Figure 13.

(a) XPS survey spectrum of a hydrogen-terminated single-crystalline diamond surface that was exposed to TFAAD and 20 mW cm⁻² UV illumination (250 nm) for 2 h. (b) The C(1s) spectrum reveals two additional small peaks at 292.9 and 288.5 eV, which are attributed to carbon atoms in the CF₃ cap group and in the C=O group, respectively. (c) The ratio of the F(1s) signal (peak area) to that of the total C(1s) signal as a function of illumination time is time dependent and follows an exponential increase (dashed line), with a characteristic time constant τ of 1.7 h. (d) Angle-resolved (with respect to the surface normal) XPS experiments show an increase in the F(1s)/C(1s) peak intensities, rising from 48 to 78°.