Formation of symmetric and asymmetric metal–semiconductor hybrid nanoparticles (original) (raw)

Formation of asymmetric one-sided metal-tipped semiconductor nanocrystal dots and rods

Nature Materials, 2005

for creating smart materials, requiring the development of the growth of different material types on one particle. Here, we report the synthesis of asymmetric metal-semiconductor heterostructures where gold is grown on one side of CdSe nanocrystal quantum rods and dots, creating nanostructures offering intrinsic asymmetry for diverse device functionalities such as diode elements, along with one-sided chemical accessibility through the gold tips. Surprisingly, one-sided growth is preceded by two-sided growth and is generally observed in different particle shapes. Theoretical modelling in a lattice-gas model and experimental analysis show that a ripening process drives gold from one end to the other, transforming two-sided growth to one-sided growth.

Selective reactions on the tips of colloidal semiconductor nanorods

Journal of Materials Chemistry, 2006

A strategy to access several types of Au-tipped dumbbell-like nanocrystal heterostructures is presented, which involves the selective oxidation of either PbSe or CdTe sacrificial domains, initially grown on CdSe and CdS nanorods, with a Au(III) : surfactant complex. The formation of gold patches is supported by TEM, XRD and elemental analysis. This approach has allowed us to grow Au domains onto specific locations of anisotropically shaped nanocrystals for which direct metal deposition is unfeasible, as for the case of CdS nanorods. We believe that this strategy may be of general utility to create other types of complex colloidal nanoheterostructures, provided that a suitable sacrificial material can be grown on top of the starting nanocrystal seeds.

Facet Specific Gold Tip Growth on Semiconductor Nanorods

High quality CdS-Au and CdSe-Au hybrid nanocrystals have been developed via facile approaches. Gold tip growth onto II-VI nanorods has been shown to occur instantaneously both via a solution and spin cast method. Gold tip size and multiplicity can be varied by changing the starting gold chloride concentration or the reaction duration. Gold tip growth typically occurs at one end of the nanorod, however we recently observed that a variation in the reaction temperature leads to the growth of a tip on both ends of the nanorod. TEM analysis showed that the gold tip growth does not always occur centrosymmetrically on the rod tip, with growth occurring on either the (001) or the (101) facet depending on the respective sizes. Spin coating gold chloride solution onto a pre-deposited perpendicular oriented array of nanorods leads to individual gold growth at the tips of each nanorod.

Gold tip formation on perpendicularly aligned semiconductor nanorod assemblies

2008

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 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 characterised by photoluminescence spectroscopy.

Self-Assembly of Gold Nanorods

The Journal of Physical Chemistry B, 2000

Self-assembly of gold nanorods (NRs) with aspect ratio of ∼4.6 (12 nm in diameter and 50-60 nm in length) has been studied using transmission electron microscopy (TEM). Under appropriate conditions such as nanoparticle concentration, solvent evaporation, narrow size distribution, ionic strength, and surfactant concentration of the parent solution, gold nanorods assemble into one-, two-, and three-dimensional structures. Some of the three-dimensional assemblies extend to superlattices of NRs. The translation and orientation symmetries of the self-assembled structures are determined. The factors affecting the formation of the ordered self-assembly are discussed.