Orbital Mapping Near Interfaces

根据量子力学，电子在所谓的围绕原子核的轨道上运动。这些轨道及其相互作用产生了许多材料性质，例如，机械稳定性和粘附性，光学、电学和磁性以及化学键。因此，轨道对于从物理到化学、从材料科学到生物学的许多领域都是至关重要的。尽管它们起着核心作用，但到目前为止，可视化和测量固体内部的单个轨道一直是困难的。在这个项目中，我们将结合透射电子显微镜和电子能量损失光谱这两种方法来表征选定样品中的单个原子。为此，轨道的大小以及所需的测量精度构成了一个巨大的挑战：它们的大小不到十亿分之一米(大约比光波长小一千倍)，为了测量它们，电子束必须向样品传递非常特定的能量。因此，测量到的信号很弱，而且有噪声。为了克服这一挑战，将使用最新一代的仪器来达到理想的成像条件。此外，还将从理论和实验上确定样品厚度、加速电压和能量传递等最佳参数。此外，我们还将研究波函数整形和差分相位对比度等新的成像技术在轨道映射中的适用性，特别是界面和缺陷在轨道映射中扮演着重要的角色。一方面，一些关于轨道方向的结论只可能是由于样品在界面或缺陷附近的局部变化而产生的。另一方面，它们对许多实际应用都有巨大的影响，如保护性涂层的附着力、电子器件的效率或新型催化剂的开发。因此，本项目将开发的轨道测绘新方法不仅将改善我们对轨道的理解，而且还将使这一理解更好地适用。

According to quantum mechanics, electrons move in so-called orbitals around the atomic nuclei. These orbitals and their interaction with one another give rise to numerous materials properties like, e.g., mechanical stability and adhesion, optical, electrical, and magnetic properties as well as chemical bonding. Therefore, orbitals are of paramount importance for many fields from physics over chemistry and materials science to biology. Despite their central role, it has been difficult to visualize and measure individual orbitals inside of solids so far.In this project, we will combine the two methods of transmission electron microscopy and electron energy loss spectrometry to characterize individual atoms inside selected samples. To that end, the size of the orbitals as well as the required measurement precision pose a significant challenge: they are less than one billionth of a meter in size (about a thousand times smaller than the wavelength of light) and for measuring them, the electron beam has to transfer a very specific amount of energy to the sample. Hence, the measured signal is very weak and noisy. To overcome this challenge, latest-generation instruments will be used to reach ideal imaging conditions. In addition, optimal parameters such as sample thickness, acceleration voltage and energy transfer will be determined both theoretically and experimentally. Moreover, we will investigate the suitability of novel imaging techniques such as wavefunction shaping and differential phase contrast for mapping orbitals.Especially interfaces and defects play an important role for orbital mapping. On the one hand, some conclusions about the direction of orbitals only become possible due to the local changes of the sample in the vicinity of interfaces or defects. On the other hand, they have a huge impact on many practical applications such as the adhesion of protective coatings, the efficiency of electronic devices, or the development of new catalysts. Thus, the novel approaches to orbital mapping that will be developed in this project will not only improve our understanding of orbitals but will also lead to a better applicability of this understanding.