns Time-resolved stroboscopic measurements Orientation sensitivity, Magnetic sensitivity (X-ray magnetic scattering)

9 Synchrotron Radiation Facilities ISA (Denmark) LURE (France) SOLEIL (France) ANKA (Germany) BESSY (Germany) DELTA (Germany) HASYLAB (Germany) ELETTRA (Italy) DAFNE (Italy) LLS (Spain) MAX (Sweden) SLS-PSI (Switzerland) DIAMOND (U.K.) SRS (U.K.) LNLS (Brazil) CLS (Canada) APS (USA) CHESS (USA) SSRL (USA) BSRF (China) INDUS (India) Photon Factory (Japan) SPring-8 (Japan) SSRC (Russia) Pohang Accel. Lab. (S. Korea) SRRC (Taiwan) Australian Synchrotron (Australia) www-hasylab.desy.de sls.web.psi.ch/view.php www-ssrl.slac.stanford.edu pfwww.kek.jp pal.postech.ac.kr How to access S.R. Dead-line Support Idea Proposal ~ 2/year Referees accepted Experiment Report conference paper conference refused paper

10 S.R. Beamlines

11 Powder diffraction set-up ESRF-BM2 ESRF-ID32 ESRF-ID13

12 Multi - detector ESRF-ID31 Area detector ESRF-BM14

13 SR Powder diffraction: Data collection strategies q=4π/λ sin θ 2θ k θ q(θ) k Area detector Angle dispersed Step scanning Energy resolution detector Energy dispersed x-ray sample

14 Characteristics Step scanning: + High resolution, wide angle, energy resolution (relatively) slow, relative orientations may affect peak intensities, noise from time instabilities and drifts, poor time resolution Angle dispersed: + fast collection time (sec. min. range), full Deby rings, accurate orientation analysis, exceptional statistics, full-pattern time resolution; medium-low 2θ resolution, poor energy resolution, reduced angular range Energy dispersed: + fast collection time (sec min range), fixed geometry time resolution; medium-low q resolution, limited count statistics, heavily affected by grain orientation

15 Detectors Step scanning: -Scintillation counters (NaI): limited count rate (~10 4 cps), E/E ~ 0.1 -Plastic: high count rate(~ cps), poor energy resolution -Plastic + Crystal Analyzer: high count rate (~ cps), E/E ~10-4, realizes the parallel beam geometry -Multi-detectors: Reduced collection time C.A. q(θ) k n q 1 2θ k θ k 2θ k 1 θ k q n

16 Angle dispersed set-up CCD camera High counting rate in-situ read-out high efficiency flat plate distortions medium 2θ resolution reduced 2θ range electronic noise high cost

17 Imaging plates High counting rate high conversion efficiency large area time resolution

18 Ex-situ read-out flat plate corrections medium 2θ resolution reduced 2θ range

19 Energy dispersed set-up Solid state detectors fixed geometry time resolution low counting rate reduced q-range poor q-resolution q(e) = sin θ ο 4πΕ/12.398

20 Energy dispersed XRD used as complementary technique High pressure XAS set-up at BM29 channel collimator project (PURS008 of the INFM)

21 Anomalous scattering f(q,e)=f o (q) + f (E) + if (E) I(q,E) ~ F hkl 2 ~ w ij f i f j I = I(E 1 ) I(E 2 ) f o (q) E 2 f f E 1

22 Example Application: Dispersed phases, background removal Pumice supported Pd-catalyst Pd 1.5 wt% Pd 0.5 wt% C. Meneghini et al. J. Synchr. Rad. 8, 1162 (2001).

23 SR-XRPD: Applications to nano-structured material science Special magnetic-electronic properties (innovative electronic devices) Biomaterials High chemical reactivity (catalysis) Nucleation phenomena (phase transitions)

24 Granular alloys XRD+ time resolved XRD Granular Magneto-resistive alloys are heterogeneous compounds in which small particles of a magnetic phase (M) are embedded into a non-magnetic (N) matrix. M x N 1-x M = Fe, Cu,... N = Ag, Cu,... GMR in g-alloys arises from large spin dependent scattering taking place at the interfaces between magnetic granules and non magnetic matrix Small particles + sharp interfaces magneto-resistance

25 g-co x Cu 1-x Co and Cu are immiscible at RT Phase diagram metastable g-alloys are produced by fastquenching and thermal treatments Annealing at ~450 C enhances MR in a wide range of compositions (x=5-20) 450

26 HR-XRPD The HR-XRD patterns were collected at room temperature using a wavelength λ= Å. Additional diffractograms with better statistics were collected in the region around the (111) Bragg peaks. (22<2θ<30 <30 deg.). Cu Rich 111 HR-XRD patterns reveal the existence of two different phases with fcc structure even in the as-prepared state. 2θ C.A. k θ q(θ) k g-cu Cu 80 Co 20 Co rich o C 600 o C 550 o C 500 o C 450 o C 400 o C AQ θ (deg)

