Single-Walled Carbon Nanotube Engendered Pseudo-1D

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Single-Walled Carbon Nanotube Engendered Pseudo-1D Morphologies of Silver Nanowire Sunil Kumar, Vikas Chandra Srivastava, Gopi Kishore Mandal, Sudip Kumar Pattanayek, and Kanai Lal Sahoo J. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 29 Aug 2017 Downloaded from http://pubs.acs.org on August 29, 2017

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The Journal of Physical Chemistry

Single-walled Carbon Nanotube Engendered Pseudo-1D Morphologies of Silver Nanowire Sunil Kumar*†, Vikas Chandra Srivastava*, Gopi Kishore Mandal*, Sudip Kumar Pattanayek#, Kanai Lal Sahoo* *CSIR-National Metallurgical Laboratory, Jamshedpur, India 831007 # Indian Institute of Technology, New Delhi, India 110016 Abstract Silver nanowires show enhancement in desired properties, due to high surface area and high aspect ratio, which increases the possibility in design and development of many advanced opto-electronic devices. The organization of silver atoms and the morphology of cylindrical nanowire highly influence the desired properties at various physical conditions during applications. Therefore, the synthesis of nanowires with desired atomic organisation becomes essential. In the present study, a pseudo-1D morphology of silver nanowires, encapsulated into a Single Wall Carbon Nanotubes (SWCNTs), has been investigated by employing Molecular Dynamics (MD) simulation. At high temperature (T = 1500 K), molten silver encapsulated into a SWCNT attaining a low energy state followed by restricted thermal motion or vibration. With increase in SWCNT diameter, various unique pseudo-1D morphologies of encapsulated silver atoms were observed during cooling from 1500 K to 10 K. Silver atoms, encapsulated into a SWCNT having diameter 10.85 Å, mainly reveal 5-fold symmetrical icosahedral (ico) having pseudo-1D morphology. With further increase in diameter (d = 40.68 Å) of SWCNT, a decagonal pattern consisting of face centered cubic (fcc), hexagonal closed packed (hcp) and body centered cubic (bcc) was evolved due to non-homogenous packing of silver atoms into SWCNT. Simulation results indicate that the diameter of SWCNT is the one of the major factors controlling the pseudo-1D morphology of silver nanowire. The present theoretical investigations provide a guideline and enhance the current understanding related to solid state physical phenomena of metal nanowires synthesis. Key words: Silver nanowire, SWCNT, Molecular Dynamics Simulations, Interface, Encapsulation. ---------------------------------------† Email: [email protected], [email protected]

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1.

Introduction Encapsulation of a variety of molecules, such as water1-2, polymers3-6, biopolymers7-9

and metals10-15 within Single-Walled Carbon Nanotubes (SWCNT) has been attracting much interest, recently, not only due to their superior composite properties but also the pseudo-1D organization of encapsulated materials. In addition, encapsulation of fullerenes (C60)16, Deoxyribonucleic acid (DNA)17,18 and graphene nano-ribbons19,20 has also generated a significance in the development of novel functionalised nano-materials for the application in biomedical and electronic devices/sensors, high performance nanocomposites, catalyst for electrochemical reactions, solar cells etc. Furthermore, the high temperature stability of metallic compounds can also be significantly improved when encapsulate within SWCNT, as the hexagonal arrangement of carbon casing inhibits oxidation17. Similarly, silver atoms can also be encapsulated into the cylindrical cavity of SWCNT, which opens the possibility of synthesizing ultrathin silver nanowires. Silver nanowires are the class of materials that have drawn considerable attention due to their fascinating electrical, thermal and optical properties, which can be constructively utilized in optical, electrochemical, biosensing21-23, anti-bacterial applications24, 25 and as additives in composite fibers26. Various experimental27-44 and simulation45-52 methodologies have been developed for the synthesis and characterization of metal nanowire. Ajayan27 developed an experimental ex-situ technique for the inclusion of metals into multi-walled carbon nanotubes (MWCNT), for the synthesis of metal nanowires, with an encapsulation yield of up to 90%. Later, Ajayan and Ebbesen28 demonstrated that this approach can be successfully applied to fill SWCNTs without performing the preliminary opening of its ends. Over the years, various research groups came up with different chemical approaches for the synthesis of 1D-nanostructureed silver nanowire. For example, silver nanowires can be synthesized by reducing silver nitrate (AgNO3) in the presence of silver bromide (AgBr) nanocrystallites29 or by arc discharge between two silver


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electrodes immersed in an aqueous sodium nitrate (NaNO3) solution30. Ultraviolet irradiation photo-reduction technique has been used to synthesize silver nanowires by passing ultraviolet light into an aqueous silver nitrate (AgNO3) solution in the presence of polyvinyl alcohol, which is known as polyol process31-33. Sun et al.32 have used polyol process for the large-scale synthesis of silver nanowires, with uniform diameters in the range of 30-40 nm and lengths up to 50 µm. The properties of silver nanowires produced by all these methods generally showed irregular morphologies, polycrystallinity, low aspect ratio and poor mechanical strength. In contrast to these methods, the template (nano-channels) directed synthesis40 engenders silver nanowires, having pseudo-1D morphology of atoms, with better and consistent mechanical, thermal and electrical peroperties. Various types of template or nano-channels such as, macroporous membranes34, mesoporous materials35, carbon nanotubes27-28,36, DNA chains37, rod-shaped micelles38 and steps or edges on solid substrates39 have been successfully used for the synthesis of metal nanowires. In the present investigation, therefore, we have used SWCNT as a template to study the encapsulation behaviour and evolution of pseudo-1D morphology of silver atoms during cooling from high temperature (1500 K) to extermely low temperature (10 K) by using molecular dynamics (MD) simulation methodology. The MD simulation technique has been used by a few research groups to investigate various properties of metal nanowire45-50. Most of such reported studies on metal nanowires are based on the estimation of mechanical, electrical, thermal properties45-47. A few studies are also available on the melting and solidification of metal nanowire with and without templates (nano-channels). Chen et al.48 have studied the melting behaviour of silver nanowire, with 5-fold twinned boundaries created without using any template, of various diameter ranging from 1.6 nm to 10 nm. They observed a decrease in melting temperature of silver nanowire with decreasing diameter, by employing MD simulation. The melting temperature of silver nanowire have found to be 1250 K (diameter = 10 nm) and 790 K (diameter = 1.6 nm). On the contrary, Arcidiacono et al.49 have studied the



