[Microscopy].

247 Support of specific " Local contacts for materials characterization " of this community at relevant neutron scattering facilities, staffed with personnel (scientists, engineers) that are experienced both in the use of neutrons and in materials research. They should be the primary contacts for materials researchers from the different institutions in the European community. Direct imaging of materials has always been an important aspect of microstructural characterization. There are various techniques for different wavelengths and instruments, namely, optical microscopy (wavelength in the range of that of visible light) scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (wavelength in the Ångstrøm or sub-Ångstrøm range) [1]. While optical microscopy is a rather mature technique, SEM and TEM have undergone major developments and advancements over the past decade. These advances have been made possible by revolutionary progress in instrumenta-tion. It is now feasible to correct fundamental aberrations of electron optical instruments. In addition, it is now possible to generate coherent electron sources. Improved detection systems exist which allow the detection of each electron. Furthermore, advancements in the understanding of elastic and inelastic scattering of high-energy electrons by crystalline and non-crystalline materials lead to a quantitative understanding of the collected data. In this chapter only transmission electron microscopy will be considered. Other new and advancing imaging techniques will be covered in Chapters 7.4 and 7.5. A major goal in materials science is the imaging of materials at the atomic level. This requires instrumentation allowing the theoretical and practical achievement of atomic resolution [2]. Resolution in the Ångstrøm range can be reached by systems which use coherent waves of a short wavelength and are equipped with imaging lenses with sufficiently small aberrations. Atomic resolution of the bulk material is so far mainly achieved by TEM. So far atomic resolution can either be reached by increasing the electron acceleration voltage (at constant aberration) or by specific techniques which allow to eliminate indirectly lens aberrations by complex procedures (Table 7.5 [3]). However, recent developments in instrumentation allow the correction of aberrations [4]. With the latter revolutionary development aberration-free imaging should be possible in the sub-Ångstrøm range. Elastic and inelastic scattering of electrons occurs in a specimen irradiated with electrons. Both types of scattered electrons can be utilized for the structural and chemical analysis of the materials and can be obtained with high spatial resolution. It is expected that a major breakthrough is within immediate reach regarding …