Cite this Article
Miao Zhenzhen, Cao Can, Zhang Bei, Duan Haiming, Long Mengqiu. Effects of 3d-transition metal doping on the electronic and magnetic properties of one-dimensional diamond nanothread. Chinese Physics B, 2020, 29(6): 066101  
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Effects of 3d-transition metal doping on the electronic and magnetic properties of one-dimensional diamond nanothread
Miao Zhenzhen1, Cao Can2, Zhang Bei1, Duan Haiming1, †, Long Mengqiu1, 2, ‡
Institute of Low-dimensional Quantum Materials and Devices, School of Physics Science and Technology, Xinjiang University, Urumqi 830046, China
Hunan Key Laboratory of Super Micro-structure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha 410083, China

 

† Corresponding author. E-mail: dhm@xju.edu.cn mqlong@csu.edu.cn

Project supported by the National Natural Science Foundation of China (Grant Nos. 21673296 and 11664038) and the Natural Science Foundation of Xinjiang Uygur Autonomous Region of China (Grant No. 2019D01C038).

Abstract

The diamond nanothread (DNT), a new one-dimensional (1D) full carbon sp3 structure that has been successfully synthesized recently, has attracted widespread attention in the carbon community. By using the first-principles calculation method of density functional theory (DFT), we have studied the effects of 3d transition metal (TM) atomic doping on the electronic and magnetic properties of DNT. The results show that the spin-polarized semiconductor characteristics are achieved by doping Sc, V, Cr, Mn, and Co atoms in the DNT system. The magnetic moment ranges from 1.00 μB to 3.00 μB and the band gap value is from 0.35 eV to 2.54 eV. The Fe-doped DNT system exhibits spin-metallic state with a magnetic moment of 2.58 μB, while the Ti and Ni-doped DNT systems are nonmagnetic semiconductors. These results indicate that the 3d TM atoms doping can modulate the electronic and magnetic properties of 1D-DNT effectively, and the TM-doped DNT systems have potential applications in the fields of electronics, optoelectronics, and spintronics.

PACS: ;61.46.-w;;62.23.Hj;;71.20.-b;;75.75.-c;
Keyword:;diamond nanothread;;transition metal atom;;doping;;electronic and magnetic property;
1. Introduction

In the past few decades, carbon-based nanomaterials have been extensively studied in the scientific community for their unique and fascinating physical and chemical properties, many new carbon allotropes, such as fullerenes (C60),[1,2] carbon nanotubes (CNTs),[3] graphene,[4,5] and graphyne,[6,7] have been added to the family of carbon. In 2015, Fitzgibbons et al.[8] successfully synthesized a new carbon nanomaterial through the high-pressure solid state reaction of benzene: diamond nanothread (DNT), which successfully became the newest member of the carbon family. Its surface is functionalized by hydrogen, the C:H ratio is 1 : 1, the C–C bond is a closely packed sp3 hybrid, and the carbon atoms are arranged in a rhombohedral tetrahedral pattern.[9] The term “nanothread” emphasizes its ultra-small diameter, which represents ideal one-dimensional (1D) material.[10] According to molecular dynamics simulations, DNT has excellent mechanical properties and thermal stability than other carbon nanostructures, which ideal strength is 26.4 nN (134 GPa), Young’s modulus is 850 GPa, and specific strength and stiffness are 4.13× 107 N⋅m/kg and 2.6× 108 N⋅m/kg, respectively.[11–14] And the thermal stability of DNT shows that when the system is heated to 300 °C–400 °C, its characteristic structure will not change over a long period of time, and its mechanical strength can be retained even after 1%–2% hydrogen analysis.[15] The excellent properties of the DNT system indicate its great potential in the development of lightweight and strong materials.

As a new sp3-hybridized 1D nanomaterial, DNT has high strength and thermal stability.[14,16–18] However, the wideband gap (∼ 3.9 eV) of DNT prevents applications in the field of electronics.[9] Traditionally, a common method of modifying the electronic properties of a material is to dope with foreign atomic species. For example, carbon nanotubes are doped via an alkali metal atom (Li or K) to cause charge transfer between an alkali metal atom and the carbon host.[19–21] Modulation of the electronic structure of boron nitrogen nanotube (BNNT) has been substantially achieved by doping the BNNT with the metal atoms Au, Al, Pt, Ti, and V.[22–25] By N-doping, the zigzag graphene nanoribbon (ZGNR) can be a spin gapless semiconductor from an antiferromagnetic semiconductor, and the energy level is changed.[26,27] Since magnetic nanostructure is an important research field in science and technology, researchers have conducted extensive study on magnetic materials by doping atoms. For example, the spontaneous magnetization of the system is achieved by replacing the boron or nitrogen atoms of the BNNTs with magnetic transition metal (TM) atoms.[28,29] The substitution of the TM atom on the phosphorene or molybdenum disulfide (MoS2), which will cause magnetization in the system.[30–35]

