Crystallography-Derived Young's Modulus and Tensile Strength of AlN

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Crystallography-Derived Young’s Modulus and Tensile Strength of AlN Nanowires as Revealed by in situ Transmission Electron Microscopy Konstantin L. Firestein, Dmitry G. Kvashnin, Joseph F. S. Fernando, Chao Zhang, Dumindu P. Siriwardena, Pavel B. Sorokin, and Dmitri Golberg Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.9b00263 • Publication Date (Web): 21 Feb 2019 Downloaded from http://pubs.acs.org on February 22, 2019

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Crystallography-Derived Young’s Modulus and Tensile Strength of AlN Nanowires as Revealed by in situ Transmission Electron Microscopy

Konstantin L. Firestein,*,† Dmitry G. Kvashnin,‡,┴, Joseph F.S. Fernando,† Chao Zhang,† Dumindu P. Siriwardena,† Pavel B. Sorokin‡,┴,§ and Dmitri V. Golberg*,†,║

†School

of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland

University of Technology (QUT), 2nd George str., Brisbane, QLD, 4000, Australia ‡Emanuel

Institute of Biochemical Physics, Russian Academy of Sciences, Kosigina 4 st., Moscow, 119334,

Russian Federation ┴National

University of Science and Technology “MISiS”, Leninskiy prospekt 4, Moscow, 119049, Russian

Federation §Technological

Institute for Superhard and Novel Carbon Materials, Centralnaya st. 7a, Troitsk, 108840, Russian

Federation ║International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS),

Namiki 1-1, Tsukuba, Ibaraki 3050044, Japan *Corresponding authors. E-mail addresses: [email protected] (D. Golberg), [email protected] (K.L. Firestein) Phone: +61731386601 (D. Golberg), +61431422403 (K.L. Firestein)

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ABSTRACT: Aluminum nitride (AlN) has a unique combination of properties, such as high chemical and thermal stability, nontoxicity, high melting point, large energy band gap, high thermal conductivity and intensive light emission. This combination makes AlN nanowires (NWs) a prospective material for optoelectronic and field-emission nanodevices. However, there has been a very limited information on mechanical properties of AlN NWs that is essential for their reliable utilization in modern technologies. Herein, we thoroughly study mechanical properties of individual AlN NWs using direct, in situ bending and tensile tests inside a high-resolution TEM. Overall, 22 individual NWs have been tested and a strong dependence of their Young’s moduli and ultimate tensile strengths (UTS) on their growth axis crystallographic orientation is documented. The Young’s modulus of NWs grown along the [1011] orientation is found to be in a range 160-260 GPa, whereas for those grown along the [0002] orientation it falls within a range 350-440 GPa. In situ TEM tensile tests demonstrate the UTS values up to 8.2 GPa for the [0002]-oriented NWs, that is more than 20 times larger than that of a bulk AlN compound. Such properties make AlN nanowires a highly promising material for the reinforcing applications in metal matrix and other composites. Finally, experimental results were compared and verified under DFT simulation which shows the pronounced effect of growth axis on the AlN NW mechanical behavior. The modelling reveals that with increasing NW width the Young’s modulus tends to approach the elastic constants of a bulk material. KEYWORDS: Aluminum nitride, nanowires, mechanical properties, in situ TEM, DFT calculations


