IMAGINE a machine that can assemble an object atom by atom. That may be a step closer with the demonstration of electrons moving like a 鈥渜uantum submarine鈥� inside a material.
Manipulating atoms directly is a major goal of nanotechnology, but remains a long way off. The best that has been achieved so far is to push individual atoms around using a scanning tunnelling microscope (STM), a device which can obtain images at the atomic scale using electrons emitted from a stylus just one atom wide at its tip.
Now Richard Palmer, Peter Sloan and Sumet Sakulsermsuk of the University of Birmingham, UK, have demonstrated an indirect but potentially more efficient way of manipulating atoms. They placed an STM stylus just above a tiny pit in the surface of a silicon wafer, causing electrons from the tip to burrow down and travel as a quantum wave within the material, avoiding surface defects that would otherwise obstruct them (see diagram). 鈥淚 call it a submarine,鈥� says Palmer.
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The electrons were able to break the chemical bonds holding chlorobenzene molecules to the silicon surface up to 10 nanometres from the tip (Physical Review Letters, ). Being able to drive off these molecules could be the first step to manipulating atoms on the surface. Palmer says the technique could lead to a new way of manufacturing, in which a silicon wafer is patterned with numerous pits or other features where electrons could be injected, and an array of STM tips is used to manipulate many atoms at a time spread over a large distance.
鈥淎 silicon wafer could have numerous pits where electrons can be injected, manipulating many atoms鈥�
Philip Moriarty of the University of Nottingham, UK, says the result is an excellent piece of fundamental science, but points out that the electrons travel in all directions from the stylus tip and cannot be directed to influence specific atoms. He and his colleagues are working instead on creating and breaking single chemical bonds directly with an atomic force microscope, which is normally used to measure interatomic forces.
Meanwhile, a group led by Damien Riedel of the University of Paris-South in France has reported using an STM to control the rate of motion of a hydrogen atom on a silicon surface. Their method works up to 2.4 nanometres away from the tip (Physical Review Letters, ).