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solidification of gold atoms inside the SWCNT template. They have shown that the solidification temperature of gold nanoparticles depends on their size and diameter of nanotubes. Choi et al.50 have studied the encapsulation of copper into SWCNT by cooling the copper melt (cooling rate 1 K/ps) from 700 K to 10 K. They have reported that copper atoms organize themselves in a face-centerd cubic (fcc) structure inside the SWCNT, as occurs in bulk material. Despite of these studies on encapsulation of Ag and other materials, the issues related to the structure and the stability of pseudo-1D morphology of silver nanowires with diameter of the cylindrical template (SWCNT) remained unanswered. The present study is an attempt to have an insight on the structure of silver nanowire inside solid cylindrical template (SWCNT) and the structural transition with the various template diameter. In this investigation, MD simulation has been used for the study of pseudo-1D morphology of silver nanowire considering SWCNT as hard cylindrical template. The simulation system consists of multiple steps: such as melting of silver at 1500 K, encapsulation of silver atoms into SWCNT (at 1500 K) and cooling of silver from 1500 K to 10 K (Cooling rate 0.1 K/ps). The radial distribution function, adaptive common neighbour analysis, mean square displacement and energy contributions have been used to characterize the encapsulation and pseudo-1D morphology of silver nanowire inside the SWCNT. To the best of the knowledge of the authors, such extensive investigations addressing a multitude of coupled phenomenological issues such as encapsulation process and evolution of pseudo-1D morphology of silver nanowire inside the SWCNT have not been attempted earlier in the light of published literature.

2.

Simulation details Constant temperature molecular dynamics simulation51 has been implemented to study

the encapsulation of silver atoms into SWCNT of various diameters and their atomic


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organization therein, as given in Table 1. A generalized Finnis and Sinclair52,53 form of embedded atom method (EAM) potentials has been employed between the silver atoms. The total energy of silver atoms, is given by

1 = V − (1) 2

= (2)

= (3)

where is the distance between !"# and $"# silver atom, and energy and lattice parameter

and %, ' and are the positive constants for silver atoms. is the pair potential to account

for the repulsion between ! "# and $ "# silver atom, and the local density associated with silver

atom !. Equations (1) - (3) can be generalized to derive the Hamiltonian pertaining to silver atoms in the following Finnis-Sinclair form -//

1 ( = )̂ )̂ − + )̂ )̂ ∅ 2

The site occupancy operators )̂ for silver atoms are defined as follows )̂ = 1

(4)

1, if site i is occupied by a silver atom, (5) 0, if site i is not occupied by a silver atom

() = F G (6)

The constant + is defined as follows

∅() = F G (7) + = × (8)

The values of , , , ' and % for the silver atoms are given in Table 1. 5 ACS Paragon Plus Environment


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The interatomic potential energy between silver and carbon atoms of SWCNT have been implemented through 12-6 Lennard Jones potential as given in the following equation. LM = 4N OP

QRSTU -/ V

W

−P

QRSTU X V

W Y

(9)

Where N , and ZN are the Lennard Jones parameters for energy minimum or welldepth and equilibrium interatomic distance at null potential respectively. The subscripts denote the silver (Ag) atom and carbon (C) atoms of graphene. The values of N = 0.0301 \ and ZN = 3.006 Å have been used for silver and SWCNT54.

The Newtonian equation of motion of a silver atom, i, of mass (w), due to the external forces arising from the sum of the various potentials, E can be written as ^×

_ ` ab _" `

= c = −d

(10)

where c is force on the ith silver atom. The equation of motion (10) is integrated according to the velocity Verlet algorithm55 with a time step of 2 femto-second as shown in equation (11) and (12). a (e + ∆e) = a (e) + h (e)∆e + (∆e)/ i (e + ∆e) /

h (e + ∆e) = h (e) + / ∆eji (e ) + i (e + ∆e)k -

(11) (12)

Here, h and i are the velocity and acceleration of the ith silver atom. The MD simulation is

carried out in a NVT ensemble. The Nose-Hoover thermostat56-57 has been implemented to maintain the appropriate temperature of the system along with velocity-Verlet algorithm. Large Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS)58, Open Visualization Tool (OVITO)59, 60 and Visual Molecular Dynamics (VMD)61 software packages have been used for molecular dynamics simulation, visualization and analysis of output data. 2.1.

Simulation system and processing steps The simulation system consists of a SWCNT and specified number of silver atoms, as

shown in Figure 1. A SWCNT is placed along the Z-direction in the centre of the simulation 6 ACS Paragon Plus Environment

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box of dimension (± 200 Å, ± 200 Å, ± 200 Å). The silver atoms with an ideal fcc structure is placed at an end of the SWCNT. The number of silver atoms (NAg) and size of armchair (n, n) SWCNT are listed in Table 2. Molecular dynamics simulation for the synthesis and characterization of silver nanowire employs three process steps. In the first step, silver is melted to a fixed temperature (T = 1500 K) and held for 100 ps, which allows the melt to achieve an equilibrium state. The experimentally determined melting temperature of bulk silver is 1234 K48. A comparatively high temperature of 1500 K was selected for melting so as to achieve a truly randomized and homogeneous liquid. The carbonaceous nano-material such as Single Walled Carbon Nanotube (SWCNT) and graphene are able to withstand temperature of up to 3300K

(estimated

by

molecular

dynamics

simulation)62

and

2073K

(estimated

experimentally)63. In the second step, silver atoms are allowed to migrate into the SWCNT at temperature 1500 K for 1000 ps, which is named as encapsulation processes. In the third and final step, the temperature of the siver decreases from 1500 K to 10 K at a cooling rate of 0.1 K/ps, in which silver shows phase transition from liquid to solid. In contrast to the reported literature64-66, compratively slower cooling rate for solidification has been adopted in the present study so as to efficiently capture the evolution of nanocrystalline structure of encapsulated silver nanowire. Most of the studies64-66, have used cooling rate ranging from 0.1 K/ps to 10 K/ps for the crystallization process of pure metals.

