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A comparative study of the interaction of nickel, titanium, palladium, and
gold metals with single-walled carbon nanotubes: A DFT approach
Article  in  Results in Physics · February 2019
DOI: 10.1016/j.rinp.2019.02.062
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Results in Physics 12 (2019) 2100–2106
Contents lists available at ScienceDirect
Results in Physics
journal homepage: www.elsevier.com/locate/rinp
A comparative study of the interaction of nickel, titanium, palladium, and T
gold metals with single-walled carbon nanotubes: A DFT approach
K.W. Kayanga, E. Nyanksona, J.K. Efavia, V.A. Apalangyab, B.I. Adetunjic, G. Gebreyesusd, R. Tiae,
E.K.K. Abavaref, B. Onwona-Agyemana, A. Yayaa,⁎
a Department of Materials Science and Engineering, CBAS, University of Ghana, Ghana
bDepartment of Food Process Engineering, CBAS, University of Ghana, Ghana
c Department of Physical Sciences, Bells University of Technology, Ota, Nigeria
dDepartment of Physics, CBAS, University of Ghana, Ghana
e Department of Chemistry, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
fDepartment of Physics, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
A R T I C L E I N F O A B S T R A C T
Keywords: Interactions between transition metal atoms, nickel, titanium, palladium and gold and (3,3), (4,2), (6,0) and
Carbon nanotubes (5,1) carbon nanotubes were studied using first principles calculations. The Fermi energy levels of the carbon
Density Functional Theory nanotubes studied were found to increase during interactions with the transition metal atoms. Amongst the four
Transition metals metals, gold atom was found to have an enhanced interaction with the nanotubes transforming from semi-
Fermi energy level conducting to a conducting tube. Titanium was also found to show similar characteristics to gold only when the
atom was placed in the middle of the carbon nanotubes. Nickel and palladium atoms interactions did not affect
much the electronic properties of the carbon nanotubes, with some slight changes in the electronic properties at
some specific sites of the nanotubes. It is proposed from this study that, the carbon nanotube-metal interactions
could be used as a guide to shed light on the electronic properties of such materials which could become pro-
mising engineering materials and revolutionize the electronic industry.
Introduction Studies on carbon nanotubes do not end with just the pristine
models; recent research work carried out shows that carbon nanotubes
The ongoing quest to miniaturize electronic devices in an effort to exhibit even better properties when interacted with metal atoms [6,7].
make life simpler has posed the materials science community with A myriad of potential applications include catalytic sensors, fabrication
newer challenges each and every day. In an attempt to solve the pro- of nanostructures, nanoelectronics [8], nano-electro mechanical sys-
blem of integration of nanoscale components on an integrated circuit, tems (NEMS) and spintronics [6] have been proposed. It is also reported
scientists have resorted to Carbon Nanotubes (CNT) [1,2]. These carbon [9] that, CNT-metal interactions are essential in the formation of na-
nanotubes have been one of the major materials under consideration in nowires and by continuously coating the sidewalls of these carbon
the field of nanoelectronics, attracting a lot of attention due to their nanotubes with metals atoms, metallic or superconducting [10] nano-
unique electrical [3], thermal, physical and mechanical properties. wires could be obtained.
Depending on their chirality and size of diameter, there exists a vast An in-depth knowledge and understanding of how CNT-metal in-
number of distinct carbon nanotubes with different electronic proper- teractions alter the electronic properties of pristine carbon nanotubes
ties [4]. Semiconducting carbon nanotubes with small band gaps can be would prove beneficial to the scientific community and the electronics
applied in CNT-based transistors while metallic semiconductors are industry [11,12]. For example, different carbon nanotubes each pos-
useful in interconnect systems [5]. sessing different electronic properties could be engineered to have si-
⁎ Corresponding author.
E-mail address: ayaya@ug.edu.gh (A. Yaya).
https://doi.org/10.1016/j.rinp.2019.02.062
Received 11 September 2018; Received in revised form 1 February 2019; Accepted 18 February 2019
Available online 20 February 2019
2211-3797/ © 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license 
(http://creativecommons.org/licenses/BY-NC-ND/4.0/).
