Depth resolution characteristics

Depth sensitivity is an equally important consideration in the analysis of surfaces. Techniques based on the detection of electrons or ions derive their surface sensitivity from the fact that these species cannot travel long distances in soflds without undergoing interactions which cause energy loss. If electrons are used as the basis of an analysis, the depth resolution will be relatively shallow and depend on both the energy of the incident and detected electrons and on characteristics of the material. In contrast, techniques based on high energy photons such as x-rays will sample a much greater depth due... 

Rutherford Backscattering (RBS) provides quantitative, nondestructive elemental depth profiles with depth resolutions sufficient to satisfy many requirements however, it is generally restricted to the analysis of elements heavier than those in the substrate. The major reason for considering depth profiling using FIXE is to remove this restrictive condition and provide quantitative, nondestructive depth profiles for all elements yielding detectable characteristic X rays (i.e.,Z> 5 for Si(Li) detectors). 

A very important characteristic of laser radiation is the beam shape. So far most LA experiments have been performed with Gaussian laser beams. Lasers with uniform distribution of the beam cross-section have been used only recently to achieve high lateral and depth resolution. Specially designed beam homogenizers must be used for this purpose [4.226-4.228]. The Cetac LSX-200 system has a flat-top distribution of the laser beam. 

To investigate the interface between polymeric materials, i.e. a so-called buried interfaces, several techniques are available schematically shown in Fig. 4 and listed in Table 2. They have quite different characteristics and depth resolution depending... 

Characteristic infrared absorption lines have been identified for various hydrogen-acceptor and hydrogen-donor complexes (see Chapter 8), and the strength of such a line in any given specimen is a measure of the quantity of the complex present. However, depth resolution is crude, and masking by free-carrier absorption is sometimes a problem. Raman lines have also been seen (see Chapter 8) and in principle should be capable of detecting species that are not infrared active however, the sensitivity is low, and the most interesting and presumably abundant species, an H2 complex, has not yet been detected in this way. 

The operational characteristics such as depth resolution, maximum accessible depth and minimum detection limit in ERD are highly subjective to each experiment condition. In our system with the conditions described in the experimental procedures section and assuming Si as the primary matrix for the target, the typical performance characteristics in routine applications are 80-100 A depth resolution, 1 pm maximum depth and about 0.1 at.% minimum detection limit. For more discussion of operation characteristics one may refer to our earlier work (2). 

The electron microprobe is a local elemental analysis technique with a depth resolution which may vary from a few tenths of a micrometre to several micrometres. It is based on spectrometry of characteristic X-rays emitted by a solid sample under the impact of a focused incident electron beam (electron probe) ... 

Each material has a characteristic stopping power and therefore the resolution and the depth of profiling will vary in different materials. The lithium particle from the boron reaction is heavier than its alpha counterpart and usually loses energy more rapidly allowing greater depth resolution however, the alpha particles have the greater range and consequently allow deeper profiles to be obtained. 

PIXE enables the determination of composition for all elements with Z, atomic number, higher than 5. An examination of PIXE spectra shows that the characteristic X-ray peaks are superimposed on a background, which forms a hmiting factor in sensitivity. It is possible to obtain limited depth profile information using ion induced X-ray emission. The depth resolution is angle and ion energy dependent and is not as good as for other techniques. 

Since the conversion electrons emitted from the sample surface have different energies depending on the depth they were generated in, it is theoretically possible to record Mdssbauer spectra characteristic of selected surface layers of the sample at different depths. Geometric effects and the relatively wide energy spectrum of the various kinds of emitted electrons (K- and L-conversion, Auger, etc.) result in rather poor depth resolution. 

Unfortunately, the actual depth resolution can deteriorate a bit as a result of different effects, such as pulse mixing and signal taihng induced during aerosol transport, and will ultimately depend on the flow characteristics of the ablation cell and the data acquisition speed of the ICPMS unit used [25,45]. Moreover, the ratio between the depth penetration and the laser beam diameter must be kept below a critical value in order to obtain representative in-depth compositional data [43,46] thus, the use of larger beam diameters yields reliable information from deeper in the sample. 

For thick films, infrared (IR) spectroscopy may be used to probe film chemistry (Kazarian and Chan, 2013). The sample is exposed to IR radiation, typically between 1000 and 4000 cm and molecules absorb energy at resonant frequencies that are characteristic of their chemical stmcture. The depth of analysis is >1 pm, meaning that the bulk properties of the film may be determined rather than just the surface chemistry. The advantage of IR spectroscopy is that differences between functional groups which are chemically similar may be obtained because the absorption peaks can generally be distinguished easily. The obvious disadvantage is the depth resolution. 

Table 4.11 compares SIMS and SNMS (cfr. also Table 8.57 of ref. [110a]). Detection limits in the sub-ppm range are accessible under optimised analytical conditions. A lateral resolution of less than 100 nm and an in-depth resolution of a few nm can be achieved. One of the unique features of SNMS is the ease of analysis of insulators. This is at variance to SSMS, GD-MS and SIMS, which are handicapped by electrical charging effects. Laser SNMS is not strictly restricted to elemental analysis, but can also be applied to the characterisation of molecular surfaces. For an optimum yield of intact molecular ions and characteristic fragments it is necessary to optimise laser power density, wavelength, and pulse width [112],... 

Ni/Cr multilayers. Factors known to limit the depth resolution include instrumental factors, sample characteristics and radiation-induced effects. 

Crystalline structure and defects since the sputtering yield depends on the crystalline orientation (46-47). a polycrystalline material will produce characteristic steps [48) and the depth resolution will be reduced. The best materials for yield measurements are either single crystals or totally amorphous materials. It has been shown that the introduction of reactive ions leads to a smoother sputtered surface (49-.5I) than that resulting from noble-gas ion sputtering. This is probably due to the formation of an amorphous surface oxide layer, which then sputters homogeneously (52). 

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