Smaller and more energy-efficient electronic chips could be made using molybdenite. Image: EPFL |
A
discovery made at EPFL could play an important role in electronics,
allowing us to make transistors that are smaller and more energy
efficient. Research carried out in École polytechnique fédérale de
Lausanne’s Laboratory of Nanoscale Electronics and Structures (LANES)
has revealed that molybdenite, or MoS2, is a very effective
semiconductor. This mineral, which is abundant in nature, is often used
as an element in steel alloys or as an additive in lubricants. But it
had not yet been extensively studied for use in electronics.
100,000 times less energy
“It’s
a two-dimensional material, very thin and easy to use in
nanotechnology. It has real potential in the fabrication of very small
transistors, light-emitting diodes (LEDs) and solar cells,” says EPFL
Professor Andras Kis, whose LANES colleagues M. Radisavljevic, Prof.
Radenovic et M. Brivio worked with him on the study. He compares its
advantages with two other materials: silicon, currently the primary
component used in electronic and computer chips, and graphene, whose
discovery in 2004 earned University of Manchester physicists André Geim
and Konstantin Novoselov the 2010 Nobel Prize in Physics.
One
of molybdenite’s advantages is that it is less voluminous that silicon,
which is a three-dimensional material. “In a 0.65-nanometer-thick sheet
of MoS2, the electrons can move around as easily as in a
2-nanometer-thick sheet of silicon,” explains Kis. “But it’s not
currently possible to fabricate a sheet of silicon as thin as a
monolayer sheet of MoS2.” Another advantage of molybdenite is that it
can be used to make transistors that consume 100,000 times less energy
in standby state than traditional silicon transistors. A semi-conductor
with a “gap” must be used to turn a transistor on and off, and
molybdenite’s 1.8 electron-volt gap is ideal for this purpose.
Better than graphene
In
solid-state physics, band theory is a way of representing the energy of
electrons in a given material. In semi-conductors, electron-free spaces
exist between these bands, the so-called “band gaps.” If the gap is not
too small or too large, certain electrons can hop across the gap. It
thus offers a greater level of control over the electrical behavior of
the material, which can be turned on and off easily.
The
existence of this gap in molybdenite also gives it an advantage over
graphene. Considered today by many scientists as the electronics
material of the future, the “semi-metal” graphene doesn’t have a gap,
and it is very difficult to artificially reproduce one in the material.
