In situ synchrotron radiation studies of functional materials prepared through CVD techniques

化学气相沉积是一种极为重要的薄膜形成技术。它是工业中应用最广泛的涂层技术，特别是在平板玻璃工业中，它被用来制造节能和自清洁涂层，直到玻璃瓶工业中，它被用来制造低摩擦涂层（总价值100亿美元）。它也是微电子制造集成电路的关键技术之一。尽管具有巨大的价值，但通过原位分析对CVD膜形成的研究却出奇地少。通常，薄膜是在沉积和冷却后研究的，而不是在生长过程中研究的。一些原位测量，特别是通过椭偏、拉曼和反射技术进行。通过XRD或EXAFS直接测量生长过程很难实现，因为样品呈薄膜形式，通常包含很少的原子层（1-100纳米厚），并且适应CVD实验和源的反应器细胞结构已被证明是严格的。这个过程只有在同步加速器提供的明亮光源下才能实现。研究在CVD过程的初始生长阶段发生了什么，将为理解该过程带来巨大的好处，并将使CVD实验更好地设计和控制。例如，确定掺杂原子在结构中的位置并将其与功能联系起来，以及了解在CVD过程中首选取向和生长如何变化。这具有社会效益-例如，如果以最佳生长方向生长，CVD制备的低能窗户涂层（如k -玻璃）的性能将提高三倍。作为透明氧化物导体的ZnO薄膜，如果以（1 0 0）取向生长，其性能将得到放大。在n掺杂的二氧化钛中，氮掺杂原子在二氧化钛中的位置受CVD条件的影响很大，可以看到取代掺杂和间隙掺杂。然而，在扩大带隙和制备可见光光催化剂方面，只有间质掺杂是重要的。这种材料可以广泛用作医院的抗菌涂层（以减少MRSA的传播），也可以用作可见光光催化剂，用于水的分解。为了实现对现有材料的改进潜力，需要对生长过程进行详细研究，并开发和理解仅导致间质N掺杂的条件。这些复杂的问题现在可以用ESRF和DIAMOND等下一代同步加速器源来解决。

Chemical vapour deposition is an enormously important technique for the formation of thin films. It is the most widely used coating technique in industry for coatings especially for the flat glass industry where it is used to make energy efficient and self cleaning coatings through to the glass bottle industry where it is used to make low friction coatings ( total value > 10B pa). It is also one of the key techniques used in microelectronics for the fabrication of integrated circuits. Despite its immense value the study of the formation of CVD films by in situ analysis has been surprisingly sparse. Typically films are studied after deposition and cool-down and not as they are grown. Some in situ measurements have been made especially by elipsometry, Raman, and reflectometry techniques. Direct measurements of the growth process by XRD or by EXAFS has been difficult to achieve because the samples are in thin-film form typically contain few atomic layers (1-100 nm thick) and construction of reactors cells that accommodate the CVD experiment and the source have proved exacting. The process is only possible with a brilliant light source such as that provided by a synchrotron. The ability to study what is happening during the initial growth phases in a CVD process will bring immense benefit to understanding the process and will enable better design and control of a CVD experiment. For example to determine the position of a dopant atom in a structure and relate this to functionality and to understand how preferred orientation and growth changes during a CVD process. This has societal benefits- for example low-energy window coatings (such as K-glass) prepared by CVD have three times better performance if grown with the optimum growth direction. The performance of ZnO thin films for use as a transparent oxide conductor is magnified if grown with a (1 0 0) orientation. The position of the nitrogen dopant atom within titanium dioxide in N-doped titania is greatly effected by CVD conditions and both substitutional and interstitial doping is seen. However only the interstitial doping is important in extending the band gap and making a visible light photocatalyst. Such a material could find widespread usage as an antimicrobial coating for use in hospitals (to reduce MRSA transmission) and also as a visible light photocatalysts that can be used for water splitting. To realize that potential to improve on existing materials the growth process needs to be studied in detail and the conditions developed and understood that lead only to interstitial N- doping. Such complex problems can now be tackled with the next generation of synchrotron sources such as ESRF and DIAMOND.