Abstracts of Scandinavian Society Jot Electron Microscopy 269

intensity measurements. Diffraction techniques may be espec-

ially powerful when used in conjunction with other techniques. An example is the combination of the two-dimensional 3 ~ resolution in HREM with the three- dimensional, high spatial frequency in- formation obtained from CBED (Olsenl) . Another example is the exploitation of diffraction effects in spectroscopy shown by Tafto 2.

1. A. Olsen and P. Goodman, Ultramicroscopy 6 (1981) 101.

2. J. Taft6, Z. Naturforsch. 34a (1979) 452.

CHANNELLING CONTRAST FROM AL-BULK SPECIMENS

J. Hjelen

SINTEF, Metallurgy Division, Trondheim, Norway

Channelling contrast from Al-bulk specimens as a function of accelerating voltage and detectors is qualitatively investigated. The specimens were super- pure and commercially pure aluminium. Deformation from the mechanical prepar- ation was removed by electropolishing. The investigation shows that the chan- nelling contrast decreases with increas- ing accelerating voltage. This is in agreement with the theory.

The applied solid state detector (back- scattered electrons) was active down to 2 kV accelerating voltage. Channelling contrast images taken with Everhart- Thornley detector were disturbed by top- ographic information even when the collector voltage was reduced to -50 V. The same disturbance from topography was also present in images taken with a Robinson detector. The best channelling contrast was found on micrographs taken with the annular solid state detector at acceleration voltage ~ i0 kV.

In STEM microscopes the channelling contrast is weak because the lowest obtainable accelerating voltage in SEM mode often is 20 kV or more.

ELECTRON MICROSCOPY AND THE DEFINITION OF MICROSTRUCTURE

E. Hornbogen

Ruhr Universitat Bochum, D-4630 Bochum, West Germany

The new insight into the structure of

matter provided by new microscopic methods, especially by TEM, requires a more comprehensive definition of the term "microstructure" of solids.

After a brief discussion of the dif- ferent levels of structure--nuclear, atomic, molecular structure, structure of phases, microstructure--a systematic approach to microstructure of metallic and ceramic materials is attempted.

Four classes of microstructural elements are defined according to their 0-, to 3-dimensional geometrical dimen- sion, for example: vacancies, disloca- tions, grain boundaries, dispersed particles. Several functions are re- quired to characterize their density, local and size distribution, their shape and orientation.

There exists an upper limit for the density of defects, such as disloca- tions and grain boundaries, at which the crystal structure disappears: "microstructure to phase" transforma- tion.

Three elementary types of two- (or multi-) phase microstructures can be defined using topological parameters (densities of grain and phase boundar- ies): disperson, duplex, net structure. Transformation of one type of micro- structure into another can take place as a function of temperature and chem- ical composition. Such "microstruc- tural transformations" can be associa- ted with discontinuous changes in macroscopic properties similar to those associated with transformation of elec- tronic or phase structure.

A complete description of the newly defined microstructure can be obtained from a combined application of differ- ent methods of microscopy.

IMAGE PROCESSING OF HREM DATA OF INORGANIC CRYSTALS

Sven Hovm~ller, George Farrants and Agneta Sj~gren

Department of Structural Chemistry, Arrhenius Laboratory, University of Stockholm,s-106 91 Stockholm, Sweden

Electron micrographs of inorganic crystals are computer processed by Fourier methods. Hereby it is possible to determine exact values for defocus and astigmatism of a micrograph from the computed diffraction pattern.

The computed Fourier transform of a crystal contains amplitude and phase values for all the reflections within