mode also emphasizes Auger fine structure, which appear as small secondary peaks surrounding the primary Auger peak. These secondary peaks, not to be confused with high energy satellites, which are discussed later, arise from the presence of the same element in multiple different chemical states on a surface (i.e. Adsorbate layers) or from relaxation transitions involving valence band electrons of the substrate. Figure 3 illustrates a derivative spectrum from a copper nitride film clearly showing the Auger peaks. The peak in derivative mode is not the true Auger peak, but rather the point of maximum slope of N(E), but this concern is usually ignored. Quantitative analysis Semi-quantitative compositional and element analysis of a sample using AES is dependent on measuring the yield of Auger electrons during a probing event. Electron yield, in turn, depends on several critical parameters such as electron-impact cross-section and fluorescence yield. Since the Auger effect is not the only mechanism available for atomic relaxation, there is a competition between radiative and non-radiative decay processes to be the primary de-excitation pathway. The total transition rate, ω, is a sum of the non-radiative (Auger) and radiative (photon emission) processes. The Auger yield, , is thus related to the fluorescence (x-ray) yield, , by the relation, where is the X-ray transition probability and is the Auger transition probability. Attempts to relate the fluorescence and Auger yields to atomic number have resulted in plots similar to figure 4. A clear transition from electron to photon emission is evident in this chart for increasing atomic number. For heavier elements, x-ray yield becomes greater than Auger yield, indicating an increased difficulty in measuring the Auger peaks for large Z-values. Conversely, AES is sensitive to the lighter elements, and unlike X-ray fluorescence, Auger peaks can be detected for elements as light as lithium (Z = 3). Lithium represents the lower limit for AES sensitivity since the Auger effect is a "three state" event necessitating at least three electrons. Neither H nor He can be detected with this technique. For K-level based transitions, Auger effects are dominant for Z < 15 while for L- and M-level transitions, AES data can be measured for Z ≤ 50. The yield limits effectively prescribe a cutoff for AES sensitivity, but complex techniques can be utilized to identify heavier elements, such as uranium and americium, using the Auger effect. Another critical quantity that determines yield of Auger electrons