Forcing the Details of Contact Charging

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Forcing the details of contact charging

When two different surfaces are brought into contact and then separated from each other, they often end up oppositely charged. Such electrostatic charging occurs when balloons rub against sweaters, shoes shuffle across carpets and toner particles in photocopiers bump into carrier beads. Now, with the aid of a novel instrument for pinpointing the location of small amounts of excess charge on an insulating surface, researchers are getting their best look yet at what happens during contact electrification.

Despite its everyday occurrence and technological importance, contact electrification has long mystified scientists. The main questions concern whether two materials in contact exchange electrons, ions or charged bits of material and precisely where those mobile charges end up when the materials are separated.

"If it were possible to identify such sites with near-atomic resolution, then a deeper understanding of the [contact] electrification process might result," Bruce D. Terris and his colleagues at the IBM Almaden Research Center in San Jose, Calif., write in the Dec. 11 PHYSICAL REVIEW LETTERS.

To locate charges deposited by a single contact between a metal and an insulator, Terris and his group use a specially modified force microscope. …