What is it?
• Silicene is a two dimensional material that consists
entirely of Silicon atoms arranged in a lattice just
one atom thick.
• It was first theorised in 1994, but only recently
has it started to generate more interest for use in
transistors.
SILICON
(Si)
Silicene as viewed using
a Scanning Tunnelling
Microscope
Atomic number: 14
Electron Structure: 1s22s22p63s23p2
The structure
•
It is usually created by condensation of Silicon
vapour onto a Silver substrate.
• 4 valence electrons across two electron subshells with
capacities of 2 and 6 means that this substance will
be chemically eager to lose 2 electrons in order to
return to a stable state (one full, and one empty
subshell).
Comparison of two
similar, but altogether
different
nanostructures;
Graphene and Silicene.
• The structure is monocrystalline; which is a periodic
layout that repeats throughout the material. It has
also been observed to have a corrugated surface
(whereas Graphene is completely flat).
• The structure consists of covalent bonds - much like
the Silicon crystal on which it is based, with three
bonds to each atom.
What are its properties, and why is it potentially so fantastic?
• Potentially highly conductive; less obstruction for the electrons means higher propagation speed and
therefore higher conductivity than bulk silicon. This could allow extremely fast transistors to be built.
• Has a bandgap; which means that if a certain amount of energy is applied to the atoms, then some of
the aforementioned valence electrons can be freed from the valence band and move to the conduction
band. This allows inherent semiconductor behaviour, and is a key advantage over Graphene.
• The use of Silicon makes this material compatible with the current Silicon based electronics industry,
as opposed to Graphene which would require new production methods and tooling in order to adopt
Carbon as a large scale material in the consumer electronics industry.
• The sparing use of Silicon gives this material the potential to be extremely efficient, and – once initial
development costs are met – cheap. After all, Silicon is second only to Oxygen in being the most
abundant element in the Earth’s crust.
Major obstacles to commercialisation
• Silicene has not yet been created in freestanding form! It has, however, been created by condensing
vaporised Silicon onto a Silver substrate. But, the conductivity of the silver substrate means that
the electrical characteristics of the Silicene are greatly altered, so that it cannot realistically be
used for electronic circuits in that form.
• Once created, it has a strong tendency to fold over into normal amorphous Silicon. Furthermore, it is
reactive with oxygen (and a great many other substances!), meaning that it is only stable in a vacuum.
The
nanostructure
of Silicene is
very unstable,
and will readily
destroy itself.
What next?
• Silicene needs to be created on an insulating substrate (or in freestanding form) in order for the
electrical properties to be unaffected. The substrate could help the Silicene to remain stable.
• The relative ease of working with Silicon means that Silicene may be more readily adopted in the
near future, being much easier than Graphene to commercialise with the current tooling. However,
Graphene could replace it in the near future if the electronics industry adopts Carbon as a large
scale consumer electronics building material.
• Silicene’s instability in a vacuum is an obstacle to commercialisation, but not an insurmountable one.
Evacuated chips could allow Silicene to exist in a stable state in a product.
• However, the instability of Silicene could be the deciding factor in the choice between Graphene and
Silicene. It is possible that the instability of Silicene will limit it to uses where vibrational shock and
movement are not a large factor e.g. supercomputers.
Hot off the press…
• A Silicene
transistor has been
created by a group
of scientists in
Italy! (Article
published
02/02/15)
The experimental process for building a Silicene transistor.
References
Boyle, R. (2012, May 1). Meet Silicene, single-atom-thick sheets of silicon that could supersede graphene Popular
Science Retrieved February 9, 2015 from http://www.popsci.com/technology/article/2012-05/meet-silicene-singleatom-thick-sheets-silicon-could-supersede-graphene
Breaux, J (2014, July 24). Silicene: To be or not to be? Argonne National Laboratory Retrieved February 9, 2015
from http://www.anl.gov/articles/silicene-be-or-not-be
Callister, WD Jnr. & Rethwisch, DG. (2008) Fundamentals of Materials Science and Engineering. John Wiley & Sons,
(Asia) Pte. Ltd.
Johnson, D. (2014, January 15). Study Shows Silicene Has 'Suicidal Tendencies‘ IEEE Spectrum Retrieved February 9,
2015 from http://spectrum.ieee.org/nanoclast/semiconductors/materials/silicene-suicidal-tendencies-research
National Institute for Materials Science. (2015, January 12). Wonder material silicene still stands just out of
reach. ScienceDaily. Retrieved February 9, 2015 from www.sciencedaily.com/releases/2015/01/150112181001.htm
Takeda, K. & Shiraishi, K. (1994, July 12). Theoretical possibility of stage corrugation in Si and Ge
analogs of graphite. PHYSICAL REVIEW 8. Retrieved February 18, 2015 from
http://journals.aps.org/prb/pdf/10.1103/PhysRevB.50.14916
Various (2013) Buckled Silicene Formation on Ir(111) NANO Letters Retrieved February 9, 2015
from
http://www.cas.ac.cn/ky/kyjz/201306/P020130624821753209831.pdf
Various (2015, February 2) Silicene field-effect transistors operating at room temperature
Nature Nanotechnology Retrieved February 9, 2015 from
http://www.nature.com/articles/nnano.2014.325.epdf?referrer_access_token=9lMobFWCZndC
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