K.W. Kayang, et al. Results in Physics 12 (2019) 2100–2106
Table 1 Table 2
Properties of pristine CNT data. Adsorption data of CNTs.
Carbon Electronic property Size of Number of Chirality Bang Carbon Adsorption Fermi energy of Range of Fermi
nanotube diameter atoms gap Nanotube concentration (%) pristine CNT energies upon
(Å) (eV) (eV) adsorption (eV)
(3,3) Metallic 4.01 48 Armchair − (3,3) 2.04 −2.22 −1.53 to −2.11
(4,2) Semiconductor 4.15 56 Chiral 0.04 (4,2) 1.75 −2.29 −1.09 to −2.01
(5,1) Metallic 4.32 124 Chiral − (5,1) 0.8 2.83 2.75 to 2.98
(6,0) Semiconductor 4.70 72 Zigzag 0.68 (6,0) 1.37 −2.11 −0.91 to −1.53
milar electronic properties [5]. Also, such knowledge would be useful the Local Density Approximation (LDA) as the exchange-correlation
in the fabrication of optimal CNT-based devices such as CNT-based field functional (XC). The plane-wave pseudopotential method and the ul-
effect transistors [7]. Therefore, the aim of this study is to investigate trasoft pseudopotential were employed in the calculations using the
and compare the electronic properties of nickel, palladium, titanium Quantum Espresso software version 5.3 [15]. The ultrasoft datasets
and gold when interacted with single-walled carbon nanotubes, (3,3), (Au.pbe-nd-rrkjus, C.pz-n-rrkjus_psl.0.1, Ni.pz-n-rrkjus_psl.0.1, Pd.pz-n-
(5,1), (6,0) and (4,2) using first principles calculations. rrkjus_psl.0.2.2 and Ti.pz-spn-rrkjus_psl.1.0.0) used were obtained from
the Quantum Espresso library [13]. The pseudopotential used for the
Model system gold had a valence electron configuration of 5d
106s1. That of titanium
and palladium were 3s23p63d24s2 and 5s0.54d9.5 respectively. Also, the
In this paper, four different carbon nanotubes, (3,3), (5,1), (6,0) and valence electron configuration for nickel and carbon potentials were2 8 2 2
(4,2) were built using the Virtual NanoLab (VNL 2017.1) software [13]. 4s 3d and 2s 2p respectively. The plane-wave cut-off energy was set
These carbon nanotubes were chosen because their theoretical dia- to 130 Rydberg and a Monkhorst-Pack k-point mesh of 1× 1×15 was
meters are in the range of 4 Å [14]. Details are provided in Table 1 chosen for self-consistent field calculations (SCF) and band structure
below. A total of sixteen (16) carbon nanotubes were built for each of calculations. For non-self-consistent field calculations (NSCF), density
the 4 different configurations of the carbon nanotubes in which the of states (DOS) and projected density of states calculations (PDOS), a
transition metal atoms; nickel, titanium, palladium and gold, were in- Monkhorst-Pack k-point grid of 2×2×30 was used. The charge
teracting with each of the carbon nanotube at different adsorption sites density of the carbon nanotube-metal models was also calculated using
on the carbon nanotube hexagonal ring to obtain 64 different CNT- the Xcrysden software, version 1.5.60. [16].
