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Cite This: ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Tuning the Electronic Structure of an Aluminum Phosphide Nanotube through Configuration of the Lattice Geometry Lauren Takahashi† and Keisuke Takahashi*,‡ †
Freelance Researcher, Central Ward, Sapporo 064, Japan Center for Materials Research by Information Integration, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 205-0047, Japan
‡
S Supporting Information *
ABSTRACT: The core lattice geometry of an aluminum phosphide (AlP) nanotube is altered from a hexagonal lattice to an octagonal lattice, and its effects on the electronic structure are investigated using first-principles calculations. The binding energy of the octagonal AlP nanotube is calculated to be −0.15 eV/atom, which denotes an exothermic reaction and results in the octagonal AlP nanotube being thermodynamically stable. Al and P atoms possess an average of 11.07 and 16.86 electrons, respectively, suggesting ionic bonding, while the atoms align to form alternating layers of elements within the nanotube wall. The electronic structure of the octagonal AlP nanotube suggests semiconductive properties of the nanotube. In addition, the presence of defects makes the nanotube more reactive against H, with an Al defect more reactive against H. By direct manipulation of the core lattice geometry and the purposeful introduction of defects, the conductivity and reactivity of an AlP nanotube can be tuned, and AlP nanotubes with properties more desirable for applications in electronics and optics can be designed. KEYWORDS: AlP nanotube, octagonal, electronic structure, density functional theory, band gap
T
have shown that two-dimensional boron nitride can form with octagonal lattice formation.18 Thus, first-principles calculations are implemented in order to investigate how manipulation of the lattice geometry affects the electronic structure of an aluminum phosphide (AlP) nanotube. For first-principles calculations, the grid-based projectoraugmented-wave method is used.19 Additionally, the Perdew− Burke−Ernzerhof (PBE) exchange correlation and spin polarization are applied for all calculations, where PBE is shown to give good accuracy for the AlP system.20,21 4 × 1 × 1 special k points of the Brillouin zone sampling are implemented, while periodic boundary conditions are applied for the x axis and 15 Å vacuum is applied to the y and z axes.22 Bader charge analysis is also carried out in order to calculate the charge transfer between Al and P atoms.23,24 Calculations for the binding energy (Eb) of the Al−P bond within the octagonal AlP nanotube are carried out using eq 1:
he discovery of carbon nanotubes has led toward the expansion and increased interest in this subfield of nanomaterials.1 Carbon nanotubes have been discovered to possess unique properties such as unusual levels of strength and increased levels of electric and thermal conductivity, making it highly attractive for applications in electronics, tissue engineering, and composite material design.2−4 Nanotubes composed of other elements have also gained attention in recent years. Boron nitride nanotubes have also become attractive for applications such as designing materials that are oxidationresistant at high temperatures, energy storage, and drug delivery.5−7 Nanotube development has also begun to extend to nanotubes composed of inorganic elements, demonstrating that nanotubes have great potential for development beyond carbon and boron nitride.8−10 In addition to carbon and boron nitride nanotubes, silicon nanotubes have also been reported to possess properties useful for applications in H storage, battery anodes, CO adsorption, and H2 dissociation.11−14 Given the similarities between carbon and boron nitride, it is possible that nanotubes consisting of Al and P atoms can be formed; in fact, reports have shown that such nanotubes can be formed.15,16 In addition, nanotubes are commonly reported to possess hexagonal lattice structures. Recent reports, however, have shown that nonhexagonal geometries such as the pentagon can be used for the lattice configuration during the design of materials.17 This possibility has also extended to two-dimensional materials, where reports © XXXX American Chemical Society
E b = E[x Aly P(tube) − xE(bulk Al) − yE(bulk P)]
(1)
Here, positive energy indicates an endothermic reaction, while an exothermic reaction is indicated by negative energy. An AlP nanotube with an octagonal lattice is designed and calculated, where the results are shown in Figure 1. The Received: December 28, 2017 Accepted: January 26, 2018 Published: January 26, 2018 A
DOI: 10.1021/acsanm.7b00403 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Letter
ACS Applied Nano Materials
The electronic structure of the octagonal AlP nanotube is investigated. The binding energy of the octagonal AlP nanotube is calculated to be −0.15 eV/atom, which denotes an exothermic reaction. Hence, the proposed AlP nanotube is thermodynamically stable. Bader analysis is also carried out in order to understand electron charge transfer. The results of Bader analysis show that Al atoms are found to have an average of 11.07 electron charges per atom. Meanwhile, P atoms are found to have an average of 16.86 electron charges per atom. These results show that Al atoms lose an average of 1.93 electron charges, while P atoms gain an average of 1.86 electron charges when present in an octagonal AlP nanotube. These results suggest ionic bonding between Al and P atoms. The density of states (DOS) is calculated where the results are collected and displayed in Figure 3. As can be seen in Figure
Figure 1. AlP nanotube with an octagonal lattice. (a) Unit cell where the lattice constant (Å) for the x axis is also listed. (b) View through the tube. (c) Side view. Atomic color code: blue, Al; yellow, P.
