Definitional boundaries - Revision history

KevinYager: /* See Also */

2019-02-19T15:27:10Z

‎See Also

KevinYager: /* Energy */

2019-02-19T15:26:11Z

‎Energy

KevinYager: /* Scattering Experiments */

2016-08-30T16:18:56Z

‎Scattering Experiments

KevinYager: /* Scattering Experiments */

2016-08-30T16:18:09Z

‎Scattering Experiments

KevinYager: /* Scattering Experiments */

2016-04-12T12:53:51Z

‎Scattering Experiments

KevinYager: /* "Kinds" of Scattering */

2015-10-21T14:02:16Z

‎"Kinds" of Scattering

KevinYager: /* "Kinds" of Scattering */

2015-01-28T17:09:17Z

‎"Kinds" of Scattering

KevinYager: /* "Kinds" of Scattering */

2015-01-28T17:02:57Z

‎"Kinds" of Scattering

KevinYager: /* Crystallography */

2015-01-28T16:29:53Z

‎Crystallography

KevinYager: /* GIXD */

2015-01-28T14:50:14Z

‎GIXD

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	==See Also==		==See Also==
−	M. Nespolo [http://scripts.iucr.org/cgi-bin/paper?to5189 Lattice versus structure, dimensionality versus periodicity: a crystallographic Babel?] ''J. Appl. Cryst.'' '''2019''', 52. [https://doi.org/10.1107/S1600576719000463 doi: 10.1107/S1600576719000463]	+	* M. Nespolo, M. I. Aroyo and B. Souvignier [http://scripts.iucr.org/cgi-bin/paper_yard?in5013 Crystallographic shelves: space-group hierarchy explained] ''J. Appl. Cryst.'' '''2018''' [https://doi.org/10.1107/S1600576718012724 doi: 10.1107/S1600576718012724]
		+	* M. Nespolo [http://scripts.iucr.org/cgi-bin/paper?to5189 Lattice versus structure, dimensionality versus periodicity: a crystallographic Babel?] ''J. Appl. Cryst.'' '''2019''', 52. [https://doi.org/10.1107/S1600576719000463 doi: 10.1107/S1600576719000463]

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		+	==See Also==
		+	M. Nespolo [http://scripts.iucr.org/cgi-bin/paper?to5189 Lattice versus structure, dimensionality versus periodicity: a crystallographic Babel?] ''J. Appl. Cryst.'' '''2019''', 52. [https://doi.org/10.1107/S1600576719000463 doi: 10.1107/S1600576719000463]

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 Modern materials may be complex and hierarchical; they are studied simultaneously across a wide ''[[q]]''-range, and may exhibit both diffraction peaks and diffuse scattering in both the small- and wide-angle. It is thus not obvious what to call these experiments or datasets.
-An evolving trend in the [[x-ray]] and [[neutron]] communities to use the term ''scattering'' as a super-class, which includes all possible experiments where there is an interaction between a sample and radiation. Then, more specific terms can be used to describe the specific kind of experiment/data (diffuse scattering, [[inelastic scattering]], diffraction, crystallography, [[coherent diffractive imaging|coherent imaging]], etc.). However this is not a universal definition, and so 'scattering' remains an ambiguous term (either being shorthand for 'diffuse scattering', or being used to define the broad class of matter-radiation experiments).
+An evolving trend in the [[x-ray]] and [[neutron]] communities to use the term ''scattering'' as a super-class, which includes all possible experiments where there is an interaction between a sample and radiation. Then, more specific terms can be used to describe the specific kind of experiment/data (diffuse scattering, [[inelastic scattering]], diffraction, crystallography, [[Coherent Diffraction Imaging|coherent imaging]], etc.). However this is not a universal definition, and so 'scattering' remains an ambiguous term (either being shorthand for 'diffuse scattering', or being used to define the broad class of matter-radiation experiments).
 ==Angle ranges==