Owing to the metal atoms have different electronic and magnetic properties, the structure, electronic, and magnetic properties of the metal-doped DNT system are intriguing and still not well understood. Moreover, the substitution doping is of great significance for the development of nanoelectronic devices.[36,37] Therefore, in this study, we have carried out a systematic study on the substitution of a single C atom in DNT by different transition metal (TM) atoms within density functional theory (DFT). Our results show that doping TM atoms can affect the electronic and magnetic properties of DNT. The rest of the paper is organized as follows. In Section 2, we detail the computational methods of the first principles calculations and the models of the TM atoms-dopped DNTs. The electronic and magnetic properties of the TM-doped DNTs are investigated in Section 3. The conclusions are given in Section 4.

2. Computational methods

In this research, our calculations are performed with DFT as implemented in Vienna ab initio simulation package (VASP),[38–40] adopting a generalized gradient approximation (GGA)[41] for the exchange–correlation potential. The ion–electron interaction is treated with the projected-augmented wave (PAW), and the plane wave cutoff energy for the wave function is set to 500 eV. The actual DNT unit cell has a lattice constant of 4.3 Å. We use a rectangular supercell with a size of 20 Å× 20 Å×8.6 Å. With the length of c in the axial or z direction[42] being twice of the periodicity of the original DNT. The supercell contains four layers of atoms in the direction of the tube axis, giving a total of 64 atoms in the supercell, which is selected as the model. A single carbon atom in the edge of the DNT is replaced by a TM atom to form a TM-doped DNT. Considering the periodic boundary condition, the closest distance between the two DNTs is no less than 15 Å to avoid possible coupling between the TM in the parallel direction of the DNT. The criterion of convergence for structure relaxation is the change of total energy less than 10−6 eV and the residual force on atom less than 0.001 eV/Å. The reciprocal space is sampled by a fine grid of 1 × 1 × 13 k-point in the Brillouin zone, respectively.

3. Results and discussions
3.1. Geometry of TM-doped DNTs

The TM-doped DNT system is constituted by replacing a single C atom in the edge of the DNT with a TM atom, as shown in Fig. 1. After relaxation, the local symmetry of the 3d TM-doped DNT is destroyed under Jahn–Teller distortion,[43] resulting in slight deformation of the system. The lattice constant, bond length, and bond angle of the 3d TM-doped DNT structure are presented in Table 1, respectively. We can find that the equilibrium lattice constants of the 3d TM-doped DNTs systems are between 8.65 Å–8.72 Å. Compared to the pure DNT system, since the doped metal atom size is larger than that of the C atom, the lattice constant value of the doped DNT is larger than that of the pure DNT (8.60 Å). And for the bond length and bond angle values between the 3d TM atom and its adjacent carbons in the doped DNT system, it can be clearly seen that, owing to the radius of the 3d TM atom is larger than that of the substituted C atom, all TM-C bond lengths (DTM–C) in the 3d TM-doped DNTs system are longer than the C–C bond length (1.570 Å) of the pure DNT system, while the bond angles are smaller than the average bond angle (110.296°) of the pure DNT system. Among them, the average bond length value of the Sc-, Ti-, Cu-, and Zn-doped DNTs system is around 2.00 Å, and the corresponding average bond angle is between 85°–90°. For the Fe-doped DNT system, we can see the bond length value is about 1.87 Å and bond angle value is about 103°, which have the smallest difference from the pure DNT. These results of the changes in bond length and bond angle indicate that there is structural distortion around the 3d TM impurity in the doped DNTs, as shown in Fig. 1.

Fig. 1. The geometry is optimized for the 3d TM-doped DNTs: (a) front, and (b) side view of the doped DNT. The grey and white balls refer to C and H atoms, and the red ball refers to the doping atoms, including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, respectively.

