Nanomaterials: Finding friends with a golden tip

May 04, 2011
Transmission electron microscopy images of (left) CdSe-seeded CdS nanorods with palladium-gold tips (dark spots), and (right) CdS nanorods with core-shell gold-iron tip structures. Credit: 2011 ACS

Quantum dots are tiny semiconductor crystals that emit bright and tunable fluorescence. They are typically made of cadmium sulfide (CdS) or cadmium selenide (CdSe), and have a wide range of applications, including bioimaging and solar cells. Recently, chemists have sought to add new capabilities to quantum dots by fusing them with metal atoms, creating ‘heterostructured’ nanocrystals. However, bonding metal cations to a semiconductor often requires strong reducing agents—electron-donating chemical reagents that can play havoc with the quantum dot’s nanostructure.

Yinthai Chan and co-workers at the A*STAR Institute of Materials Research and Engineering and the National University of Singapore have now developed a technique that makes depositing metals onto semiconductor nanoparticles easier than ever. By using ultraviolet light to activate special gold-tipped ‘nanorods’, the researchers have successfully incorporated catalytic palladium and magnetic iron atoms into heterostructured nanocrystals using mild reducing agents, paving the way for a diverse range of new quantum-dot applications.

The nanorods contain a ‘seed’ particle, a spherical CdSe quantum dot, surrounded by a cylindrical shell of CdS molecules, tens of nanometers long. Under the right conditions, the researchers found that the tips of these nanorods act as nucleation points for metal growth. Gold cations, for example, deposited spontaneously on one or both ends of the CdS rods because they could be easily transformed into crystalline atoms using a mild reducing agent. Less-reactive metal cations like palladium and iron, however, would not nucleate onto either the bare or gold-tipped nanorods with the use of mild reagents.

Chan and his co-workers realized that one way around this problem was to exploit the semiconductor’s sensitivity to light. Exposing this material to ultraviolet radiation produces a photogenerated electron and a positive ‘hole’ within the nanorod. Normally, these particles recombine within a fraction of a second, but the researchers believed that in the presence of a hole-scavenging molecule like ethanol, electrons could migrate to the gold tip and enhance its reductive capabilities. Experiments revealed that this hypothesis was correct—the photo-powered gold tips reacted with palladium cations to give a surprising alloyed nanostructure, while iron cations bonded to the nanorod with a core–shell organization (see image).

“This study shows that the light-activated transfer of an electron from a semiconductor to a gold tip can allow deposition of metals that ordinarily would not be easily reduced using mild conditions,” says Chan. The researchers are currently exploring how combinations of metal tips and different semiconductors can affect the efficiency of other photo-induced catalytic processes.

Explore further: Thinnest feasible nano-membrane produced

More information: Li, X., et al. Light-induced selective deposition of metals on gold-tipped CdSe-seeded CdS nanorods. Journal of the American Chemical Society 133, 672–675 (2011).

Provided by Agency for Science, Technology and Research (A*STAR)

5 /5 (1 vote)
add to favorites email to friend print save as pdf

Related Stories

In Brief: Quantum dot-Induced transparency

Dec 01, 2010

Using rigorous and realistic numerical simulations, staff in the Nanophotonics and Theory and Modeling groups at the Argonne National Laboratory have recently demonstrated that a single semiconductor nanocrystal, ...

Gold-tipped nanocrystals developed by Hebrew University

Jun 17, 2004

"Nanodumbells" – gold-tipped nanocrystals which can be used as highly-efficient building blocks for devices in the emerging nanotechnology revolution – have been developed by researchers at the Hebrew University of Jer ...

Coupling of Single Quantum Dots to Smooth Metal Films

Jul 20, 2009

Scientists at Argonne National Laboratory's CNM Nanophotonics Group have measured how light emission from individual colloidal semiconductor nanocrystals, or quantum dots, is modified when in proximity to ...

Recommended for you

Thinnest feasible nano-membrane produced

Apr 17, 2014

A new nano-membrane made out of the 'super material' graphene is extremely light and breathable. Not only can this open the door to a new generation of functional waterproof clothing, but also to ultra-rapid filtration. The ...

Wiring up carbon-based electronics

Apr 17, 2014

Carbon-based nanostructures such as nanotubes, graphene sheets, and nanoribbons are unique building blocks showing versatile nanomechanical and nanoelectronic properties. These materials which are ordered ...

Making 'bucky-balls' in spin-out's sights

Apr 16, 2014

( —A new Oxford spin-out firm is targeting the difficult challenge of manufacturing fullerenes, known as 'bucky-balls' because of their spherical shape, a type of carbon nanomaterial which, like ...

User comments : 0

More news stories

'Exotic' material is like a switch when super thin

( —Ever-shrinking electronic devices could get down to atomic dimensions with the help of transition metal oxides, a class of materials that seems to have it all: superconductivity, magnetoresistance ...

Innovative strategy to facilitate organ repair

A significant breakthrough could revolutionize surgical practice and regenerative medicine. A team led by Ludwik Leibler from the Laboratoire Matière Molle et Chimie (CNRS/ESPCI Paris Tech) and Didier Letourneur ...

Impact glass stores biodata for millions of years

( —Bits of plant life encapsulated in molten glass by asteroid and comet impacts millions of years ago give geologists information about climate and life forms on the ancient Earth. Scientists ...