TOF ERDA

A schematic diagram of the Berlin TOF-ERDA setup is shown in Figure 4.28. 

Bruder and Brenn (1992) studied the spinodal decomposition in thin films of a blend of deuterated polystyrene (dPS) and poly(styrene-co-4-bromostyrene) (PBrxS) by TOF-ERDA. They examined the effect of different substrates on the decomposition process. In one series of experiments, a solution of the polymers in toluene was spread on a silicon wafer to form a film of thickness 550 nm which was then heated in vacuum at 180°C for various times. 

After quenching to ambient temperature the laterally averaged volume fraction versus depth profile was measured by TOF-ERDA, and Figure 4.29 shows a series of dPS profiles for increasing annealing times. After 10 min annealing at 180°C,... 

The lateral structure was studies by optical microscopy, and contrast arises from the fact that after irradiation of the samples with the ion beam in the TOF-ERDA apparatus, the PBrxS-rich structures appear darker than those rich in dPS, giving an excellent contrast (Figure 4.30). 

Bohne et al. (2000) have employed heavy-ion TOF-ERDA to analyse Cr when used as a p-type dopant in FeSi2 films. Cr and Fe have similar masses, and these authors show that heavy-ion ERDA is a powerful tool in this context, being superior to RBS. 

E. Arai, A. Zounek, M. Sekino, K. Takemoto, O. Nittono, Depth profiling of porous silicon surface by means of heavy-ion TOF ERDA, Nucl. Instr. Meth. B85 (1994) 226-229. 

Elemental characterization of electroluminescent SrS Ce thin films using ERDA with an absorber and time-of-flight (ToF)-ERDA has been made by Li et al. (1998) The major impurities in the SrS bulk were found to be H, C, and O. The concentrations of these impurities in SrS Ce films, the films prepared by the reactive evaporation, were found to be 0.6-1.8 at.% H, 0.2-0.7 at.% C and 0.5-1.8 at.% O. 

Fig. 3.17. ToF-ERDA energy vs. mass histograms showing Al and Si recoils from a 170 nm thick ALD-grown AI2O3 film on a soda lime glass substrate measured with 43 MeV C1, 48 MeV Br, 53 MeV and 48 MeV Au ions...

Figure 14 TOF-ERDA volume fraction profiles for a film of dPEP and hPEP undergoing surface-directed spinodal decomposition. Reprinted with permission from Heier, J. Kramer, E. J. Revesz, P. etal. Macromolecules 32, 3758. ° Copyright 1999, American Chemical Society.

As a second example, results from a TOP ERDA measurement for a multi-element sample are shown in Fig. 3.65 [3.171]. The sample consists of different metal-metal oxide layers on a boron silicate glass. The projectiles are 120-MeV Kr ions. It can be seen that many different recoil ions can be separated from the most intense line, produced by the scattered projectiles. Figure 3.66 shows the energy spectra for O and Al recoils calculated from the measured TOF spectra, together with simulated spectra using the SIMNRA code. The concentration and thickness of the O and Al layers are obtained from the simulations. 

Elastic recoil detection analysis (ERDA) of a pyrex-glass sample has been carried out by Grigull et al. (1997) in the elemental range of Z = 5 — 20 using element dispersive ionization chambers and a time-of-flight (ToF-E) system. 

Depth profiling glasses with ion beam techniques is also difficult due to surface charging problems. Pulsed ion beams in ToF-SIMS with relatively long interpulse periods have been used successfully, however. ARXPS can be used to study variation in composition and chemical states over the outer 10 nm. Nuclear techniques, such as PIXE, NRA, RBS and ERDA, are particularly useful in studying the composition of deeper lying altered layers to depths of pm. The latter techniques generally have depth resolutions of the order of 10 nm which is sufficient in most cases [93]. 

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