Forward-recoil spectrometry

23 Electron Paramagnetic Resonance Spectroscopy and Forward Recoil Spectrometry 

Only a brief description of the technique is provided in the following subsections. 

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Forward recoil spectrometry (FRS) [33], also known as elastic recoil detection analysis (ERDA), is fiindamentally the same as RBS with the incident ion hitting the nucleus of one of the atoms in the sample in an elastic collision. In this case, however, the recoiling nucleus is detected, not the scattered incident ion. RBS and FRS are near-perfect complementary teclmiques, with RBS sensitive to high-Z elements, especially in the presence of low-Z elements. In contrast, FRS is sensitive to light elements and is used routinely in the detection of Ft at sensitivities not attainable with other techniques [M]- As the teclmique is also based on an incoming ion that is slowed down on its inward path and an outgoing nucleus that is slowed down in a similar fashion, depth infonuation is obtained for the elements detected. 

Tirira J, Serruys Y and Trooeiiier P 1996 Forward Recoil Spectrometry —Applications to Hydrogen Determination in Solids (New York Pienum)... 

Other technique—for example, dynamic secondary ion mass spectrometry or forward recoil spectrometry—that rely on mass differences can use the same type of substitution to provide contrast. However, for hydrocarbon materials these methods attain a depth resolution of approximately 13 nm and 80 nm, respectively. For many problems in complex fluids and in polymers this resolution is too poor to extract critical information. Consequently, neutron reflectivity substantially extends the depth resolution capabilities of these methods and has led, in recent years, to key information not accessible by the other techniques. 

Tirira, J., Serruys, Y., Trocellier, P. (1996) Forward Recoil Spectrometry, Plenum Press, New York, London. 

Fig. 6.52 Interfarial excess in thin films of blends of a dPS-P2VP diblock (A PS = 391, jVP2Vp = 68) with PS homopolymer (NK = 6440) (Dai et al. 1992). Since the homopolymer is much longer than the diblock, the diblock forms a dry brush. The circles are the results from forward recoil spectrometry, the lines correspond to theoretical calculations. The dashed line was computed using the theory of Leibler (1988), and the solid line is from the self-consistent mean field calculation of Shull and Kramer (1990).

J. Tirira, Forward Recoil Spectrometry, Plenum, New York, 1996. 

Fig. 33. a Volume fraction of deuterated poly(ethylenepropylene), dPEP (full dots) and pro-tonated PEP (open circles) versus depth, for a degree of polymerization N-2300 for both constituents, after a 4 h quench to T=294 K (Tcb 365 K). Profiles are obtained with the time of flight forward recoil spectrometry (TOF-FRES). The dashed line indicates the surface domain thickness l(t). b Plot showing the growth of the surface domain thickness (t) vs t1/3. From Krausch et al. [136]... 

Barbou J. C. and Doyle B. L. (1995) Elastic recoil detection ERD (or forward recoil spectrometry FRES). In Handbook of Modern Ion Beam Analysis (ed. J. R. Tesmer). Materials Res. Soc. Warren Hale, PA, pp. 83-138. 

For all these specialty polymers, deuterium can be used as a label on one or the other monomer. Deuterium labeling allows the use of techniques based on ion detection such as forward recoil spectrometry (FRES), nuclear reaction analysis (NRA) or secondary ion mass spectrometry (SIMS). If a high-resolution depth profile of the interfacial region is needed, neutron reflectivity can also be used. The main drawback of that approach is the cost of the deuterated polymers while deuterated styrene and methyl methacrylate are expensive but commercially available, other monomers need to be synthesized and the cost can be quite prohibitive. 

The application of ion beam analysis techniques to determine pore size and pore volume or density of thin silica gel layers was first described by Armitage and co-workers [114]. These techniques are non-destructive, sensitive and ideally suited for the analysis of thin porous films such as membrane layers (dense support is needed for backscattering). However, apart from a more recent report on ion-beam analysis of sol-gel films [115] using Rutherford backscattering and forward recoil spectrometry, ion beam techniques have not been developed further despite their potential for membrane characterisation. This is probably due to the limited availability of ion beam sources, such as charged particles accelerators. 

PS/PVP poly(styrene-b-2-vinyl pyridine) Forward recoil spectrometry, ERES, was used to study diffusion of copolymer randomly dispersed in PS layer of a PS/PVP bi-layer sample. Free copolymer chains were detected at the interface below whereas, above it, copolymer chains were also found at the PS/air surface as well as micellar segregation at the interface was visually confirmed. Shull eta/., 1991... 

As a last example of the migration kinetic and the power of the interface driven segregation, Schulze et al. showed by Forward recoil spectrometry that amino end-group polystyrene could go through more than 5(X) nm of non-functional PS to reach the interface with PMMA during a vacuum annealing at 174 °C (Fig. 5.10) [81]. 

Figure 3.23. The schematic geometry of a typical forward recoil spectrometry experiment.

Shull, K. R. (1992). Forward recoil spectrometry of polymer interfaces. Physics of Polymer Surfaces and Interfaces. I. C. Sanchez. Boston, Butterworth-Heinemann. 

Figure 4.18. Diffusion of deuterated polystyrene (d-PS) in normal polystyrene (h-PS), measured by forward recoil spectrometry (FReS). A 10-20 nm film of d-PS of relative molecular mass 225 000 was floated onto a 2 pm film of h-PS analysis of the deuterium depth profile shows that the d-PS layer was localised, to within the resolution of the technique, at the surface. After atmealing at 170 °C for 3600 s FReS revealed that substantial diffusion into the film had occurred the solid line is a fit to the solution of Fick s equation assmning that > = 8X10 cm s". After Mills et al. (1984).

Figure 4.24. Diffusion coefficients as functions of the composition in the miscible blend polystyrene-poly(xylenyl ether) (PS-PXE) at a temperature 66 °C above the (concentration-dependent) glass transition temperature of the blend, measured by forward recoil spectrometry. Squares represent tracer diffusion coefficients of PXE (VpxE = 292), circles the tracer diffusion coefficients of PS and diamonds the mutual diffusion coefficient. The upper solid line is the prediction of equation (4.4.11) using the smoothed curves through the experimental points for the tracer diffusion coefficients and an experimentally measured value of the Flory-Huggins interaction parameter. The dashed line is the prediction of equation (4.4.11), neglecting the effect of non-ideality of mixing, illustrating the substantial thermodynamic enhancement of the mutual diffusion coefficient in this miscible system. After Composto et al. (1988).

Surface-directed spinodal decomposition was first observed in an isotopic polymer blend (Jones et al. 1991) thin films of a mixture of poly(ethylene-propylene) and its deuterated analogue were annealed below the upper critical solution temperature and the depth profiles measured using forward recoil spectrometry, to reveal oscillatory profiles similar to those sketched in figure 5.30. Similar results have now been obtained for a number of other polymer blends, including polystyrene with partially brominated polyst)u-ene (Bruder and Brenn 1992), polystyrene with poly(a-methyl styrene) (Geoghegan et al. 1995) and polystyrene with tetramethylbisphenol-A polycarbonate (Kim et al. 1994), suggesting that the phenomenon is rather general. 

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