3D and 2D structural characterization of 1D Al/Al2O3 biphasic nanostructures

Summary 1D Al/Al2O3 nanostructures have been synthesized by chemical vapour deposition (CVD) of the molecular precursor [tBuOAlH2]2. The deposited nanostructures grow chaotically on the substrate forming a layer with a high porosity (80%). Depending on the deposition time, diverse nanostructured surfaces with different distribution densities were achieved. A three-dimensional (3D) reconstruction has been evaluated for every nanostructure density using the Focus Ion Beam (FIB) tomography technique and reconstruction software tools. Several structural parameters such as porosity, Euler number, geometrical tortuosity and aspect ratio have been quantified through the analysis with specified software of the reconstructions. Additionally roughness of the prepared surfaces has been characterized at micro- and nanoscale using profilometry and AFM techniques, respectively. While high aspects ratio around 20–30 indicates a strong anisotropy in the structure, high porosity values (around 80%) is observed as a consequence of highly tangled geometry of such 1D nanostructures. Lay Description 1D nanostructures have tube or wire-like shapes with diameters below 100 nm and lengths of several micrometers. There are various methods to fabricate such ultrafine structures. The growth out of a chemical synthesis is the most elegant and simplest approach for fabrication of these ultra-small wires. Some of these methods are known as wet chemical syntheses since the material fabrication takes place within a solution. The chemical synthesis may also be carried out in the gas phase. Chemical Vapour Deposition (CVD) is such a chemical method, which leads to the fabrication of solid materials through accumulation of the vapour phase chemical species on a solid substrate. In this work, we have used a special CVD process to fabricate the nano-wires. The obtained wires have core-shell geometry. The inner core is made of aluminium and the outer surrounding shell is made of aluminium oxide. These ultrafine and extremely long wires form an assembly, which is similar to a bundle of spaghettis. It is difficult to analyse their shape, assembly, voids and other structural properties easily, just by looking from the top-view using a high-resolution electron microscopy. This microscopic method can give extremely high-resolution images (more than 500,000 times magnification) to analyse any fine detail. On the other hand, the gathered information is limited only to the planar 2D surface of the material. To get 3D information, we cut several slices perpendicular to the surface of the nano-wire assembly by edging and analysed every slice in terms of their morphology (destructing process). Afterwards, all these 2D projection images are brought together in order to get a reconstructed 3D image. This method allows observing every fine detail in the assembly just by rotating 3D image along any axis of interest.