The use of porous templates containing aligned nanopores is a versatile method to fabricate arrays of aligned nanowires. However, it remains still a challenge to extend the range of functional target materials that can be formed into one-dimensional nanostructures and microstructures with low defect density and high aspect ratios. To this end, we have exploited ordered porous alumina and macroporous silicon not only as shape-defining moulds but also as reactants. If a compound containing carbon atoms that can be oxidized is heated inside porous alumina, tubes containing amorphous carbon form on the pore walls. Under certain conditions, this holds even for common solvents such as acetone. Fig. 1 shows an amorphous carbon tube containing gold nanoparticles fabricated by heating porous alumina infiltrated with a solution of tetrachloroauric acid in acetone.
Figure 1: Dark-field transmission electron microscopy image of an amorphous carbon tube containing gold nanoparticles fabricated by heating porous alumina infiltrated with a solution of tetrachloroauric acid in acetone.
Depending on the experimental conditions applied, one-dimensional nanostructures and microstructures consisting of an entire set of functional target materials are accessible from one single source precursor. Arylchalcogenolates of group 12 and 14 metals are a versatile class of such single-source precursors with similar molecular architecture and thermal properties. For example, templated thermolysis of Sn(SePh)4 inside porous alumina and macroporous Si yields tubes and wires of SnSe, SnO2 and Sn (Fig. 2).
Figure 2: Scanning electron microscopy image of released Sn microtubes prepared from SnSe inside macroporous silicon, which acted as a redox-active host.
Zn(TePh)2 • TMEDA (TMEDA: tetramethylethylenediamine) and self-ordered porous alumina templates represent a construction kit for the synthesis of single-crystalline nanowires of zinc telluride (ZnTe) (Fig. 3), zinc spinel/tellurium (ZnAl2O4-Te) and elemental tellurium (Te) as well as ZnAl2O4 nanotubes.
Figure 3: a) Transmission electron microscopy image and corresponding selected electron diffraction pattern (inset, zone axis [1 -1 2]) of a single-crystalline ZnTe nanowire. (b) High resolution transmission electron microscopy image of a ZnTe nanowire showing (111) lattice planes (d = 0.348 nm).