Poly beam damage

The electron beam damage is often utilized for TEM visualization. In SAN/poly(methyl methacrylate) (PMMA) blends, TEM contrast was... 

Figure 1 Relative intensities of diagnostic fragments from poly(methyl methacrylate) (+ rniz 126 and rn/z 185) as a function of primary ion dose (using 8keV Cs+). Individual spectra were acquired with a dose of <5 x 10 ionscm. (Reproduced with permission from Briggs D and Fletcher IW (1997) Cs ion beam damage of poly(vinyl chloride) and poly(melhyl methacrylate) studied by high mass resolution ToF-SIMS. Surface and Interface Analysis 25 167-176 John Wiley Sons Ltd.)...

Note that the shapes of the two carbon peaks are quite different in Fig. 6.16. This relates to the different chemical bonding in the two polymers in principle this information can be used in analysis, but it has been shown in PMMA that chemical changes due to electron beam damage rapidly alter the peak structure [339]. For many polymers, the low energy loss region may not contain any distinct features for use in analysis or imaging, but aromatic compounds do have a peak at about 7 eV, which has been used to identify polystyrene in a polystyrene/ polybutadiene / poly(methyl methacrylate) sample [340]. 

Exposure of thick layers of TDF (on the order of several monolayers) condensed on either Ag(poly) or Li/Ag(poly) at 135 K to the (AES) electron beam for as little as 1 min led to development of a dark spot at the beam position clearly visible with the naked eye. No significant amounts of carbon could be found with AES anywhere on the specimen upon raising the temperature above 300 K, except in the area originally probed by the beam at 135 K. This indicates that the layer of TDF is irreversibly damaged by the electron beam (at least for the current... 

The method of differential radiation induced contrast depends on enhancement of contrast in multicomponent polymers where the components have different electron beam-polymer interactions [173]. Contrast has been observed in sections of styrene-acrylonitrile/poly(methyl methacrylate) (SAN/PMMA) polymers where the PMMA exhibits a high rate of mass loss compared to SAN, creating contrast between the phases. It is well known that electron irradiation results in chain scission and crosslinking, loss of mass and crystallinity [75]. Polystyrene, polyacrylonitrile and SAN crosslink and thus are stable in the electron beam whereas polymers exhibiting chain scission, PMMA and poly(vinyl methyl ether), degrade in the beam. It is suggested that experiments be conducted on the homopolymers to determine the expected irradiation damage mechanism in the multi-component system [173]. 

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