In this subjet we will develop off-axis electron holography for the measurement of electrostatic fields in AlGaN quantum well structures for UV emission. Electron holography measures the phase of electrons from an interference pattern. As the phase change of the electrons is proportional to the potentiel in the specimen, then this can be used to provide maps with high spatial resolution. To provide UV-C emission quantum wells of dimensions of 1 nm are required. This will push the limits of off-axis electron holography in terms of spatial resolution, thus we will work on implementing phase shifting holography that provides phase reconstructions in real space. As such a spatial resolution of less than 1 nm should be possible. Dynamical diffraction coming from the presence of dislocations and strain at interfaces leads to measurements of phase that are incorrect. Thus the effects of beam tilting will be also examined, such that it should be possible to remove the effects of dynamical diffraction in the phase reconstruction and build up an accurate potential map with high spatial resolution. This subject will be performed in the frame of the ANR project FUSSL which will run from Jan 2023 to Jan 2027, led by Eva Monroy at IRIG.