Standards Development

Scope

This document specifies a method for determining the thickness of thin crystalline specimens by convergent beam electron diffraction (CBED) using a transmission electron microscope/ scanning transmission electron microscope (TEM/STEM).

This method is applicable to determine the thickness of thin crystal specimens. In principle, all crystalline thin specimens, including metalls, ceramics, semiconductors, mineral substance etc, can be studied by CBED method. However, deformation or defects of the specimen may affect the quality of the CBED pattern hence the resullts.

 The thickness that can be measured is in the range of tens to hundreds of nano-metres. The maximum measurable thickness is limited by the energy of the incident electron beam and mass thickness of the specimen. However, the minimum value of the measurable thickness depends on the diffraction condition of the diffracted beam, which is excited for the mesurement. When the specimen is thin enough the adequate dynamic diffraction fringes will not appear. In such case, this CBED technique is not able to carried out to measure the specimen thickness, owing to that obtaining the dynamic diffraction contrast within the diffracted disc is the prerequisite for CBED study.

 Since the thickness of the thin specimens is often uneven, the thickness determined by CBED method is the local thickness of a specimen area where is illuminated by the incident beam. This document is not applicable for non-crystalline specimens.

Purpose

The microstructure at nano-meter scale is essential for evaluating and controlling the performance properties of all kinds of materials, especially for developing new materials. The thickness of a thin crystal is an important parameter for a wide variety of applications by transmission electron microscopy, such as absorption correction of EDS analysis, the beam broadening effect, structure factor determination, high-resolution image simulation and estimate characteristics of materials such as density of crystal defects, number density or volume fraction of small particles etc. Among several methods for the thickness measurement of thin crystals, convergent beam electron diffraction (CBED) method is the accurate and implementable technique, it can achieve a relative standard deviation of about 1% under appropriate working conditions. The CBED technique is a very important method in material analysis and is already widely applied worldwide. It is necessary to be standardized in order to have better applications.