2.2.

Radial distribution function g(χ) The probability of finding a silver atom at a distance χ from an average central silver

atom is calculated through the radial distribution function l(m)67 defined by the following equation (13): RS 〉 (13) l(m) = o` 〈∑ ustr` ∆r

n

RS

o

(r)



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where, w and V are the total number of silver atoms and volume of the system, respectively.

%(m) is the number of silver atoms in a spherical shell of radius χ and thickness ∆χ around the central silver atom.

2.3.

Adaptive common neighbor analysis The adaptive Common Neighbour Analysis (a-CNA)59,

60

are used to characterize the

organization of silver atoms inside the SWCNT. The a-CNA has the capability to identify the silver atoms belonging to various structure types such as face centered cubic (fcc), hexagonal closed packed (hcp), body centered cubic (bcc), icosahedra (ico) and others using only the position (x, y, and z coordinates) of each silver atom. In the a-CNA analysis, the local crystal structure of silver atoms was recognized by estimation of three integers (ncn, nb, and nlcb) for each central silver atom64, 68-70. ncn is the number of silver atoms that are neighbours to both atoms in the pair, which are identified as common neighbours. nb is the total number of bonds between ncn common neighbours of silver atoms. nlcb is the number of bonds in the longest continuous chain formed by the nb bonds between common neighbours of silver atoms. For the perfect fcc structure, all pairs are of the type (ncn, nb, nlcb) = (4, 2, 1) or simply known as 421. Similarly, for the perfect hcp, 50% integers are of type 422 and other 50% integers are of type 421. Furthermore, bcc structure is consisting of both 441 and 661 types. This algorithm for identification of crystal structure is inbuilt in the Open Visualization Tool (OVITO) software by its developers, which we have used for analysis in this study. OVITO software package, randomly organized silver atoms identified as liquid/glassy state. However, in the crystalline state of silver, atoms are organized in fcc, bcc and hcp structure. Icosahedra (ico) organization of atoms are found in a metastable glassy state.

2.4.

Mean square displacement (MSD) 8 ACS Paragon Plus Environment

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The mean square displacement (MSD)51 of silver atoms are calculated to quantify the atomic mobility in both encapsulation and cooling process. The MSD of silver atoms can be computed by the following equation (14):

xyz = 〈|(e) − (0)|/ 〉 (14)

where, (0) and (e), are the position of silver atom at time t = 0 and t = t, respectively. The calculation of MSD has been performed by using compute msd command within LAMMPS during each simulation run.

3.

Results and Discussion The results obtained from the present attempt on MD simulation of silver atom

encapsulation within a SWCNT have been presented and discussed. This contains various aspect of the encapsulation e.g. migration into a SWCNT, evolution of pseudo 1-D morphologies of silver atoms and the effect of SWCNT diameter on structural transitions.

3.1. Encapsulation of silver atoms into SWCNT Silver atoms (NAg = 6912) are placed near an open end of a SWCNT, diameter d = 40.68 Å, at temperature of T = 1500 K to study their encapsulation process into cylindrical cavity of SWCNT. Figure 2 depicts the snapshots of temporal evolution of encapsulation process. In the early stage of simulation (up to 250 ps), most of the silver atoms travel along Zdirection (axis of SWCNT) and occupy all the available space inside the SWCNT. A stable encapsulated state of silver atoms inside the SWCNT has been observed after 1000 ps. For a monoatomic metal system, the non-bonded interaction potential energy between carbon atoms of SWCNT and silver atoms (PEAg-C), along with intra-atomic potential energy of silver atoms (PEAg-Ag), are expected to be the driving force for the encapsulation process. The similar observations of encapsulation process has been reported in our previous publications3, 4. During



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encapsulation process, the potential energies PEAg-C and PEAg-Ag decreases due to gradual increase in contact with the carbon atoms of SWCNT and also with neighboring silver atoms, as shown in Figure 3. The first peak of g(χ) vs χ plot increases slightly during encapsulation process, which depicts the increase in the number of 1st nearest neighbour atoms (i.e. increase in contact number) as shown in Figure 4. The increase in number of 1st nearest neighbour will increase the PEAg-Ag. From the energy calculations, it can be concluded that SWCNT provides a favourable potential energy well and a strong hexagonal network of carbon atoms. At high temperature i.e. once the silver is in liquid state, the possibility of decrease in potential energy leads to encapsulation of silver atoms into SWCNT. At the same time, strong hexagonal network of carbon atoms will reduce the thermal vibration of encapsulated silver atoms. These observations clearly reveal that silver atoms encapsulate into the SWCNT to reach a stable and lower energy state, compared to the their energy state in bulk i.e. outside the SWCNT.

3.2.

Organization of silver atoms inside the SWCNT During the cooling process, the temperature of silver decreases from 1500 K to 10 K

and silver atoms form a one dimensional clylindrical structure within the SWCNT at low temperature, as shown in figure 5. At a temperature of 1275 ± 25 K, which is slightly higher than the melting temperature of 1234 K48,81,82, silver atoms witness phase transition and commences arranging themselves into crystalline phase, due to the presence of the SWCNT wall49. Further, as temperature decreases, silver atoms organize into a pseudo-1D morphology, which consist of various structural organizations such as fcc, bcc, hcp, ico and others. The average potential energy of silver atoms decreases due to both intra-atomic interactions of silver atoms (PEAg-Ag) and also between silver and carbon atoms of SWCNT (PEAg-C) during cooling process, as shown in Figure 6. With decreasing temperature, reduction in thermal


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vibration facilitates the crystallization process inside the SWCNT. A sharp decreases in both the potential enegies is indicative of the phase transition from liquid to crystalline phase. This type of energy change is also observed during crystallization of pure metals in bulk71-73. We have done simulation of pure silver (as in bulk) to estimate the crystallization temperature of silver. It has been found that silver start to crystallize in fcc structure with twin plane of hcp at nearly 850 ± 15 K (diameter of silver globule d ≈ 6 nm, number of silver atom = 6912) as shown in figure 7(a) and (b). Tian et al.74 have also found similar crystallization temperature, T = 862 K (for 5000 silver atoms) and T = 871 K (for 10000 silver atoms) of silver in bulk by using molecular dynamics simulation. However, the crystallization temperature of encapsulated silver into SWCNT depicts 1290 K. It can be conclude that encapsulation of silver into SWCNT increases the crystallization temperature significantly.

