Hi Yu-Chuan, There are several possibilities. One is sample prep. If you have an extremely uneven sample (lots of pinholes, etc.) in transmission it can lead to results like you're describing. Another is normalization. If you're using Athena for background subtraction make sure you look at the pre-edge line and post-edge curve and see that they look reasonable. Sometimes if the background has a funny shape to it Athena can create a post-edge curve that shoots way up at the edge energy; this could also lead to the effect you're describing. Finally, look at the correlation between S02 and sigma2...if it is very high (say 0.95 or above) it may simply be coming up with low estimates for each. There are, of course, other possibilities as well, but in my experience those are the most common. --Scott Calvin Sarah Lawrence College
This is Yu-Chuan. I am now trying to fit my sample, magnesium orthovanadate. I try to follow Bruce's Cu example and Scott's ZnO example steps and I found a problem come to my fitting. At the beginning of the fitting, the S02(amp) are far away from 0.9 (just about 0.3). It's much different than Bruce's and Scott's examples. For Cu and ZnO examples, the fitting results of amp are close to 0.9 at the beginning even if you set just four parameters (guess:amp, e0, delr, and ss). Also, John have said that the S02 value should be around 0.9. That's why I am wondering if there is anything wrong with my data processing? Does anyone happen to have this kind of problem? Thank you for your help.