The Proximity effect on Semiconducting Mineral Surfaces

摘要本课题研究一种新型的反应机理：不同物质在半导体矿物表面或半导体矿物内部的共反应。因此，反应物可以彼此相隔一定距离，尽管如此，增强或抑制其他反应物与矿物的相互作用。我们在一年前首次描述了这种反应机制，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性。在这个项目中，提出了一个系统的研究这种接近效应，主要是对硫化物，但也对一些重要的反应氧化物。方铅矿和黄铁矿/毒砂中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过程，如偶联取代和金优先掺入毒砂和砷黄铁矿（与黄铁矿相比）。此外，表面扩散过程的详细描述将阐明在硫化物表面或体内形成团簇或纳米颗粒的机制。了解这些过程对于建立一个关于含金银矿床形成的一致理论是很重要的。此外，邻近效应可能在硫化物的氧化和风化中起重要作用，因此对酸性矿山排水中环境重要过程的评价具有重要意义。此外，环境和技术上重要的反应氧化物将进行评估。前人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明显的不同。因此，定向接近效应将沿着台阶进行研究，这将增强Fe2O3表面上的电子转移，从而在这些台阶上吸附和氧化Mn。此外，根据邻近效应，将水和氧在不同UO2表面的联合攻击与之前观察到的黄铁矿氧化斑的形成进行比较。该效应有助于解决FeS2（001）表面复杂的氧化和风化机制，并可能解决铀矿腐蚀的反应路径，这是贮存放射性物质时不希望出现的效应。尽管拟议的研究旨在对接近效应有一个基本的了解，但它将对环境地球化学、矿床评价、金属提取技术的未来选择以及其他技术应用，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等各种应用产生更广泛的影响。由于这些增强的共反应过程的一般特征，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。这个项目的早期阶段和规划已经引发了跨校园和其他大学的合作。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.