The radial distribution function among silver atoms, l(m), has been calculated and is

shown in Figure 8. At high temperatures i.e. 1500 K and 1300 K, a peak of l(m) is present only at m = 2.89 Å, which is due to a short range ordered structure. This peak corresponds to the

first nearest neighbour of silver atoms that is found to be at ×

√/ /

= 2.892 Å, where is the

lattice parameter ( = 4.090 Å). However, m > 2.89 Å, no any distinct and identifiable peak was found, which may be due to the loss of long range ordered correlations. These observations show that the silver atoms exhibit only short range ordered correlations at high temperature. At moderate temperatures, the peaks of l(m) are identified to evolve gradually at various values of

m due to phase transition from liquid to crystalline state. At low temperatures i.e. 300 K and

10K, distinct peaks of l(m) are found at m = 2.89 Å and 4.685 Å, which corresponds to 1st and 2nd nearest neighbours of silver atoms, respectively. These observations indicate that the silver

atoms exhibit both short and long range ordered correlations at low temperature. The similar description of 1st and 2nd nearest neighbour of atoms in bulk has been reported in literature75, 76.



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Figure 9 shows the evolution of ico, fcc, bcc and hcp atoms during the cooling from 1500 K to 10 K. It is observed that, at high temperatures (T > 1290 K), most of silver atoms are in liquid state which is organized randomly. Further, with decrease in temperature below (T < 1290 K), a phase transition from liquid to solid (crystalline) is observed. The figure clearly depicts that bcc is the most favourable intermediate organization during phase transition at the crystallization temperature T = 1290 K. Similar bcc configuration has also been reported by Desgranges and Delhommelle77 for the crystallization of pure metal in bulk. The solid crystalline structure mainly consists of fcc, bcc and hcp atom along with scattered random ico atoms. At low temperatures i.e. T < 300 K, most of the silver atoms organize themselves in a stable combination of fcc, bcc and hcp compared to pure fcc in bulk. This difference in organisation of atoms encapsulated within cylindrical SWCNT may be attributed to the nonhomogenous distribution of energy evolved due to presence of carbon atoms of the SWCNT. Figure 10 (a) depicts the snapshot of internal view of organization of silver atoms inside the SWCNT and shows their evolution into an interesting cylindrical pattern consisting of long chains of fcc and bcc atoms along the SWCNT axis. Figure 10 (b) shows a slice cut top view of the 1D nanowire depicting a decagonal pattern of silver atom organization inside the SWCNT of diameter d = 40.68 Å. The decagon pattern consists of bcc, fcc and hcp atoms. The ensuing organizational pattern of atoms inside the SWCNT can be divided in ten similar triangular shape geometry, where fcc atoms organize at the base of the triangle, hcp at the interior region of the triangle and bcc and ico atoms at the corners. However, the atomic organization at the ends of SWCNT evolves into a five fold twinned symmetry (Figure 10 (c)), which consists of twin planes of hcp atoms due to thermally induced stress concentration at the solid-liquid interface. Fivefold twinned structure has been widely found in elemental nanocrystals such as aluminium, iron, copper, gallium etc.78-80 However, the reported origins for the formation of five fold twinned structure are the effect of applied stresses, local internal shear stresses,


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thermally induced stresses during annealing. Figures 11 (a) and (b) depict a landscape view of the potential energies of silver atoms and the distribution of average potential energies of atoms, respectively, pertaining to the hcp, fcc, bcc, ico and other configurations. The distribution of average potential energy reveals that the fcc atoms have lowest potential energy compared to others. The trend pertaining to potential energy can be observed as: fcc < hcp < bcc < ico < others; which may be attributed to non-homogeneous distribution of packing density of silver atoms that are under the influence of carbon atoms of the SWCNT.

3.3. Dependence of atomic organization on SWCNT diameter In the previous section, it has been observed that the non-homogeneous energy of silver atoms encapsulated within a SWCNT might lead to a combination of different atomic organisational configurations of the atoms as against a fcc organisation in bulk. This contrast is attributed to the atomic interaction of the carbon atoms with those of the silver atoms up to several atomic distances into the nanowires. This implies that the size of the nanotubes may also influence the atomic organisation of the silver atoms upon encapsulation. Therefore, in the present investigation, an attempt has been made to look for the organisational variation of the silver atoms inside SWCNT with different diameters. A wide range of SWCNT diameters were selected for the purpose, as listed in Table 2. The snapshots of silver atoms encapsulated into a SWCNT of different diameters are shown in Figure 12 (a) to (e), that includes the snapshot from the SWCNT with diameter 40.68 Å also (Figure 12b) that has been described in the previous section. Similar to the atomic organisation within 40.68 Å SWCNT, 54.60 Å SWCNT also shows fcc and bcc dominated outer layer, hcp in the interior of the nanowire and fivefold twinned plane. However, at some locations outer layers also depicted the presence of hcp atoms and ico atoms were not observed in the centre of the nanowire. This may be attributed to the larger system size and less time for energy equilibration at a cooling rate of 0.1 K/ps. The



