Yes, we have seen this in samples where presumably Mn was doped into ZnO nanoparticles. it turns out that the Mn was on the surface and bound to the surfactants used to cap the nanoparticles. In our undulator beam, the Mn spectrum changes from one scan to another and this clued us into the fact that Mn was on the surface. Carlo On Thu, 5 Feb 2009, Eugenio Otal wrote:

Dear Carlo, with changes in function of time, you mean that repetitions of the spectra in the same sample are different from the firs to the last? What does this indicates? Thanks for you help, euG

-- Carlo U. Segre -- Professor of Physics Associate Dean for Special Projects, Graduate College Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@iit.edu http://www.iit.edu/~segre segre@debian.org