**5.2 RBS analysis of Ti0.7Al0.3N/MoN and CrN/MoN multilayer films**

Bin Han et al. [22] report of the analysis of Ti0.7Al0.3N/MoN and CrN/MoN multilayer films on Si(001) substrates using RBS. The incident ions used were 2.42 MeV and 1.52 MeV Li2+ ions at varying incident angles. The RBS data was supplemented by XPS, SEM and HR-TEM. The measurement using the 2.42 MeV energy beam at 0<sup>o</sup> incidence was able to resolve the Ti and Mo signals from first seven pairs of bi-layers of 44 nm Ti0.7Al0.3N and 32 nm MoN. **Figure 5** shows the experimental and SIMNRA simulated spectra for extracting the depth profiles [22]. For Al this was possible only for the first three bilayers—beyond which the overlap of the Al signal with that of Ti and Mo from deeper layers precluded Al analysis. A pertinent observation that Bin Han and co-workers make from their results is that the low energy incident beam gave a much a higher backscattering yield (an indication of enhanced sensitivity—see Eq. (3)) and better depth resolution, but for a shallower analytical depth. For a fixed beam energy, increasing the tilt angle improved the depth resolution but again at the expense of the analytical depth. Another important observation that highlights a chink in the armoury of RBS is that while the surface sensitive XPS confirmed nitrogen in the topmost layers, it also pointed out presence of oxygen in those layers. RBS could not, because of the 'shadowing' effect of the (heavier) substrate element signal on that of light elements.

#### **5.3 RBS and ERDA analysis of a solar thermal absorber stack**

In *A study of solar thermal absorber stack based on* CrAlSiNx/CrAlSiNxOy *structure by ion beams*, AL-Rjoub et al. [23] describe RBS and ERDA measurements of a four-layer solar absorber film stack. The RBS data leads to rather inconclusive findings due to extensive overlap of signals from the different layers. On the other hand, the mass dispersive detector of the ToF-ERDA system allows separation of all the elements in the layer stack according to mass. Depth profiles are then extracted from Monte Carlo simulation using the MCERD code [17].

**Figure 5.**

*RBS spectra from the analysis of Ti0.7Al0.3N/MoN and CrN/MoN multilayer films using 2.42 MeV Li2+ ions at 0o incidence angle (a) and at varying tilt angles (b). Similar spectra are shown in (c) and (d) respectively for a 1.52 MeV Li2+ incident beam. (taken from ref. [22], reproduced under the terms of the creative commons CC BY licence).*

**Figure 6** shows, raw data from ToF and energy detectors, experimental and simulated energy spectra of oxygen recoils from different layers and, the depth distribution of oxygen in the layer stack. While the obtained profiles are rather unrealistic step functions, it is widely accepted that due to the *one ion at a time* nature of the treatment of ion-target collisions in MC simulations, they produce the closest description to reality of a target structure.

#### **5.4 Real-time RBS analysis of a hydrogen storage Pd/Ti/Pd layer stack**

Another unique application of IBA techniques is the study of solid state reactions in real-time. This is a technique which has been pioneered by among other labs, the iThemba LABS (formerly known as the National Accelerator Centre) in South Africa [24]. Magogodi et al. [25] report of in-situ real-time RBS analysis of a 125 nm thick Pd/ Ti/Pd film stack to investigate diffusion kinetics and stoichiometric evolution under different annealing environments. This formed part of a study aimed at developing hydrogen storage materials. The measurement described used 2 MeV He2+ ions to probe the layer structure as the samples were annealed in vacuum and in hydrogen environments, with the data taking starting from 160°C up to 600°C, at 30-second intervals.

*Depth Profiling of Multilayer Thin Films Using Ion Beam Techniques DOI: http://dx.doi.org/10.5772/intechopen.105986*

**Figure 6.**

*Raw energy vs. ToF data (left), experimental and simulated oxygen energy spectra (Centre), and depth distribution of oxygen (right) in a SiAlOx/CrAlSiNxOy/CrAlSiNx/W layer stack. (reproduced with permission from ref. [23]).*

**Figure 7** is a 2-D plot of the colour coded spectral yield as the temperature increases. For the sample annealed in vacuum, **Figure 7a**, the authors surmise that there is complete reaction between the Pd and Ti layers by the time the sample temperature reaches 550°C, and for the one annealed in a H2 environment, their conclusion is that the Ti-Pd reaction is, to a great extent, inhibited. The obvious advantage of such a measurement is that by monitoring the reaction in real-time, any intermediate phases that may form are also detected, and not just the end-point—thus facilitating the study of solid-state reaction mechanisms. Indeed this has been applied in, for example, studies of growth kinetics of Ni(Pt) silicides [26], where the analysis of the huge data generated was done using artificial neural networks.

### **6. Summary**

Multilayer thin film structures have become ubiquitous in many device structures in the current era of nanotechnology driven advances in electronics, medicine, energy

**Figure 7.**

*Contour plots comparing the onset of reaction between atomic species in Pd/Ti/Pd layers annealed in (a) vacuum and in (b) hydrogen environments. (reproduced with permission from ref. [25]).*

and other technological fields. Ion beam analysis techniques can readily generate invaluable structural information about multilayer films through standard-free analyses that are not possible with other analytical techniques. The physics behind RBS and ERDA techniques described in this chapter is well established and there are data analysis tools available to the materials analyst that can facilitate interpretation of experimental data with reasonably good accuracy. The selected applications described showcase the versatility of these analytical tools in addressing different problems from simple film thickness measurements to tracking solid state reactions in real-time.
