  In this communication, we report results of a high resolution sputter depth
profiling analysis of a stack of 16 alternating MgO and ZnO nanolayers grown by
atomic layer deposition (ALD) with thickness of ~5.5 nm per layer. We used an
improved dual beam approach featuring a low energy normally incident direct
current sputtering ion beam (first beam). Intensities of 24Mg+ and 64Zn+
secondary ions generated by a pulsed analysis ion beam (second beam) were
measured as a function of sample depth by time-of-flight secondary ion mass
spectrometry (TOF SIMS). Experimental results of this dual beam TOF SIMS depth
profiling processed in the framework of the mixing-roughness-information (MRI)
model formalism demonstrate that such an approach is capable of providing
structural information for layers just a few nm thick. Namely, it was
established that the interfacial roughness of the MgO/ZnO multilayer structure
equals 1.5 nm. This finding by TOF SIMS was cross-validated by independent
measurements with specular X-ray reflectivity (XRR) technique. In addition, the
TOF SIMS-MRI analysis suggests that the obtained 1.5 nm roughness should be
attributed to the native roughness (jagged type) of the interface rather than
to interdiffusion at the interface during the ALD synthesis.
