Real-time deformation of individual multiwalled boron nitride nanotubes (BNNTs) was investigated using an atomic force microscopy (AFM) stage installed inside the chamber of a transmission electron microscopy (TEM) system. These in situ AFM-TEM experiments were conducted in following two deformation regimes: a small-angle (∼65°) and a large-angle (∼120°) cyclic bending process. BNNTs survived from the low-angle test and their modulus was determined as ∼0.5 TPa. Fracture failure of individual BNNTs was discovered in the large-angle cyclic bending. The brittle failure mechanism was initiated from the outermost walls and propagated toward the tubular axis with discrete drops of applied force

Ghassemi, Hessam Mir Shah

Lee, C. H.

Shahbazian-Yassar, Reza

Yap, Yoke Khin

English

H. M. Ghassemi

C. H. Lee

Y. K. Yap

R. S. Yassar

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Journal of Applied Physics

Real-time fracture detection of individual boron nitride nanotubes in severe cyclic deformation processes

Michigan Technological University

Michigan Technological University Digital Commons @ Michigan Tech Department of Physics Publications Department of Physics 7-29-2010 Real-time fracture detection of individual boron nitride nanotubes in severe cyclic deformation processes Hessam Mir Shah Ghassemi Michigan Technological University C. H. Lee Michigan Technological University Yoke Khin Yap Michigan Technological University Reza Shahbazian-Yassar Michigan Technological University Follow this and additional works at: https://digitalcommons.mtu.edu/physics-fp  Part of the Physics Commons Recommended Citation Ghassemi, H. M., Lee, C. H., Yap, Y. K., & Shahbazian-Yassar, R. (2010). Real-time fracture detection of individual boron nitride nanotubes in severe cyclic deformation processes. Journal of Applied Physics, 108(2), 024314. http://dx.doi.org/10.1063/1.3456083 Retrieved from: https://digitalcommons.mtu.edu/physics-fp/296 Follow this and additional works at: https://digitalcommons.mtu.edu/physics-fp  Part of the Physics Commons J. Appl. Phys. 108, 024314 (2010); https://doi.org/10.1063/1.3456083 108, 024314© 2010 American Institute of Physics.Real-time fracture detection of individualboron nitride nanotubes in severe cyclicdeformation processesCite as: J. Appl. Phys. 108, 024314 (2010); https://doi.org/10.1063/1.3456083Submitted: 15 March 2010 . Accepted: 21 May 2010 . Published Online: 29 July 2010H. M. Ghassemi, C. H. Lee, Y. K. Yap, and R. S. YassarARTICLES YOU MAY BE INTERESTED INBoron nitride nanotubes: Pronounced resistance to oxidationApplied Physics Letters 84, 2430 (2004); https://doi.org/10.1063/1.1667278Elastic modulus and resonance behavior of boron nitride nanotubesApplied Physics Letters 84, 2527 (2004); https://doi.org/10.1063/1.1691189Mechanical strength of boron nitride nanotube-polymer interfacesApplied Physics Letters 107, 253105 (2015); https://doi.org/10.1063/1.4936755Real-time fracture detection of individual boron nitride nanotubes in severecyclic deformation processesH. M. Ghassemi,1 C. H. Lee,2 Y. K. Yap,2,a and R. S. Yassar1,b1Department of Mechanical Engineering-Engineering Mechanics, Michigan Technological University, 1400Townsend Dr., Houghton, Michigan 49931, USA2Department of Physics, Michigan Technological University, 1400 Townsend Dr., Houghton, Michigan49931, USAReceived 15 March 2010; accepted 21 May 2010; published online 29 July 2010Real-time deformation of individual multiwalled boron nitride nanotubes BNNTs was investigatedusing an atomic force microscopy AFM stage installed inside the chamber of a transmissionelectron microscopy TEM system. These in situ AFM-TEM experiments were conducted infollowing two deformation regimes: a small-angle 65° and a large-angle 120° cyclic bendingprocess. BNNTs survived from the low-angle test and their modulus was determined as 0.5 TPa.Fracture failure of individual BNNTs was discovered in the large-angle cyclic bending. Thebrittle failure mechanism was initiated from the outermost walls and propagated toward thetubular axis with discrete drops of applied forces. © 2010 American Institute of Physics.doi:10.1063/1.3456083I. INTRODUCTIONBoron nitride nanotubes BNNTs possess lattice struc-tures similar to carbon nanotubes CNTs but have a largetheoretical band gap of 5.5 eV.1 These one-dimensionalnanostructures are predicted to have exceptional mechanicalproperties and applicable for high-strength composites. Veryfew experiments have been performed to date with respect tothe experimental examination of mechanical