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Analytical Chemistry

Controlling Charge At The Atomic Level

Surface patterning selectively alters the charge state of silicon atoms, which could help improve electronic devices

by Mitch Jacoby
January 3, 2011 | APPEARED IN VOLUME 89, ISSUE 1

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Credit: Jason Pitters
The presence of a TiSi2 island (red) causes silicon atoms to appear bright in this STM image (white arrow); otherwise they would appear as faint spots (black arrow).
Credit: Jason Pitters
The presence of a TiSi2 island (red) causes silicon atoms to appear bright in this STM image (white arrow); otherwise they would appear as faint spots (black arrow).

The charge state of individual silicon atoms deposited on a surface can be selectively controlled via nanoscale contacts, according to researchers at Canada’s National Institute for Nanotechnology. The results of the investigation show that a sometimes worrisome silicon surface phenomenon that can hamper the performance of electronic devices can instead be exploited to advance atomic-scale circuitry. Jason L. Pitters explained that unsatisfied electron valencies on silicon atoms—so-called dangling bonds—can dictate the chemical and electronic properties of silicon-based nanostructures. For that reason, researchers would like to be able to control the dangling-bond charge state, which can be positive, neutral, or negative, depending on the number of electrons associated with the dangling bond. By decorating a silicon surface with nanoscale TiSi2 islands, Pitters and coworkers altered silicon’s surface potential and caused a depletion of electrons in the nearest silicon atoms, thereby changing the occupancy of the dangling bonds on those atoms. The team detected the change via scanning tunneling microscopy, which revealed that atoms closest to the islands appeared as bright protrusions, indicating that those atoms’ dangling bonds are uncharged. In contrast, nearly all other atoms on the silicon surface appeared as dark spots, signifying negatively charged dangling bonds.

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