Chains of Individual Gold Atoms

Chains of individual gold atoms exhibit bonds that are about twice as strong as bonds between atoms in bulk gold, according to the quantum theory. Now researchers have directly measured the strength of gold chains, as well as other mechanical properties, by stretching strings of the precious atoms between two scanning tunneling microscope (STM) probes (also see Update 455).

In a collaboration between researchers from the Universidad Autónoma in Madrid and the Technical University of Denmark in Lyngby, Gabino Rubio-Bollinger, Karsten Jacobsen (kwj@fysik.dtu.dk, 011-4545-253186), and colleagues drew chains of up to seven atoms out of gold electrodes. By monitoring the conductance of the chains and the tension between the STM probes, the researchers could observe chain growth as atoms popped out of the electrodes at one end or the other and joined the atomic strand, until the chains finally broke under the strain (see figure at Physics News Graphics).

In addition to confirming theoretical predictions of bond strengths, the study shows that the atomic chains have electrical conductance very close to the smallest value permitted by quantum mechanics, and that the side-to-side chain stiffness is strongly affected by the atomic arrangement at the locations where they are anchored to the electrodes.

While it's not yet clear that gold atom chains will have any practical use, the study is an example of engineering analysis on the very smallest scale. As technologies at tiny dimensions progress toward practical micro- and nano-sized devices, such mechanical tests will become crucial to developing minuscule structures consisting of small numbers of molecules or atoms. (G. Rubio-Bollinger et al, Physical Review Letters, 9 July 2001; text at Physics News Select.)

Physics News Graphics