Pattern formation during Electropolishing

我们正在开发一个新的研究领域，“电抛光过程中的模式形成”，它有潜力成为许多需要多孔或纳米图案表面或尖锐尖端的应用的强大工具箱。电解抛光在很大程度上（尽管不是全部）以一维的方式被理解，作为与电极表面距离的函数，但在平行于电极表面的平面上假设均匀行为。不稳定性或不均匀性通常不会导致对称性破坏和图案形成。我们努力开发三维模型，考虑到许多近地表过程，可以解释各种不同模式的形成。虽然对单一系统进行深入研究的文献中有孤立的例子，但我们是世界上第一个对一系列系统和现象采取综合方法的团队。具体来说，在文献中有几个相互竞争和矛盾的模型的例子，特别是关于阳极氧化物的作用。导致多孔阳极氧化物、阳极氧化纳米管或浅金属图案的过程之间的机制差异是完全不清楚的，目前任何模型都无法解释。由于这些结构（特别是用于催化、光伏和生物医学应用的过渡金属氧化物纳米管）的实际重要性，更好地了解它们是如何形成的将是非常可取的，并且具有经济意义。我们在小组中观察到的现象包括浅金属图案的形成（酒窝、丘疹、条纹和迷宫图案）、多孔金属层、分离和粘附的多孔氧化物、有序的过渡金属纳米管、颈缩和尖端的形成，以及导致阶梯金属台面的电流振荡。到目前为止，还没有连贯和全面的电抛光三维模型可以解释我们所有的观察结果，但我们正在努力获得对这一强大工具集的完全预测控制。

We are developing a new field of research, 'Pattern Formation during Electropolishing', which has the potential of being a powerful tool chest for many applications requiring porous or nanopatterned surfaces, or sharp tips. Electropolishing is largely (albeit not entirely) understood in a one-dimensional manner, as a function of distance from the electrode surface but assuming homogeneous behavior in plane parallel to the electrode surface. Instabilities or inhomogeneities that can lead to symmetry breaking and pattern formation are not usually accounted for. We strive to develop 3-dimensional models that take into account a number of near-surface processes that can explain the formation of a variety of different patterns. While there are isolated examples in the literature of in-depth studies of a single system, we are the first group in the world to take a comprehensive approach across a range of systems and phenomena. Specifically, there are several examples in the literature of competing and contradictory models, in particular with regards to the role of anodic oxides. The mechanistic differences between the processes leading to porous anodic oxides, anodic oxide nanotubes or shallow metallic patterns are entirely unclear and not explained in any current model. Due to the practical importance of these structures (especially transition metal oxide nanotubes for catalytic, photovoltaic and biomedical applications), a better understanding of how they are formed would be highly desirable and economically relevant. Phenomena that we have observed in our group include shallow metallic pattern formation (dimples, pimples, stripes and labyrinthine patterns), porous metal layers, detaching and adherent porous oxides, ordered transition metal nanotubes, necking and tip formation, as well as current oscillations resulting in stepped metallic mesas. No coherent and comprehensive 3-dimensional model of electropolishing exists as of yet that could account for all of our observations but we are working to gain full predictive control over this powerful set of tools.