Roland Piquepaille's Technology Trends
How new technologies are modifying our way of life

vendredi 18 juin 2004

A group of chemists at the Hebrew University of Jerusalem has developed 'nanodumbbells' -- gold-tipped nanocrystals which can be used as building blocks for future electronic devices. These 'nanodumbbells', which are shaped like mini-weightlifting bars, will apparently solve two nanotechnological problems: assembling billions of nanocrystals into a single integrated electrical circuit; and provide good electrical contact. And they will be used to create self-assembling chain structures of nanocrystals. [Additional note, totally unrelated to the scientific content: there is not a single reference to 'nanodumbbells' by Google, at least right now when I'm typing this.]

"Nanodumbbells" -- 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 Jerusalem.
The technology, developed by a research group headed by Prof. Uri Banin of the Department of Physical Chemistry and the Center for Nanoscience and Nanotechnology of the Hebrew University, is described in an article in the current issue of Science magazine (see below).

First, what problem are these researchers trying to solve?

The challenge that lies ahead in adapting these nanocrystals to real-world application lies in wiring them to operate in electronic circuits. How, in the manufacturing process, will it be possible to join billions of them together and incorporate them into a single, integrated, electrical circuit? Another problem is that of establishing good electrical contact in order to ensure speedy and faultless channels of communication.

Here is the solution devised by Barin and his team.

The new technology developed by Prof. Banin and his team provides the solution to these two limiting problems. They succeeded in attaching gold tips onto nanorods by a simple chemical reaction. The resultant structure resembles a nanodumbbell, in which the central, nanocrystal, semiconductor part of the rod is linked via a strong chemical bond to the gold tips. These nanodumbbells provide strong chemical bonds between the gold and the semiconductor, leading to good electrical connectivity. This provides the path towards solving the problem of wiring the nanocrystals intro electrical circuitry.

Below are pictures of 29x4 nanometers quantum rods before (left) and after gold growth (right). "The presence of the high-contrast tips on the treated rods, forming nanodumbbells, is evident."

Quantum rods before and after gold growth

[Note: the above images and legend are extracted from online material provided by Science (PDF format, 8 pages, 1.68 MB) and belongs to the Hebrew University of Jerusalem.]

What is a possible future for these 'nanodumbbells'?

By adding to the nanodumbbell solution specific "linker" molecules, the gold tips are attracted to each other, thus creating self-assembling chain structures of nanocrystals, linked end-to-end. This strategy can serve as the basis for future manufacturing that will connect billions of nanorods to nanoelectronic circuitry. It is also possible to create other shapes, such as tetrapods, in which four arms expand from a central unit, making gold-tipped "anchor" points for different forms of self-assembly and wiring.

As mentioned above, the research work is described in the June 18, 2004 issue of Science under the name "Selective Growth of Metal Tips onto Semiconductor Quantum Rods and Tetrapods." Here is a link to the abstract.

We show the anisotropic selective growth of gold tips onto semiconductor (cadmium selenide) nanorods and tetrapods by a simple reaction. The size of the gold tips can be controlled by the concentration of the starting materials. The new nanostructures display modified optical properties caused by the strong coupling between the gold and semiconductor parts. The gold tips show increased conductivity as well as selective chemical affinity for forming self-assembled chains of rods. Such gold-tipped nanostructures provide natural contact points for self-assembly and for electrical devices and can solve the difficult problem of contacting colloidal nanorods and tetrapods to the external world.

Sources: Hebrew University of Jerusalem, June 17, 2004, via EurekAlert!; Science, Vol. 304, Issue 5678, Pages 1787-1790, June 18, 2004

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