X-ray absorption fine structure analysis of functional thin films

一些几微米厚的薄膜是制造磁信息存储器件、传感器、光学器件表面涂层、腐蚀金属电镀等的重要材料。为了提高这些薄膜的性能，原子级结构的信息是至关重要的。然而，通常很难获得沉积在厚衬底上的非常薄的薄膜的结构信息。本研究的目的是通过X射线吸收精细结构(XAFS)分析来研究这些薄膜，这对于研究局域原子结构是很有用的。XAFS通常通过透射法获得，因此很难应用于厚衬底上的薄膜。本文用全转换电子产额法(TCEY)获得了XAFS光谱。由于俄歇电子的平均自由程小于几微米，TCEY-XAFS方法非常适合于表面材料的研究。本文研究了以LaAlO_3和MgO为衬底的SrTiO_3薄膜。从几个不同厚度的样品的XAFS信号强度来看，SrK和TiK边的探测深度分别为300 nm和30 nm。EXAFS对薄膜中锶和钛的分析表明，锶的局域结构随薄膜厚度的变化而变化，钛的局域结构不随薄膜厚度的变化而变化。硅酸铁或氮化铁是一种有趣的磁性材料。它们可以通过溅射的方法沉积在玻璃上。将它们的局部结构与大块样品中的结构进行了比较。TCEY-XAFS光谱特别适用于这些非晶态沉积材料。

Some of the thin films of a few micrometers in thickness are important materials for magnetic information storage devices, sensors, surface coating for optical devices, plating for corrosive metals, etc. In order to improve the functions of these thin films the information of their atomic scale structures is crucial. However, it is often difficult to obtain structural information of very thin films deposited on thick substrates. The purpose of this research is to investigate these thin films by X-ray absorption fine structure (XAFS) analysis which is known to be useful for studying the local atomic structure. XAFS is normally obtained by transmission method, thus it is difficult to be applied to thin films on thick substrate. Here the XAFS spectra are obtained by total-conversion electron-yield method (TCEY). Since the mean free path of Auger electrons is less than a few micrometers, TCEY-XAFS method is useful for the study of surface materials.TCEY-XAFS of deposited thin films of SrTiO_3 on single crystals, LaAIO_3 and MgO, as substrates have been studied. From the XAFS signal intensities for several samples with different thicknesses, Sr K- and Ti K-edge detecting depths are found to be 300 nm and 30 nm, respectively. The EXAFS analyses for Sr and Ti in thin films concluded that the local structure of Sr changes with the film thickness, but that of Ti does not.Amorphous iron silicates or iron nitrides are interesting magnetic materials. They can be deposited on glass by sputtering method. Their local structures are compared with those in bulk samples. The TCEY-XAFS spectroscopy is especially suitable for these amorphous deposited materials.