metal atom models. The transition metal atoms interacted with the
single walled carbon nanotubes via adsorption and doping. Adsorption
onto the carbon nanotube was done, with no replacement of the carbon Results and discussions
atoms, at three different sites. The first site was at the top left corner of
the carbon nanotube hexagonal ring, the second adsorption site was at Electronic properties
the bottom right corner of the hexagonal ring and the last site was in the
middle of the carbon nanotube as illustrated in Fig. 1. Adsorption studies
Four 3d transition metals, Au, Pd, Ti and Ni were considered to be
adsorbed onto each of the carbon nanotubes, (3,3), (4,2), (5,1) and
Computational methods (6,0) at three different sites as shown in Fig. 1. The C-Au bond length
was determined to be ∼2.20 Å. For Pd adsorption, the CePd bond
The ab initio calculations of the carbon nanotube-metal interactions length was determined as ∼2.15 Å while those of CeTi and CeNi bond
were performed using Density Functional Theory (DFT) method, with lengths were calculated as ∼2.13 Å and ∼1.97 Å, respectively. Table 2
Site 1 Site 2 Site 3 Doped 
Fig. 1. Different interaction sites for Gold (yellow) and Palladium (blue) metal atoms on a (5,1) CNT and (3,3) CNT. (For interpretation of the references to colour in
this figure legend, the reader is referred to the web version of this article.)
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K.W. Kayang, et al. Results in Physics 12 (2019) 2100–2106
Fig. 2. a- Band structure of a pristine (3,3) CNT, b- DOS of a pristine (3,3) CNT, c- Band structure of a pristine (4,2) CNT, d- DOS of a pristine (4,2) CNT, e- Band
structure of a pristine (5,1) CNT, f- DOS of a pristine (5,1) CNT, g- Band structure of a pristine (6,0) CNT, h- DOS of a pristine (6,0) CNT.
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K.W. Kayang, et al. Results in Physics 12 (2019) 2100–2106
Fig. 3. Where a- Band structure of a (3,3) CNT with Ni adsorbed at Site 2, b- PDOS of a (3,3) CNT with Ni adsorbed at Site 2, c- DOS of a (3,3) CNT with Ni adsorbed
at Site 2, d- Charge density plot for a (3,3) CNT with Ni adsorbed at Site 2.
below shows the adsorption data of the carbon nanotubes. From the A nickel atom adsorbed at site 2 on a (3,3) carbon nanotube
data below, it can be seen that the Fermi energies increased upon metal maintained its conducting nature as seen in the band structure diagram
adsorption implying that more states were added to the valence region in Fig. 3a. There was however an increase in the states in the valence
of the carbon nanotubes. band as shown in the PDOS and DOS graphs in Fig. 3b and Fig. 3c,
The electronic band structures, DOS, PDOS and charge densities of respectively. The low density of states at the Fermi level also indicated
the different carbon nanotube models at zero pressure and temperature, that the carbon nanotube has a weak metallicity. Furthermore, it can be
along high symmetry path of the Brillouin zone are presented in seen that the d-orbital of the nickel atom provided most of the con-
Figs. 3–5, in order to understand the electronic properties of the metal tribution to the overall density of states. The charge density plot
atom interacting with the nanotubes. Fig. 2 provides the band structure (Fig. 3d) shows a homogenous charge distribution between the nickel
and DOS for pristine carbon nanotubes, (3,3), (4,2), (5,1) and (6,0) atom and carbon atom signifying that a significant bonding took place.
respectively. From Figs. 3a, 4a and 5a with high symmetry Γ→ Z, it was When a titanium atom interacted with a (4,2) CNT in the middle, it
observed that the minimum conduction band and the maximum valence was observed that the electronic properties of the carbon nanotube
band intersected indicating that the carbon nanotube possessed metallic changed from semiconducting to metallic as shown in the band struc-
properties. The pristine carbon nanotubes (4,2) and (6,0) are semi- ture in Fig. 4a. The PDOS graph in Fig. 4b, indicates that the d-orbital of
conducting CNT as shown in Table 1. However, when they were in- titanium contributed significantly to the total density of states. The
teracting with Ti, and Au respectively, their properties changed from reason for this can be deduced from the charge density plot in Fig. 4d.
semiconducting to conducting. The plot shows a higher density of charges around the carbon atoms
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K.W. Kayang, et al. Results in Physics 12 (2019) 2100–2106
Fig. 4. Where a- Band structure of (4,2) CNT with Ti interacting at site 3, b- PDOS of (4,2) CNT with Ti interacting at Site 3, c- DOS of (4,2) CNT with Ti interacting at
Site 3, d- Charge density of (4,2) CNT with Ti interacting at Site 3.
than the titanium atom. This is apparently due to carbon being more a site specific interaction that will give an optimal energy. Once again,
electronegative than titanium. As a result, the carbon atoms drew more more states were added to the valence region resulting in the increase of
electrons to themselves. the Fermi energy.
