Electron holography at atomic dimensions - Present state

An electron microscope is a wave optical instrument where the object inform ation is carried by an electron wave. However, an important information, th e phase of the electron wave, is lost, because only intensities can be reco rded in a conventional electron micrograph. Off-axis electron holography so lves this "phase problem" by encoding amplitude and phase information in an interference pattern, the so-called hologram. After reconstruction, a rath er unrestricted. wave optical analysis can be performed on a computer. The possibilities as well as the current limitations of off-axis electron holog raphy at atomic dimensions are discussed, and they are illustrated at two a pplications of structure characterization of epsilon-NbN and YBCO-1237. Fin ally, an electron microscope equipped with a Cs-corrector, a monochromator, and a Mollenstedt biprism is outlined for subangstrom holography. (C) Else vier Science Inc., 1999 All rights reserved.