@@ Line 10: / Line 10: @@
 Modern materials may be complex and hierarchical; they are studied simultaneously across a wide ''[[q]]''-range, and may exhibit both diffraction peaks and diffuse scattering in both the small- and wide-angle. It is thus not obvious what to call these experiments or datasets.
-An evolving trend in the [[x-ray]] and [[neutron]] communities to use the term ''scattering'' as a super-class, which includes all possible experiments where there is an interaction between a sample and radiation. Then, more specific terms can be used to describe the specific kind of experiment/data (diffuse scattering, [[inelastic scattering]], diffraction, crystallography, etc.). However this is not a universal definition, and so 'scattering' remains an ambiguous term (either being shorthand for 'diffuse scattering', or being used to define the broad class of matter-radiation experiments).
+An evolving trend in the [[x-ray]] and [[neutron]] communities to use the term ''scattering'' as a super-class, which includes all possible experiments where there is an interaction between a sample and radiation. Then, more specific terms can be used to describe the specific kind of experiment/data (diffuse scattering, [[inelastic scattering]], diffraction, crystallography, [[coherent diffractive imaging|coherent imaging]], etc.). However this is not a universal definition, and so 'scattering' remains an ambiguous term (either being shorthand for 'diffuse scattering', or being used to define the broad class of matter-radiation experiments).
 ==Angle ranges==

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 The terms [[diffuse scattering]], [[scattering]], [[diffraction]], [[crystallography]], etc. are used somewhat inconsistently. Traditionally, ''diffraction'' was used to refer to the study of highly crystalline materials, where distinct [[Bragg peak]]s would be observed. If the material was a single-crystal, it would be thought of as ''crystallography'', whereas if it was poly-crystalline, it would be a ''powder diffraction'' experiment. In this context, ''scattering'' was thus implicitly ''diffuse scattering'': the unwanted [[background]] coming from disorder. This is similar to how ''scattering'' is used for visible-light: where ''light scattering'' refers to the diffusion of light through disordered media. ''[[SAXS]]'' (small-angle x-ray scattering) was so-named because traditionally the small-angle regime was used to quantify the diffuse scattering from disordered systems (such as polymers in solution).
-However, as nanoscience has evolved, a wide variety of well-defined nanoscale structures became available. These structures give rise to well-defined peaks in the small-angle regime; these are diffraction peaks arising from the nano [[superlattice]], strictly analogous to the wide-angle diffraction peaks one obtains for atomic or molecular [[lattices]]/crystals. However, these experiments were historically still called SAXS (or [[SANS]]) experiments, and thus [[GISAXS]] similarly inhereted the term ''scattering'' even when though it was very frequently used to study diffraction [[Scattering features|features]]. (They should have perhaps been called 'small-angle diffraction' experiments.)
+However, as nanoscience has evolved, a wide variety of well-defined nanoscale structures became available. These structures give rise to well-defined peaks in the small-angle regime; these are diffraction peaks arising from the nano [[superlattice]], strictly analogous to the wide-angle diffraction peaks one obtains for atomic or molecular [[lattices]]/crystals. However, these experiments were historically still called SAXS (or [[SANS]]) experiments, and thus [[GISAXS]] similarly inhereted the term ''scattering'' even though it was very frequently used to study diffraction [[Scattering features|features]]. (They should have perhaps been called 'small-angle diffraction' experiments.)
 Modern materials may be complex and hierarchical; they are studied simultaneously across a wide ''[[q]]''-range, and may exhibit both diffraction peaks and diffuse scattering in both the small- and wide-angle. It is thus not obvious what to call these experiments or datasets.

