(July 23, 2015) Semiconductors,
metals and insulators must be integrated to make the transistors that are the
electronic building blocks of your smartphone, computer and other
microchip-enabled devices. Today’s transistors are miniscule—a mere 10
nanometers wide—and formed from three-dimensional (3D) crystals.
But a disruptive new technology looms that uses
two-dimensional (2D) crystals, just 1 nanometer thick, to enable ultrathin
electronics. Scientists worldwide are investigating 2D crystals made from
common layered materials to constrain electron transport within just two
dimensions. Researchers had previously found ways to lithographically pattern
single layers of carbon atoms called graphene into ribbon-like “wires” complete
with insulation provided by a similar layer of boron nitride. But until now
they have lacked synthesis and processing methods to lithographically pattern
junctions between two different semiconductors within a single nanometer-thick
layer to form transistors, the building blocks of ultrathin electronic devices.
Now for the first time, researchers at the Department of
Energy’s Oak Ridge National Laboratory have combined a novel synthesis process
with commercial electron-beam lithography techniques to produce arrays of
semiconductor junctions in arbitrary patterns within a single, nanometer-thick
semiconductor crystal. The process relies upon transforming patterned regions
of one existing, single-layer crystal into another. The researchers first grew
single, nanometer-thick layers of molybdenum diselenide crystals on substrates
and then deposited protective patterns of silicon oxide using standard
lithography techniques. Then they bombarded the exposed regions of the crystals
with a laser-generated beam of sulfur atoms. The sulfur atoms replaced the
selenium atoms in the crystals to form molybdenum disulfide, which has a nearly
identical crystal structure. The two semiconductor crystals formed sharp
junctions, the desired building blocks of electronics. Nature Communications
reports the accomplishment.