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Neutron Scattering Studies of Materials for Information Technology II. SANS. G.J. Mankey S. Al-Ghamdi, H. Alouach, F. Liu, P. Mani, Z. Zhao, I. Zoto V.V. Krishnamurthy Bhandar, M.Piao, A. Lane, D. Nikles, J. Weist, H. Fujiwara, J.W. Harrell MINT Center, The University of Alabama

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Neutron scattering studies of materials for information technology ii sans l.jpg

Neutron Scattering Studies of Materials for Information Technology II. SANS

  • G.J. Mankey

  • S. Al-Ghamdi, H. Alouach, F. Liu, P. Mani, Z. Zhao, I. Zoto

  • V.V. Krishnamurthy

  • Bhandar, M.Piao, A. Lane, D. Nikles, J. Weist,

  • H. Fujiwara, J.W. Harrell

  • MINT Center, The University of Alabama

  • J.L. Robertson (ORNL), L. Porcar (NIST), C. Glinka (NIST),

  • W.-T. Lee (ANL), F. Klose (ANL),

  • J. Mitchell (ANL), N. Cavadini (PSI)

These projects are funded by grants from NSF and DOE/EPSCoR


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Measurement Techniques Technology II. SANS

  • You won’t know the result until you open the box that contains the cat.

  • Only the correct measurement will answer your question.

  • Persistence and dedication are necessary.


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Small Angle Neutron Scattering Technology II. SANS

  • Neutrons probe length scales comparable to TEM and soft x-rays.

  • Neutrons are a gentle probe since their energies are of the order of a few milli electron volts as opposed to hundreds to thousands of electron volts for x-rays and electrons.

ref: Charles Glinka, NIST


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SANS Instrumentation Technology II. SANS

  • Nanoscale lengths are probed.

ref: Charles Glinka, NIST


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Small Angle Neutron Scattering Technology II. SANS

  • Probe must match momentum transfer to particle size via the relation: k = 2p/particle size



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Beamline NG7 at NIST Center for Neutron Research Technology II. SANS

  • Measurement Conditions

  • Radial Scan

  • sample-detector distance= 15.5 m

  • neutron wavelength

  •  = 6 Å

  • Couette shear cell

  • magnetic field:

  • 0-180 Oe

  • room temperature

  • shear rate: 0-4000 s-1


Tem images of self assembled fe 49 pt 51 88 ag 12 nanoparticle films 25 tdot in 2 l.jpg
TEM Images of Self-Assembled [Fe Technology II. SANS49Pt51]88Ag12 Nanoparticle Films (25 Tdot/in2)

Before Annealing

Annealed at 400oC for 30 min


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Schematic of SANS from Domains of Hexagonal Nets Technology II. SANS

f

  • The small angle neutron scattering pattern is basically the Fourier transform of the arrangement of particles in-plane.

  • At low q, a ring with radius 2p/a, where a is the average spacing, is observed for a domains of randomly oriented hexagonal array.

  • We integrate the intensity over f to represent the scattering pattern.

FFT

SANS

Pattern

Real Space

Reciprocal Space


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Schematic of SANS of Sintering Technology II. SANS

  • The ring characteristic of long range order loses intensity in the partially sintered system.

  • Intensity is shifted to low q from the ring.

  • The sintered system has a single circular blob of intensity at low q and no ring.

Ordered

Partial

Sintered


Feptau drop dried samples sans intensity l.jpg
FePtAu Drop Dried Samples: Technology II. SANSSANS Intensity

  • The sample with no heating (NH), exhibits a ring of intensity at 2p/particle spacing.

  • Annealing at 250 C produces larger particles as the intensity at low q is dramatically enhanced and the ring pattern disappears.


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Spin Coated FePtAu Films: Technology II. SANSScattering Intensity vs. Scattering vector

  • For the spin coated particle array, the 250 C anneal does not destroy the order.

  • There is a shift of the peak to higher q which shows the in-plane spacing is reduced by annealing.

  • Annealing at higher temperatures results in agglomeration.




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Small Angle Neutron Scattering Technology II. SANSExperimental GeometryShear Cell Environment


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Data Analysis Technology II. SANS

  • For Fe, magnetic scattering is expected to be about 1/3 of the nuclear scattering.

  • The magnetic scattering contribution is expected to add to the nuclear scattering as the magnetization of the particles is along their long axis.

  • The neutron scattering intensity is fitted with: I() = A + B sin2( +  )

  • B/A is anisotropy.

  •  is the azimuthal angle.

  •  is the tilt angle.


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Scattering Anisotropy Technology II. SANS

  • Scattering is isotropic in zero field and zero shear conditions.

  • Particles are randomly oriented in zero field and zero shear

  • Anisotropic scattering is observed either in applied field or under the influence of shear particles align along the field or shear


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Shear Rate Dependence of Tilt Angle Technology II. SANS

  • Tilt angle follows a power law behavior of

    shear rate:

     = c-z

    z is a dynamic exponent.

    z depends on

    (a) dimensionality

    (b) type of aggregation

    process

  • Experimental data shows

    the field dependence of z.

V. V. Krishnamurthy et al., Phys. Rev. E 67, 51406 (2003).


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Theoretical Study of Nanoparticle Dynamics Technology II. SANS

  • The behavior of Fe nanoparticles in the magnetic dispersion under the influence of steady shear flow and static magnetic field is theoretically studied using the constitutive model.

  • The constitutive model: A. S. Bhandar and J. M. Wiest, J. Colloid and Interface Sci. (2002).

  • single-particle mean-field approach

  • the particles as rigid dumbbells dispersed in a solvent.

  • incorporates

    • Brownian motion

    • anisotropic hydrodynamic drag

    • a steric potential

    • magnetic forces (dipolar)


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Comparison of the SANS Results with the Constitutive Model Calculations: Order Parameter S

  • f(u,t) is the orientational distribution function

  • f(u,t) du is the probability that a particle is within the solid angle du of orientation u at time t.

  • The scalar invariant S= tr(S.S.S)1/3 is the order parameter

S=0 Random orientation, S=1 perfect order

S<0 oblate ordering, S>0 prolate ordering


Constitutive model calculations director flow angle l.jpg
Constitutive Model Calculations: Director Flow Angle Calculations: Order Parameter S

  • Shear rate dependence of tilt angle is qualitatively similar to SANS observations.

  • The transition from field oriented state to shear oriented state is abrupt in the model.

  • Polydispersity plays a role in determining the sharpness of the transition.

V. V. Krishnamurthy et al., Phys. Rev. E 67, 51406 (2003).


Magnetic devices l.jpg

60 Oe Calculations: Order Parameter S

18 Oe

0 Oe

Ha

-18 Oe

-47 Oe

-10 Oe

MFM of CoNiFe Bars: 2.6 mm x 10.9 mm x 100 nm

Magnetic Devices


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