Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Electronic Structure of Single Wall Carbon Nanot ubes With Vacancy Defect
Gülay Dereli 1 *, 1 , Necati Vardar 1
1 Department of Physics, Yildiz Technical University, 34210, Turkey
Abstract-Electronic structure of (12,0) and (14,0) single wall carbon nanotubes (SWCNT) with vacancy defect are studied using Order (N) Tight
Binding Molecular Dynamics simulation method (O(N) TBMD) [1-3]. We have obtained the total energy per atom and Fermi energy levels of
(12,0) and (14,0) SWCNTs with vacancy defect. The effect of vacancy defects on the electronic band gap is investigated in real space. Change of
the electronic band gap values are discussed.
An important property of carbon nanotubes is that SWCNT
can be either metallic or semiconducting depending on the
geometrical structure. Geometrical structure of SWCNT is
given by the chiral vector ( ). The armchair
SWCNTs ( ) are metallic, and the zigzag SWCNTS
( ) are only metallic when n is a mu ltiple of 3.
SWCNTs may have various kinds of defects such as vacancy,
either during their growth or when they are part of an
electronic circuit. Defects may influence the physical
properties of SWCNTs. Theoretical calculations have shown
that vacancy defects in SWCNTs can substantially modify their
electronic properties [4-12].
In this study, energetic and electronic structures of (12,0) and
(14,0) SWCNTs with multi-vacancy defects are studied using
order (N) tight binding molecular dynamic (O(N) TBMD)
simulation code designed by Dereli et al [1-3] and applied to
nanotube simulations successfully [13-16]. We simulated
(12,0) metallic and (14,0) semiconducting SWCNTs with multi
vacancy defect . We calculated the total energy per atom and
the Fermi energy levels during the simulation .
(a)
eDOS
1,0
nvac=0
(12,0)
0,8
0,6
0,4
0,2
0,0
-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0
1,0
0,8
0,6
0,4
0,2
0,0
-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0
1,0
0,8
0,6
0,4
0,2
nvac=0+1
nvac=0+2
0,0
-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0
Energy (eV)
DOS
1,0
0,8
0,6
0,4
0,2
0,0
-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0
1,0
0,8
0,6
0,4
0,2
0,0
-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0
1,0
0,8
0,6
0,4
0,2
nvac=0 (14,0)
nvac=1
nvac=4
0,0
-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0
Energy (eV)
Figure 2. Electronic density of states of (12,0) and (14,0) SWCNTs
with vacancies.
Our studies have shown that the vacancy defects can
effectively change the energetics and hence the electronic
structure of SWCNTs.
The research reported here is supported through the Yildiz
Technical University Research Fund Project No: 24-01-01-04.
The simulations are performed at the Carbon Nanotubes
Simulation Laboratory at the Department of Physics, Yildiz
Technical University, Istanbul, Turkey.
*Corresponding author: gdereli@yildiz.edu.tr
(b)
Figure 1. a) (12,0) b) (14,0) SWCNTs with vacancy defect
We showed that the total energy values increase with the
number of vacancies and the Fermi energy levels decrease.
The effects of multi vacancy defects on the electronic band gap
are given in figure2. Band gap is obtained in real space through
the behavior of electronic density of states (eDOS) near the
Fermi level . The band gap of (12,0) SWCNT increases from
0.01 eV (perfect CNT) to 0.07eV for one vacancy and 0.13
eV for two vacancies. For (14,0) SWCNT, band gap rapidly
decreases from 0.55eV to 0.09 eV for one vacancy and
semiconductor-metal transition occurs.
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6th Nanoscience and Nanotechnology Conference, zmir, 2010 401