XAFS Classroom

Foreword: Hello everyone, the number of people who have followed our series has increased a lot recently, thank you very much for your support, and I hope you can forward it more. At the request of many XAFS users, we will gradually launch data processing tutorials, which will be first published on our official account: RapidXAFS and Catalysis, and XAFS principle analysis will be carried out simultaneously.

Due to the limited level of the authors, if there are any shortcomings, please actively put forward comments, you can contact: rapidxafs@rapid-xas.com

Software installation section

In this issue, the author will lead you to learn how to import data. First of all, let's learn the download and installation of the XAFS processing software Demeter, which is currently the most commonly used XAFS processing software, which includes three processing programs: Athena, Artemis and Hephaestus, which correspond to data preprocessing, data fitting, atomic data query and other functions. Software address:https://bruceravel.github.io/demeter/,You can find the version related to your computer after opening the URL,As shown in the figure below,We can get the relevant download resources by clicking on the system category at the top of the page。

When installing the software, you need to pay attention to the installation address must not have any non-English characters, such as Chinese characters, special characters, etc. Once the installation is complete, three icons for the software will appear on the desktop:

At the same time, the Demeter folder will appear in the start menu, which contains other programs in addition to the three software in the picture above, and its functions will be explained in detail in the future.

Data import section

The first step of data processing is data import, it should be noted that there can be no non-English characters in the XAFS data name, nor in the storage path, nor can the subsequent saved data!

1、双击Athena软件，出现如下界面

2、点击File，随后点击import data，选取要导入的数据，点击打开。

3、重点来了，如下图所示，此时需要选择能量和吸收系数列。在此之前，我们再学习下XAFS透射测试的基本公式：

其中I₁是后电离室的光子数，I₀是前电离室的光子数。

变种之后可以获得：

对于荧光模式：

其中I_f是荧光探测器的光子数。因此我们需要首先知道数据的测试信息，包括测试模式，哪一列是能量，哪一列是前电离室强度等。以下图中Fe箔XAFS数据为例，通过透射模式采集，其第二列是能量，第三列是I0，第四列是I1。所以Energy选择第二列，Numerator（分子）选择第三列，Denominator（分母）选择第四列，同时需要勾选上Natural log（自然对数）。也可以通过界面中下方的的m(E)公式实时观察选取参数的正确与否。同时在选取好分子之后，会自动显示图像，也可以根据图像选择参数。同时注意Data type和Energy unit（能量单位），有的线站可能采用keV作为能量单位。

4、对于使用Lytle探测器荧光数据选择，如下图所示，分子选择I1，分母选择I0，但注意此时不要勾选自然对数选项。

5. For the fluorescence data measured by the solid detector, as shown in the figure below, the denominator is selected I0, and the numerator is selected as the relevant counting channel.

6. At this time, you should be able to find that it is too cumbersome to consider what the numerator and denominator are every time? Yes, especially it is not friendly to beginners. Of course, the line station scientists have taken into account that in the data collected by the line station, a column of data will be automatically calculated according to the collected mode, and the energy column will be selected when importing, and the calculated data will be selected as the molecule, and the natural logarithm can be checked without checking the natural logarithm. Here, we take the Fe foil transmission XAFS data of Shanghai Light Source BL14W1 line station as an example, and directly calculate the absorption coefficient in the transmission mode in the fifth column, as shown in the following figure:

7、讲到这里相信大家也已经掌握了主要的数据导入流程。此时，大家手上突然有了一个国外光源的一组数据，再按照上述的方法导入，突然发现报错了或者导入不了，这是什么原因呢？这是因为不同的光源的数据模式不一样。我们可以这样做：双击Athena之后，打开界面中的main window，选择Plugin registry，然后选择相关光源、线站的名称，然后再导入即可。对于一般数据，选择PFBL12C即可。

8、数据导入成功后，应显示如下：

9、如果在数据导入的时候data type选择错了，有可能出现如下界面，下半段变成了灰色不可点击，此时也无需重新导入，直接按住键盘的Ctrl+Alt，鼠标左键点击红色圈主的蓝色字Datatype: xanes即可，此时数据模式就由xanes转换为xmu，为正常模式。