properties ofBNNTs. In order to enable the future application of BNNTsin future nanoscale or microscale devices, it is, therefore,important to understand the failure and deformation mecha-nisms of these nanotubes.The authors of this manuscript recently conducted athorough literature review of the theoretical and experimen-tal understanding of BNNT’s mechanics.2 Theoretical studiespredict that the Young’s modulus of BNNTs can be up to 1.2TPa.3,4 Experimentally, the Young’s modulus was measuredto be 0.5 TPa using a direct force method5 and 0.8 TPausing the electric-field-induced resonance method.6 Theoreti-cally, a bending angle of 70° can lead to failure or breakingof B–N bonds in pristine single-wall BNNTs.7 Recently, Gol-berg et al.5 reported that at bending angles of 115°, a re-sidual plastic buckle could remain in the structure of thenanotube. This resulted in the formation of 30° angled-kinks on BNNTs after unloading. We also recently studiedthe high temperature structural degradation of BNNTs.8 Inthe current research, we investigated the cyclic behavior ofBNNTs, an area not previously studied. Our objective was tounderstand the performance limits of BNNTs under severebending condition.II. EXPERIMENTAL PROCEDUREWe have studied the cyclic deformation of individualBNNTs under two different deformation regimes usingsmall-angle 65° and large-angle 120° cyclic bending.Our experiments were conducted by atomic force micros-copy AFM under in situ monitoring using JEOL JEM-4000FX transmission electron microscopy TEM operatedat 200 keV. The reliability of such in situ AFM/TEM mea-surements has been well-documented.5,9,10 Our BNNTs weredirectly deposited on Si substrates by thermal chemical va-por deposition at 1100–1200 °C in a conventional tubefurnace.11 Powders including MgO, Fe2O3, and pure B wereused as precursors, and NH3 gas was used as the source ofnitrogen. These BNNTs have a band gap 5.9 eV, which ishigher than those used in previous reports 5.4 eV, prom-ising the high purity of sample.5,10 Figure 1 represents a highresolution TEM image of the synthesized BNNTs and theline intensity shown in b along the dashed line in a indi-cates that the distance between walls is around 0.35 nm.Individual BNNTs were then attached on a Pd–Au wireshown in Fig. 2 with silver paste by light mechanicalscratching on the as-grown samples. The Pd–Au wire wasthen fixed on a Au hat, which can be placed on a sapphireball that enables the coarse motion of the sample toward theAFM tip. The piezotube that is made of stacks of piezocrys-tal layers enables the fine motion nanometer resolutionsample toward the AFM tip Fig. 2. Using the Nanofactory™software NFC3, the sample position was adjustable with aprecision of 1 nm in X, Y, and Z directions.III. RESULTS AND DISCUSSIONFigure 3 shows the position of one individual BNNT50 nm in diameter in contact with the AFM tip before,during, and after the bending process. The nanotube was bentat the vicinity of the center, suggesting that there was noimperfection or filled part on the nanotube. Filled nanotubeswere shown to deform at the vicinity of the filled part orimperfection sites.10 The maximum in-plane bending anglein our case was measured as 65°3° Fig. 3 at 10 s,which is in good comparison with the 70° angle reported byaCorresponding author. Electronic mail: ykyap@mtu.edubCorresponding author. Electronic mail: reza@mtu.edu.JOURNAL OF APPLIED PHYSICS 108, 024314 20100021-8979/2010/1082/024314/4/$30.00 © 2010 American Institute of Physics108, 024314-1Golberg et al.5 for multiwalled BNNTs. For single-walledBNNTs, theoretical simulations by Enyashin and Ivanovskii7predicted this angle to be 30°–40°. We found that our nano-tube can completely recover its initial tubular structure afterunloading from the bending Fig. 3, released. There was nonoticeable defects formation or failure in the structure of thissample even after applying 50 cycles of bending to the samebending angle and unloading.Figure 4 displays the force-displacement F-D plots ob-tained after 1 and 10 bending cycles which corresponds tothe 65° of bending deformation. As shown, there was nosudden drop in the applied forces, indicating that the bendingcycles introduce no structural failure in the nanotube. Thereare some deviations between these curves owing to the nano-scopic changes in contact condition between the AFM tipand the nanotube during the loading and unloading cyclingprocesses.Considering the ionic nature of bonding in BNNTs, oneexpects to observe a brittle-type behavior. Such high flexibil-ity motivated