Electric Fields by 4D scanning transmission electron microscopy

现代技术的未来将由测量和控制功能材料的电子特性的能力来塑造。透射电子显微镜（TEM）一直是材料开发的关键工具，因为它能够可视化内部结构和成分，现在它能够分辨和测量单个原子。然而，功能特性的测量（在这里，我们感兴趣的是内部电场）一直很困难;信号相对微妙。直到最近，直接测量内部场的最佳方法是电子全息术。这不是一个简单的技术，需要一个专门的显微镜（电子双棱镜）和几何限制，灵敏度和分辨率都是相互关联的。然而，这些信息也存在于扫描透射电子显微镜（STEM）数据中，尽管它不能被传统的闪烁体探测器看到。它在它们产生的信号中丢失了，该信号在整个散射图案上平均。新的像素化探测器可以高速运行，捕获每一个电子，并提供几个数量级的更多细节，从而可以直接测量内部场和其他性质。为了获得这些信号，我们必须开发新的方法，从大量数据中提取它们。我们将开发的技术有许多可能的应用。我们将与一系列正在开发材料的合作伙伴合作，从技术上重要的有用材料，如高功率半导体和发光器件，到铁电材料自发产生和响应内部电场的方式的基本问题。

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.