By rotating the sample the cratering due to sputtering is more symmetric in depth profile and thus regions of equal depth are probed by XPS and AES. Zalar who originally used azimuthal rotation of a sputtered sample to improve the depth resolution of depth profiles using Auger electron spectroscopy. 'Zalar' rotation or rotational depth profiling, RDP, is named after A.

The ion gun enters from the top right at about 2 o'clock. The white material on the stage is a Macor insulator, allowing one to float the stage or ground the stage through an ammeter. The gear ratio is chosen to yield roughly 1 rotation/minute. A horizontal shaft turns a mitre gear that engages another mitre gear. The stage enters from the right on a 4.5' conflat flange. Shown in the photo is the X-ray source entering from the top of the image.

This stage was designed and fabricated by Ian Winger of the FSU Department of Physics machine shop. The CMMP XPS has a custom-made Zalar rotation stage for depth profiling. Jim Zheng, FSU COE for the RuCl 3 sample. Point of this application note: use the FIG 5 CE to neutralize charge using a very low energy neutralizing beam- or use larger energies to larger separate the signal from conducting and insulating parts of the sample. This portion of the sample probed by the XPS did not shift because it is conducting. The 500 eV ion beam shifts the Ru 3d doublet by about 20 eV, making the C1s peak from the carbon tape visible. Charging shifts only apply to insulating portions of the sample. This example shows another useful application of the ion gun. As above, the 10 eV neutralizer brings the Ru 3d 5/2 peak for RuCl 3 very close to it's tabulated value minimizing the effects of charging. The Ru 3d 5/2 peak is shifted by ~ +5 eV just as was the Cl 2p peak. The data is shown again without the 10 eV neutralizer beam and with the 500 eV Ar+ beam which makes charging matters worse. The bottom image shows the Ru 3d region of RuCl 3 taken with Mg K О±. For comparison, the red curve shows the same data taken with a 500 eV Ar+ ion beam which makes the charging worse, shifting the Cl 2p XPS peak by ~ +20 eV. The green curve shows the same data taken with a 10 eV neutralizing beam. The blue curve shows the Cl 2p peak taken without any charge neutralization, and shows the XPS peak shifted by ~ +5 eV due to sample charging. The figure above shows the XPS Cl 2p region of RuCl 3 taken with Mg K О±. These low energy ions are not energetic enough to sputter the sample or generate secondary electrons (and thus making the sample charging worse), but are able to donate charge to the sample and neutralize the charging induced during an XPS experiment. The column can be floated allowing for the production of very low energy ions. The FIG 5 CE ion gun has a mode that acts as a charge neutralizer. As this C 1s signal comes from a conducting part of the sample, unless there is significant C 1s contamination of the insulating sample one will always see the C 1s signal at ~ 284 eV. One problem is that carbon tape is often used to mount powder systems. The shift of C 1s can then be used to calibrate the BE of other shifted peaks in the system. One approach in dealing with charging shifts is to look at the corresponding BE shift of C 1s which is typically adventitiously present on all samples. These charging shifts can be significant, equal to or larger than chemical shifts, and can complicate the identification of chemical shifts. However, because of the high energy resolution of surface electron spectroscopies, the deceleration of the photo-electrons leaving a positively charged sample manifests as something like a chemical shift- a shift towards higher binding energy. The excitation source, X-rays, is charge neutral, and has no problem exciting a charged sample. In such cases quantitation becomes impossible, but not the identification of X-ray lines. In EDS sample charging becomes an issue when it is so extreme that the probe is deflected and one can not be certain of the current in the excitation area or the location of the excitation area itself. In EDS charging of the sample is not an acute problem since X-rays are not charged and do not experience a shift in energy when being emitted from a sample at potential.

Sample charging xps peak shift