Fe, Ni, AND B DOPED ON THE SINGLE-WALL CARBON NANOTUBE: COMPUTATIONAL STUDY
MATERIALS SCIENCE and TECHNOLOGY
Edited by Evvy Kartini et.al.
Fe, Ni, AND B DOPED ON THE SINGLE-WALL CARBON
NANOTUBE: COMPUTATIONAL STUDY
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1 Muflikhah , Setyo Purwanto
1 Center for Technology of Nuclear Industry Material (PTBIN). BATAN
Kawasan Puspiptek, Serpong, Tangerang 15314, Indonesia
e-mail: muflikhah@batan.go.id
ABSTRACTComputational method has been used for predicting and understanding the structure and properties of single-wall nanotube (SWNT) as well as Fe, Ni and B doped-nanotube. This study aimed as an early understanding for the interaction between metal atom Fe and Ni as catalists and dopant in the single-wall carbon nanotube, and the second study we investigate the interaction and the effect of doping non-metal atom boron (B) on the single-wall carbon nanotube. In this paper we present the optimization geometry and energy interaction between dopant atom and the SWNT. Our calculation result showed that transition metal atom (Fe and Ni) can make stable bonding with two carbon atoms in the entrance of the carbon nanotube. Whereas non-metal atom B has some stable configuration with SWNT, and hence, It can bind directly in the tube and on the outside of the tube. Doping metal atom and non-metal atom to SWNT lead electrical properties and behavior changing in the SWNT, this is due to the electron transfer from the SWNT to the adatom and the electronic potential effect. Doping of metal atoms and non-metal atoms on SWNT led to electrical properties and behavior changes in the SWNT. It can be concluded that computational method can give predictive power in the interaction of SWNT and dopant atoms. Our calculation results of doping carbon nanotube with metal adatom or non-metal adatom also suggest a wide range application, such as gas sensor or biosensor.
Keywords: SWNT, doped-nanotube, computational study
INTRODUCTION
The research about carbon base material become fascinating since the discovery of carbon nanotube in 1991 [4,8]. The electrical and mechanical properties of carbon nanotube which are very unique have stimulated much research about this field. One of its challenge application is as electronic material which uses metal and semiconductor properties of carbon nanotube[9].
Many researchers included experiment and simulation (theory) about carbon nanotube (CNT). These has been done in order to understand and explore the wide application of nanotube[2]. Simulation or theoretical study of carbon nanotube using various calculation method, like HF, DFT, Moller Plesset, etc have been used to predict, understand and complete eksperiment. However, it was known that model and level of computation affect the calculation result[5].
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Several methods to synthesis carbon nanotube include arc discharge method in which it is mixed with transition metal like Fe, Ni and Co. The transition metal are known to play important role in that method, which is as catalyst[5,10]. From this factual experiment, it is very interesting to do some research using computational study about interaction between transition metal atom (Fe, Ni) with single-walled carbon nanotube. Some theoretical reference explain that transition metal which used as catalyst in CNT growth have high bonding energy with CNT[4,5]. On the other hand, various research explored the changing of electrical properties of CNT by dopping one or some adatom such as B or N[1,3].
In this paper we will present two theoritical studies. We first present the calculation of interaction between transition metal Fe and Ni with singled-walled nanotube. In the second is the theoritical study of Boron dopping in single-walled nanotube. The calculation determine potential interaction energy and geometry of interaction of Fe and Ni with SWNT, and then predict the energy and the stable position of B in the single-walled nanotube system. In this study we use CNT 10,10 fragment with 80 C atoms and CNT 4,4 with 72 C atoms.
COMPUTATIONAL METHOD
In this computational study we used Gaussian03 packages. Calculations have been done in two methods; calculation for interaction of Fe and Ni with single-walled nanotube used HF/3-
21G theory level and B3LYP/3-21G for calculation single-walled Boron doped nanotube. Computational study for interaction between Fe and Ni with single-walled nanotube have been done due to determinstion of optimization geometry and interaction energy, the calculation for these systems in relax condition. Beside that, from calculation we can get other information such as bond distance, atom charge and atom posistion.
