Singel Crystalline Silicon
- Practical Electron Microscopy and Database -
- An Online Book -

http://www.globalsino.com/EM/  



 

 

=================================================================================

Crystalline silicon (c-Si) can be considered as a four-fold coordinated network, where each Si atom is tetrahedrally bonded to four neighboring Si atoms. In this way, these tetrahedral structures are periodically ordered to form a lattice.

Table 2393a lists the electronic properties that are affected by structural disorders in amorphous and crystalline Si.

Table 2393a. The electronic properties affected by structural disorders in amorphous and crystalline Si.

Electronic properties
Structural disorders
Bonding disorder
Electronic states in band gap
Structural defects

Electronical, metastable states

Alternative bonding configurations

Note that the comparison of the properties between single, polycrystalline, and amorphous Si is listed in page2019.

As an example of CBED applications, Figure 2393 (a) shows a CBED diffraction pattern from a [111] zone-axis Si crystal. The non-uniform intensity within the CBED discs as well as the lines and features inside the discs can be extremely useful in analysis of crystal structure. The symmetry of the patterns within the discs can be used to determine the point group symmetry of the crystal structure. The 6-fold rotational symmetry of the white discs in the CBED pattern matchs the conventional FCC diffraction pattern as shown in Figure 2393 (b). Furthermore, CBED patterns are capable of providing information about the third dimension of crystals, but not just the two-dimensional projections. In Figure 2393 (a), a bright ring with dashed spots marked by the red arrow presents 3-fold rotational symmetry. However, this 3-fold symmetry cannot be shown in conventional diffraction pattern, indicated by Figure 2393 (b). On the other hand, the rings of intensity fringes shown in the inset are related to the specimen thickness.

CBED diffraction pattern from [111] Si obtained at low (main pattern) and high (inset) camera-lengths
Conventional single crystal diffraction pattern from [111] Si, showing 6-fold symmetry.
(a)
(b)
Figure 2393. (a) CBED diffraction pattern from a [111] Si crystal obtained at small (main pattern) and large (inset) camera-lengths, [1] and (b) Conventional single crystal diffraction pattern from [111] Si, showing 6-fold symmetry.

 

 

 

 

 

 

 

 

 

 

 

[1] D. B. Williams: Practical Analytical Electron Microscopy in Materials Science (Philips Electron Optics Publishing Group, Mahwah, NJ 1984). Figure reprinted with the courtesy of FEI Company.

 

 

=================================================================================