Being able to construct ever more complex nanostructures has allowed researchers to study many fundamental physics and chemistry phenomena, and to develop applications for use in a variety of different fields. For example, some 1D nanostructures can be used to manipulate light–matter interactions in novel sensing and light harvesting devices. Nanoelectronics devices based on 1D silicon nanowires can also be employed in bioelectronics and drug-delivery devices.

Further developing the architecture and compositions of such structures with metal-based and polymeric materials could lead to even more sophisticated applications. Electrodeposition could come into its own here since it has proved itself to be an efficient way to deposit films of different materials on flat materials. To date, however, it had never been used to modify nanowire structures with uniform shells or to prepare multiple coaxial shell layers.

A team led by Charles Lieber and Daniel Nocera has now developed a fast, room-temperature, solution-phase electrodeposition method to uniformly deposit a large library of materials, including metals, metal oxides, chalcogenides and polymers, on these high-aspect-ratio 1D nanostructures. “Some of the materials we studied are a selection of catalytically, magnetically or plasmonically active materials (such as Au, Ag, Cu, Pt, Pd, Ru, Rh, Ni and Fe), catalytic metal oxides (MnOx, CoOx), semiconducting metal chalcogenides (CdS, CdSe) and conductive polymers (polyaniline, polypyrrole, poly-3,4-ethylenedioxythiophene),” explains team member and lead author of the work, Tuncay Ozel.

Nanowire arrays as conductive substrates

The researchers used doped silicon micro- and nanowire arrays as conductive substrates for electrodeposition. Deposition can take place on wire arrays with different diameters (70 nm to 4 μm), pitch (5 μm to 15 μm), aspect ratios (4:1 to 75:1), shapes (cylindrical, conical or hourglass), resistivity (0.001-0.01 to 1-10 ohm/cm2) and orientation. Once the wires have been soaked in an electrolyte containing metal ions or organic monomers, deposition takes place because of reduction or oxidation of the ions or monomers with precisely-tuned thicknesses that are controlled by the amount of charge passing through the system during the process. Multiple layers of various materials can be sequentially deposited to prepare complex and hybrid structures.

“1D silicon micro- and nanowires have recently advanced our understanding in many areas of science and have led to many technological applications,” says Ozel. “We expect that the versatility of our new approach will find diverse applications in chemistry, physics and medicine. In particular, we are currently looking into how we can exploit our results in the fields of energy conversion and storage, sensing and bioelectronics.

“The fact that our technique is scalable and compatible with organic molecules means that it can be integrated with well-established silicon-based industrial processes as a potential route for fabricating arrays of single nanowire devices in parallel,” he tells nanotechweb.org.

The team, reporting its work in Nano Letters DOI: 10.1021/acs.nanolett.7b01950, says that it is now using its approach to prepare nanostructured catalysts and study how to control their catalytic activity by modulating the space between the nanowires and changing the height of the wires.