In the case of the (5,1) CNT, when interacted with a palladium atom A (6,0) CNT doped with a gold atom modified the electronic prop-
at Site 1, the metallic properties of the carbon nanotube were main- erties to conducting as seen in the band structure diagram in Fig. 6a.
tained as seen in the band structure (Fig. 5a) and DOS (Fig. 5c). Al- The DOS graph (Fig. 6c) also indicated high densities of states in the
though the carbon nanotube displays conduction properties, there ap- valence band near the band gap and in the conduction band. A study of
pears to be very little contribution from the palladium orbitals to the the PDOS in Fig. 6b showed that the high density of state in the valence
total density of states as observed in Fig. 5b. This is as a result of very region was as a result of some contribution from the p and d orbitals of
weak coupling between the d- and s- orbitals of the palladium metal the gold atom whereas the s and p orbitals contributed to the high-
and that of the nanotube respectively. In terms of charge distribution, density states in the conduction bands. The charge density plot in
there is a uniform sharing between the palladium and carbon atoms as Fig. 6d also showed an excellent distribution between the gold and
seen in Fig. 5d. carbon atoms because of their very similar electronegativities.
Doping studies Conclusion
The four different carbon nanotubes were each doped with nickel,
palladium, titanium and gold as shown in Fig. 1. Table 3 displays the Employing density functional theory within the local density ap-
doped CNT data. This was done in order to understand whether there is proximation exchange-correlation functional, the electronic properties
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K.W. Kayang, et al. Results in Physics 12 (2019) 2100–2106
Fig. 5. Where a- Band structure of (5,1) CNT with Pd adsorbed at Site 1, b- Projected DOS of (5,1) CNT with Pd adsorbed at Site 1, c- DOS of (5,1) CNT with Pd
adsorbed at Site 1, d- Charge density of (5,1) CNT with Pd adsorbed at Site 1.
nanotubes to conducting irrespective of the interaction site. The tita-
Table 3 nium atom showed similar effects only when interacted in the middle of
Doped CNT data. the carbon nanotube. The electrical properties of the (5,1) carbon na-
Carbon Doping Fermi energy of Range of Fermi notube was not affected by any of the atom interactions due to a low
Nanotube concentrations (%) pristine CNT energies after adsorption and doping concentration.
(eV) doping (eV) The projected density of state plot indicated that the d-orbital of the
metal atoms was generally the highest contributor to increasing the
(3,3) 2.08 −2.22 −1.88 to −2.23
(4,2) 1.79 −2.29 −1.80 to −2.01 density of states in the carbon nanotubes except in the (5,1) carbon
(5,1) 0.81 2.83 2.76 to 2.82 nanotube where there was generally no contribution from the metal
(6,0) 1.39 −2.11 −1.09 to −1.30 atoms.
Acknowledgments
of four small diameter carbon nanotubes and their interactions with A.Y acknowledges financial support from BANGA-Africa, University
four transition metal atoms, Ni, Ti, Pd and Au, were extensively studied. of Ghana and the Carnegie cooperation, New York. A.Y & K. Kayang are
It was found that, nickel, palladium, titanium and gold atoms, changed grateful to the Centre for High Performance Computing (CHPC), South
the electrical properties of the carbon nanotubes when interacting at Africa for computer time on the Lengau cluster. Authors are also
specific sites. Gold, however, proved to be the best metal for carbon grateful to Prof. Boniface Kayang, University of Ghana, Legon, for
nanotube adsorption since it changed the semiconducting carbon proofreading the manuscript.
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K.W. Kayang, et al. Results in Physics 12 (2019) 2100–2106
Fig. 6. Where a- Band structure of (6,0) CNT doped with Au atom, b- PDOS of (6,0) CNT doped with Au atom, d- Charge density of (6,0) CNT doped with Au atom.
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