Thesis presented October 17, 2023

Abstract:
The measurement of the electric field is of huge interest as its position, orientation and strength will control the properties of an electronic device. However, this measurement with the required resolution and accuracy has been difficult. TEM is well-adapted for field measurements as the incident electrons are sensitive to both the electromagnetic fields and electromagnetic potentials. In this PhD thesis, 4D-STEM technique was developed and compared to two other techniques that are better known. These techniques are the TEM-based off-axis electron holography (which will now be referred as electron holography) and segmented differential phase contrast (DPC). By electron holography, maps of the electrostatic potential can be obtained using electron interference. The negatively charged electron beam is deflected either side of a positively charged wire or birpsim to interfere with itself. From the position of the interference fringes contains information about the phase of the electrons from which the local potential can be obtained. If measurements of the electric field are required, then it can be derived from the potential map. This technique is well-developed in several labs around the world and has been the focus of many years of development at CEA LETI. Therefore, it will used as the benchmark for this work in terms of potential and field mapping. The second technique, DPC is based on the detection of the deflection of a convergent beam as it passed through a region containing an electric field. This is done by measuring the changes in beam current measured on a segmented detector. The pixelated differential phase contrast approach uses the same principle as DPC, but uses a pixelated detector to collect the full distribution of the scattered electron beam from which we hope to be able to quantify the measurements of the electric field.
The different studies done during this PhD​ allowed us to determine what are the best parameters for 4D-STEM field mapping. These studies also permitted us to highlight how 4D-STEM can overcome the limits encountered when performing both DPC and holography and also the new limits that 4D-STEM reaches.

Keywords:
DPC, 4D-STEM, Transmission electronic microscopy, electric field, Holography