Electrochemical material synthesis in ultra-high vacuum: elementary steps of electrochemical deposition of tantalum and niobium in ionic liquids

钽和铌等难熔金属用于各种技术应用中。例如，钽电解电容器对当今的微电子学尤为重要。钽的物理化学性质允许生产具有高电容的电容器。由于钽的出现率较低，铌越来越多地用作电容器的替代材料。此外，钽由于其生物相容性而广泛用于植入物的医学中。在电化学上，难熔金属由于其相对负的标准电极电位而不能从水溶液和有机溶液中沉积。迄今为止，只有高温熔盐被证明是几μm厚难熔金属电化学沉积的有效槽。然而，这些电解质存在许多技术和经济问题，例如由于金属在其沉积后部分溶解而导致电解过程的电流效率损失。此外，在必要的高温下会发生腐蚀问题。由于其宽的电化学窗口（高达6 V），离子液体（ILs）提供自己作为电解质，这些金属的电沉积在低温下作为一种替代。结果表明，在一系列对空气和水稳定的离子液体中，TaF5可电沉积出Ta薄层。Ta和Nb的电沉积是相当复杂的，并且没有详细了解。此外，金属的高反应性使得难以用非原位方法分析沉积层。该项目现在利用离子液体通常具有非常低的蒸汽压的事实，因此可以使用基于真空的方法进行研究，例如超高真空（UHV）中的X射线光电子能谱（XPS）。我们想研究的电化学过程中难熔金属沉积在离子液体一步一步直接在超高真空与单色XPS原位使用钽和铌前体。专门设计的光谱单元可用于这种类型的材料合成。从纯离子液体的超高真空电化学分析开始，我们将专门研究前体对沉积的影响。这也将为我们提供有关离子液体和溶液的稳定性的信息，由于电化学的影响，在一个非常受控的气氛。通过这种方法，我们将从根本上阐明钽和铌是如何电化学沉积的。在中期，我们希望展示电化学表面工程方法，在温和条件下存款难熔金属。

Refractory metals such as tantalum and niobium are used in a variety of technical applications.For example, tantalum electrolytic capacitors are particularly important for today'smicroelectronics. The physico-chemical properties of tantalum allows miniaturised capacitors with high capacitance to be produced. Due to the lower occurrence of tantalum, niobium is increasingly used as a replacement material for capacitors. In addition, tantalum is widely used in medicine for implants due to its biocompatibility. Electrochemically, refractory metals cannot be deposited from aqueous and organic solutions due to their relatively negative standard electrode potentials. Hitherto, only high-temperature molten salts have proven to be efficient baths for the electrochemical deposition of several μm thick refractory metals. However, these electrolytes suffer from many technical and economic problems, such as the loss of current efficiency of the electrolysis process due to the partial dissolution of the metal after its deposition. Furthermore, corrosion problems occur at the necessary high temperatures. Due to their wide electrochemical windows (up to 6 V), ionic liquids (ILs) offer themselves aselectrolytes for the electrodeposition of these metals at low temperatures as an alternative. Ithas been shown that Ta can be electrodeposited in thin layers from TaF 5 in a range of air and water stable ionic liquids. The electrodeposition of Ta and of Nb is quite complex and not understood in detail. In addition, the high reactivity of the metals makes it difficult to analyse the deposited layers with ex-situ methods. This project now takes advantage of the fact that ionic liquids generally have a very low vapour pressure and can therefore be investigated with vacuum-based methods such as X-ray photoelectron spectroscopy (XPS) in ultra-high vacuum (UHV). We want to investigate the electrochemical processes during refractory metal deposition in ILs step by step directly in UHV with monochromatic XPS in-situ using tantalum and niobium precursors. A specially designed spectroscopy unit is available for this type of material synthesis. Starting with the analysis of the UHV electrochemistry of the pure ILs, we will then specifically investigate the influence of the precusors on the deposition. This will alsoprovide us with information about the stability of ILs and solutions due to the influence ofelectrochemistry in a very controlled atmosphere. With this approach, we will fundamentally clarify how tantalum and niobium are deposited electrochemically. In the medium-term we would like to show to electrochemical surface engineering ways to deposit refractory metals under mild conditions.