Recent progress in instrumentation, namely the invention of the corrector for the spherical aberration of the objective lens (Cs-corrector), allows now the almost dislocalization-free imaging of the atomic structure in a transmission electron microscope (TEM). Since the atomic structure determines the macroscopic properties, the answering of the key question "which atoms are where" is an important step for derivation of structure-properties relationships.

But even a Cs-corrected TEM is a compromise because aberrations are deliberately introduced to produce phase contrast imaging. Furthermore, the recording of conventional image intensity causes the loss of the electron wave's phase resulting in a considerable lack of long-ranging object information like e.g. inner electric potentials and magnetic fields.

In a TEM, off-axis electron holography solves the phase loss problem of imaging by interfering the object-modulated electron wave with an unmodulated reference wave. From the recorded interference pattern, amplitude and phase of the electron wave is numerically reconstructed using the laws of Fourier optics.

By this, a new window into the nanoworld is opened allowing direct measurements of tiny phase differences caused by electric potentials and magnetic fields. For example, the structured incorporation of dopants into the crystalline Si-substrate produce potential differences in semiconductor devices. Since the phase shift of the electron wave is directly proportional to the potential difference, magnitude and position can be measured by holography, giving important insights into the relationships between the microscopic electric structure and the macroscopic performance of the device.

The close cooperation with the group of Prof. Hannes Lichte from Triebenberg Lab (TU Dresden) is gratefully acknowledged.

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