EUTRON GRATING INTERFEROMETRY PART II · 1 2 cos +𝜗+ 1 2 cos ( −𝜗) 29.08.2017 - IAEA...

NEUTRON GRATING INTERFEROMETRY PART II

QUANTITATIVE DFI

Alexander Backs alexander.backs@frm2.tum.de

Dark Field Images

10.07.2017 - Combining Neutron Scattering and Imaging to Investigate Domain Structures in Superconductors- alexander.backs@frm2.tum.de

nGI reveals scattering

• from small structures (~ μm)

• under very small angles

What does that mean exactly ?

Quantitative DFI: Size Matters

• varying particle diameter • constant volume fraction

• constant absorbtion • varying DFI value

Polysterene Colloids in Solution

Particle Size (μm)

29.08.2017 - IAEA workshop AUNIRA - alexander.backs@frm2.tum.de

T. Reimann et al., J.Appl.Cryst. (2016)

Origin of the DFI

Model Case: One Single Scattering Angle

without sample:

𝑉𝑜𝑏 = cos 𝑥

Origin of the DFI

without sample:

with sample:

𝑉𝑠 =1

2cos 𝑥 + 𝜗 +

2cos(𝑥 − 𝜗)

Origin of the DFI

𝜗 = ξ𝐺𝐼𝑞𝑥 ξ𝐺𝐼 = λ𝐿𝑠,𝑒𝑓𝑓

𝑉𝑠 = cos 𝑥 cos(ξ𝐺𝐼𝑞𝑥)

𝐷𝐹𝐼 =𝑉𝑠𝑉𝑜𝑏

= cos ξ𝐺𝐼𝑞𝑥

without sample:

with sample:

𝑉𝑠 =1

2cos 𝑥 + 𝜗 +

2cos(𝑥 − 𝜗)

Origin of the DFI

Real Case: Distribution of Scattering Angles

𝐷𝐹𝐼 = 𝑆 𝑞𝑥 cos ξ𝐺𝐼𝑞𝑥 𝑑𝑞𝑥

𝐷𝐹𝐼 = cos ξ𝐺𝐼𝑞𝑥

Origin of the DFI

Real Case: Distribution of Scattering Angles

𝐷𝐹𝐼 = cos ξ𝐺𝐼𝑞𝑥

What defines 𝐒 𝐪𝐱 ?

𝑆 𝑞𝑥 “probability of scattering a neutron with a certain momentum transfer 𝑞𝑥 “

S qx : A Bit of Scattering Theory

𝑑σ(𝑞)

𝑑Ω=

neutrons scattered into 𝑑Ω

incomingneutronsperunitarea

𝑑Ω

Reciprocal Space: the differential cattering cross section (looking at momenum)

𝑑σ(𝑞)

𝑑Ω=

𝑑Ω

Real space: the pair correlation function (looking at space coordinates)

γ(𝑟) = Δρ 𝑅 Δρ 𝑅 + 𝑟 𝑑𝑅

γ(𝑟)

Distribution of scsattering strength

𝑑σ(𝑞)

𝑑Ω=

𝑑Ω

Real space: the pair correlation function (looking at space coordinates)

γ(𝑟) = Δρ 𝑅 Δρ 𝑅 + 𝑟 𝑑𝑅

γ(𝑟)

Distribution of scsattering strength

fourier transformation

𝑑σ

𝑑Ω

S qx : Reducing the Dimensions

Step 1: no scattering along the beam direction 𝑞𝑧 = 0

𝑑σ(𝑞)

𝑑Ω→𝑑σ(𝑞𝑥, 𝑞𝑦 , 0)

𝑑Ω

𝐺(𝑥, 𝑦) = 𝛾(𝑥, 𝑦, 𝑧)𝑑𝑧

𝑑σ(𝑞)

𝑑Ω→𝑑σ(𝑞𝑥, 𝑞𝑦 , 0)

𝑑Ω

𝐺(𝑥, 𝑦) = 𝛾(𝑥, 𝑦, 𝑧)𝑑𝑧

S qx : Reducing the Dimensions

Step 1: no scattering along the beam direction

𝑞𝑦 = −∞ → +∞

𝐺 𝑥, 𝑦 → 𝐺(𝑥, 0)

𝑑σ(𝑞𝑥)

𝑑Ω𝑠𝑙𝑖𝑡

= 𝑑σ(𝑞𝑥 , 𝑞𝑦 , 0)

𝑑Ω𝑑𝑞𝑦

Step 2: projection along the grating lines

𝑞𝑧 = 0

𝑑𝑞𝑦

𝑑σ

𝑑Ω

Quantitative DFI: The Formula

𝑆 𝑞𝑥 ≈𝑑σ(𝑞𝑥)

𝑞𝑧 = 0 𝑞𝑦 = −∞ → +∞

Reciprocal Space:

T. Reimann, Ph.D. Thesis (2016)

Quantitative DFI: The Formula

𝑆 𝑞𝑥 ≈𝑑σ(𝑞𝑥)

𝑞𝑧 = 0 𝑞𝑦 = −∞ → +∞

Reciprocal Space:

T. Reimann, Ph.D. Thesis (2016)

𝐷𝐹𝐼 = 𝑒𝑥𝑝 Σ𝑡𝐺(ξ𝐺𝐼)

