XANES and HERFD

X-ray Absorption Near Edge Structure (XANES) and High Energy Resolution Fluorescence Detection (HERFD)

The absorption edge is a direct probe of the unoccupied electronic density of states of the absorbing atom giving valence and coordination geometry information. Hybridization of 3d metal electrons with p electrons from ligand elements opens bound states giving rise to interesting pre-edge peaks.

For some elements with many electrons, the absorption edge becomes broad. This can be resolved by collecting only a specific energy of the fluorescence signal. The technique is called HERFD, and utilizes the sliced crystal analyzer shown at right. An example is shown below for Hg.

HERFD 3-crystal spectrometer

Our newest HERFD spectrometer holds three 1/2-meter Si crystal analyzers. Each is equipped with its own set of motorized positioners for independent motion and precise angular adjustment, so that the reflected signal can be captured on the area detector shown below. This spectrometer has three times the solid angle as our previous single analyzer system.

Si crystals available: Si(111), (100), (110), (211), (311), (773), (911)
Common edges: Cr, Mn, Fe, Co, Ni, Cu, Zn, As, W, Au, Hg, Pb, U, Ce

HERFD setup at 25-ID

Below are two examples of HERFD data collected at 25-ID, illustrating how the absorption edge feature becomes more pronounced.