To analyze the stability of the doping configurations, we calculated the formation energy Ef of the 3d TM-doped DNTs, which is defined as follows:

where E(doped) is the total energy of the 3d TM-doped DNT system, μ(C) is the chemical potential of the C atom, μ(TM) is the chemical potential of the isolated 3d TM atom, E(pure) is the energy of pristine DNT, and n, m represent the number of doped TM atoms and substituted C atoms, respectively.[36,44] The corresponding calculated Ef of these TM atom-doped DNTs is shown in Table 2. Among them, we can find that there are positive formation energies for the Cu- and Zn-doped DNTs, and the corresponding values are 1.986 eV and 3.770 eV, respectively. In addition, the other 3d TM-doped DNTs have negative formation energies and the negative maximum is –2.22 eV for the Ti-doped DNT system. According to the fact that the positive value of the formation energy is endothermic and the negative value is exothermic. Compared with the Cu- and Zn-doped DNT system, other 3d TM-doped DNT systems would be more stable. Furthermore, it can also be seen from the formation energy in Table 2 that other TM atoms are good substitution for the C in the DNT because they can be well combined with the doped structure. Therefore, in the following calculations, we have considered only the DNT systems doped with other 3d TM atoms (except Cu and Zn dopings).

Table 1.

Lattice constant of an atom replaced by a transition metal (TM) atom in the DNT, the bond length and the corresponding bond angle between TM and its three nearest neighbor C atoms.

.
Table 2.

Formation energy and band gap of the 3d TM-doped DNT systems and pure DNT system.

.
3.2. Electronic structures

The spin-dependent electronic structures of 3d TM-adsorbed DNTs are plotted in Fig. 2. The previous study has demonstrated that the pure (3,0) DNT is a direct band gap semiconductor with a band gap of 3.92 eV.[10] After TM atoms are doped, the band gap is significantly reduced, which makes the carrier concentration increase, and a flat band gap appears at the Fermi level (FL). Because the transition metal atoms are doped, the outermost electrons of the metal atoms will be transferred, which changes the overall charge properties of the DNT system. The internal charge of the DNT system is reorganized, and the overall energy level will be relatively displaced. As shown in Figs. 2(a)–2(h), we can find that the band structures of the TM-doped DNTs substantially depend on the specific impurity atoms. Firstly, it is seen that the spin-up and spin-down states are degenerated in the Ti- and Ni-doped systems, and a direct band gap of 2.45 eV and 1.78 eV can be observed respectively, becoming markedly narrower than that of the pure DNT. Then, we observed that both the spin-up and the spin-down states across the FL in Fig. 2(f), which indicates that the Fe-doped system behaves the spin-splitting metallic property, as displayed in the plug-in of Fig. 2(f). Thirdly, with regard to Sc-, V-, Cr-, Mn-, and Co-doped DNTs systems, we can find that the spin-splitting semiconductor properties, and the spin-up (spin-down) band gap values are in the range of 0.35 eV – 1.71 eV (0.56 eV–2.54 eV), which would be useful in spintronic applications. From the above analyses, we can conclude that the doping of 3d TM atoms can modulate the band gap of the DNT system effectively, and transforming the DNT conversion from metal characteristics to spin-splitting semiconductor characteristics.

Fig. 2. Electronic structures of different 3d TM atom-doped DNT, panels (a)–(h) refer to Sc, Ti, V, Cr, Mn, Fe, Co, Ni, respectively. The black and red lines describe the spin-up and spin-down bands.

From the band structure we can also find that the spin-up and spin-down states of the 3d TM-doped DNTs system are non-degenerate (except Ti- and Ni-doped DNTs systems) with spin polarization generation. The 3d TM atom is doped with the DNTs system, and the impurity band is introduced in the band structure to reduce the band. In order to further understand the electronic structure and reveal the origin of magnetism, figure 3 shows the partial density of states (PDOS) of the TM atom and its three C atoms (C3) connected to the TM atom. As can be seen from Figs. 3(a)–3(b), the PDOS peaks of Sc- and Ti-doped DNTs are primarily composed of the TM 3d states and also contain some C3 2p states near FL. As shown for the Sc-doped DNT system, an interaction can be seen between 3d orbital of Sc atoms and 2p orbital of C3 atoms. Therefore, we conclude that the magnetic moment of the doped DNT system would be originated from the polarization of TM 3d electrons and C3 2p electrons. For the V-, Cr-, Mn-, Fe-, Co-, and Ni-atoms-doped DNT systems, as can be seen in Figs. 3(c)–3(h), it is clearly seen that the PDOS is mainly provided by the 3d orbital of the metal atom at the FL. In the case of Ti and Ni doping, figures 3(b) and (3h) show a symmetrical PDOS for spin-up and spin-down states below the FL indicating the nonmagnetic phenomenon. Moreover, we also studied the d electron distribution at the FL in Fig. 3. In spin-polarized systems, we found that the major source of spin polarization of each TM atom originated from different d orbitals. For instance, the major contribution to the magnetic moment in Mn doping stems from the dx2 orbital. In the V-doped system, mostly the dxz and dx2 orbitals are the major source of spin polarization. In Cr and Fe doping, three different orbitals such as dxz, dx2, and dyz give rise to the magnetic moment of the Cr and Fe atoms. These results correspond with the calculated band structures and spin densities.