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twinned plane consists of hcp silver atoms. However, the organization inside the 32.50 Å diameter SWCNT shows the decagonal symmetry with mainly hcp atoms, both at the surface and interior, as shown in figure 12(c). In this case also, no ico atom was observed at the central axis of the nanowire. The organisation within SWCNT of diameter 20.30 Å cosists of ico atoms at the central axis of SWCNT and hcp atoms at the surface and the interior. In contrast, encapsulation of silver atoms into SWCNT of diameter 20.30 Å and 10.85 Å showed evolution of ico-atoms at the central axis. In addition to ico-atoms, a few hcp atoms also evolve inside the SWCNT fo 20.30 Å. However, in these small diameter SWCNTs, atoms in fcc and bcc configurations have not been seen. Figure 13 (a) and (b) depict the organization of silver atoms inside the SWCNT of diameter d = 10.85Å during cooling from 1500K to 10K. We have observed the silver atom with icosahedra (ico) gradually evolve as temperature decreases below ≈1100K . However, atom with structural organization with fcc, bcc and hcp does not appear throughout the cooling process. The organization of silver atoms inside the SWCNT of diameter d = 10.85 Å is given in Figure 14(a) to (c). Figure 14 (a) and (b) shows the full view of the encapsulated atoms with and without the SWCNT, respectively. It is obvious from the figures that the atoms organize with 5-fold symmetry along the central axis of SWCNT. This 5-fold symmetry seems to evolve by stacking of two alternating atomic layers containing a single atom and a five-atom ring, which form a 1−5−1−5−1 stacking structure along the axis of SWCNT (Figure 14c). A total of thirteen silver atoms in a 1−5−1−5−1 stacking sequence is defiend as a unit cell of the silver nanowire. The overall pseudo-1D morphology of silver atoms along the central axis of SWCNT can be considered as a single silver atom chain surrounded by five-silver atoms ring. Similarly, the organization of silver atoms encapsulated into SWCNT of diameter d = 20.30 Å has been depicted in Figure 15(a) to (c). A full view of the encapsulated SWCNT is given in Figure 15 (a) and (b), with and without the covering by SWCNT, respectively. In contrast to the


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configuration observed for the encapsulated atoms in 10.85 Å diameter SWCNT, the atoms in 12.20 Å SWCNT organize themselves in a 6-fold symmetry along the axis of SWCNT. The 6fold symmetry of silver atoms evolves due to two alternating atomic layers containing a single atom and a six-atom ring stacked together to form a 1−6−1−6−1 stacking structure along the axis of SWCNT. The unit cell of silver nanowire thus created contains fifteen silver atoms in the 1−6−1−6−1 sequence. The pseudo-1D morphology of silver atoms along the axis of SWCNT of 20.30 Å diameter can be considered as a single silver atom chain surrounded by six-silver atoms ring. Figure 16 shows the variation in the total energy of silver atoms, during cooling from 1500 K to 10 K, encapsulated into SWCNTs of various diameters ranging from 10.85 to 54.00 Å. The figure clearly reveals that the total energy of silver atoms, encapsulated within SWCNT of diameter d = 10.85 Å and 13.56 Å, gradually decreases with decrease in temperature. However, for SWCNT of diameter d = 20.30 Å, 40.60 Å and 54.00 Å, initially energy gradually decreases during cooling from 1500 K to 1300 ± 25 K. At temperature 1300 ± 25 K, energy of silver quickly decreases due to phase transition from liquid to crystalline. Further, as temperature below 1290 K, energy of silver atoms gradually decreases again. From energytemperature plot, it can be concluded that phase transition from liquid to crystalline have found for silver atom encapsulated into SWCNT of diameter d =20.30 Å, 40.60 Å to 54.00 Å. On the contrary, a meta-stable phase evolves of silver atoms encapsulated into SWCNT of diameter d = 10.85 Å to 13.56 Å. Figure 17 shows the mean square displacement of silver atoms encapsulated into SWCNT of various diameter. Mean square displacement increases sharply in liquid state. However, as silver atoms solidify into crystalline state, mean square displacement become stagnant. It is confirmed from mean square displacement that silver atoms encapsulate in SWCNT of diameter d = 20.30 Å, 40.60 Å to 54.00 Å exhibit phase transition from liquid to



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crystalline state. However, silver atom encapsulated into SWCNT of diameter d = 10.85 Å to 13.56 Å, shows super cooled liquid or metastable state.

4.

Conclusions In this study, we have sought to understand the encapsulation and organization process of silver atoms into a SWCNT of diameter ranging from d = 10.85 Å to 54.00 Å by using molecular dynamics simulations. It has been found that the silver atoms encapsulate into a SWCNT in the liquid state. The interaction potential between silver and carbon atoms of SWCNT along with the intra-atomic potential of silver atoms are responsible for encapsulation processs. The organization of encapsulated silver atoms is found to be started at 1290 K during the cooling process (1500 K to 10 K). The major finding pertaining to phase transition from liquid to crystalline phase are as given below:

A cylindrical pattern of crystalline phase of silver nano-wire have evolved which consist of fcc, bcc, hcp, ico and others atoms inside the SWCNT of diameter d = 40.60 Å.

A five and six fold symmetry of crystalline silver nanowire have been observed inside the SWCNT of diameter d = 10.85 Å and 12.20 Å

The phase transition from liquid to crystalline depends on the diameter of the SWCNT. At low diameter (d = 10.85 and 13.56 Å), a meta stable solid phase has been found. On the contrary, silver atoms encapsulated into SWCNT of diameter (d = 20.30 and 54.00 Å), has been transformed in liquid to crystalline phase.

In low diameter case, silver atoms kinetically trape in metastable state and unable to crystallize. However, in large diameter case, silver atoms have found enough thermal mobility in liquid state prior to crystallization as confirmed from mean square displacement.


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The above results also implies that the SWCNT engendered the organization of silver nanowire in a significant extant. The presence of numerous type of nano-structural organization metal nanowire encapsulated into SWCNT will influence overall properties such as thermal and electrical conductivity along with mechanical properties. The catalytic activity, optical, electrochemical, bio-sensing, anti-bacterial properties of silver nano-wire implicitly/explicitly relate to length/diameter ratio and structural organization of silver atoms. However, in future, we will further investigate to relate length/diameter ratio and structural organization of silver nanowire (or nano-structure) with these properties.

