Facile thermal treatment process for assembling vertically aligned semiconductor nanorods in solution

Abstract

Large-area films of vertically-aligned semiconductor nanorods have the potential to be useful, active materials for optoelectronic devices. We demonstrate here a highly facile thermal annealing approach for reversibly assembling 28 nm long CdSe nanorods into vertically aligned arrays in solution. Using temperature to control solvent strength, aggregated nanorods in a marginally poor solvent mixture were first dispersed at elevated temperatures and then reassembled into freely suspended, ordered sheets of aligned nanorods up to 24 μm in diameter upon slow cooling. The assembly method was tolerant of nanorod polydispersity and was effective over a wide range of solvents and nanorod concentrations. The pre-assembled nanorods could be directly drop-cast from solution onto a substrate and rapidly dried to obtain a film of vertically aligned nanorods.

Optical Properties, Synthesis, and Potential Applications of Cu-Based Ternary or Quaternary Anisotropic Quantum Dots, Polytypic Nanocrystals, and Core/Shell Heterostructures

“…For example, it has been simulated that if CdSe-CdTe NRs are aligned in the LSC with their long axis perpendicular to the top surface in the LSC, they emit anisotropic luminescence parallel to the top surface, thus reducing the escape of emitted light from the LSC [179]. There are a range of techniques that have been developed for the alignment of NRs in solution and the corresponding matrix, such as the solvent effect [180,181], thermal annealing [182], controlled drying [183], and electric field [184]. As for Cu-based multicomponent polytypic or heterostructured rod and TP structures, they have excellent light absorption abilities due to their large absorption cross section and carrier-guiding directions.…”

Self-Assembled CdSe/CdS Nanorod Sheets Studied in the Bulk Suspension by Magnetic Alignment

“…[20][21][22] For example, Zanella et al 20 found that NR superstructures could be grown equally well on a variety of substrates, suggesting that pre-organization takes place in the bulk solution. However, until now these important pre-organized NR structures have not been investigated in detail, and their existence has only been proven indirectly.…”

“…[10][11][12][13][14][15][16][17] In particular, nanorods (NRs) with a spherical CdSe core and a rodshaped CdS shell have been shown to be chemically stable, have interesting optical properties, 18,19 and be able to form 2-dimensional superstructures. 16,[20][21][22] Previously, we reported an in situ study of the self-assembly dynamics of such NRs at the liquid/air interface, using grazing incidence small angle X-ray scattering (GISAXS). 16 Although the limited penetration depth (20 nm) of the X-ray beam into the solution prohibited direct visualization, our results suggested the formation of pre-ordered NR sheets in the bulk dispersion as a potentially important factor for the NR ordering at the liquid/air interface.…”

Full alignment of dispersed colloidal nanorods by alternating electric fields

“…Various reports describe the organization of nanorods in two-dimensional sheets of a single layer of parallel quantum rods by depletion attraction, 25 specic surface functionalization schemes 26 or a reduction of the dispersion stability. 27,28 Although it proved possible to orient such 2D sheets in solution by magnetic elds, 29 the size of the sheets leads to considerable scattering of light and results in patchy deposits upon solvent drying. Opposite from this alignment-byaggregation, the collective orientation or alignment of nonaggregated nanorods is possible by means of an electric eld.…”