"The ability to reproducibly synthesize and assemble nanostructures into functional architectural structures is extremely important for many practical applications in nanoscale science and technology," Hou Tee Ng of NASA Ames and Eloret told nanotechweb.org. "This is even more true when trying to interface the nanostructures with suitable substrates for any desired applications."
Ng and colleagues grew the structures onto two substrates - highly oriented pyrolytic graphite, which is a conductor, and sapphire, which is an insulator. They used a thin layer of gold catalyst on the substrate and a carbothermal reduction process. For gold films thicker than 1.5 nm, quasi-3D nanostructures grew. The structures contained vertical 1D nanowires on top of a 2D network of vertical nanowalls in a random honeycomb-like pattern. The nanowires grew from the nodes (or junctions) of the nanowalls and were around 80 nm in diameter. The nanowalls were also about 80 nm thick.
The researchers believe the pattern of nanowalls grew because of the limited wettability of gold on the substrates, which caused gold network patterns - rather than isolated droplets or a continuous film - to form at high temperature. Growth of the nanowalls and nanowires took place epitaxially. Ng reckons the approach could also be extended to other nanostructured systems.
"Because of the favourable surface-to-volume ratio of the multi-dimensional nanostructures, we envision potential applications in energy storage/conversion and data storage," added Ng. "We are actively exploring the integration of these unique nanostructures into functional devices that could eventually meet our mission-critical tasks for space exploration."
The researchers reported their work in Science.