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Table 1 Parameters for Embedded Atoms Method (EAM) potential due to Finnis-Sinclair (FS) [52, 53] for silver atoms. m

n

ε(eV)

c

a(Å)

6

12

0.025415

144.41

4.09


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Table 2 The details of simulation system such as surface architecture, diameter and length of SWCNT along with the number of silver atoms (NAg) for the synthesis of a silver nanowire.

1. 2. 3. 4. 4. 5. 6. 7. 8. 9.

Armchair (n, m) SWCNT (8,8)SWCNT (9,9)SWCNT (10,10)SWCNT (12,12)SWCNT (15,15)SWCNT (20,20)SWCNT (25,25)SWCNT (30,30)SWCNT (35,35)SWCNT (40,40)SWCNT

Diameter of SWCNT (Å) 10.85 12.20 13.56 16.24 20.30 27.12 33.85 40.68 47.43 54.00

Length of Number of carbon Number of silver SWCNT (Å) atoms in a SWCNT atoms (NAg) 100 1312 220 100 1476 320 100 1640 400 100 1968 732 100 2460 1298 100 3280 2500 100 4100 4400 100 4920 6912 100 5740 10000 100 6560 13500



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1 Simulation system consisting a globule of silver atoms and a SWCNT, which has been placed in the centre of the simulation box of size (±200 Å, ±200 Å, ±200 Å). The axis of SWCNT is along the Z-direction. The silver globule, with a temperature of 1500 K, is placed at an open end of SWCNT.


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Top view

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Side view

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Time = 1ps Time = 100ps Time = 250ps Time = 500ps Time = 1000ps T = 1500K T = 1500K T = 1500K T = 1500K T = 1500K Figure 2 Snapshots of side and top view of silver during encapsulation process into a SWCNT of diameter d = 40.68Å, with increasing simulation time at a fixed temperature of 1500K. Red colour arrows are indicating the progress of encapsulation process.



0.0

Εncapsulation

process PE (eV/atom)

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PEAg- SWCNT

-0.1 -2.50

PEAg- Ag -2.55 0

250

500

750

1000

Time (ps) Figure 3 Variation in potential energies of silver atoms (PEAg-Ag) and between silver and carbon atoms of SWCNT (PEAg-C) during encapsulation process. (SWCNT diameter d = 40.68Å; Temperature T=1500K)


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900

600

g(χ)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


300

Time=1000ps Time=100ps Time=1ps 0

5

0

10

χ (A ) Figure 4 Radial distribution function g(χ) of silver atoms during encapsulation process within the SWCNT of diameter d = 40.68Å at 1500K.


Top view

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Side view


1500K

1300K

1250K

750K

300K

10K

10K

Figure 5 Snapshots of phase transition from liquid to crystalline state of silver encapsulated into SWCNT of diameter d = 40.68Å during cooling from 1500K to 10K. Blue, red, green and yellow colour atoms pertain to bcc, hcp, fcc and ico structure, respectively. For clear visualization, atoms with random organization have not been shown in the snapshot. SWCNT has not been shown in right most snapshot due to clear visualization of solidified silver. Red colour arrows are indicating the progress of phase transition.


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-0.075

PE (eV/atom)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


PEAg-C

-0.090

Transition from liquid to crystalline state

-2.6

PEAg-Ag

-2.8

1500

1000

500

0

Temperature (K)

Figure 6 Variation in potential energies of silver atoms (PEAg-Ag) and between silver atoms and carbon atom of SWCNT (PEAg-C) of diameter d = 40.68Å during cooling from 1500K to 10K.



1500K

850K

825K

300K

(a)

80

others

40

% of atoms

0.1

ico

0.0 10

hcp

0 60 Τ = 850 Κ

30

fcc

0 6 bcc

3 0 Total energy

-2.4 Total energy eV/atom

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Τ = 850 Κ

-2.8 1500

1200

900

600

300

Temperature (K)

(b) Figure 7 Liquid to solid phase transition of pure silver during cooling from 1500K to 10K: (a) snapshot of structure evolution and (b) variation of fcc, hcp, bcc, ico and other atom during cooling from 1500K to 10K. Blue, red, green and yellow colour atoms pertain to bcc, hcp, fcc and ico structure, respectively. Red colour arrows are indicating the progress of phase transition.


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10K 100K 200K 300K 400K 500K 600K 700K 800K 900K 1000K 1100K 1200K 1300K 1400K 1500K

st

Arbitrary unit

1500

g(χ)

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1 N. N.

1000

500

0 5

10 0

χ (Α ) Figure 8 Radial distribution function g(χ), of silver atoms encapsulated within the SWCNT of diameter d = 40.68Å during cooling from 1500K to 10K. The first nearest neighbours (1st N. N.) of silver atoms is indicated by arrows. Amorphous or liquid, transition and crystalline regions are shown by black, red and green colour lines at respective temperatures.



100 75

% of atoms

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 63

Other bcc fcc hcp ico

other fcc hcp

10

T=1290K bcc ico

0 1500

1000

500

0

Temperature (K) Figure 9 Evolution of atomic content (in %) corresponding to fcc, hcp, bcc and ico structure of silver atoms encapsulated into SWCNT of diameter d = 40.68Å during cooling from 1500K to 10K.


Page 37 of 63

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(b)

(a)

(c)

Figure 10 Organization of silver atoms inside the SWCNT of diameter d = 40.68Å: (a) pattern of bcc, fcc and hcp atom, (b) decagon symmetry and (c) five-fold symmetry of twinned plane of hcp atoms at the end of SWCNT. Red, blue, green and yellow color atoms have been indicated hcp, bcc, fcc and ico atoms.



0.50

Fraction

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 63

bcc fcc hcp ico other 0.25

0.00 -3.00

-2.75

Potential energy (eV/atom)

(a)

(b)

Figure 11 (a) A landscape view of potential energy of silver atoms and (b) average potential energy distributions of fcc, hcp, bcc, ico and other atoms. Each distribution has been normalized by the unit areas under each curve.


