Spectrum Auger

Figure 8.24 Auger spectrum of sulphur in Na2S203- (Reproduced, with...

Figure 8.25 shows the AXn,m. ii,iii Auger spectrum of a gaseous mixture of SFe, SO2 and OCS, all clearly resolved. The three intense peaks are due to sulphur in a >2 core state, but there are three weak peaks due to a core state also. The S 2p X-ray photoelectron spectrum of a mixture of the same gases is shown for comparison, each of the three doublets being due to sulphur in a 1/2 or 3/2 core state. 

In Figure 8.26 is shown the AXumLum Auger spectrum of sodium in crystalline NaCl. Once again, the formation of the >2 weakly, the core states can be observed. Also shown are peaks resulting from additional processes in which the initial photoelectron with... 

Figure 8.25 (a) The ( 2 Xq) Auger spectrum of sulphur in a gaseous mixture... 

Figure 8.26 The ( 2 q) Auger spectrum of sodium in solid NaCl.

The KLii iiiLii iii Auger spectrum of magnesium, and how it changes on conversion at the surface to magnesium oxide, is shown in Figure 8.27. Two peaks due to >2 core... 

Figure 8.27 The Auger spectrum of magnesium showing how it changes as the...

There are at least four kinds of information available from an Auger spectrum. The simplest and by far most frequently used is qualitative information, indicating which elements are present within the sampling volume of the measurement. Next there is quantitative information, which requires a little more care during acquisition to make it extractable, and a little more effort to extract it, but which tells how much of each of the elements is present. Third, there is chemical information which shows the chemical state in which these elements are present. Last, but by far the least used, there is information on the electronic structure of the material, such as the valance-band density of states that is folded into the line shape of transitions involving valance-band electrons. There are considerations to keep in mind in extracting each of these kinds of information. 

The number of Auger electrons from a particular element emitted from a volume of material under electron bombardment is proportional to the number of atoms of that element in the volume. However it is seldom possible to make a basic, first principles calculation of the concentration of a particular species from an Auger spectrum. Instead, sensitivity factors are used to account for the unknown parameters in the measurement and applied to the signals of all of the species present which are then summed and each divided by the total to calculate the relative atomic percentages present. 

Fig. 2.24. Examples of the effect of different chemical states on the KLL Auger spectrum of carbon [2.130] (SiC and graphite denote Ar -bombarded surfaces ofSiCand graphite, respectively).

Figure 7. Typical Auger spectrum of the surface of the 2% wt Pt/Ti02 powder.

This surface had an Auger spectrum similar to that of the surface produced during the reaction and exhibited a catalytic activity similar to that of the clean surface. This suggests that during the reaction the amount of nitrogen deposited on the surface is close to that present in the compound PeN and possibly that this is actually present at the surface during the reaction (6). 

Another application is to the study of the Auger states in which a further electron ionization of attachment may occur, leaving the system with holes in more than one shell. Such states were considered in some detail by Firsht and McWeeny [9] for free atoms here we have made a preliminary applieation to the nitrogen moleeule. The initial aim is simply to identify and assign the principal peaks and satellites in the Auger spectrum of gaseous N2. 

Figure 1 Experimental gas phase Nj Auger spectrum (Siegbahn et al [6]) and estimated transition energies for normal processes (vertical lines) and for the other most important processes (dashed vertical lines).

Figure 5.31. An Auger spectrum from a stainless steel surface (a) the undifferentiated N(E) mode, (b) the differentiated mode. (After Flewitt and Wild 1985.)...

A typical Auger spectrum of the sample following electrodepostion of Cu is shown in Figure 6 (16). For this experiment-the sample was immersed in a solution of 0.2 HCIO, and... 

Figure 6. Auger spectrum after electrodeposition of Cu on Ru(0001) from an electrolyte of 0.2 M HC104 and 0.96 mM Cu2+. The sample was emersed without rinsing at 40 mV (SCE). (Data from ref. 16.)...

FIG. 45. Auger spectrum for Au(lOO) (A) after ion bombardment and annealing, (B) after emersion following Cd UPD, (C) after emersion following first Te UPD, (D) after emersion following Cd UPD on first Te UPD, and (E) after emersion following Cd UPD on second Te UPD. (From Ref. 162.)... 

