Pinpoint splitting of molecules.
Each decaborane molecule consists of 10 boron atoms and 14 hydrogen atoms. When deposited on a silicon surface and viewed with a scanning tunneling microscope, these molecules appear as rounded, elongated protrusions about 7 angstroms across. Warming up the coated silicon slab frees these molecules, and they tend to migrate to certain irregularities in the otherwise orderly arrangement of silicon atoms at the slab's surface. The molecules break apart at these defects, and boron atoms slip into the silicon structure.
Instead of heating up the entire crystal to produce borondoped silicon, Avouris and his team selectively excite individual decaborane molecules to dope only small, specific regions of the silicon surface. They use a scanning tunneling microscope to locate the surface-hugging molecules. Then, by carefully readjusting the voltage applied to the microscope's tip, they send a pulse of electrons of just the right energy to excite a particular molecule, which dissociates.
Avouris suggests that the same procedure could be used for controlling surface chemistry on a molecular scale in a variety of situations.
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|Title Annotation:||use of scanning tunneling microscope|
|Article Type:||Brief Article|
|Date:||Mar 28, 1992|
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