Sliced cut view of middle section of SWCNT Top view at the open end of SWCNT

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Side view

Page 39 of 63

(a)

(b)

(c)

(d)

(e)

Figure 12 The organization of silver atoms in a nanowire encapsulated into a SWCNT of various diameter: (a) 54.00Å, (b) 40.68Å, (c) 33.85Å, (d) 20.30Å and (e) 10.85Å. Red, blue, green and yellow color atoms have been indicated hcp, bcc, fcc and ico atoms. For clear visualization, SWCNT have not shown in snapshots.



100

90

80

% of atom

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 63

others

bcc fcc hcp ico others

Τ=300Κ

ico 10 Τ=1100Κ

0 1500

1000

500

Temperature (K)

1500K

1100K

600K (a)

300K

10K (b)

Figure 13 Organization of silver atoms inside the SWCNT (d = 10.85Å) during cooling from 1500K to 10K: (a) snapshot of silver atoms at various temperatures and (b) variation in % of silver atoms with fcc, bcc, hcp, ico and others structures with decreasing temperature. Yellow and gray colour atoms depict the ico and other atoms. Red arrows indicate the sequence of snapshots during the cooling from 1500K to 10K.


0

Page 41 of 63

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a)

(b)

(c)

Figure 14 Silver atoms organization into a SWCNT of diameter d = 10.85Å: (a) snapshot of silver atom encapsulated into SWCNT, (b) magnified view of pseudo 1-D organization of encapsulated silver atoms and (c) an unit cell consist of 13 silver atoms organization as 1-5-1-51.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a) (b) (c) Figure 15 Silver atoms organization encapsulated into a SWCNT of diameter d=12.20Å: (a) snapshot of silver atom encapsulated into SWCNT, (b) magnified view of pseudo 1-D organization of encapsulated silver atoms and (c) an unit cell consist of 15 silver atoms organization as 1-6-1-6-1.


Page 42 of 63

Page 43 of 63

-2.4

Liquid phase Transition from liquid to crystalline phase

Total energy (eV/atom)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-2.6 Crystalline phase -2.8

-3.0

1500

0

d=10.85A 0 d=13.56A 0 d=20.30A 0 d=40.60A 0 d=54.00A

1250

Μetastable phase

1000

750

500

250

Temperature (K) Figure 16 Variation in potential energy of silver atoms encapsulated into a SWCNT of diameter ranging from d= 10.85Å to 54.00Å during cooling from 1500K to 10K.



1500 0

d = 10.85A 0 d = 13.56A 0 d = 20.30A 0 d = 40.60A 0 d = 54.00A

Liquid to crystalline transition

ph

0

2

ase

1000

MSD (A )

ui d

Crystalline phase

Liq

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 44 of 63

500

0 1500

Crystalline phase

Metastable phase

1250

1000

750

500

250

0

Temperature (K)

Figure 17 The mean square displacement of silver atoms encapsulated into a SWCNT of diameter ranging from d = 10.85Å to 54.00Å during cooling from 1500K to 10K.


Page 45 of 63

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC graphic

SWCNT

Encapsulation process at T=1500K

Cooling process T=1500K to T=10K Decagonal symmetry at inside the SWCNT

Silver (at T=1500K)

Internal view

Fivefold twinned plane symmetry at open ends of SWCNT

Blue, red, green and yellow colour atoms depict to bcc, hcp, fcc and ico organization, respectively



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 46 of 63

[For table of contents only] Single-walled Carbon Nanotube Engendered Pseudo-1D Morphologies of Silver Nanowire Sunil Kumar*†, Vikas Chandra Srivastava*, Gopi Kishore Mandal*, Sudip Kumar Pattanayek#, Kanai Lal Sahoo* *CSIR-National Metallurgical Laboratory, Jamshedpur, India 831007 # Indian Institute of Technology, New Delhi, India 110016 Graphical abstract

SWCNT

Encapsulation process at T=1500K

Cooling process T=1500K to T=10K Decagonal symmetry at inside the SWCNT

Silver Internal view

(at T=1500K)

Fivefold twinned plane symmetry at open ends of SWCNT

Blue, red, green and yellow colour atoms depict to bcc, hcp, fcc and ico organization, respectively

ACS Paragon Plus Environment

Page 47 of 63

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1 Simulation system consisting a globule of silver atoms and a SWCNT, which has been placed in the centre of the simulation box of size (±200 Å, ±200 Å, ±200 Å). The axis of SWCNT is along the Z-direction. The silver globule, with a temperature of 1500 K, is placed at an open end of SWCNT.


Top view

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 48 of 63

Side view


Time = 1ps T = 1500K

Time = 100ps T = 1500K

Time = 250ps T = 1500K

Time = 500ps T = 1500K

Time = 1000ps T = 1500K

Figure 2 Snapshots of side and top view of silver during encapsulation process into a SWCNT of diameter d = 40.68Å, with increasing simulation time at a fixed temperature of 1500K. Red colour arrows are indicating the progress of encapsulation process.


Page 49 of 63



0.0

ncapsulation

process PEAg- SWCNT

-0.1



PE (eV/atom)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-2.50

PEAg- Ag -2.55 0

250

500

750

1000

Time (ps) Figure 3 Variation in potential energies of silver atoms (PEAg-Ag) and between silver and carbon atoms of SWCNT (PEAg-C) during encapsulation process. (SWCNT diameter d = 40.68Å; Temperature T=1500K)







900

600



g()

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 50 of 63

300

Time=1000ps Time=100ps Time=1ps 0

5

0

 (A )

10

Figure 4 Radial distribution function g(χ) of silver atoms during encapsulation process within the SWCNT of diameter d = 40.68Å at 1500K.


Top view

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Side view

Page 51 of 63

1500K

1300K

1250K

750K

300K

10K

10K

Figure 5 Snapshots of phase transition from liquid to crystalline state of silver encapsulated into SWCNT of diameter d = 40.68Å during cooling from 1500K to 10K. Blue, red, green and yellow colour atoms pertain to bcc, hcp, fcc and ico structure, respectively. For clear visualization, atoms with random organization have not been shown in the snapshot. SWCNT has not been shown in right most snapshot due to clear visualization of solidified silver. Red colour arrows are indicating the progress of phase transition.





