Mean escape depth

The depth of analysis (d) in XPS is approximately given by 3/ sin 6 [21] where l is the mean escape depth and 6 is the take-off angle of the photoelectron with respect to the sample surface plane. Thicknesses of surface coverage layers on different samples were estimated from the attenuation of the XPS signal from the substrate by the overlayer using the relation [22] In [/ // +1] = d/l sin 6, where d is the overlayer thickness, R is the ratio of photoelectron signal intensities from the overlayer to substrate of any particular element, and is the photoelectron intensity from the same element of infinite thickness. 

Surface segregation depends strongly on the mobility of the atoms in the solid and annealing of the Ir-Cu sample has indeed dramatic influence on composition and surface structure. As by a good choice, the composition has been determined with a combination of ISS and XPS measurements. The different surface sensitivities of the two methods (topmost layer for ISS versus an average over some surface layers for XPS determined by the mean escape depth of the photo-electrons) can be used to find the actual composition of the surface layers (Fig. 11). 

From various compilations of escape depth data as a function of the kinetic energy of the emitted electron " ), it appears that between 30 and 500 eV, the mean escape depth can be estimated to be 5 2 A in densely packed inorganic solids thus AES truely is a surface-sensitive technique. Following Eastman and Nathan ), we define the surface region as the outermost atomic layers including any foreign atoms adsorbed onto or absorbed into them, either substitutionally or interstitially. 

SEi Generated close to the beam impact point, these electrons carry high-lateral resolution information of the order of the mean escape depth, 2, The obtainable lateral resolution is typically 1-5 nm. 

In-depth distribution analysis of chemical composition is a special case of local microanalysis, for which the third (axial) dimension is of primary interest. In principle, this task requires the compositional analysis of thin sections (in the ultimate dimension of monatomic layers) defined on a depth scale. It can be obtained either by non-destructive or destructive techniques. Non-destructive techniques are based on an analytical signal parameter (e.g. intensity and/or energy), which has a weU-deflned dependence on its depth of origin. For example, in electron spectroscopy, non-destructive profiling methods are based on either the energy or the emission angle dependence of the mean escape depth of the emitted electrons e.g. ARXPS). Confocal microscopy... 

Quantification of AES and XPS has been a challenge for many years, but substantial progress has been made [5, 6]. We will focus here on two subjects that are very important for quantitative measurements by these techniques, first, it is often necessary to obtain different measures of the surface sensitivity of AES and XPS, such as those that are required for a quantitative analysis, a measurement of an overlayer-film thickness, and a statement of sampling depth. The following four terms can be used for these purposes the IMEP, the EAL, the mean escape depth (MED), and the information depth (ID). We show why these terms are conceptually different as well as often numerically different, for this purpose, it is useful to first introduce the concept of the depth distribution function (DDE) for the detected signal. We give information on five databases available from the... 

Figure 3.2.S.6 Emission-angle dependence of the mean escape depth and the information depth calculated for Au 4s photoelectrons excited by Mg Kor X-rays and for...

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