Directing the growth of highly aligned gold nanorods through a surface chemical amidation reaction

This paper describes the seed-mediated growth of highly aligned gold nanorods (Au NRs) over large areas directly on a Si(100) surface. The Si(100) surface is NH2-functionalized with (aminopropyl)triethoxysilane (APTES) followed by a DCC-catalyzed surface amidation reaction with acetic acid. After exposure to a gold nanoparticle (Au NP) "seed" solution, chemical seed-mediated growth of the surface-bound seeds via reduction of AuCl4- by ascorbic acid in the presence of cetyltrimethylammonium bromide leads to the growth of highly aligned Au NRs on the surface. About 80% of the NRs are aligned in the same direction within a +/-30 degrees range. Au NRs account for 19% of the nanostructures with average aspect ratio (AR) of approximately 20. The alignment direction did not correlate with the atomic arrangement of the Si(100) crystal since it varied over different regions of the sample, rotating by 90 degrees from top to bottom of an approximately 5 mm sample. Si crystallinity may still be important since alignment is not observed on amorphous glass. Surface functionalization is the key since alignment is only observed following the amidation reaction and not on NH2-functionalized, SH-functionalized, or bare Si(100) surfaces. Alignment also occurred for Au NRs grown on Si(100)/APTES reacted with succinic acid and on Ag NRs grown on Si(100)/APTES/acetic acid surfaces. This unique alignment of metal NRs promoted by a surface amidation chemical reaction may find use in nanoelectronics, chemical sensing, and plasmonics applications.