Centimetre scale assembly of vertically aligned and close packed semiconductor nanorods from solution.

Assembly of CdS nanorods (8 × 100 nm) into vertically aligned arrays over very large areas on a substrate either as a monolyaer or severaly multilayers is shown by electrophoresis

Self-assembly of vertically aligned nanorod supercrystals using HOPG

Supercrystallisation of CdS nanorods (10 nm × 25 nm) into perpendicular superlattices was obtained by controlled evaporation of a nanorod solution trapped between a smooth substrate and a block of highly ordered pyrolytic graphite (HOPG). Hexagonal oriented domains, 2 μm2 in size were routinely obtained on a variety of substrates without external electric fields

Gold tip formation on perpendicularly aligned semiconductor nanorod assemblies

A facile spin cast process is used for the instantaneous asymmetric formation of gold tips on perpendicularly aligned CdS nanorod superlattices. Tip size varies as a function of precursor solution concentration and growth time. A single uniform tip occurs on the end facets of each nanorod in the array when an optimised gold chloride solution is used, with multiple tipping 10 occuring with variations in precursor concentration. HRTEM shows that the gold tip growth does not always occur centro-symmetrically on the nanorods, with growth occuring on the (101) or the (001) facet of the wurtzite nanocrystal depending on the rod shape. X-ray diffraction confirms that the gold tips are crystalline with a 60% lattice mismatch with the wurtzite CdS nanocrystal suggesting strain relief may be a factor in tip formation. The gold tipped nanorods are further 15 characterised by photoluminescence spectroscopy

Evolution of pseudo-spherical silicon nanocrystals to tetrahedra, mediated by phosphonic acid surfactants.

Silicon nanocrystals were synthesised at high temperatures and high pressures by the thermolysis of diphenylsilane using a combination of supercritical carbon dioxide and phosphonic acid surfactants. Size and shape evolution from pseudo-spherical silicon nanocrystals to well faceted tetrahedral-shaped silicon crystals with edge lengths in the range of 30-400 nm were observed with sequentially decreasing surfactant chain lenghts. The silicon nanocrystals were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), photoluminescence (PL), scanning electron microscopy (SEM) and Raman scattering spectroscopy

Controlled semiconductor nanorod assembly from solution: influence of concentration, charge and solvent nature

Spontaneous supercrystal organisation of semiconductor nanorods (CdS and CdSe) of different aspect ratios into ordered superstructures was obtained by controlled evaporation of a nanorod solution. The rods either align into two dimensional close packed perpendicular arrays or into one dimensional rail tracks depending on the total interaction energy between the rods in solution. A detailed study has 10 identified critical factors that affect this interaction energy such as nanorod concentration, surface charge, dipole moment and solvent nature (polarity and volatility), thereby allowing a general approach to control the nature of nanorod assembly (1D or 2D). Molecular dynamics (MD) of small charged nanorods showed that opposite dipolar alignment (antiferromagnetic) was the preferred rod orientation during self-assembly

Water dispersible semiconductor nanorod assemblies via a facile phase transfer and their application as fluorescent biomarkers.

We demonstrate the formation of water dispersed nanorod assemblies by phase transfer of semiconductor (CdS, CdSe, CdTe) nanorods from the organic to the aqueous using pluronic triblock copolymers. On phase transfer, the randomly dispersed nanorods in the organic medium close pack in the form of discs encapsulated in the hydrophobic core of water dispersible micelles. The assemblies showed excellent cellular uptake exhibiting membrane and cell specific fluorescence at low light intensity under confocal microscopy

Spontaneous room temperature elongation of CdS and Ag2S nanorods via oriented attachment

Spontaneous elongation from nanorod to nanowire in the presence of an amine is reported for nanocrystals of cadmium sulfide and silver sulfide (cation exchanged from CdS). Elongation occurs instantaneously where the final aspect ratio is a controllable multiple of the original nanorod length. The influential factors on the attachment process are the alkyl-amine chain length, concentration of amine, duration and temperature of the reaction. The nanorods are characterized by high resolution transition electron microscopy (HRTEM), X-Ray diffraction (XRD), photoluminescence (PL), ultraviolet-visible spectroscopy (UV-Vis) and X-ray photoelectron spectroscopy (XPS). A mechanism of oriented attachment is evidenced by the doubling in length of asymmetrically gold tipped CdS nanorods with the corresponding absence of elongation in symmetrically tipped nanorods