Scattering features - Revision history

KevinYager: /* Speckled Rings */

2015-01-29T21:34:57Z

‎Speckled Rings

KevinYager at 21:34, 29 January 2015

2015-01-29T21:34:36Z

KevinYager at 21:32, 29 January 2015

2015-01-29T21:32:45Z

KevinYager: /* Speckled Rings */

2015-01-29T21:30:18Z

‎Speckled Rings

KevinYager: /* Broad Rings */

2015-01-29T21:25:03Z

‎Broad Rings

KevinYager: /* Rings */

2015-01-29T21:23:32Z

‎Rings

KevinYager at 17:56, 29 January 2015

2015-01-29T17:56:29Z

KevinYager: /* Spots */

2015-01-29T17:53:19Z

‎Spots

KevinYager at 19:36, 3 December 2014

2014-12-03T19:36:36Z

KevinYager: /* Diffuse Scattering */

2014-12-03T19:35:52Z

‎Diffuse Scattering

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 A sharp ring that is speckled indicates that the material is poly-crystalline, but the grains are exceptionally large. As such, only a small number of grains within the [[scattering volume]] satisfy the [[Bragg's law|Bragg condition]], leading to just a small number of spots. A sharp, speckled ring thus indicates a highly ordered system, with large grains. (The [[ring graininess]] can be quantified to measure grain size.)
-[[Image:N-10_th030_spot1_10sec_WAXS.png|300px|center|thumb|Example [[WAXS]] for a material (metal alloy) with highly 'speckled' scattering rings, indicating a well-ordered poly-crystalline phase with large grains.]]
+[[Image:N-10_th030_spot1_10sec_WAXS.png|300px|center|thumb|Example [[GIWAXS]] for a material (metal alloy) with highly 'speckled' scattering rings, indicating a well-ordered poly-crystalline phase with large grains.]]
 ==Bragg Rods==

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 ==Diffuse Scattering==
 Many samples will exhibit [[diffuse scattering]]: scattering intensity over a broad range of angles, without a distinct peak or maximum. This kind of scattering usually comes from disorder within the sample. For instance, low-''q'' diffuse scattering can come from nanoscale or microscale porosity, or from surface roughness in [[GISAXS]]. High-''q'' diffuse scattering can arise from the defects in atomic lattices (and from the [[Debye-Waller factor|thermal motion]] of atoms in a lattice). Although one can generally assign diffuse scattering to some kind of disorder, it is difficult to make an unambiguous link, because there are many effects that can generate diffuse scattering.
 ==Spots==

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 ==Spots==
 A sharp spot on a 2D detector is typically a [[Bragg peak]]: i.e. diffraction at a [[Bragg's law|well-defined angle]] due to a [[realspace]] [[lattice]]. An array of sharp spots typically indicates that the sample is a single-crystal (or at least [[Sample orientation|oriented]]; e.g. in-plane powder).
 ==Rings==
 A ring typically indicates an isotropic material generating [[Bragg peak]] that is spread orientationally. Thus, the sample is poly-crystalline, with crystallites at every possible orientation, but with a well-defined [[unit cell]] giving rise to diffraction spots. These spots are smeared orientationally, giving rise to a set of distinct rings. The ring position can be [[Q value|converted]] into a [[realspace]] repeat distance (e.g. to determine a packing distance). With enough rings, one can determine the unit cell symmetry (i.e. it becomes a powder diffraction experiment, from which one can fit the crystallographic symmetry).
-[[Image:Standard-AgBH-gisaxs th000 spot3 60sec SAXS.png|thumb|right|200px|Example [[SAXS]] with a distinct isotropic ring ([[AgBH]])]]
+[[Image:Standard-AgBH-gisaxs th000 spot3 60sec SAXS.png|thumb|center|300px|Example [[SAXS]] with a distinct isotropic ring ([[AgBH]])]]
 ==Broad Rings==
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 A sharp ring that is speckled indicates that the material is poly-crystalline, but the grains are exceptionally large. As such, only a small number of grains within the [[scattering volume]] satisfy the [[Bragg's law|Bragg condition]], leading to just a small number of spots. A sharp, speckled ring thus indicates a highly ordered system, with large grains. (The [[ring graininess]] can be quantified to measure grain size.)
-[[Image:N-10_th030_spot1_10sec_WAXS.png|200px|thumb|Example of a material (metal alloy) with highly 'speckled' scattering rings, indicating a well-ordered poly-crystalline phase with large grains.]]
+[[Image:N-10_th030_spot1_10sec_WAXS.png|300px|center|thumb|Example [[WAXS]] for a material (metal alloy) with highly 'speckled' scattering rings, indicating a well-ordered poly-crystalline phase with large grains.]]
 ==Bragg Rods==

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 ==Speckled Rings==
-TBD
+A sharp ring that is speckled indicates that the material is poly-crystalline, but the grains are exceptionally large. As such, only a small number of grains within the [[scattering volume]] satisfy the [[Bragg's law|Bragg condition]], leading to just a small number of spots. A sharp, speckled ring thus indicates a highly ordered system, with large grains. (The [[ring graininess]] can be quantified to measure grain size.)
 ==Bragg Rods==

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 ==Broad Rings==
-TBD
+A very [[Peak width|broad]] ring (or halo) indicates a poorly ordered system, with very small grain sizes. For instance, the sample may be poly-crystalline, with very small grain sizes. Alternatively, the material may be essentially amorphous, with the ring indicating a preferred local packing distance, but no long-range coherent order.
 ==Speckled Rings==

← Older revision		Revision as of 19:36, 3 December 2014
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−	[[Scattering]] experiments ([[x-ray]] or neutron) generates images which can be thought of as the [[Fourier transform]] of the material's [[realspace]] structure. I.e. the image is a slice through a conceptual 3D [[reciprocal-space]]. Although a scattering pattern can be arbitrarily complex, there are usually various features that can be analyzed separately, and from which one can learn much about a sample's structure. In particular, samples with well-defined structural order give rise to distinct '''scattering features''', such as sharp rings or even distinct spots on the area [[detector]] image.	+	[[Scattering]] experiments ([[x-ray]] or [[neutron]]) generates images which can be thought of as the [[Fourier transform]] of the material's [[realspace]] structure. I.e. the image is a slice through a conceptual 3D [[reciprocal-space]]. Although a scattering pattern can be arbitrarily complex, there are usually various features that can be analyzed separately, and from which one can learn much about a sample's structure. In particular, samples with well-defined structural order give rise to distinct '''scattering features''', such as sharp rings or even distinct spots on the area [[detector]] image.

	==Rings==		==Rings==