Experimental methods for determining crystal structure: Difference between revisions
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==Bragg's Law== | |||
[[Image:500px-Bragg_law.png|thumb|right|250px|A visual depiction of the relation of wavelength, atomic spacing, and scattering angle.]] | |||
The core principle behind using waves scattered off atomic centers to obtain information about the internal structure of a crystal is that of Bragg's Law. Bragg's Law gives a relation between wavelength of the incident waves which are being used to scatter <math> \lambda </math>, the distance between the scattering centers, in this case, the atomic nuclei <math> d </math>, and the angle between the waves and the plane formed by the atoms in the lattice <math> \theta </math>. | |||
When the incident waves reflect of the plane formed by the atomic centers, they reflect and can interfere either constructively or destructively. Where they constructively interfere, a film placed in the path of the waves will record a dot, and places with destructive interference record nothing. Doing this sort of scattering process from many different angles will give a 3-D pattern representing the location of atoms in the lattice. | |||
==X-ray scattering== | ==X-ray scattering== | ||
X-rays are scattered off the periodically arranged atoms, the particular ways the X-rays scatter give information about the location of atoms in the crystal lattice. | X-rays are scattered off the periodically arranged atoms, the particular ways the X-rays scatter give information about the location of atoms in the crystal lattice. | ||
Revision as of 22:53, 16 April 2009
Bragg's Law
The core principle behind using waves scattered off atomic centers to obtain information about the internal structure of a crystal is that of Bragg's Law. Bragg's Law gives a relation between wavelength of the incident waves which are being used to scatter , the distance between the scattering centers, in this case, the atomic nuclei , and the angle between the waves and the plane formed by the atoms in the lattice .
When the incident waves reflect of the plane formed by the atomic centers, they reflect and can interfere either constructively or destructively. Where they constructively interfere, a film placed in the path of the waves will record a dot, and places with destructive interference record nothing. Doing this sort of scattering process from many different angles will give a 3-D pattern representing the location of atoms in the lattice.
X-ray scattering
X-rays are scattered off the periodically arranged atoms, the particular ways the X-rays scatter give information about the location of atoms in the crystal lattice.
Electron scattering
Because electrons do have a wave nature, they can also be scattered off atoms in a crystal lattice, this process is similar to X-ray scattering. Some differences are that
- Electrons used in this way have a smaller wavelength than X-rays, this allows for greater resolution.
Neutron diffraction
Similar to electron and X-ray diffraction, neutrons with wavelength ~0.1nm are used to scatter off atomic centers in a crystal to create a pattern from which its atomic structure can be derived.