Symmetry-Breaking Segmented Selenium Nanorods and Nanowires: Synthesis via Coupling of Nanorods

We present a facile route to prepare selenium nanorods (SeNRs) with alternating symmetry-breaking segments dispersed in aqueous solution. The key roles in this preparation include an assistance provided by the carboxymethyl-cellulose (CMC) and a careful control in particle's nucleation and growth. Thus, prepared symmetry-breaking segmented SeNRs, namely, SBS-SeNRs, show discrete trigonal and quasi-trigonal phases in the form of repeating quasi-trigonal-trigonal-quasi-trigonal, (t(q)-t-t(q))(n), where t(q) stands for the quasi-trigonal phase in the space group of P321 and t is the trigonal phase in the space group of P3(1)21. Evidence from the particle dimensions analysis during the growth and the result of post-synthesis surface modification showed that the SBS-SeNRs grow via two different particle couplings. The first one was found in the early stage that very short monoclinic Se nanorods couple together with a simultaneous phase transition to trigonal SeNR. The second coupling occurs at the later stage by the coupling of the (t(q)-t-t(q))-SeNRs, which are formed via a growth of symmetry-breaking Se at both ends of the t-SeNR. Meanwhile, we designed an experiment by conducting the silica coating via sol-gel process to further prove the symmetry-breaking segmented nanostructure. The coating proceeded preferentially on the trigonal segments of SBS-SeNRs rather than the quasi-trigonal segments to form a float-like core shell nanostructure, as well as a string of beads-like one in the case of selenium nanowires (SeNWs). The synthesis of SBS-SeNRs demonstrates the segmented nanomaterials are no longer limited in the combination of different compositions, but opens up a possibility for the versatile intriguing segmented nanomaterials in the future.