Convergent-beam electron diffraction (CBED) should be an ideal technique for determining the lattice parameters of regions as small as a nanometer in size. This capability was first demonstrated about fifteen years ago and CBED has been used in a number of analyses since this time. In general though, the technique has been slow to catch on, except in the semiconductor area, where CBED has been usedextensively to measure lattice parameters in Si/SixGe1-x superlattices. Possible reasons for the slow adoption of this technique by the electron microscopy and materials science communities may be that: 1) CBED is usually dynamical, and it has become apparent that the use of simple kinematical calculations can lead to substantial errors (or at least some uncertainty) in quantitative lattice parameter determination, 2) a standardized procedure for determining the lattice parameters in the most general case, when six parameters are unknown, has not been established, and 3) surface relaxation associated with the thin foils used in transmission electron microscopy (TEM) may distort the sample and cause it to be unlike bulk material. The purpose of this paper is to assess the present status of lattice parameter measurement by CBED, particularly with respect to the three areas just mentioned.
Determination of Strain Relaxation at the Free Surfce of Strained-SiGe Film Using Convergent Beam Electron Diffraction