The calculation for interaction Fe and Ni with CNT are focused using fragment SWNT 10,10 with 80 C atoms. Calculation steps for system SWNT-M are optimization geometry of CNT (10,10), CNT (10,10) with one Fe atom, CNT (10,10) with one Ni atom.
Metal atom Fe and Ni are position at the entrance of the tube and dangling bond at the end of the tube are passifed with hydrogen atoms. Total of dangling bond for SWNT (n,m) is n+m for each edge of the tube, so amount of dangling bond in system SWNT-M is 20 due to keep curvature of the structure. Then, interaction energy calculate using equation E int = E ab -E a -E b (equation 1), with ’a’ for CNT; ’b’ for metal atom and ’ab’ for CNT-M.
The second calculation, for boron doped single-walled nanotube has been done using different method but with calculation step like in SWNT-M system. Computational study for boron doped nanotube due to understand effect of adatom boron. We used fragment CNT 4,4 with 72 carbon atoms. In this study we calculate the possible orientation of boron atom in CNT system, first orientation is boron include in carbon nanotube and second orientation is boron outside of the tube. First orientation was calculated at relax condition and the second one at rigid. From calculation for first orientation we can get information about energy minimum, atom charge and parameter optimization. Calculation for second orientation had the purpose of gettng energy interaction between boron and CNT with configuration boron at outside of the tube. Interaction energy calculation has been done with bond distance variation, and interaction energy determined using equation 1. Potential energy curve interaction boron and CNT 4,4 maked as function energy to distance.
RESULTS AND DISCUSSION
First step from computational study interaction of Fe, Ni and B with CNT is optimization of their geometry. The purpose of geometry optimization was to get three dimensional structure with global minimum energy (stable condition) and some informations such as molecule
Fe, Ni, and B Doped on the Single-Wall Carbon Nanotube……
energy, atomic charge, total charge and dipol moment. Optimization structure of CNT 10,10 as shown in figure 1. Calculation result of minimum energy for CNT 10,10 (80 C atoms) is -
5 3022,7949 Hartrees (-79,3635. 10 kJ/mol), length inside diameter of the tube is 1,378 nm.
Optimization parameter bond distance ( Ǻ) for C-C ranging from 1,2- 1,47 Å; bond angels C-
C-C 116˚-122˚. Structure optimization parameter for bond distance of C-C are shown in figure 1.c. Structure optimization of CNT 10,10 with potential electrostatic surface is shown in figure 1d. Red colour shows negative potential electrostatic and the yellow one less negative, so that outside of the tube has the potential electrostatic which is more negative.
3 This is because of in CNT. Knowing the potential
π electron from orbital bonding sp electrostatic can assist to predict possible position of metal atom to CNT.
(a) (b) (c) (d)
Figure 1: (a) Structure optimization of CNT 10,10 neutralized with Hydrogen (b) CNT 10,10 without hydrogen
atom (c) optimization parameter bond distance of C-C for CNT 10,10 (d) Potential electrostatic surface of CNT
10,10.After getting the stable structure of CNT 10,10 then optimization geometry for system SWNT-M where metal atom positioned at the entrance of the tube growth, this is reasonable because metal atom (Fe and Ni) have potential electrostatic possitive. Calculation result of global minimum energy system SWNT-M (M= Fe and Ni) are used to calculate interaction energy or bonding energy between Fe and Ni with CNT. Calculation of geometry optimization system SWNT-M shows that metal atom Fe and Ni bonded with two cabon atoms (between C-C) as shown in figure 2a and 2c. The existance of metal atom Fe and Ni neutralize dangling bond of two carbon in the tube entrance and didn’t make deffect to the tube. Electron
π from CNT increase the effectiveness to Fe and Ni bonding. Metal atom Fe and Ni effect electrostatic properties of CNT whic is shown in figure 2b and 2d. This result can be used as an early study that Fe and Ni bonded in the entrance of nanotube can control and give direction in nanotube growth. Beside charge transfer from Cnt to metal atom this is because there is magnetic changing in the p-d hibridisation between CNT with transition metal Fe and Ni.
