The Proximity effect on Semiconducting Mineral Surfaces

本项目涉及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部的共反应。因此，反应物可以彼此相距一定距离，尽管如此，增强或抑制另一种反应物与矿物的相互作用。我们首先描述了这种反应机制，我们称之为邻近效应，并已开始评估反应伙伴之间的距离依赖性。 本项目拟对这种邻近效应进行系统的研究，主要研究硫化物的邻近效应，同时也研究氧化物上的一些重要反应。 量子力学评价的反应伙伴，如砷/Au或Bi/Ag在方铅矿和黄铁矿/毒砂将有助于理解先前描述的过程，如耦合的替代和优先纳入金毒砂和砷黄铁矿（与黄铁矿相比）。 此外，表面扩散过程的详细描述将阐明硫化物表面或体内的簇或纳米颗粒形成的机制。 了解这些过程对于发展一个关于含金、银矿床形成的一致性理论是重要的。 此外，邻近效应可能在硫化物的氧化和风化中起重要作用，因此，有助于评价酸性矿山废水中对环境重要的过程。此外，将评价氧化物的环境和技术重要反应。 以前观察到，赤铁矿表面台阶上的电子结构与平坦表面的价带结构显著不同。 因此，定向邻近效应将被检查沿着步骤，这增强了电子转移沿着Fe 2 O3表面上的步骤，因此，在这些步骤中的吸附和氧化的Mn。此外，水和氧在不同的二氧化铀表面的联合攻击将与以前观察到的形成氧化补丁黄铁矿的邻近效应。 这种效应有助于解决FeS 2（001）表面复杂的氧化和风化机制，并可能解决在储存放射性物质时不希望出现的晶质铀矿腐蚀的反应路径。尽管拟议的研究旨在对邻近效应进行基本了解，但它将对环境地球化学、矿床评价、在今后的金属提取技术备选方案中，以及在其他技术应用中，如使用赤铁矿作为过滤材料净化饮用水，或评估氧化铀矿物风化造成的潜在危害。 由于这些增强共反应性过程的一般特征，理论和发现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整个校园和与其他大学的合作。 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用作半导体量子力学界面的实际应用，以及矿物表面反应性的更经典方法。

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.