Hydration Structure on Ice Nucleating Mineral Surfaces

非均质冰成核在自然界中无处不在，对云的形成和降水等许多过程起着至关重要的作用。虽然对冰核粒子的研究已经有几十年了，但目前还不清楚为什么有些粒子表现出有效的冰核作用，而另一些粒子则没有。在本项目中，将研究两类重要的冰核矿物。我们将研究不同化学成分的长石矿物(斜长石、微斜长石等)以及热力学上最稳定的碘化银(碘银矿)改性。这个项目的目标是阐明在水存在下表面的原子结构，并绘制界面上的室温水合结构图。富钾长石样品的高成冰能力被认为是高能的(100)面，可能暴露在缺陷位置和表面裂纹处。为此，我们将解决这样一个问题：与高能(100)面相比，自然解理面(001)、(010)上的水化结构是否有显著不同。此外，我们将研究不同于富钾正长石的长石，以阐明水化结构是否随矿物化学成分的不同而存在差异的问题。关于碘化银，需要回答的首要和关键的问题是极性(0001)解理面的稳定机制。到目前为止，所有的理论研究都是在考虑体积截断表面的情况下进行的，而没有实验证据来证明稳定机制的作用。此外，从理论上预测了银的成冰能力与端碘表面相比存在显著差异。因此，我们将调查这两个终端，以揭示原子尺度的表面结构，并确定可能的表面重建。我们将调查这两个末端的水化层的结构是否为不同的冰核能力提供了一个指示。综上所述，我们将在分子水平上收集矿物-水界面的直接空间信息。有了这些信息，我们希望有助于我们理解矿物颗粒控制非均质冰成核的基本机制。

Heterogeneous ice nucleation is omnipresent in Nature and pivotal for many processes such as cloud formation and precipitation. Although ice nucleation particles have been studied since decades, it remains unclear at present why some particles exhibit efficient ice nucleation while others do not. In this project, two important classes of ice nucleating minerals shall be investigated. We will study feldspar minerals of different chemical composition (orthoclase, microcline and others) as well as the thermodynamically most stable modification of silver iodide (iodargyrite). The goal of this project is to elucidate the atomic structure of the surface in the presence of water and to map the room temperature hydration structure at the interface. The high ice nucleating ability of potassium-rich feldspar samples has been assigned to the high-energy (100) plane, which might be exposed at defect sites and surface cracks. To this end, we will address the question whether or not the hydration structure is significantly different atop the natural cleavage planes (001), (010) as compared to the high-energy (100) surface. Moreover, we will study feldspars different from potassium-rich orthoclase for elucidating the question whether or not differences in the hydration structure can be found as a function of the chemical composition of the mineral. Regarding silver iodide, the primary and pivotal question to be answered concerns the stabilization mechanism of the polar (0001) cleavage plane. So far, all theoretical studies are performed with the bulk-truncated surface in mind while no experimental evidence exists for the stabilization mechanism in action. Moreover, significant differences in the ice nucleating ability of the silver- as compared to the iodide-terminated surface have been predicted by theory. Consequently, we will investigate both terminations to shed light onto the atomic-scale surface structure and to identify possible surface reconstructions. We will investigate whether the structure of the hydration layers on the two terminations provides an indication for the different ice nucleating ability. In summary, we will gather direct-space information of the mineral-water interface at the molecular level. With this information we hope to contribute to our understanding of the fundamental mechanisms governing heterogeneous ice nucleation by mineral particles.