Electric Fields by 4D scanning transmission electron microscopy

The future of modern technology will be shaped by the ability to measure and control the electronic properties of functional materials. Transmission electron microscopy (TEM) has always been a key tool for materials development due to its ability to visualise internal structure and composition, and it is now able to resolve and measure individual atoms. However, measurement of functional properties (here, we are interested in internal electric fields) has been difficult; signals are relatively subtle. Until recently, the best method to directly measure internal fields was electron holography. This is not a straightforward technique, requiring a specialised microscope (with an electron biprism) and limitations on geometry, sensitivity and resolution that are all interlinked. However, this information is also present in scanning transmission electron microscopy (STEM) data, although it is not seen by conventional scintillator detectors. It is lost in the signal that they produce, which averages over the whole scattering pattern. New pixelated detectors that run at high speeds, capture every electron, and give several orders of magnitude more detail open the possibility to measure internal fields - and other properties - in a straightforward way. To access these signals, we will have to develop new methods to extract them from the large volumes data produced. There are many possible applications of techniques that we will develop. We will work with a range of partners who are developing materials from technologically important useful materials such as high-power semiconductors and light emitting devices, to fundamental questions about the way that ferroelectric materials can spontaneously generate and respond to internal electric fields.