September 2003, Marc S. Lavine,
Science Editor's Choice
nanoparticles from the liquid and gas phases using
created in a three-step process. First, light reflected from
the white parts of the original is focused onto a charged
printing "drum," where it locally dissipates charge. Next,
positively charged toner particles are attracted to the
remaining charged areas that were dark in the original.
Finally, paper is run over the drum to pick up the toner.
Barry et al. use similar steps to create a nanoxerographic
process that can pattern very small carbon and metal particles
with a resolution about 1000 times better than that of a
typical photocopier. A silicon wafer was coated with either
silicon dioxide or poly(methylmethacrylate) as the electret,
which corresponds to the charged drum in the photocopier. A
pattern was transferred from a stamped or lithographed master
by bringing the two together and applying an external voltage.
In a liquid-phase process, the charged electret and an
aggregate of carbon or iron particles were both placed in a
solvent and sonicated. Within a few seconds, the aggregate was
broken up and the nanometer-sized particles assembled onto the
electret. A gas-phase process was also tested in which
particles were generated in a furnace and directed by an
electric field toward the charged electret. The process is
partially limited by the resolution of the master, but 100-
and 200-nanometer features sizes were achieved for the gas-
and liquid-phase processes, respectively.
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