More recent work involving surface chemistry in an F.CAT.F. cycle centers on the formation of the first few monolayers of CdSe. Again, the chalcogenide serves as the first atomic layer due to Cd instability upon emersion. Figure 52C is the Auger spectrum for a Au(lOO) crystal covered with Cd UPD, while Fig. 52D is the spectrum for Cd UPD on the crystal... 

For a compound semiconductor to be useful as a substrate in studies of electrodeposition, it is desirable that clean, unreconstructed, stoichiometric surfaces be formed in solution prior to electrodeposition. For CdTe, the logical starting point is the standard wet chemical etch used in industry, a 1-5% Brj methanol solution. A CdTe(lll) crystal prepared in this way was transferred directly into the UHV-EC instrument (Fig. 39) and examined [391]. Figure 66B is an Auger spectrum of the CdTe surface after a 3-minute etch in a 1% Br2 methanol solution. Transitions for Cd and Te are clearly visible at 380 and 480 eV, respectively, as well as a small feature due to Br at 100 eV. No FEED pattern was visible, however. As described previously, a layer of solution is generally withdrawn with the crystal as it is dragged (emersed) from solution (the emersion layer). After all the solvent has evaporated, the surface is left with a coating composed of the... 

The mechanism we believe is responsible for the large SiOj-to-Si etch-rate ratios which have been obtained in fluorine-deficient discharges is based on several experimental observations. First of all, it has been shown that there are several ways in which carbon can be deposited on surfaces exposed to CF, plasmas. One way is to subject the surface to bombardment with CF ions which are the dominant positive ionic species in a CF plasma. The extent to which this can occur is shown by the Auger spectra in Fig. 3.3. Curve (a) is the Auger spectrum of a clean silicon surface and curve (b) is the Auger spectrum of the same surface after bombardment with 500 eV CFj" ions. Note that the silicon peak at 92 eV is no longer visible after the CFj bombardment indicating the presence of at least two or three monolayers of carbon. Another way in which carbon can be deposited on surfaces is by dissociative chemisorption of CFj or other fluorocarbon radicals. 

Fig. 5 Auger spectrum of the sample before a catalytic test.

Both phenomena may disfavour the flat adsorption of the molecule of prenal to the benefit of an adsorption through the C=0 double bond with a partial raising up of the molecule. If oxygen atoms are actually present on the surface as suggested by the Auger Spectrum, they... 

The Auger spectrum consisted of a broad, weak band near 340.0 eV and a stronger, sharper band near 336.8 eV. Combining the photoelectron line near... 

These conclusions were supported by results obtained from angle-resolved XPS. The band near 932.4 eV in the Cu(2pV2) photoelectron spectrum of the mirror coated with y-APS increased in intensity relative to that near 934.9 eV when the take-off angle was increased from 15° to 75°. Similarly, the band near 336.8 eV in the Auger spectrum also increased in intensity relative to that near 340.0 eV. Such behavior would be expected if the bands near 932.4 eV in the photoelectron spectrum and near 336.8 eV in the Auger spectrum were related to an oxide that was covered by a thin film of silane. 

Fig. 3. Shape of the Auger spectrum depending on the type of the chemical bond (Reproduced by permission from Ref. 47).

An interesting result was the appearance of F+ in the residual gas analysis when the electron beam in AES was placed on the sample, suggesting easy desorption and a very unstable surface. In fact, when electron beam currents were not minimized, the fluorine frequently was desorbed completely, and did not appear in the Auger spectrum. 

V. Carravetta, H. Agren, Stieltjes imaging method for molecular Auger transition rates Application to the Auger spectrum of water, Phys. Rev. A 35 (1987) 1022. 

R.W. Shaw Jr., J.S. Chen, T.D. Thomas, Auger spectrum of ammonia, J. Elec. Spec. Rel. Phen. 11 (1977) 91 J.M. White, R.R. Rye, J.E. Houston, Experimental Auger electron spectrum of ammonia, Chem. Phys. Lett. 46 (1977) 146 R. CamiUoni, G. Stefani, A. Giardini-Guidoni, The measured Auger electron spectrum of ammonia vapour, Chem. Phys. Lett. 50 (1977) 213. 

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