Performance of Xps Analysis of Model Biochemical-compounds

The performance of the XPS analysis of the chemical functions of biosurfaces has been assessed by examining model biochemical compounds (homopeptides, glucose related compounds,...). The components of the C-1s, O-1s and N-1s peaks may be attributed to classes of chemical functions. The FWHM of the components is controlled by sample charging heterogeneity and the same FWHM can usually be used for the different components of a given peak. The reproducibility of the binding energy (same function, different compounds) is better than 0.15 eV for most of chemical functions. The repeatability of the concentration ratios (same compound) is within a few percent. Internal consistency is demonstrated by the agreement between atom concentration ratios deduced from total intensities, on the one hand, and relative intensities of the C-1s components, on the other hand. A chemical composition in the range C15H26-30O4-6 is representative of common contamination overlayers. Modelling the effect of surface contamination overlayers indicate that the underestimation of O/C and N/C due to contamination is practically compensated by neglecting the kinetic energy dependence of the transmission function of the SSX-100 spectrometer. The accuracy of the O/C and N/C atom concentration ratios (underestimation of about 10 %) is within the range of the precision obtained when the whole set of model compounds is taken into consideration.