𝐺(0)− 1

Σ = Δρ 2λ2Φ𝑣𝐺(0)

ξ𝐺𝐼

Total scattering crossection

Real Space:

sample thickness 𝑡

nGI correlation length ξ𝐺𝐼

A Simple Example: Hard Spheres

Pair Correlation Function

A Simple Example: Hard Spheres

γ(𝑥, 𝑦, 𝑧)

calculate:

𝐺(𝑥, 𝑦)

𝐺(𝑥, 0)

𝑑σ(𝑞𝑥, 𝑞𝑦 , 𝑞𝑧)

𝑑Ω

𝑑σ(𝑞𝑥, 𝑞𝑦 , 0)

𝑑Ω

𝑑σ(𝑞𝑥)

fourier transform:

Real Space Reciprocal Space

Polysterene Colloids in Water

Real Space: Pair Correlation function

Reciprocal Space: Scattering cross section

Polysterene Colloids in Water

𝐺(0)− 1

𝑹 dependence: • G = 𝐺(𝑅) • Σ = Σ(𝑅)

λ dependence: • ξ𝐺𝐼 = ξ𝐺𝐼(λ)

• Σ = Σ(λ)

DFI depends only on one value of the pair correlation function

More information can be gained by:

Changing G

Different particle sizes

𝐺(ξ𝐺𝐼)

Only possible in rare cases

Possibilities and Restrictions

Changing ξ𝑮𝑰

Change the setup or

Sample position

Changing G

𝐺(ξ𝐺𝐼)

Various geometric constraints

Tedious callibrations

Changing ξ𝑮𝑰

Change the setup or

Sample position Vary the wavelength

Changing G

𝐺(ξ𝐺𝐼)

Only a small range is accessible

Various geometric constraints

Tedious callibrations

Inhomogeneous Scattering

𝑑𝑞𝑦

𝑑σ

𝑑Ω

homogenious inhomogenious

𝑑𝑞𝑦

𝑑σ

𝑑Ω

𝑑𝑞𝑦

𝑑σ

𝑑Ω

𝑑𝑞𝑦

Rotate sample

Rotate gratings

𝑑σ(𝑞𝑥)

𝑑Ω 𝑠𝑙𝑖𝑡depends on the relative orientation of sample and gratings

𝑑𝑞𝑦

𝑑σ

𝑑Ω

𝑑𝑞𝑦

𝑑σ

𝑑Ω

𝑑𝑞𝑦

Rotate sample

Rotate gratings

𝐷𝐹𝐼(ω) = 𝑒𝑥𝑝 Σ𝑡𝐺(ξ𝐺𝐼 cos ω ,−ξ𝐺𝐼sin(ω))

𝐺(0)− 1

𝑑σ(𝑞𝑥)

𝑑Ω 𝑠𝑙𝑖𝑡depends on the relative orientation of sample and gratings

𝑑𝑞𝑦

𝑑σ

𝑑Ω

Anisotropic scattering in Brass

Extrusion Moulded Brass: anisotropic • production • crystallites • scattering

T. Neuwirth, Master Thesis (2017)

𝐷𝐹𝐼(ω) = 𝑒𝑥𝑝 −ξ𝐺𝐼2σ𝑥2 + σ𝑦

2 − σ𝑥2 𝑠𝑖𝑛2 ω− φ σ𝑎𝑛 = σ𝑥

2 − σ𝑦2

Bi gaussian scattering cross section

Different distribution of crystallite size in x and y direction

𝝈𝒙𝟐 𝝈𝒚

𝝈𝒂𝒏 𝝋

2 − σ𝑦2

𝑫𝑭𝑰(𝝎)

2 − σ𝑦2

Magnetic Domains in Superconductors

Normal Conductor Superconductor

low field high field

𝑩 𝑩 𝑩

Meissner state Schubnikov state

Magnetic Domains in Superconductors

Normal Conductor Superconductor

low field high field

𝑩 𝑩 𝑩

𝑩⊙

flux line lattice intermediate mixed state

E. H. Brandt & M. P. Das, J. Supercond. Nov. Magn. (2011) U. Essmann & H. Träuble, Phys. Lett. A (1967)

The Intermediate Mixed State in Niobium

B = 40mT

Field Cooling into the IMS

What changes? • domain size • domain density • scattering contrast

The Intermediate Mixed State in Niobium

Supression of the IMS

Additional field enters the sample • IMS in the center • FLL at the edge • pinning along crystal axes

Heterogeneous Phase transition T. Reimann, Ph.D Thesis (2016)

From USANS to nGI

𝐺(𝑥, 0)

𝑑σ(𝑞𝑥)

𝐺(0)− 1

USANS Measurement

DFI Signal

T. Reimann, Ph.D Thesis (2016)

From USANS to nGI

Magnetic Field Scan Wavelength Scan

Domain size changes (USANS result)

Probedξ𝐺𝐼 changes

T. Reimann, Ph.D Thesis (2016)

EUTRON GRATING INTERFEROMETRY PART II · 1 2 cos +𝜗+ 1 2 cos ( −𝜗) 29.08.2017 - IAEA...

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