Golden goal

Gold wires just one atom thick and connected to a single molecule are the goal for a team of European researchers. They are laying the foundations for faster, smaller computers based on molecular-scale structures.

They have already broken new ground by obtaining direct images of the orbital reorganisation that takes place when a gold atom and a pentacene molecule form a complex on a surface. The team is led by scientists at IBM’s Zurich Research Lab and includes LiverpoolUniversity’s Prof Mats Persson, with others from Finland and Sweden.

‘There will come a time when electronic material will become so small that we will need to control the structure down to the atomic scale and the chemical bonds between single molecules and atoms,’ said Persson. ‘The atomic scale control of single-molecule chemistry in this experiment opens up new perspectives in the emerging field of molecular electronics, particularly in connecting organic molecules with electronic components. This could be important in creating electronics for future computers which are faster, smaller and have less power consumption.’

By using a scanning tunnelling microscope (STM), the team demonstrated that it is not only possible to control the atomic-scale geometry of a metal-molecule contact but also its coupling strength and the phase of the orbital wave function at the contact point. ‘We can take an image of the molecular orbitals before and after bond formation and thus directly see the changes in shape, energetic position, and occupation of the orbitals,’ said IBM’s Jascha Repp. ‘One can take the complex apart again, attach the gold atom in a different position, and have a look at the new orbitals.’

‘In this way, within the general limitations of chemistry, one can engineer the orbital structure of molecules, and create different kinds of contacts between, in our case, a gold atom and a pentacene molecule,’ said IBM scientist Gerhard Meyer.

With the continuing trend to ever-smaller electronic building blocks, the amount of control in terms of precise geometry and even of the phase of the electronic wave functions, will become crucial. ‘Eventually chip dimensions might be so small that interference effects will become important,’ said Rolf Allenspach, head of IBM’s nanoscale research. ‘So one needs to understand and exploit them.’