Destructive depth resolution

Information Element range Destructive Lateral resolution Depth profiling Depth probed Detection limits Quantitative Imaging... 

Depth resolution Quantification Lateral resolution Destructive... 

Destructive Chemical bonding Quantification Accuracy Detection limits Depth probed Depth resolution Lateral resolution Imaging/ mapping... 

Ion Beam Analysis (IBA) utilizes high-energy ion beams to probe the elemental composition of the surface of a specimen in a non-destructive way. It can establish the composition as a function of depth to several microns, with a typical depth resolution of 10-20 nm. It is a fast and standardless technique which quantifies the absolute atomic ratios, and can also determine the film thickness. 

A flat surface required for best depth resolution and for ion microscopy Destructive analysis. 

Sputter-Ion Depth Profiling. Although it is essentially a destructive technique, SIMS depth profiling is rapid, and possesses parts per million or even parts per billion sensitivity to all elements and isotopes, coupled with a depth resolution of a few nanometres. Concentration-depth plots can be accurate to 5%. 

From a specimen surface of typical area 5x15 mm2, ERDA may thus provide a non-destructive determination of hydrogen isotopes and their depth profiles in polymers and other solids with a sensitivity of 0.01 atomic %, a depth resolution of about 10 nm close to the surface, but decreasing with increasing depth. The maximum depth of analysis is about 1 pm (depending on the material). Measurements of other light elements (Z < 9) are also possible if heavy ions such as Cl or Au are used. 

Advantages brought about by the direct analysis of solid samples as compared with the analysis of dissolved samples include a shorter total analysis time (prior dissolution steps are not required), low cost (chemical reagents are not used), less risk of contamination and less destruction of the sample. In addition, some techniques can extract information about chemical speciation e.g. XPS provides information about oxidation states and chemical bonds) and spatial composition, i.e. information with lateral resolution allowing mapping of the surface and analysis with depth resolution, of particular interest for thin-film analysis. 

Destructive methods involve mechanical and chemical erosion (low resolution) and ion sputtering, which is by far the most widely used of any of the depth profiling techniques. Surface atoms are progressively removed by ion bombardment and are analysed by SIMS. Alternatively, the residual surface may be analysed, generally by AES. The method is universally applicable and in principle is capable of near-atomic depth resolution. In practice, conversion of the observed signal, as a function of time, into concentration as a function of depth may not be easy for a complex system. It should be noted that the information obtained is reliable for the first layer, but for deeper layers the possibility of scrambling of the atomic layers... 

Surface chemical changes created by these surface chemical reactions will be monitored by Electron Spectroscopy for Chemical Analysis (ESCA)(2), a very powerful spectroscopic technique for investigating surface compositions extending from 1-20 monolayers in depth from the surface. When the spectrometer is equipped with angle resolution capability, it also offers a means of non-destructive depth profiling of the upper 50A of substrate layers. 

Secondary ion mass spectroscopy (SIMS) is a destructive analytical technique in which material is removed from a surface by ion beam sputtering and the resultant positive and negative ions are mass analysed in a mass spectrometer [63]. The technique is element specific and is capable of detecting all elanents as well as isotopes and molecular species. Of all the beam techruques it is the most sensitive with detection limits for some elements in the range 10 " to lO cm" if there is very little background interference signal. Lateral resolution is typically 100 pm but can be as small as 0.5 pm with a depth resolution of 5-lOmn [34]. 

SIMS Depth resolution 0.5 nm Destructive method Vickerman... 

Various elemental and molecular microanalysis techniques are now available. Characterisation is usually carried out with (micro)beam techniques. By interaction of a primary beam (electrons, photons, ions), secondary signals are generated at the material (electrons, photons, ions, neutrals), which contain information on the composition and/or structure of the material. The various techniques differ in the type of information obtained, i.e. information depth, depth resolution, possibility to obtain depth profiles, lateral resolution, compatibility with certain types of materials (conductors v. insulators), destructive or nondestructive character, and type of information (elemental, isotopic, molecular). The polymer/additive analyst s challenge is to understand and choose from the vast array of available analysis and imaging techniques. 

A. 10.3.3 SNMS and RIMS Secondary Neutral Mass Spectrometry (SNMS), also referred to as Sputtered Neutral Mass Spectrometry, is a destructive technique primarily used for examining elemental constituents within solid samples. This technique is closely related to Dynamic SIMS in that an ion beam is used to sputter the solid of interest. The difference lies in the fact that the sputtered neutral population, once ionized, is passed through a mass spectrometer. Ionization is induced via the action of a laser, an electron beam, or plasma (ionization yields vary from 10% for lasers to 1% for plasmas). As the greatest fraction of the sputtered population departs in the neutral state, this methodology provides the advantage of improved detection limits and reduced matrix effects relative to SIMS. Depth resolution can extend to 1 nm. Spatial imaging is generally not carried out. No prior sample preparation is needed, but HV or better conditions are required. 

Destructive Chemical bonding Depth profiling Quantification Accuracy Detection limits Sampling depth Lateral resolution Imaging/mapping... 

Destructive Quantification Sensitivity Depth probed Lateral resolution... 

Technique Primary probe Elemental range Type of information Depth of information Lateral resolution Sensitivity (at. %) Ease of quantification Insulator analysis Destructive UHV environment... 

On the other hand, SIMS takes advantage of the destructive nature of the ion probe. Atoms can be knocked free (sputtered) from the surface by the bombarding ions and those that become ionized are analyzed by conventional mass spectrometry I70). A large number of different kinds of ions can be emitted from the surface. The resolution is also quite good. Thus, although SIMS is not as surface sensitive as ISS, it does provide more detailed information about the surface chemistry. ISS and SIMS, therefore, complement one another. Furthermore, since the ion probe sputters away the surface that is being analyzed, the change in the chemistry of the surface as a function of depth below the surface can be studied by these techniques. 

SIMS is a very surface-sensitive technique because the emitted particles originate from the uppermost one or two monolayers. The dimensions of the collision cascade are rather small and the particles are emitted within an area of a few nanometers diameter. Hence, SIMS can be used for microanalysis with very high lateral resolution (50 nm to 1 pm), provided such finely focused primary ion beams can be formed. Furthermore, SIMS is destructive in nature because particles are removed from the surface. This can be used to erode the solid in a controlled manner to obtain information on the in-depth distribution of elements.109 This dynamic SIMS mode is widely applied to analyze thin films, layer structures, and dopant profiles. To receive chemical information on the original undamaged surface, the primary ion dose density must be kept low enough (<1013 cm-2) to prevent a surface area from being hit more than once. This so-called static SIMS mode is used widely for the characterization of molecular surfaces (see Figure 3.10). 

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