Fig. 3. Calculated partial density of states (PDOS) of the 3d TM atom and its nearest-neighbor C atom for each substitutional doped DNT: (a) Sc-DNT, (b) Ti-DNT, (c) V-DNT, (d) Cr-DNT, (e) Mn-DNT, (f) Fe-DNT, (g) Co-DNT, (h) Ni-DNT. The FL is set to zero energy and indicated by the vertical green dashed line.
3.3. Magnetic properties

The magnetic moments of the TM-doped DNTs are depicted in Fig. 4. The magnetic moments of the TM-doped DNTs should mainly originate from the doped TM impurities, since the ground states of the pristine DNT are nonmagnetic. As the atomic number increases, the variation of magnetic moment in Fig. 4 can be divided into three categories. Firstly, the magnetic moments of Ti- and Ni-doped systems are zero. Secondly, the magnetic moments of the Cr-, Mn-, and Fe-substituted systems are larger than 1 μB. Particularly, the magnetic moment of the Mn substituted system is the maximum (3 μB) owing to the outermost valence electron of the Mn atom is half full. Thirdly, for the Sc-, V-, and Co-doped systems, the magnetic moment appears as a fixed value (1 μB). Furthermore, we find that most of the TM-doped DNTs exhibit a magnetic moment, which is mainly due to the local magnetic moment of the doped atoms caused by the strong spin polarization.

Fig. 4. Magnetic moments of the 3d series TM atoms substituted DNT as a function of the number of valence electrons.

In order to obtain insight into the magnetic origin, we have calculated the spin density diagram for the 3d TM-doped DNTs as displayed in Fig. 5. From Fig. 5, we notice that the magnetism is mainly attributed to the TM atom with a strong localized magnetic moment. First of all, it is hardly any spin density can be observed for the Ti- and Ni-doped DNT systems. Then, For the V-, Cr-, Mn-, and Fe-doped DNTs systems, the TM and its adjacent C3 atoms provide most of magnetic moments in the spin-up state, while the C3 atoms around the doped Cr and Mn atoms provide spin-down state. Thirdly, in Sc-doped DNT system, it can be seen that in addition to the metal atom, the C3 atoms connected to the metal atoms also provide spin density and have contributions to the magnetic moment.

Fig. 5. Spin density for single TM substitutionally doped DNT systems. Top and side views of (a) Sc-DNT, (b) Ti-DNT, (c) V-DNT, (d) Cr-DNT, (e) Mn-DNT, (f) Fe-DNT, (g) Co-DNT, (h) Ni-DNT. Yellow and blue represent spin-up and spin-down, respectively. The isosurface is taken as 0.0002 e/Å3 for panel (a); and 0.01 e/Å3 for panels (b)–(h).
4. Conclusions

In summary, based on the first-principles study of the density functional theory, the effects of TM atomic doping on the electronic and magnetic properties of DNT were investigated. Our results show that the TM atom doping retains the original band gap characteristics in the spin-polarization state except the impurity band near the FL. For Sc-, V-, Cr-, Mn-, and Co-doped DNT systems, the characteristics of the spin-polarized semiconductor are realized. The magnetic moments are in the range from 1.00 μB to 3.00 μB, wherein the maximum magnetic moment is generated by doping Mn atom in the DNT system, and the spin-up (spin-down) band gap value ranging from 0.35 eV to 1.71 eV (0.56 eV to 2.54 eV). The Fe-doped DNT system exhibits metallic state with a magnetic moment of 2.58 μB, while the Ti- and Ni-doped DNTs systems are nonmagnetic semiconductors. These results have demonstrated that the doping of 3d TM atoms can reduce the band gap value of the DNT system and have potential to generate spin polarization, thereby, providing a viable mean for designing materials in electronic and spintronics devices.

