XAFS Classroom

In the previous chapter, we learned together how to import data. The first step after importing the data is energy calibration. This is a non-negligible step, and it is directly related to the subsequent Ek®transformation, Fourier transform, etc. The data for this demonstration was collected from our RapidXAFS spectrometer.

Due to the constant deviation of the spectrometer during data acquisition, there will be energy shifts in samples collected in different batches, which is unavoidable on both synchrotron radiation devices and desktop spectrometers, and therefore requires manual calibration. First, we use the Calibrate function in the Athena software to perform energy calibration on the elemental metal standard.

As shown in the figure above, the absorption spectrum data is automatically converted to a first derivative. At this point, we need to recall the definition of the absorption edge in XAFS: where the X-ray absorption coefficient changes the fastest, so that the absorption edge corresponds to the highest point in the first derivative. It is also necessary to be flexible when finding the highest point of the first-order guide, because due to the sample content, step size selection, etc., the position of the absorption edge slows down, which leads to the decrease of the intensity of the first-order guide. In this case, it is necessary to select a peak position that is close to the theoretical value of the absorption edge. In this set of data, we click the Select a point button and in the right image we double-click on the peak closer to 8333 eV, which is the peak at 8326 eV. Then click Calibrate to complete the energy calibration of the standard, as shown in the figure below:

能量校准结束后，Athena的main window中的Energy shift将会由0边为相应的偏移值。一般认为同批次的样品的能量偏移是一致的，所以需要将同批次的样品数据的Energy shift设定为和标样一致的数值。如下图：

After the above operation, the energy offset error of the instrument itself has been calibrated. But this is not enough, we need to further use Calibrate to set the sample data to E0. As with the standard calibration process, click the Select a point button and double-click on the highest point in the first-order map. Note: At this time, the E0 setting has been completed, do not click Calibrate! below

Since then, the calibration of the data has been completed. Below, we've listed a few key points in energy calibration:

1. The energy shift of different batches of samples should be consistent with the standard samples tested in the same batch, and the data of different batches of tests can also be compared together after calibration;

2. After the energy shift of the sample is set, be sure to select E0, otherwise it will affect the subsequent k space and R space.