Deuterated depth profiles

Figures (a) Scattering geometry for ERS (b) ERS spectrum from 200-A partially deuterated polystyrene on Si, E h 3.0 MeV (adapted from ref. 101 and (cl schematic ERS depth profile spectrum.

Fig. 6. The ripple experiment at the interface between a bilayer of HDH- and DHD-labeled polystyrene, showing the interdifussion behavior of matching chains. The protonated sections of the chain are marked by filled circles. The D concentration profiles are shown on the right. Top the initial interface at / = 0. The D concentration profile is flat, since there is 50% deuteration on each side of the interface. Middle the interface after the chain ends have diffused across (x < / g). The deuterated chains from Que side enrich the deuterated centers on the other side, vice ver.sa for the protonated sections, and the ripple in the depth profile of D results. A ripple of opposite sign occurs for the H profile. Bottom the interface when the molecules have fully diffused across. The D profile becomes flat [20,56].

Fig. 5. Hydrogen depth profile of a deuterated polystyrene PS(D) film deposited on a protonated polystyrene PS(H) film on top of a silicon wafer as obtained by l5N-nuclear reaction analysis ( 5N-NRA). The small hydrogen peak at the surface is due to contamination (probably water) of the surface. The sharp interface between PS(D) and PS(H) is smeared by the experimental resolution (approx. 10 nm at a depth of 80 nm) [57], The solid line is a guide for the eye...

Zink et al. used a blend of polystyrene (hPS) and its deuterated counterpart (dPS), both of molecular weight 1.95 x 106 (abbreviated 1.95 M). The average volume fraction (4>dPS) of deuterated polystyrene was 30%. The polymers were dissolved in toluene and spin cast on thin silicon wafers (about 10 x 10 mm), the resulting film thickness being about 300 nm. The samples were annealed at 245°C for 8 days, and the measurement of the resulting depth profiles was conducted by NRA using a monoenergetic 700 keV 3He beam. The nuclear reaction employed can be written ... 

Fig. 4. Depth profile of deuterium in boron-doped Si after deuteration at 150°C for 30 min. After Johnson (1985).

Fig. 7. Depth profiles of deuterium in n-type (P-doped) silicon after deuteration in a remote plasma system at 150°C (a) entire profile after a 120 min deuteration and (b) near-surface profiles after different durations of deuteration. Also shown is the uniform P concentration.

Fig. 20. SIMS profiles of total deuterium density across p-n junctions formed by implanting phosphorus into a (100) silicon water uniformly doped with 1 x 1017 boron atoms per cm3 for various times of deuteration at 150°C (Johnson, 1986a). The phosphorus profile is also shown and serves to locate the pre-deuteration depth of the junction at 0.5 Deuteration was from downstream gases from a plasma discharge (Johnson and Moyer, 1985).

Both the ability to detect hydrogen and the ability of SIMS to differentiate between isotopes were exploited in a study of deuterium diffusion in hydrogenated amorphous Si (14). Layered samples of hydrogenated and deuterated films were depth profiled before and after various heat treatments. The diffusion coefficient for deuterium obtained from these experiments implied that degradation of these films due to hydrogen out-di fusion at 100 C would not be significant until after more than 10 years. 

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. 

We have studied binary blends dxx/hx2 of random olefinic copolymers x=(Ex x EEx)n, with one blend constituent protonated (hx) and the other deuterated (dx). The blends examined were grouped in four pairs of structurally identical mixtures xx/x2 but with a swapped isotope labeled component (dxx/hx2 and hxx/dx2). For such blend pairs the bulk interaction parameter % (and hence also the critical point Tc) has been found (see Sect. 2.2.3 and references therein) to be higher when the more branched (say xx>x2) component is deuterated, i.e., X(dx /hx2)>x(hx /dx2) or Tc(dxx/hx2)>Tc(hxx/dx2) (see Fig. 9). An identical pattern is exhibited here by the force driving the segregation at the free surface. This is illustrated in Fig. 26a,b where the composition vs depth profiles of the more branched (xx) component are shown for blend pairs with swapped isotope... 

Fig.44. Typical [255] composition-depth profiles of dPS blocks (after 3 days of annealing at 190 °C) in thin PS (m.w.=2.89X106) homopolymer films with binary mixtures of short and long copolymers. Deuterated short copolymers dS=PI(NA=114)-dPS(N=89) or their proto-nated analogs hS=PI (NA=143)-PS(N=124) as well as long deuterated dL=PI (NA=114)-dPS(N=9551) copolymers are used in pairs of samples with hS/dL (Q profiles) and dS/dL ( profiles) mixtures. The overall compositions of short (dS, hS) and long (dL) diblocks are 2.1 and 6.7% for (a) as well as 4.2 and 3.3% for (b), respectively...

Figure 3.25. The depth profile of deuterated polystyrene deduced from the FRES spectrum shown in figure 3.24. After Jones et al. (1989).

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).

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. 

By using dynamic mode SIMS the lateral distribution of phases in three dimensions can be resolved (Fig. 31). Thin films (thickness ca. 500 nm) of binary mixtures of deuterated or partially brominated PS, polyisoprene and poly(vinylpyridine) were investigated with a lateral resolution of approximately 120 nm and composition versus depth profiles with a resolution better than 10 nm [208]. The brominated PS formed continuous phase-domain structures in the interior of the films whereas they were encapsulated by deuterated PS layers at the interfaces. Moreover a very thin layer (ca. 3 nm) of polyisoprene covered the surface of a binary mixtme of poly(isoprene)/deuterated PS [208]. 

A number of papers have appeared giving a complete description of this technique which is sometimes known in the literature as elastic recoil detection (ERD). The discussion presented here will therefore be brief. FRES is used to determine the volume fraction versus depth profile of a species labelled by deuteration which was allowed to diffuse into an unlabelled host. The diffusion coefficient is extracted from this profile using a solution to the diffusion equation. 

The mutual diffusion couples consisted of two films of deuterated polystyrene (D-PS). -protonated PXE blends which have a small difference in the volume fraction of d-PS (--lOj), from 2 in the 350 nm-thick top film to < )-j in the 2 pm-thick bottom film. The initial step function of the d-PS concentration profile was broadened by mutual diffusion at T in vacuum (<10" torr). The volume fraction versus depth profile of d-PS was... 

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