Application of serial sectioning FIB/SEM tomography in the comprehensive analysis of arrays of metal nanotubes

Abstract

The ever‐increasing interest in nanostructured materials and shrinking dimensions of state‐of‐the‐art devices pose new challenges both in synthesis and metrology. Although an extensive range of nanotubular materials of different compositions and for various applications are reported in the literature, often detailed structural characterisation of these materials is limited. This is due to the fact that techniques and characterisation protocols for structural analysis of ‘buried’ nano‐scale features, defects or inhomogenities that are difficult to obtain by conventional imaging methods, are still not fully developed. In the case of 1D nanoporous structures, the continuity of the nano‐tubular channels, their uniformity and orientation is of particular interest. Herein, we employ a serial sectioning technique on a dual beam FIB followed by 3D volume reconstruction for comprehensive analysis of tubular metal nanostructures encapsulated within porous anodic alumina. Using this technique, we demonstrate a nano‐tomography characterisation protocol that can be used for analysis of nanoporous structures with emphasis on their channel uniformity and orientation. We demonstrate that high‐resolution nano‐tomography can be performed to visualise pores as small as 60 nm in diameter, with conical or globular shapes, and to quantitatively estimate their localisation and distribution along one‐dimensional metal structures. We specifically chose to examine Cu‐nanotubes, deposited electrochemically within anodic alumina template, because there is a great deal of debate regarding the deposition process. Hence, the comprehensive analysis shown here is not only demonstrating the applicability of the developed characterisation methodology but it is also, in conjunction with other advanced electron microscopy methods such as elemental nano‐scale STEM/EDX mapping, providing conclusive evidence of the key factors at play during the deposition process.