the authors to conduct a close examination ofthe bent nanotube in high resolution TEM. Figure 5 corre-sponds to serious of images that reveal the mechanism bywhich the BNNTs accommodate high bending angles closeto 65°. The dashed lines shown in Fig. 5c represent a tilt inatomic planes along a particular set of atoms. The compres-sion, C and tension, T, sides of the nanotube are schemati-cally shown in the inset of Fig. 5a. In several locationsalong the compressive side of the nanotube these tiltedplanes were observed in Fig. 5b. This mechanism washighly reversible and, after unloading, no sign of tilted planecould be detected.Using the maximum applied forces in the F-D curves,the Young’s modulus of nanotubes can be estimated based onthe Euler’s formula for nanotubes assuming that both endsare fixed,12 where the maximum applied force is FEuler=2EI /L2. Here, L is the length of the BNNT between thetwo contacts =1.5 m, E is the elastic modulus, and themoment of inertial,I =d24− d1464,where d1 and d2 are the internal and external BNNT diam-eters, respectively. Table I shows the calculations for fivedifferent nanotubes. The average Young’s modulus detectedhere was 0.5 TPa0.1 TPa. The data were reproducibleafter multiple tests with different individual BNNTs.FIG. 1. Color online a High resolution TEM image of a multiwalled BNNT. b The line intensity along the dashed line in a indicates that the distancebetween walls is around 0.35 nm.FIG. 2. Color online Schematic of the in situ AFM setup inside the TEM.BNNTs were placed on the Pd–Au wire and brought into contact with theAFM cantilever through movement of the piezotube and sapphire ball.FIG. 3. In situ TEM observation shows small-angle 65° bending of anindividual BNNT at 300 nm displacement within 10 s. Bending pointcircled appears near the middle of the nanotube and is fully recoveredupon releasing the applied force. The images captured from the recordedvideo.024314-2 Ghassemi et al. J. Appl. Phys. 108, 024314 2010For the large-angle bending tests, we increased the de-formation angle up to 120° to capture the pertinent structuralchanges. Interestingly, BNNTs failed in a fracture mode. Fig-ure 6 shows the represented real-time process of the failureof an individual BNNT after numerous cycling bending. TheF-D curve corresponding to this fracture event illustrates thechanges in the force applied to the nanotube Figs.6a–6e. We have recorded three discrete drops in appliedforces. The first drop, at the beginning of the experiment, isdue to the nanoscopic sliding of the nanotube on the AFMtip. This results in the drop of the applied force. The othertwo drops 200 nN each represent the process of failureinitiation and propagation in the nanotube shell-walls Figs.6c–6e. As the TEM images show, the fracture initiatesfrom the outermost shells Fig. 6c that are under tensilestress and propagates Fig. 6e toward the axis of nanotube,almost perpendicular to the applied force axis. As this par-ticular BNNT has a wall thickness 12 nm, this nanotubeswas having 36 layers of hexagonal boron nitride h-BNshells. Since the fracture processes initiated only two discretedrops of applied forces within this particular cycle of bend-ing, apparently multiple h-BN shells are broken simulta-neously in two patches resembling a brittle-type fracture. Itis noted that a few layers of shells still remained after thisbending cycle as shown in Fig. 6e. By repeating the bend-ing cycles Figs. 6f–6h, the nanotube was eventuallybroken into two parts Fig. 6i.We think that the rupturing in the outermost shells maybe initiated by structural imperfections such as the Stone–Wales defects.13 Yu et al.14 reported the breakage of multi-walled CNTs MWCNTs in the outermost layer. They as-sumed that structural defects, such as Stone–Wales, producedduring the synthesis process, were responsible for the frac-ture. Espinosa et al.15 also reported failure of outer shells ofMWCNTs as a function of irradiation dose. Ding et al.16 alsoobserved similar failure mechanism. They estimated that de-fects in the outer shell can cause stress concentrations andthus failure.We then examined the cross-section of the fracturednanotube by using the broken segment 2 to lift the othersegment 1. As shown in Fig. 7, we used segment 2 to rotatesegment 1 so that the cross-section is perpendicular to theelectron beam. Figures 7a–7c demonstrate this manipula-tion. In Fig. 7d, the broken cross-section marked in acircle is shown as a ring shape, indicating the presence ofthe tubular structures. The inner channel at the center