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.     

Material symmetries versus wavefront symmetries

We show that, in general, wavefronts are more symmetric thanthe medium in which they propagate. This means that we cannotdetermine the symmetries of the medium based solely on the symmetriesof the wavefronts. However, we show that we can determine thesymmetries of the medium from the symmetries of wavefronts andpolarizations together.     

Improved method for the simultaneous absorptiometric determination of cobalt and nickel with quinoxaline-2,3-dithiol

A new, more stable reagent, S-2-(3-mercaptoquinoxalinyl)thiuronium chloride (MQT), is proposed for the simultaneous absorptiometric determination of cobalt and nickel. It is hydrolysed rapidly to quinoxaline-2,3-dithiol (QDT) in ammonia buffer at pH 10. In the presence of zinc(II), QDT is stabilized by complex formation and the reagent blanks are reduced. Samples containing cobalt(II) and nickel(II) react with the mixture on warming to give 1:3 cobalt and 1:2 nickel complexes, with maximum absorbances at 472 and 520 mmu respectively. The sensitivity of the method is high, 0.0017 and 0.0028 mug cm (2) for cobalt and nickel respectively, and there is a significant improvement in accuracy and precision, which is about +/-1 % over a 15-fold change in cobalt to nickel ratio. The selectivity is moderate; Ag(I), Cu(II), Pd(II), Cd(II), Hg(II), Sn(II), Pb(II), Bi(III) and Pt(IV) cause significant interference but most other common cations and anions can be tolerated.