Electronic structures, field effect transistor
and bipolar field-effect spin filtering behaviors
of functionalized hexagonal graphene nanoflakes
J. Li, Z.H. Zhang
*
, D. Wang, Z. Zhu, Z.Q . Fan, G.P. Tang, X.Q. Deng
Institute of Nanomaterial & Nanostructure, Changsha University of Science and Technology, Changsha 410114, China
ARTICLE INFO
Article history:
Received 4 September 2013
Accepted 30 November 2013
Available online 8 December 2013
ABSTRACT
We report first-principles calculations on the electronic properties, spin magnetism, and
potential applications of the functionalized hexagonal armchair graphene nanoflakes
(GNFs). It is found that the gap of the GNF changes in an obvious oscillating manner with
the size of its hexagonal defect (antidot), and when the antidot is large enough, it will lead
to a prominent splitting of the a-spin and b-spin orbitals and the intriguing property of
bipolar magnetic semiconductors for the GNF. And also shown is that the electronic struc-
tures of the GNF can be tuned from semiconducting to metallic properties by different edge
modifications. More importantly, based on the suitable hexagonal defective GNFs, we
design a field effect transistor (FET) and a bipolar field-effect spin-filtering (BFESF) device,
and find that they all exhibit extremely high performances. For this FET, its ON/OFF ratio
reaches 10
5
, subthreshold swing 90 meV per decade, and the transconductance
10
3
S/m, and for this BFESF device, the spin polarization nearly reaches 100% with differ-
ent spin directions only by altering signs of gate voltages.
2013 Elsevier Ltd. All rights reserved.
1. Introduction
Since its successful experimental fabrication, graphene [1],a
new class of materials in the carbon family [2], has attracted
tremendous research interest due to its unique material
properties and promising applications in nanoelectronics.
So far, lots of experimental and theoretical breakthroughs
have been made on two-dimensional graphene [1,3,4].How-
ever, graphene can also be cut into other various shapes
and sizes by different techniques [5], such as 1D graphene
nanoribbons(GNRs) [6,7]. graphene quantum dots [8,9], quan-
tum ring [10,11], and quantum antidot arrys [12,13], further
opening the door to develop graphene-based nanodevices.
Among these nanodevices, the field effect transistor (FET) is
one of the most important and fundamental components in
future integrated circuits. Currently, some works have been
made on it [2,14–18]. But their ON/OFF ratios are still lower,
and other parameters are not desirable as well, which seri-
ously restricts its realistic applications.
Hexagonal graphene nanoflakes (GNFs), a class of particu-
lar graphene quantum dots with a 6-fold rotational symmetry,
are a new research focus, and related several works have been
presented [19–22]. For instance, the synthesis on the copper
surface [19], the comparative study on the energy levels
between the tight-binding model and Dirac equation ap-
proach [20], the magnetic levels and optical properties with
the external magnetic field [21], and the electronic shell struc-
ture near the Fermi level [22]. However, these studies are still
very preliminary. Their outstanding electronic structures,
especially for their various functionalized features and re-
lated application potentials, such as effects of switch, transis-
tor, rectifier, and spin filter, need to be explored further.
Recent progresses in fabricating and characterizing stable
graphene nanostructures also provides the opportunity to
0008-6223/$ - see front matter 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.carbon.2013.11.076
* Corresponding author: Fax: +86 073185040376.
E-mail address: lgzzhang@sohu.com (Z.H. Zhang).
CARBON 69 (2014) 142– 150
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