(a) (b) (c) (d)
Figure 2: (a) Structure optimization CNT 10,10-Ni (b) Potential electrostatic surface CNT 10,10-Ni (c)
Structure optimization CNT 10,10-Fe (d) Potential electrostatic surface CNT 10,10-fe.Calculation result of interaction energy between Fe and Ni with CNT are presented in tabel 1, that show interaction energy Ni with CNT stronger than Fe with CNT. Bonding energy of Ni with CNT is -257,6654 kJ/mol (-2,67 eV) and Fe with CNT -179,5757 kJ/mol (- 1,86 eV). Bond distance determine for shortest distance from metal atom to carbon atom of CNT, bond distance for Ni-C is shorter than Fe-C; 1,78 Å and 1,92 Å respectively, and both of them are covalen bonding. From Mulliken analysis for metal atom charge, Ni has more
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possitive charge than Fe in the SWNT-M system, that it may make Ni bond stronger to CNT than Fe beside electron π effect.
Tabel 1: Interaction Energy of Fe and Ni with CNT 10,10 (80 atom) in relax state by HF/3-21G.
Atom Interaction Energy (kJ/mol) Bond Distance (Å) Metal Atom charge
Fe -179,5757 1,92 1,186 Ni -257,6654 1,78 1,298
In second study, we start to study doping effect boron to nanotube CNT 4,4 with 72 carbon atoms with optimize geometry CNT 4,4 shown in figure 3a.We used different type of nanotube because of computer price, and there is no significant effect about type and lenght of nanotube for several case. Global minimum energy of CNT 4,4 in B3LYP/3-21G theory
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level is -2715,0453 Hartrees (-71,284. 10 kJ/mol) and tube lenght 9,67 Å, potential electronic surface CNT 4,4 (figure 3b) is like in CNT 10,10.
(a) (b) Figure 3: (a) Structure optimization CNT 4,4 (b) Potential electrostatic surface CNT 4,4.
Calculation of one atom of boron dopped in carbon nanotube is shown in figure 4a. According to calculation result, boron is very mobile in this system, and we got local
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minimum energy of -2719,4698 Hartrees (-71,399. 10 kJ/mol) with bond distance B-C longer than C-C (B-C=1,52 Å and C-C=1,41-1,45 Å). Doping boron in nanotube system is more complicated than transition metal atom (Fe and Ni). Calculation results give information that boron is possible in this position, and the excistance of boron change electronic properties carbon nanotube as shown in potential electronic surface in figure 4b and this is interesting for electrical application.
(a) (b) Figure 4: (a) Structure optimization CNT 4,4-B (b) Potential electrostatic surface CNT 4,4-B.
Other review in this computational study of boron doped nanotube is to put boron as impurity on outside CNT. Purpose of this calculation is determine interaction energy between boron and CNT in rigid condition. Energy interaction of possible orientation of boron in
Fe, Ni, and B Doped on the Single-Wall Carbon Nanotube……
outside of CNT calculate with distance variation so that we got the most stable distance and
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energy (figure 5a). Energy interaction of boron with CNT is -46,464. 10 kJ/mol with distance B-C 1,85 Å. According to the power and distance bonding, interaction between B and CNT have covalent bonding.
(a) (b)
Figure 5: (a) Structure interaction B to CNT 4,4 (b) Potential interaction energy curve of Boron with CNT 4,4.
CONCLUSIONComputational study interaction transition metal (Fe and Ni) using HF/3-21 theoretical level showed that interaction of the metal Ni was stronger than Fe. Transition metal atom Fe and Ni can bind directly in the entrance of carbon nanotube growth, so they can control CNT growth. Calculation for boron doped CNT indicated that boron can bind in the tube system and outside of the tube as impurity with covalent bonding. Boron as doppant or impurity in carbon nanotube changed the electrical properties of CNT.
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