Medium resolution off-axis electron holography with millivolt sensitivity

Focused ion beam prepared silicon calibration specimens with boron doped layers have been examined using off-axis electron holography. By using a state-of-the-art FEI Titan microscope with unprecedented stability, we have been able to record holograms for time periods of $128s$ with contrast levels of almost 40% and an average signal on the charge coupled device camera of 30 000 counts. A consequence of this is a significant improvement of the signal-to-noise ratio in the phase images allowing steps in potential of less than $0.030±0.003V$ to be measured if sufficient care is taken during specimen preparation.