nanotube is designed using a unit cell (shown in Figure 1) composed of a total of 48 atoms24 Al atoms and 24 P atomsand a lattice constant of x = 10.18 Å. Additionally, the nanotube forms a ring of six octagons. As can be seen in Figure 1b, the wall of the nanotube is composed of alternating layers of Al and P atoms, giving a zigzagged appearance. This can also be observed in Figure 1c. This effect has also been reported previously for an AlP nanotube with a hexagonal lattice.15 In contrast, nanotubes consisting of carbon, boron nitride, and silicon are reported in which the atoms remain flat.11,25,26 In addition, vibrational analysis is performed for reference. See the Supporting Information for intensities and frequencies in vibrational analysis. Figure 2 shows a unit cell of the octagonal AlP nanotube where an isolated octagon (circled in red) is investigated. A
Figure 3. DOS of an AlP nanotube with an octagonal lattice configuration.
3, the octagonal AlP nanotube possesses a band gap of 1.80 eV, suggesting semiconductive properties. This band gap is found to be smaller than those previously reported for AlP nanotubes with a hexagonal lattice, which are reported to possess band gaps of 2.68 and 2.89 eV with comparable diameter lengths.15 This is also in contrast to reports of bulk AlP, which has been reported to possess a band gap of 2.5 eV.28 The difference in the band gaps can be considered to be due to the lattice configuration of the nanotube itself. Previous reports have shown that the octagonal lattice configuration can affect the conductivity.29 Thus, one can consider that the geometry of the lattice can play an important part in the design of materials for applications in electronics and optics. The effects of defects on octagonal AlP nanotubes are explored. Additionally, H is deposited on pure octagonal AlP nanotubes and on octagonal AlP nanotubes with Al and P defects in order to understand the reactivity. Figure 4 shows the structures of the octagonal AlP nanotubes with Al and P defects (Figure 4a,b) as well as the defect sites with the presence of H (Figure 4c,d). Two types of defects are considered: an Al defect (where an Al atom is missing) and a P defect (where a P atom is missing). The formation energies of the Al and P defects in octagonal AlP nanotubes are calculated to be −0.08 and −0.05 eV, respectively. The binding energy for the defect nanotubes is calculated to be −0.07 eV (Al defect) and −0.10 eV (P defect), showing that the defected octagonal AlP nanotube is
Figure 2. (a) Cross section of an octagonal AlP nanotube unit cell (a full octagon shape circled in red). (b) Side view of the full octagon (circled in red). Atomic color code: blue, Al; yellow, P. x, y, and z axes included to clarify how the unit cell is moved.
fully formed octagon is isolated (as seen in Figure 2a) in order to determine Al−P bond distances. The average Al−P bond distance within the isolated octagon is calculated to be 2.31 Å. These bond distances are found to be comparable to the bond distances 2.30 and 2.31 Å, which have been previously reported for AlP nanotubes with a hexagonal lattice.27 Additionally, these bond distances are found to be consistent throughout the AlP nanotube. Also, as can be seen in Figure 2b, the Al−P bonds form where the octagon appears to be concave, which can be considered the reason behind the alternation of Al and P atoms within the nanotube wall. B
DOI: 10.1021/acsanm.7b00403 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Letter
ACS Applied Nano Materials
Figure 4. AlP nanotubes with the presence of Al and P defects. (a) An Al defect. b) H is adsorbed onto the P atom nearest the Al defect. c) A P defect. d) H is adsorbed onto the Al atom nearest the P defect. Atomic color code: blue- Al, yellow- P, white- H.
