Molecular Assembly in a Nanotechnology Laboratory

By Earl Boysen, Nancy C. Muir, Desiree Dudley, Christine Peterson

When researchers can move atoms around, the potential for manufacturing at the nano level gets really interesting. After researchers demonstrated the ability to move atoms, the next logical step was toward creating the molecular assemblers used in atomically precise assembly.

To begin to create molecular assemblers, you adapt scanning tunneling microscopes (STMs) or atomic force microscopes (AFMs) to add atoms or molecules to a surface, which allows you to construct a structure atom by atom or molecule by molecule. Depositing two carbon atoms on a diamond surface is an example of molecular assembly.

Depositing carbon atoms in a molecular assembly process. [Credit: Image © 2004 Robert A. Freit

Credit: Image © 2004 Robert A. Freitas Jr. All Rights Reserved
Depositing carbon atoms in a molecular assembly process.

One of the key issues in designing a tip used in molecular assembly is to get the chemistry right so that the atoms you want to deposit on a target bond to the tip initially and then release from the tip at the target location and bond to target atoms.

Robert Freitas, a researcher in molecular manufacturing and nanomedicine, suggests that the atoms on a tip that are bonded to carbon atoms be made of a substance such as germanium or tin. These substances form relatively weak covalent bonds with carbon.

When the tip delivers the carbon atoms to the surface, the atoms form covalent bonds with nearby carbon atoms on the surface (in Freitas’ research, he uses a diamond surface). This carbon-to-carbon covalent bond is much stronger than the covalent bond to atoms on the tip. As a result, when you pull away the tip, the carbon atoms stay in place on the surface.

Researchers are planning to build molecular assemblers that can use techniques such as the one just discussed to build objects atom by atom or molecule by molecule. Freitas received a patent in 2010 covering methods to build the type of tool tip that would be used in molecular assemblers, but it will probably be a while before this kind of assembly becomes a reality.