Signal surface roughness

Although it is, in principle, feasible to quantify LEIS results, the determination of absolute ion fractions is far from trivial. In LEIS experiments, the surface composition is therefore generally obtained in a relative measurement by comparison of signals of the element in the sample of interest with those of reference samples, assuming that the matrix does not have a significant role and that the surface roughness is similar. 

Figure 3.29 Cyclic current (a) and mass signal (b,c,d) voltammograms for 0.1 M CH3OH in 1 M HCI04 at porous platinum, and room temperature. The sweep rate was 20mVs 1 and the surface roughness c. 50, After Iwasita and Vielstich (1990).

Electrodes. The first observations of SERS were made from species on silver electrodes. An essential prerequisite for a strong SERS signal from molecules adsorbed on the electrode, surface roughness, is obtained by running electrochemical oxidation-reduction cycles (ORC) (Chang and Laube, 1984 Koglin and Sequaris, 1986 Roth et al., 1993). During the oxidation half cycle a metal salt, usually a halide, is formed at the electrode surface ... 

DelPriore et have shown that in film deposition, carbon and oxygen impurities may pose a problem, in fact, may cover most or all of the surface (however, Pockrand and Otto, for instance, have relatively small cathedral peaks indicating only slight surface contamination). Monitoring the Raman signal from the impurity bands, combined with SEM, DelPriore et al conclude that strong SERS is seen with a surface roughness scale smaller than 10 nm (their resolution limit). 

The film composition was determined by ESCA. During ESCA analysis, the absolute value of the signal is influenced by instrumental parameters and the surface roughness of the samples. 

---