Progress Towards Greater Atomically Precise Manipulation

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Richard Palmer, Peter Sloan and Sumet Sakulsermsuk of the University of Birmingham, UK, have demonstrated using electrons to break the chemical bonds holding chlorobenzene molecules to the silicon surface up to 10 nanometres from the tip. They placing an STM (scanning tunneling microscope) 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.

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.

Moriarty has a five year project to experimentally test the computational chemistry work of Robert Freitas and Ralph Merkle on basic capabilities with molecular tooltips. The experimental work takes time to set up with practical difficulties of getting a molecularly perfect diamond surface.

Physical Review Letters – Nonlocal Desorption of Chlorobenzene Molecules from the Si(111)-(7×7) Surface by Charge Injection from the Tip of a Scanning Tunneling Microscope: Remote Control of Atomic Manipulation

We report the nonlocal desorption of chlorobenzene molecules from the Si(111)-(7×7) surface by charge injection from the laterally distant tip of a scanning tunneling microscope and demonstrate remote control of the manipulation process by precise selection of the atomic site for injection. Nonlocal desorption decays exponentially as a function of radial distance (decay length ∼100  Å) from the injection site. Electron injection at corner-hole and faulted middle adatoms sites couples preferentially to the desorption of distant adsorbate molecules. Molecules on the faulted half of the unit cell desorb with higher probability than those on the unfaulted half.

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

Physical Review Letters – Nonlocal Activation of a Bistable Atom through a Surface State Charge-Transfer Process on Si(100)-(2×1):H

The reversible hopping of a bistable atom on the Si(100)-(2×1):H surface is activated nonlocally by hole injection into Si-Si bond surface states with a low temperature (5 K) scanning tunneling microscope. In the contact region, at short distances (< 1.5  nm) between the hole injection site and the bistable atom, the hopping yield of the bistable atom exhibits remarkable variations as a function of the hole injection site. It is explained by the density of state distribution along the silicon bond network that shows charge-transfer pathways between the injection sites and the bistable atom.

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