thermodynamically stable. In addition, there is no band gap for either of the Al/P-defected AlP nanotubes. These results show that the octagonal AlP nanotube with an Al defect is more likely to form compared to the P defect. See the Supporting Information for the DOS of the defected octagonal AlP nanotubes. H is deposited over a defect-free octagonal AlP nanotube, an octagonal AlP nanotube with an Al defect, and an octagonal AlP nanotube with a P defect. In the case of a defect-free AlP nanotube, the binding energy is calculated to be 0.82 eV when H is deposited over an Al atom. Additionally, the binding energy is calculated to be 1.00 eV when H is deposited over a P atom on a defect-free octagonal AlP nanotube. These binding energies are both endothermic against H, suggesting that a defect-free octagonal AlP nanotube does not react in the presence of H. In contrast, the reactivity is seen when H is deposited onto octagonal AlP nanotubes with the presence of defects. In the case of the Al defect, a H atom is deposited over the P atom closest to the defect site and is calculated to have a binding energy of −1.20 eV with a P−H bond distance of 1.44 Å. Bader analysis shows that after adsorption the H atom has 1.34 electron charges, while the P atom it bonds to has a total of 15.82 electron charges. When a P defect is present, a H atom is deposited over the Al atom closest to the defect site and is calculated to have a binding energy of −1.04 eV with an Al−H bond distance of 1.67 Å. In this case, Bader analysis also shows that, after adsorption, the H atom has 1.77 electron charges, while the Al atom has 11.05 electron charges. In both cases, the H atom gains electrons from the Al and P atoms that it is
bonding with. The band gaps of the Al defect with the H atom and the P defect with the H atom are also calculated to be 0.28 and 1.35 eV, respectively. See the Supporting Information for the DOS of the defected octagonal AlP nanotubes with an H atom. The binding energies of H adsorption on both defect cases are exothermic, suggesting that octagonal AlP nanotubes are able to adsorb H if defects are present within the nanotube. From these results, one can come to understand that the lattice configuration of the nanotube has an impact on various properties of a nanotube. Although the average Al−P bond distances of the octagonal AlP nanotube are in good agreement with the reported bond distances of a hexagonal AlP nanotube, its octagonal lattice allows for a more pronounced alternation of the Al and P atoms. This results in alternating layers of Al and P atoms within the nanotube. Additionally, the octagonal lattice results in a band gap of 1.80 eV, which is smaller than those reported for an AlP nanotube with a hexagonal lattice and suggests semiconductive properties. Furthermore, the presence of defects makes the octagonal AlP nanotube reactive against H, where Al defects are found to be more reactive than P defects. One can see that the lattice configuration of an AlP nanotube can directly impact the electric structures of the nanotube. Thus, by manipulation of the lattice geometry of the AlP nanotube and through the purposeful introduction of defects, it becomes possible to tune the conductivity and reactivity of an AlP nanotube more directly, and AlP nanotubes can be designed with properties more desirable for applications in electronics and optics. C
DOI: 10.1021/acsanm.7b00403 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Letter
ACS Applied Nano Materials
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Calculations to Grand Canonical Monte Carlo Simulations. J. Phys. Chem. C 2008, 112, 5598−5604. (12) Park, M.-H.; Kim, M. G.; Joo, J.; Kim, K.; Kim, J.; Ahn, S.; Cui, Y.; Cho, J. Silicon Nanotube Battery Anodes. Nano Lett. 2009, 9, 3844−3847. (13) Beheshtian, J.; Baei, M. T.; Peyghan, A. A. Theoretical study of CO adsorption on the surface of BN, AlN, BP and AlP nanotubes. Surf. Sci. 2012, 606, 981−985. (14) Beheshtian, J.; Soleymanabadi, H.; Kamfiroozi, M.; Ahmadi, A. The H2 Dissociation on the BN, AlN, BP and AlP nanotubes: a Comparative Study. J. Mol. Model. 2012, 18, 2343−2348. (15) Lisenkov, S.; Vinogradov, G. A.; Lebedev, N. New Class of NonCarbon AlP Nanotubes: Structure and Electronic Properties. JETP Lett. 2005, 81, 185−189. (16) Ahmadi Peyghan, A.; Pashangpour, M.; Bagheri, Z.; Kamfiroozi, M. Energetic, Structural, and Electronic Properties of Hydrogenated Al 12 P 12 Nanocluster. Phys. E 2012, 44, 1436−1440. (17) Li, X.; Zhang, S.; Wang, F. Q.; Guo, Y.; Liu, J.; Wang, Q. Tuning The Electronic and Mechanical Properties of Penta-Graphene Via Hydrogenation and Fluorination. Phys. Chem. Chem. Phys. 2016, 18, 14191−14197. (18) Sheng, X.