Reference
[1] Liu J Rinzler A G Dai H Hafuer J H Bradley R K Boul P J Lu A Iverson T Shelimov K Huffman C B Rodriguez-Macias F Shon Y S Lee T R Colbert D T Smally R E 1998 Science 280 1253
[2] Kroto H W Heath J R O’Brien S C Curl R F Smalley R E 1985 Nature 318 162
[3] Xia Y Yang P Sun Y Wu Y Mayers B Gates B Yin Y Kim F Yan H 2003 Adv. Mater. 15 353
[4] Zhang D Long M Q Zhang X Ouyang F Li M Xu H 2015 J. Appl. Phys. 117 014311
[5] Zhang H 2015 ACS Nano 9 9451
[6] Peng D D Zhang X J Li X B Wu D Long M Q 2018 J. Appl. Phys. 124 184303
[7] Long M Q Tang L Wang D Li Y L Shuai Z 2011 ACS Nano 5 2593
[8] Fitzgibbons T C Guthrie M Xu E S Crespi V H Davidowski S K Cody G D Alem N Badding J V 2015 Nat. Mater. 14 43
[9] Stojkovic D Zhang P Crespi V H 2001 Phys. Rev. Lett. 87 125502
[10] Wu W Bo T Shan G Yang S A Gang Z 2018 J. Phys. Chem. 122 3101
[11] Silveira J F R V Muuiz A R 2017 Carbon 113 260
[12] Feng C Xu J Zhang Z Wu J 2017 Carbon 124 9
[13] Xiao J Chen M M Liu W J He J Pan C N Long M Q 2019 Physica 111 37
[14] Podlivaev A I Openov L A 2017 Semiconductors 51 636
[15] Openov L A Podlivaev A I 2016 JETP Lett. 104 193
[16] Zhan H Gang Z Zhang Y Tan V B C Bell J M Gu Y 2016 Carbon 98 232
[17] Zhan H Gang Z Bell J M Gu Y 2016 Carbon 107 304
[18] Zhu T Ertekin E 2016 Nano Lett. 16 4763
[19] Zhao J Buldum A Han J Ping L J 2000 Phys. Rev. Lett. 85 1706
[20] Jing L Nagase S 2004 Phys. Rev. 69 205304
[21] Jo C Kim C Lee Y H 2002 Phys. Rev. 65 035420
[22] Mirzaei M Nouri A 2010 J. Mol. Struct. Theochem. 942 83
[23] Dong Q Li X M Tian W Q Huang X R Sun C C 2010 J. Mol. Struct. Theochem. 948 83
[24] Durgun E Jang Y R Ciraci S 2007 Phys. Rev. 76 73413
[25] Yao K L Min Y Zhu S C Gao G Y Liu Z L Cheng H G 2008 Phys. Lett. 372 5609
[26] Li Y F Zhou Z Shen P W Chen Z F 2009 ACS Nano 3 1952
[27] Shan S Y Wei T Z Jiang Q 2010 IEEE T. Nanotechnol. 9 78
[28] He K H Zhang G Chen G Wan M Ji G F 2008 Physica 403 4213
[29] Li X M Wei Q T Qi D Huang X R Sun C C Lei J 2011 Comput. Theor. Chem. 964 199
[30] Yang G Xu S Wei Z Ma T Wu C 2016 Phys. Rev. 94 075104
[31] Jiang J Wang X Yan S 2018 Comput. Mater. Sci. 153 10
[32] Luo Y Ren C Wang S Li S Zhang P Yu J Sun M Sun Z Tang W 2018 Nanoscale Res. Lett. 13 282
[33] Babar R Kabir M 2016 J. Phys. Chem. 120 14991
[34] Yu W Zhu Z Niu C Y Li C J Cho H Jia Y 2016 Nanoscale Res. Lett. 11 77
[35] Andriotis A N Menon M 2014 Phys. Rev. 90 125304
[36] Li Y J Li S L Gong P Li Y L Fang X Y Jia Y H Cao M S 2018 Physica 104 247
[37] Lia Y H Gong P Li S L Ma W H Fang X Y Yang Y Y Cao M S 2020 Phys. Lett. 384 126106
[38] Kresse G Joubert D 1999 Phys. Rev. 59 1758
[39] Kresse G 1995 J. Non-Cryst. Solids 192-193 222
[40] Kresse G Furthmülle J 1996 Phys. Rev. 54 11169
[41] Sun M L Slanina Z Lee S L 1995 Chem. Phys. Lett. 233 279
[42] Li Y L Gong P Fang X Y 2020 Chin. Phys. 29 037304
[43] Ma Y Lehtinen P O Foster A S Nieminen R M 2004 New J. Phys. 6 68
[44] Stern R Dongre B Madsen G K H 2016 Nanotechnology 27 334002