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

化学气相沉积是一种非常重要的薄膜形成技术。它是工业中最广泛使用的涂层技术，特别是用于平板玻璃行业，用于制造节能和自清洁涂层，以及玻璃瓶行业，用于制造低摩擦涂层（总价值> 100亿帕）。它也是用于制造集成电路的微电子学中的关键技术之一。尽管其巨大的价值的CVD膜的形成的原位分析的研究已经令人惊讶地稀少。典型的薄膜是在沉积和冷却之后研究的，而不是在它们生长的时候。特别是通过椭圆偏振法、拉曼和反射计技术进行了一些原位测量。通过XRD或EXAFS直接测量生长过程是很难实现的，因为样品是薄膜形式的，通常含有很少的原子层（1-100 nm厚），并且适应CVD实验和源的反应器单元的构造已被证明是严格的。这个过程只有在同步加速器等明亮光源的情况下才有可能。研究CVD过程中初始生长阶段发生的事情的能力将为理解该过程带来巨大的好处，并将使CVD实验的设计和控制更好。例如，确定结构中掺杂剂原子的位置并将其与功能性相关联，以及了解CVD工艺期间优选取向和生长如何变化。这具有社会效益-例如，通过CVD制备的低能量窗口涂层（如K玻璃）如果以最佳生长方向生长，则性能提高三倍。ZnO薄膜用作透明氧化物导体的性能如果以（1 0 0）取向生长则被放大。氮掺杂剂原子在N掺杂的二氧化钛中的二氧化钛内的位置受CVD条件的影响很大，并且可以看到置换掺杂和间隙掺杂。然而，只有间隙掺杂在扩展带隙和制备可见光光催化剂方面是重要的。这种材料可以广泛用作医院中使用的抗菌涂层（以减少MRSA传播），也可以用作可见光催化剂，用于水分解。为了实现改进现有材料的潜力，需要详细研究生长过程，并开发和理解仅导致间隙N掺杂的条件。这些复杂的问题现在可以通过下一代同步加速器源（如ESRF和DIAMOND）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.