Particularities of high-voltage electron microscopy: instrument design, defect imaging and in situ investigation in 'thick' specimens

The present paper gives a critical analysis and a reflection on the particu larities of HVEM, illustrated by practical examples. The instrument, i.e. t he attachments and the microscope itself, will be considered first. In this context the physical approach, which has led to the development of efficie nt equipment, will be emphasized. As regards the microscope itself, the spe cific design of the 1.2 MV GESPA microscope, which has not only permitted s uccessful in situ experiments in 'thick' specimens, but has also attained a very good resolution in an adapted version, will be considered. The dual a spect of defect imaging will also be discussed, i.e. a positive aspect in w hich good quality images of defects in 'thick' specimens may be obtained un der given conditions and a negative aspect, which is emphasized in high tem perature observations of defects in ordered phase superalloys. Finally, the fact that in situ experiments on 'thick' specimens should not be considere d independently but as a part of a broader investigation involving many oth er mesoscopic, macroscopic or nanoscopic techniques will be emphasized and illustrated by examples.