| After several years of concerted
efforts, NIST researchers have succeeded in producing the world's most
accurate electron counter. An outgrowth of NIST's work to find better
ways to determine capacitance (a measure of a capacitor's charge-holding
ability), the counter can place 70 million electrons on a capacitor
with an uncertainty of just one electron. The heart of the counter is
special microcircuit that "pumps" electrons one at a time
to a capacitor. In the atomic force micrograph above, the bullet-shaped
regions in the center are micrometer-sized islands of aluminum, separated
by tiny "tunnel junctions of aluminum oxide (yellow dots). The
capacitance of the islands is so small that at temperatures near absolute
zero (less than 0.1 kelvin) only one excess electron can occupy a given
island at a time. |