of thebroken cross-section can be clearly observed. The diametersof the two broken parts were almost similar Fig. 7d sug-gesting that the breakage of the nanotube shells is brittle.This is in agreement with the existing belief about BNNTbrittleness due to the partially-ionic character of chemicalbonding between the B and N atoms.IV. CONCLUSIONSIn summary, we tested the mechanical properties of in-dividual BNNTs by cyclic bending using an in situ AFM/TEM system. The structures of BNNTs remained after thelow-angle 65° cyclic bending. For the high-angle 120° cyclic bending, in situ TEM imaging allowed thereal-time recording of the shell-walls failure initiation andpropagation process. Brittle failure mechanism was observedfor bending failure of BNNTs. The drops of the measuredTABLE I. The estimated structural parameters for five different BNNTs andthe calculated Young’s modulus and standard deviation are shown.d1nmd2nmLnmFnNElastic modulusTPaNanotube 1 34 51 1400 600 0.45Nanotube 2 29 44 1600 390 0.68Nanotube 3 25 50 1500 600 0.48Nanotube 4 26 48 1800 420 0.58Nanotube 5 22 38 1300 350 0.66FIG. 4. F-D curves during the cyclic bending deformation of an individualBNNT at deformation cycles of 1 and 10.FIG. 5. Color online TEM images of a BNNT at the bended area reveal the mechanism by which the nanotubes accommodate high bending angles close to65°. The compression, C, and tension, T, sides of the nanotube are schematically shown in the inset of a. The dashed lines shown in c represent a tilt inatomic planes along a particular set of atoms.024314-3 Ghassemi et al. J. Appl. Phys. 108, 024314 2010force corresponding to the failure of shell-walls determinedthe contribution of shell-walls on the overall strength ofnanotubes.ACKNOWLEDGMENTSR. S. Yassar and Y. K. Yap acknowledge support fromNational Science Foundation Award No. 0820884, Divisionof Materials Research. R.S.Y. would like to thank theMichigan Space Grant Consortium Fund for providing thepartial of financial support MSGC under Grant No.2000433 to conduct the current investigation. Y. K. Yap ac-knowledges his National Science Foundation CAREERaward Award No. 0447555 and the U.S. Department ofEnergy, the Office of Basic Energy Sciences Grant No. DE-FG02-06ER46294 for supporting the efforts on the synthe-sis of boron nitride nanotubes.1X. Blase, A. Rubio, S. G. Louie, and M. L. Cohen, Europhys. Lett. 28, 3351994.2H. M. S. Ghassemi and R. S. Yassar, Appl. Mech. Rev. 63, 020804 2010.3V. Verma, V. K. Jindal, and K. Dharamvir, Nanotechnology 18, 4357112007.4E. Hernández, C. Goze, P. Bernier, and A. Rubio, Phys. Rev. Lett. 80,4502 1998.5D. Golberg, X. D. Bai, Y. Bando, C. Y. Zhi, C. C. Tang, M. Mitome, andK. Kurashima, Nano Lett. 7, 2146 2007.6A. P. Suryavanshi, M. Yu, J. Wen, C. Tang, and Y. Bando, Appl. Phys.Lett. 84, 2527 2004.7A. N. Enyashin and A. L. Ivanovskii, Neorg. Mater. 42, 1336 2006.8H. M. S. Ghassemi, C. H. Lee, Y. K. Yap, and R. S. Yassar, JOM 62, 692010.9H. Ghassemi, Y. K. Yap, and R. S. Yassar, Tech. Proc. 2009 Nanotech.Conf. Expo, NSTI Nanotech. 1, 318 2009.10D. Golberg, X. D. Bai, M. Mitome, C. C. Tang, C. Y. Zhi, and Y. Bando,Acta Mater. 55, 1293 2007.11C. H. Lee, J. Wang, V. K. Kayatsha, J. Y. Huang, and Y. K. Yap, Nano-technology 19, 455605 2008.12S. Akita, H. Nishijima, T. Kishida, and Y. Nakayama, Jpn. J. Appl. Phys.,Part 1 39, 3724 2000.13A. J. Stone and D. J. Wales, Chem. Phys. Lett. 128, 501 1986.14M. Yu, O. Lourie, M. J. Dyer, K. Moloni, T. F. Kelly, and R. S. Ruoff,Science 287, 637 2000.15H. D. Espinosa, Z. Yong, and N. Moldovan, J. Microelectromech. Syst. 16,1219 2007.16W. Ding, L. Calabri, K. M. Kohlhaas, X. Chen, D. A. Dikin, and R. S.Ruoff, Exp. Mech. 47, 25 2007.FIG. 6. Process of fracture in an individual BNNT after the large-angle120° bending cycles. a–e Represent one cycle of bending. f–iShowing nanotube breaking into two parts after pulling and stretching. jF-D plot represents the changes in force upon failure initiation and propa-gation during one cycle a–e. Scale bars are 20 nm.FIG. 7. Color online a–c Manipulation of the broken BNNT on the left1 using the broken segment on the right 2. d Cross-section view of thebroken nanotube as marked in a circle. The empty area at the center repre-sents the inner channel of the BNNT. Scale bars are 20 nm.024314-4 Ghassemi et al. J. Appl. Phys. 108, 024314 2010

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Real-time fracture detection of individual boron nitride nanotubes in severe cyclic deformation processes

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