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 * '''Complex objects in disordered states''': Colloids and nanoparticles in solutions, proteins folding/aggregating in solution, [[Example:Polymer_clustering|polymer gels]], etc. In this case, the scattering data is frequently refereed to as ''the'' form factor. Strictly speak, there is still a structure-factor contribution (from which one can deduce inter-particle distances, packing, etc.); but for disordered states, <math>\scriptstyle S(q) \to 1</math> for large ''q''. Thus, at least at large ''q'', the scattering curve is essentially the form factor. Form factors may be indistinct (scaling law), or may have a subtle hump or shoulder. The form factor for monodisperse systems with well-defined shape (e.g. [[Form Factor:Sphere|sphere]]) will have distinct oscillations.
 * '''Simple objects in ordered states''': The perfect single crystals typically measured in [[crystallography]] have atoms (point-like isotropic scatterers) arranged in an ordered [[lattice]]. The resultant scattering is strongly dominated by the structure factor (a.k.a. [[lattice factor]]): sharp [[Bragg peaks]] are observed owing to the constructive interference of scattering from crystal planes that have very well-defined repeat-spacings in [[realspace]].
-* '''Complex objects in ordered states''': Complex objects can be arranged into well-defined lattices. For instance, nanoparticles (which may have complex shapes, including multi-component structures like core-shell) can be arranged into [[superlattices]]. Self-assembling materials (e.g. [[block-copolymers]]) are another example where one must consider both the symmetry of the lattice, and the shape of the elements sitting on that lattice. In this case, the [[scattering intensity]] has non-negligible contributions from both the structure factor, and the form factor. Analysis of such data can thus be more complicated.
+* '''Complex objects in ordered states''': Complex objects can be arranged into well-defined lattices. For instance, [[nanoparticles]] (which may have complex shapes, including multi-component structures like core-shell) can be arranged into [[superlattices]]. Self-assembling materials (e.g. [[block-copolymers]]) are another example where one must consider both the symmetry of the lattice, and the shape of the elements sitting on that lattice. In this case, the [[scattering intensity]] has non-negligible contributions from both the structure factor, and the form factor. [[Lattices of nano-objects|Analysis of such data can thus be more complicated]].
 Again, it must be emphasized that these categories do not have hard boundaries. There is a continuum between all of these states (e.g. a continuous variation from a perfect single-crystal, to a [[paracrystal|disordered crystal]], to a poly-crystal, to an amorphous material, to a gas-like organization).

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 =="Kinds" of Scattering==
-'''TBD'''
+[[Image:Kinds of scattering.png|500px|center]]
 ==Energy==

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 ''Crystallography'' typically refers to measuring a single-crystal sample to generate a 2D image with a large number of [[diffraction]] peaks. [[Tutorial:Indexing|Peak indexing]] can be used to determine the symmetry and size of the [[unit cell]]. The peak intensities can then be used to fit for the probable electron-density distribution within the unit cell; i.e. to solve the crystal structure. Conceptually, a ''crystal'' is thus assumed to be a material that has a well-defined unit cell, which is repeated translationally throughout space (normally in all three dimensions). However, the more recent discovery of [[quasicrystals]] has forced a rethink of this definition. Quasicrystals do not have translational symmetry, yet they have well-defined local packing that is repeated throughout space, and indeed their diffraction patterns have well-defined peaks. Modernly, a crystal might instead be defined by as an ordered solid that exhibits an essentially discrete diffraction pattern.
 *  Carlos Basílio Pinheiroa and Artem M. Abakumov [http://journals.iucr.org/m/issues/2015/01/00/gq5003/index.html Superspace crystallography: a key to the chemistry and properties] ''IUCrJ'' '''2015''', 2(1), 137-154. [http://dx.doi.org/10.1107/S2052252514023550 doi: 10.1107/S2052252514023550]
 ==Energy==

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 ==GIXD==
-Grazing-incidence experiments collecting data at large angles may be called ''[[GIWAXS]]'' (Grazing-Incidences Wide-Angle X-ray Scattering), or may be called GIXRD/GIXD (Grazing-Incidence X-ray Diffraction), or simply GID. These terms are sometimes used interchangeably. On the other hand, GIWAXS may be more appropriate when discussing disordered or partially-ordered materials, whereas GIXRD may be more appropriate when discussing data with sharp diffraction peaks.
+Grazing-incidence experiments collecting data at large angles may be called ''[[GIWAXS]]'' (Grazing-Incidences Wide-Angle X-ray Scattering), or may be called GIXRD/GIXD (Grazing-Incidence X-ray Diffraction), or simply GID. These terms are sometimes used interchangeably. Instrumentally, GIWAXS is typically used to describe collection of wide-angle data with an area detector, whereas GID implies a point or line detector with collimation (i.e. a diffractometer). In terms of materials, GIWAXS may be more appropriate for disordered or partially-ordered materials, whereas GIXRD may be more appropriate for materials with sharp diffraction peaks.
 ==Crystallography==