ABSTRACT
In addition to x-ray diffraction, x-ray photoelectron spectroscopy (XPS) is used to measure the [F] concentration of Q F samples. A typical XPS spectrum for Q F materials, as shown in Fig. 4 for a Q ^ F fiber, indicates peaks for carbon, oxygen, and fluorine. In this figure the peaks are labeled according to the mech anism for their origin: Is indicating the XPS Is atomic levels, and A indicating peaks arising from the Auger process. The presence of XPS oxygen peaks is observed in all Q F materials that have been exposed to air and does not imply the presence of oxygen in the bulk of the samples. With regard to the C-and F-related peaks, no changes in the XPS spectrum of the fibers were observed by sputtering the surface and remeasuring the XPS spectrum, which suggests that the fluorine concentrations in the bulk and at the surface of the fibers are very similar, consistent with the difficulty for fluorine to diffuse perpendicular to the graphene planes. From the ratio of the areas below the carbon Is and the fluorine Is peaks and the measured cross sections of carbon and fluorine for the capture of photoelectrons, the relative fluorine/carbon concentration in Q F sam ples can be determined. The results thus obtained are in good agreement with the weight-uptake characterization measurements mentioned above and the re sistivity property measurements described in Section III.A. In principle, the
Figure 4 Typical XPS spectrum for a C3 .1 F fiber. The peaks labeled with the subscript “A” correspond to Auger peaks, whereas the peaks labeled “I s ” correspond to the Is core levels of the carbon atom. (From Refs. 10,69.)
[F]/[C] concentration ratio can also be found from the integrated intensity of the carbon and fluorine Auger peaks (see Fig. 4), taking into account the dif ferent Auger cross sections for carbon and fluorine.