-L.; Cui, H.-J.; Ye, F.; Yan, Q.-B.; Zheng, Q.-R.; Su, G. Octagraphene As a Versatile Carbon Atomic Sheet For Novel Nanotubes, Unconventional Fullerenes, and Hydrogen Storage. J. Appl. Phys. 2012, 112, 074315. (19) Mortensen, J. J.; Hansen, L. B.; Jacobsen, K. W. Real-Space Grid Implementation of the Projector Augmented Wave Method. Phys. Rev. B: Condens. Matter Mater. Phys. 2005, 71, 035109. (20) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865. (21) Jianping, S. Stability and Electronic Structures of Single-walled AlP Nanotubes by First Principle Study. Procedia Eng. 2011, 15, 5062− 5066. (22) Monkhorst, H. J.; Pack, J. D. Special Points for Brillouin-Zone Integrations. Phys. Rev. B 1976, 13, 5188. (23) Tang, W.; Sanville, E.; Henkelman, G. A Grid-based Bader Analysis Algorithm without Lattice Bias. J. Phys.: Condens. Matter 2009, 21, 084204. (24) Henkelman, G.; Arnaldsson, A.; Jonsson, H. A Fast and Robust Algorithm for Bader Decomposition of Charge Density. Comput. Mater. Sci. 2006, 36, 354−360. (25) Zhao, J.; Buldum, A.; Han, J.; Lu, J. P. Gas Molecule Adsorption in Carbon Nanotubes and Nanotube Bundles. Nanotechnology 2002, 13, 195. (26) Golberg, D.; Bando, Y.; Tang, C.; Zhi, C. Boron Nitride Nanotubes. Adv. Mater. 2007, 19, 2413−2432. (27) Mirzaei, M.; Mirzaei, M. Aluminum Phosphide Nanotubes: Density Functional Calculations of Aluminum-27 and Phosphorus-31 Chemical Shielding Parameters. J. Mol. Struct.: THEOCHEM 2010, 951, 69−71. (28) Berger, L. Semiconductor Materials; CRC Press, 1996; p 125. (29) Takahashi, L.; Takahashi, K. Structural Stability and Electronic Properties of an Octagonal Allotrope of Two Dimensional Boron Nitride. Dalton Trans. 2017, 46, 4259−4264.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsanm.7b00403. Vibrational frequency analysis of the octagonal AlP nanotube, the DOS of octagonal AlP nanotubes with Al and P defects, and the DOS of Al- and P-defected octagonal AlP nanotubes with H (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Lauren Takahashi: 0000-0001-9922-8889 Keisuke Takahashi: 0000-0002-9328-1694 Author Contributions
The authors contributed equally. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work is funded by a JSPS KAKENHI Grant-in-Aid for Young Scientists (B) (Grant JP17K14803) and Materials Research by Information Integration Initiative (MI2I) project of the Support Program for Starting Up Innovation Hub from Japan Science and Technology Agency (JST). Computational work is supported in part by the Hokkaido university academic cloud, information initiative center, Hokkaido University, Sapporo, Japan.
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REFERENCES
(1) Oberlin, A.; Endo, M.; Koyama, T. Filamentous growth of Carbon Through Benzene Decomposition. J. Cryst. Growth 1976, 32, 335−349. (2) Yu, M.-F.; Lourie, O.; Dyer, M. J.; Moloni, K.; Kelly, T. F.; Ruo, R. S. Strength and Breaking Mechanism of Multiwalled Carbon Nanotubes Under Tensile Load. Science 2000, 287, 637−640. (3) Newman, P.; Minett, A.; Ellis-Behnke, R.; Zreiqat, H. Carbon Nanotubes: Their Potential and Pitfalls For Bone Tissue Regeneration and Engineering. Nanomedicine 2013, 9, 1139−1158. (4) Zhang, M.; Fang, S.; Zakhidov, A. A.; Lee, S. B.; Aliev, A. E.; Williams, C. D.; Atkinson, K. R.; Baughman, R. H. Strong, Transparent, Multifunctional, Carbon Nanotube Sheets. Science 2005, 309, 1215−1219. (5) Chen, Y.; Zou, J.; Campbell, S. J.; Le Caer, G. Boron Nitride Nanotubes: Pronounced Resistance to Oxidation. Appl. Phys. Lett. 2004, 84, 2430−2432. (6) Arico, A. S.; Bruce, P.; Scrosati, B.; Tarascon, J.-M.; Van Schalkwijk, W. Nanostructured Materials for Advanced Energy Conversion and Storage Devices. Nat. Mater. 2005, 4, 366−377. (7) Weng, Q.; Wang, B.; Wang, X.; Hanagata, N.; Li, X.; Liu, D.; Wang, X.; Jiang, X.; Bando, Y.; Golberg, D. Highly Water-Soluble, Porous, and Biocompatible Boron Nitrides For Anticancer Drug Delivery. ACS Nano 2014, 8, 6123−6130. (8) Tenne, R. Inorganic Nanotubes and Fullerene-Like Nanoparticles. J. Mater. Res. 2006, 21, 2726−2743. (9) Fan, R.; Karnik, R.; Yue, M.; Li, D.; Majumdar, A.; Yang, P. DNA Translocation in Inorganic Nanotubes. Nano Lett. 2005, 5, 1633− 1637. (10) Rao, C. N. R.; Nath, M. Inorganic Nanotubes. Dalton Trans. 2003, 1−24. (11) Lan, J.; Cheng, D.; Cao, D.; Wang, W. Silicon Nanotube as a Promising Candidate For Hydrogen Storage: From the First Principle D
DOI: 10.1021/acsanm.7b00403 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
