Hydration Structure on Ice Nucleating Mineral Surfaces

非均匀冰核在自然界中是普遍存在的，并且对于云的形成和降水等许多过程是关键的。虽然冰核粒子已经研究了几十年，但目前仍不清楚为什么有些粒子表现出有效的冰核，而另一些则没有。在这个项目中，两个重要类别的冰成核矿物应进行调查。我们将研究不同化学成分的长石矿物（正长石、微斜长石等）以及化学上最稳定的碘化银变体（碘银矿）。该项目的目标是阐明水存在下表面的原子结构，并绘制界面处的室温水合结构。富钾长石样品的高冰成核能力被归因于高能（100）面，其可能暴露在缺陷部位和表面裂纹处。为此，我们将解决这样一个问题：与高能（100）表面相比，天然解理面（001）、（010）顶部的水合结构是否显著不同。此外，我们将研究与富钾正长石不同的菱镁矿，以阐明水化结构的差异是否可以被发现作为矿物的化学组成的函数的问题。关于银碘化物，要回答的主要和关键问题涉及极性（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整体截断表面的情况下进行的，而没有实验证据表明稳定机制在起作用。此外，冰成核能力的显着差异的银-相比，碘化物终止的表面已被理论预测。因此，我们将研究这两种终端，以揭示原子尺度的表面结构，并确定可能的表面重建。我们将调查是否在两个终端的水化层的结构提供了不同的冰成核能力的指示。总之，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了解的基本机制，非均质冰成核矿物颗粒。

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.