Directing semiconductor nanorod assembly into 1D or 2D supercrystals by altering the surface charge

Abstract

Coulomb repulsion due to the surface charge on semi-conductor nanorods works against the dipole-dipole attraction that tends to direct the nanorods to self-assemble; the nature of this selfassembly for CdSe nanorods can be thus altered by pyridine washing, which charges the rods surface-thereby allowing the Coulomb repulsion to tailor the alignment.

Silver Tip Formation on Colloidal CdSe Nanorods by a Facile Phase Transfer Protocol

“…The fitting clearly showed the presence of single species for Cd coming from CdSe. The deconvolution of Se 3d peak showed the presence of two 25 decoupled components at 53.5 and 54.6 eV ( Figure S1B and Figure 4B) due to 3d 5/2 and 3d 3/2 which appeared from CdSe. Absence of any extra components in the fitted curve ruled out the probability of the presence of un-reacted Se.…”

“…The phenomenon of multiple Ag tip formation and their Oswald ripening to form one larger single tip could be explained in terms 20 of significant lattice mismatch for Ag and the semiconductor materials used in this study due to a strain relief mechanism. 26,[29][30][31] The lattice mismatch and associated strain relief had already been reported to grow small islands of noble metals of a critical atom density which ripen into larger islands as the reaction 25 continued. Robinson and co-workers observed similar straindependent island formation on CdS nanorods during the partial cation exchange of Cd 2+ with Ag + .…”

“…A further magnified TEM image clearly showed the vertically arranged Ag tipped wurtzite rods adopted a hexagonal close packed super-structure with individual rods separated at 1-2 nm by interdigitation of the surfactant ligands, Figure 6B. The planes corresponding to both 25 CdSe and Ag could be distinguished on the top end of a vertical rod through HRTEM imaging ( Figure 6C). The tipped rods adopted an orthogonal orientation with the CdSe component in contact with the substrate similar to Au-tipped CdSe structures reported by Zhao et al 14 and O'Sullivan et al 26 Brighter contrast 30 due to Ag tips was also clearly visible on vertically aligned CdSe rods under scanning electron microscope, Figure 6D.…”

“…[1][2][3][4][5] These bulk applications are possible as the nanorods can be readily assembled into scaleable perpendicular architectures 25 where length dependent properties such as total absorption or emission can be independently tuned from diameter dependent properties such as band gap. 2,6,7 Recent advances allow the formation of gold tips on the ends of the semicondunctor nanorods as a sequential synthetic step in solution or by post-30 synthetic spin casting on a preformed assembly.…”

“…The density of packing will likely find significant application where silver metal-semiconductor hybrids are needed in high density arrays such as photovoltaics or 70 photocatysis. [25][26][27] …”