Copper tubes having diameters between about 100 and about 200 nm have been fabricated by electrodeposition of copper into the pores of alumina nanopore membranes. Copper nanotubes are under consideration as alternatives to copper nanorods and nanowires for applications involving thermal and/or electrical contacts, wherein the greater specific areas of nanotubes could afford lower effective thermal and/or electrical resistivities. Heretofore, copper nanorods and nanowires have been fabricated by a combination of electrodeposition and a conventional expensive lithographic process. The present electrodeposition-based process for fabricating copper nanotubes costs less and enables production of copper nanotubes at greater rate.
The demonstration of this process began with the selection of alumina membranes containing pores having diameters in the approximate range of 100 to 200 nm. The estimated porosity of these membranes was 43 percent. Each of these membranes was evaporation-coated on one side with a 100-nm-thick gold film to render that side electrically conductive. Each membrane was then mounted on a gold-coated silicon substrate by use of adhesive tape, and the substrate was carefully masked with tape to prevent electrodeposition on the substrate. Next, the membrane-and-substrate unit was immersed for about 10 minutes in a solution comprising 4 volume parts of water and 1 volume part of a potassium-based, buffered developer solution commonly used in lithography. The purpose and effect of this immersion was to render the surfaces of the pores electrically conductive.
Next, electrodeposition into the pores was performed at room temperature in a commercially available copperplating solution, using platinum-coated titanium mesh counter electrodes and galvanostatic control set to a current density of, variously, 10 or 20 mA/cm2. Copper nanotubes were thus formed in the pores at a deposition rate of 100 nm/min at the current density of 10 mA/cm2 or 150 nm/min at the current density of 20 mA/cm2.
This work was done by E. H. Yang, Christopher Ramsey, Youngsam Bae, and Daniel Choi of Caltech for NASA’s Jet Propulsion Laboratory.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, NASA Management Office–JPL. Refer to NPO-42261.