SURFACE SPECTROSCOPY OF APATITIC MATERIALS - LIMITATIONS AND CONCERNS

The use of x-ray photoelectron spectroscopy for the study of biologica l materials has provided mixed results. The experimental difficulties associated with the application of this technique to the study of biol ogical materials include the effects of ultra-high vacuum, x-ray expos ure, surface charging, and, for insulating materials, the inherent lac k of an intrinsic energy reference. Since most biological materials ar e insulators, the lack of an intrinsic energy reference complicates on e's ability to draw direct comparisons between different studies. In t his paper, the results from two different apatites are compared with t he results obtained from the use of two conventional techniques for re ferencing binding energies. The results presented here are referenced only to the Pt Fermi level; no further energy modifications are perfor med. A comparison with the results of other investigators indicates a large difference in binding energies for all involved core levels. The se results indicate that, in the study of insulating materials with x- ray photoelectron spectroscopy, it is essential that all data be acqui red under exacting conditions on the same experimental system.