-0.075

PEAg-C

-0.090



PE (eV/atom)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 52 of 63

Transition from liquid to crystalline state

-2.6

PEAg-Ag

-2.8

1500

1000

500

0

Temperature (K)

Figure 6 Variation in potential energies of silver atoms (PE Ag-Ag) and between silver atoms and carbon atom of SWCNT (PEAg-C) of diameter d = 40.68Å during cooling from 1500K to 10K.


Page 53 of 63

1500K

850K

825K

300K

(a)

80

others

40

% of atoms

0.1

ico

0.0 10

hcp

0 60 30



fcc

0 6 bcc 3 0 Total energy

-2.4

Total energy eV/atom

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60




-2.8 1500

1200

900

600

300

Temperature (K)

(b) Figure 7 Liquid to solid phase transition of pure silver during cooling from 1500K to 10K: (a) snapshot of structure evolution and (b) variation of fcc, hcp, bcc, ico and other atom during cooling from 1500K to 10K. Blue, red, green and yellow colour atoms pertain to bcc, hcp, fcc and ico structure, respectively. Red colour arrows are indicating the progress of phase transition.



10K 100K 200K 300K 400K 500K 600K 700K 800K 900K 1000K 1100K 1200K 1300K 1400K 1500K

st

1500

 N. N.

1000

500





g() Arbitrary unit

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 54 of 63

0 5

10 

  Figure 8 Radial distribution function g(χ), of silver atoms encapsulated within the SWCNT of diameter d = 40.68Å during cooling from 1500K to 10K. The first nearest neighbours (1st N. N.) of silver atoms is indicated by arrows. Amorphous or liquid, transition and crystalline regions are shown by black, red and green colour lines at respective temperatures.


Page 55 of 63



100

Other bcc fcc hcp ico

other fcc 

75

% of atoms

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hcp 10

T=1290K bcc

ico

0 1500

1000

500

0

Temperature (K) Figure 9 Evolution of atomic content (in %) corresponding to fcc, hcp, bcc and ico structure of silver atoms encapsulated into SWCNT of diameter d = 40.68Å during cooling from 1500K to 10K.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 56 of 63

(b)

(a)

(c)

Figure 10 Organization of silver atoms inside the SWCNT of diameter d = 40.68Å: (a) pattern of bcc, fcc and hcp atom, (b) decagon symmetry and (c) five-fold symmetry of twinned plane of hcp atoms at the end of SWCNT. Red, blue, green and yellow color atoms have been indicated hcp, bcc, fcc and ico atoms.


Page 57 of 63



0.50

bcc fcc hcp ico other 0.25



Fraction

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.00 -3.00

-2.75

Potential energy (eV/atom)

(a)

(b)

Figure 11 (a) A landscape view of potential energy of silver atoms and (b) average potential energy distributions of fcc, hcp, bcc, ico and other atoms. Each distribution has been normalized by the unit areas under each curve.


Sliced cut view of middle section of SWCNT Top view at the open end of SWCNT

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 58 of 63

Side view


(a)

(b)

(c)

(d)

(e)

Figure 12 The organization of silver atoms in a nanowire encapsulated into a SWCNT of various diameter: (a) 54.00Å, (b) 40.68Å, (c) 33.85Å, (d) 20.30Å and (e) 10.85Å. Red, blue, green and yellow color atoms have been indicated hcp, bcc, fcc and ico atoms. For clear visualization, SWCNT have not shown in snapshots.


Page 59 of 63



100

90 others

bcc fcc hcp ico others





80

% of atom

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ico 10



0 1500

1000

500

Temperature (K)

1500K

1100K

600K (a)

300K

10K (b)

Figure 13 Organization of silver atoms inside the SWCNT (d = 10.85Å) during cooling from 1500K to 10K: (a) snapshot of silver atoms at various temperatures and (b) variation in % of silver atoms with fcc, bcc, hcp, ico and others structures with decreasing temperature. Yellow and gray colour atoms depict the ico and other atoms. Red arrows indicate the sequence of snapshots during the cooling from 1500K to 10K.


0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

(b)

Page 60 of 63

(c)

Figure 14 Silver atoms organization into a SWCNT of diameter d = 10.85Å: (a) snapshot of silver atom encapsulated into SWCNT, (b) magnified view of pseudo 1-D organization of encapsulated silver atoms and (c) an unit cell consist of 13 silver atoms organization as 1-5-15-1.


Page 61 of 63

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a) (b) (c) Figure 15 Silver atoms organization encapsulated into a SWCNT of diameter d=12.20Å: (a) snapshot of silver atom encapsulated into SWCNT, (b) magnified view of pseudo 1-D organization of encapsulated silver atoms and (c) an unit cell consist of 15 silver atoms organization as 1-6-1-6-1.





-2.4

Liquid phase Transition from liquid to crystalline phase

-2.6 Crystalline phase 

Total energy (eV/atom)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 62 of 63

-2.8

-3.0

1500

0

d=10.85A 0 d=13.56A 0 d=20.30A 0 d=40.60A 0 d=54.00A

1250

etastable phase

1000

750

500

250

Temperature (K) Figure 16 Variation in potential energy of silver atoms encapsulated into a SWCNT of diameter ranging from d= 10.85Å to 54.00Å during cooling from 1500K to 10K.


Page 63 of 63



1500 0

d = 10.85A 0 d = 13.56A 0 d = 20.30A 0 d = 40.60A 0 d = 54.00A

Liquid to crystalline transition

ph

0

2

ase

1000

u id

Crystalline phase

L iq



MSD (A )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


500

0 1500

Crystalline phase

Metastable phase

1250

1000

750

500

250

0

Temperature (K)

Figure 17 The mean square displacement of silver atoms encapsulated into a SWCNT of diameter ranging from d = 10.85Å to 54.00Å during cooling from 1500K to 10K.


Single-Walled Carbon Nanotube Engendered Pseudo-1D

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