The Proximity effect on Semiconducting Mineral Surfaces

本项目研究了一种新型的反应机理：不同物种在半导体矿物表面或半导体矿物内的共反应。因此，反应物可以彼此相隔一段距离，但仍能增强或抑制另一反应物与矿物的相互作用。一年前，我们首次描述了这种反应机理，我们称之为邻近效应，并开始评估反应伙伴之间的距离依赖关系。在这个项目中，系统地研究了这种邻近效应，主要是对硫化物的影响，但也对氧化物上的一些重要反应进行了研究。对方铅矿和黄铁矿/毒砂中的As/Au或Bi/Ag等反应伙伴的量子力学评价将有助于理解先前描述的耦合取代和金优先进入毒砂和砷黄铁矿(与黄铁矿相比)的过程。此外，对表面扩散过程的详细描述将阐明团簇或纳米颗粒在硫化物表面或块体内形成的机制。了解这些过程对于形成一致的含金、含银矿床理论具有重要意义。此外，邻近效应可能在硫化物的氧化和风化过程中发挥重要作用，因此有助于评估酸性矿山废水中对环境重要的过程。此外，还将评估氧化物在环境和技术上的重要反应。以前观察到赤铁矿表面台阶上的电子结构与平面上的价带结构有很大的不同。因此，我们将沿着台阶考察定向邻近效应，该效应增强了Fe_2O_3表面沿台阶的电子转移，从而在这些台阶上促进了Mn的吸附和氧化。此外，根据邻近效应，将水和氧对不同UO2表面的联合攻击与先前观察到的在黄铁矿上形成氧化斑的情况进行了比较。这一效应有助于解决FeS2(001)表面复杂的氧化和风化机理，并可能解决铀矿腐蚀的反应路径，这是储存放射性物质时不需要的效应。尽管拟议的研究旨在基本了解邻近效应，但它将对环境地球化学、矿藏评估、未来金属提取技术的选择以及其他技术应用产生更广泛的影响，如使用赤铁矿作为过滤材料净化饮用水，或评估铀氧化物矿物风化的潜在危险。由于这些增强的协同反应过程的共性，该理论和结果可以应用于其他领域，如物理、化学工程、材料科学和核工程。该项目的早期阶段和规划已经引发了校园内以及与其他大学的合作。最后，密歇根大学关于矿物和材料表面的新教学计划可以将这些过程作为半导体量子力学界面和更经典的矿物表面反应性方法的实际应用。

AbstractThis project deals with a new type of reaction mechanism: the co-reaction of different species on semiconducting mineral surfaces or within a semiconducting mineral. Hereby, the reactants can be some distance apart from each other and, nonetheless, enhance or inhibit the interaction of the other reactant with the mineral. We first described this reaction mechanism, which we call the proximity effect, a year ago and have begun to evaluate the distance dependence between the reaction partners. In this project, a systematic study is proposed on such proximity effects, mainly on sulfides but also on some important reactions on oxides. The quantum mechanical evaluation of the reaction partners such as As/Au or Bi/Ag in galena and pyrite/arsenopyrite will help to understand previously described processes such as coupled substitutions and the preferred incorporation of gold into arsenopyrite and arsenian pyrite (compared with pyrite). Furthermore, the detailed description of surface diffusion processes will elucidate the mechanism of cluster or nanoparticle formation on sulfides surfaces or within the bulk. Understanding these processes is important to develop a consistent theory on the formation of gold and silver-containing ore deposits. Furthermore, the proximity effect may play an important role in the oxidation and weathering of sulfides and is, therefore, instrumental for the evaluation of environmentally important processes in acid mine drainage.In addition, environmentally and technically important reactions on oxides will be evaluated. It was previously observed that the electronic structure on hematite surface steps is significantly different from the valence band structure of flat surfaces. Therefore, the directed proximity effect will be examined along steps, which enhances electron transfer along steps on Fe2O3 surfaces and thus, the adsorption and oxidation of Mn at these steps. Furthermore, the combined attack of water and oxygen on different UO2 surfaces will be compared with the previously observed formation of oxidation patches on pyrite in light of the proximity effect. This effect helped resolve the complicated oxidation and weathering mechanism on a FeS2 (001) surface and may resolve the reaction path of uraninite corrosion, which is an unwanted effect in storing radioactive materials.Even though the proposed studies aim at a basic understanding of the proximity effect, it will have a broader impact on a wide variety of applications in environmental geochemistry, in the evaluation of ore deposits, in future options for metal extraction techniques, and for other technical applications such as the purification of drinking water using hematite as a filter material, or the evaluation of potential hazards due to the weathering of uranium oxide minerals. Due to the general character of these enhanced co-reactivity processes, the theory and findings can be applied to other fields such as physics, chemical engineering, materials science, and nuclear engineering. Early stages and planning of this project have already sparked collaborations across campus and with other universities. Finally, the new teaching program on minerals and materials surfaces at the University of Michigan can use these processes as a practical application of the interface of quantum mechanics of semiconductors and more classical approaches to mineral surface reactivity.