27 - Lattice parameters for Cu-rich and Co-rich phases does not changes with the composition. This implies that the metastable solid solutions formed during preparation have similar composition (Vergard s Law), and only their relative proportion is different. Vergard s Law a x = x a Co + (1-x)a Cu R(Å) 1000 Grain size Cu-rich Co-rich T A ( o C) Cu-rich and Co-rich phases evolve with the thermal treatments that cause the segregation of the minority atomic species out of the host matrix: The structural evolution is related to peculiarity of phase diagram of Co-Cu system instead of to the sample composition.

28 Time Resolved XRD C. Meneghini et al. J. Magn. Magn. Mat. 262, 92 (2003). and NIM B 200, 215 (2003). t~ 2min

29 increasing of Cu-rich particle size (a) + decreasing of Co-rich particle size (b) + dissolution of Co-rich phase (c) = MR Drop Structural changes are largely independent from heating velocity GMR

30 A (possible) structural model AQ 1. As prepared g-co x Cu 1-x present Cu-rich and Co-rich phases (XRD) ( o C) Annealing provokes the expulsion of Cu from the Co environment. Into the Cu-rich phase small (some 10 Å) Co particles are created while the expelled Cu atoms 450 join together at the surface producing well defined interfaces, this being the optimal situation for the larger MR effect ( o C) the segregation stops: the Cu atoms are 550 partially reabsorbed roughening the Co -Cu interface causing the MR drop. 600 Lower solubility of 650 Cu in Co Higher solubility of Cu in Co 4. Above 550 o C the Co granules coalesce and growth, the system evolves toward a complete phase separation.

31 Nano-particles in catalysis P. Canton et al. J. Phys. Chem B 105, 8088 (2001). Rietveld refinement XRD (full-ip set-up)

32 Time Resolved - XRD

33 Biomaterials Structural evolution of human bone at the foetal stage probed by XRD S. Nuzzo, et al. J. Bone and Min. Res.18, 760 (2003); C. Meneghini et al. Biophys. J. Human foeti vertebra

34 Sinchrotron Radiation computed microtomography SR-µCT CT: : 3D computed images 0.2 µm m spatial resolution C The analysis of SR-µCT data show that: a) the global bone network in foeti is 2-3 times denser than in adults; A B D BV/TV(%) b) In the inner region the thickness of the structures is similar to that found in adults (~100 µm) while the spacing between the trabecules is much smaller in foeti than in adults. Microarchitectural parameters averaged over all the investigated foetal vertebra samples Age(weeks)

35 XRD The analysis XRD data: a) demonstrate the growth of bioapatite crystallites as a function of age b) Point out the evolution of the bioapatite structure related to changes in composition.

36 µ XRD OHAp adult 0 ~ 5 µm spot foetus

37 XRD: foetal age effects on bone mineral microstructure µ XRD: effects of bone maturation on mineral microstructure

38 The structure of Zr containing phase in CaO-ZrO2-SiO2 ceramics (SiO 2 /CaO=3/2; ZrO 2 =10%) B-glass

39 XRD (full IP set-up) AQ θ ZrO 2 Monoclin ZrO 2 tetragonal ZrO 2 cubic SiCaZrO-ISCD79453 SiCaZrO-ISCD73801 Wollastonite

40 Anomalous XRD set-up 1050 f' f" E=17 KeV E=17.99 KeV Anomalus dispersion corrections calculated for Zr E (KeV) θ (deg.) Difference XRD patterns were collected tuning the x-ray beam energy far below (17 kev) and near (17.99 ev) the Zr K edge (18 kev). The difference pattern: Difference = I 17 -I only retains the structural information concerning to the Zr-containing phases.

41 ZrO 2 Monoclin ZrO 2 tetragonal ZrO 2 cubic X θ (deg.) Resonant XRD analysis reveals t-zro 2 and m-zro 2 phase segregation as a function of firing temperature.

42 Quantitative Rietveld Analysis t-zro 2 particles remain small (< 20 nm) m-zro 2 particles are large (> 20 nm)

43 XAS: complementary structural information m-zro 2 t-zro 2 1) Zr is found only as: t-zro 2 m-zro 2 (crystalline) Si 2 CaZrO 7 (amorphous) Si 2 CaZrO 7 2) No c-zro 2 contributions are detected

44 Conclusions Synchrotron Radiation sources provide x-ray beam - versatile - intense - stable - energy tunable well suited for high quality powder diffraction studies on nano-structured materials.