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Over the last two decades nanowire (NW)-related research became one of the most rapidly developing topics in Materials Science. Various wire‐like nanomaterials have found applications as a core component of semiconductor devices,1–3 light-emitting diodes,4–6 chemical gas sensors,7,8 piezoelectric sensors9 and high‐performance composites.10 Electrical, optical, and mechanical properties of semiconducting (Si, GaN, ZnO, InAs), metallic (Au, Cu, Ni) and ceramic (SiC, Al2O3) NWs have extensively been studied over the recent years. One of the relatively unexplored NW systems is AlN. These nanostructures have started to gain an increasing attention because of their unique combination of properties, such as high chemical and thermal stability, nontoxicity, high melting point (over 2300 °C), large energy band gap (6.1 eV), high thermal conductivity (320 W·m-1·K-1), low electron affinity (~0.6 eV) and intensive light emission.11–14 Such combination makes AlN NWs a prospective material for optoelectronic and field-emission applications. However, for the reliable utilization of these NWs in emerging micro- or nanodevices it is essential to first unambiguously uncover their mechanical properties. In addition, understanding of the mechanical properties of such NWs is also important with respect to their possible utilization as a reinforcing agent in novel composite materials. It has indeed been reported that AlN nanostructures can be used in polymeric,15 ceramic16 and metallic17 matrix composites. Especially promising looks the application of AlN NWs as additives in Al-based metal matrix composites – low thermal expansion, no reaction or decomposition in molten Al,18 high wettability by liquid Al19 and one-dimensional shape – all these parameters would stimulate an effective load transfer to the NW fraction and, as a result, guarantee the increased composite strength. However, wide practical applications of AlN NWs in different fields and technologies have still been limited due to the lack of detailed knowledge on their mechanical behavior. In recent years, numerous studies have been focused on characterisation of mechanical properties at the nanoscale, including deformation physics, elasticity, plasticity and strength of different NWs.20 For instance, the mechanical properties of Si, Si/Ge, ZnO, GaN NWs have thoroughly been investigated.21–24 By contrast, almost no information is available on AlN NW mechanical behaviot. Previously, the Young’s modulus of AlN NWs has only been roughly estimated by electrostatic bending in a scanning electron microscope (SEM),25 but direct measurements of the Young’s modulus and tensile strength of individual AlN NWs have not been carried out to date. Other important, yet very challenging topic, is a dependence of mechanical parameters on the precise nanomaterials’ crystallography. As well as other NWs with wurtzite structures, AlN can have different crystallographic orientations along the growth axis. This is envisaged to dramatically influence the mechanical properties. For example, the regarded orientation effects have been studied for ZnO, GaN and CdS NWs.23,26–28 It is noted that the only possible technique to unambiguously conduct such delicate crystallography-dependent experiments and to get a clear atomic structure-mechanical properties relationship is in situ transmission electron microscopy (TEM); this allows one to combine


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precise electron diffraction analysis and high-resolution imaging with direct, real time mechanical testing of individual NWs. Thus, in the present work we have fabricated Al NWs and studied their mechanical properties using a combination of direct in situ bending and tensile tests inside a high-resolution TEM (HRTEM), and theoretical calculations. Overall, 22 individual NWs have been tested and their Young’s modulus and the ultimate tensile strength (UTS) are defined under bending and tension conditions, correspondently. The key influence of NW growth axis crystallographic orientation on the Young’s modulus and tensile strength has been documented. Experimental results have then been compared and confirmed under theoretical modelling in the frame of Density Functional Theory (DFT) calculations. The latter verified a clear dependence of NW mechanical properties on their width and crystallography. AlN NWs were synthesized using a high-temperature solid-gas reaction. An Al foil and FeCl (purity 99.9%, Sigma Aldrich) were used as starting materials. They were taken at the following weight ratio Al:FeCl – 0.20 g: 0.03 g. The materials were placed in the centre of a tubular furnace and heated up to 1200 oC in N2 atmosphere. After annealing at high temperature for 30 min, the furnace was naturally cooled down to room temperature. After the synthesis the leftovers of Al foil were covered by a white-color thin layer of AlN NWs. Detailed description of the synthesis method, as well as the images of initial and resulting materials could be found in the Supporting Information (Figure S1). Morphology, chemical composition and atomic structure of the as-synthesized products were characterised using a field-emission SEM TScan MIRA3 and a Jeol 2100 TEM equipped with scanning TEM and Energy dispersion X-ray (EDX) detectors. Growth axis orientation of individual NWs was determined via selected area electron diffraction (SAED) and Fast Fourier transforms (FFT) of the highresolution TEM images. Mechanical properties of NWs with different growth orientations were tested by in situ TEM probing using an AFM-based holder (Heracles, Zeptools, P.R. China). The NW Young’s modulus with respect to the determined NW growth axis crystallography was measured under the bending tests. Direct tensile tests allowed us to measure the ultimate tensile strength. The scheme of experimental setup for in situ mechanical tests is shown in Figure 1a. The exact NWs length, their diameters and elongations during in situ TEM nanomanipulations were measured by the “Image J” software. Atomic structure and elastic property computations were carried out by means of first-principles DFT calculations using the plane-wave basis set Vienna ab initio simulation package.29–32 The projected augmented-wave

formalism33

in

the

generalized

gradient

approximation

with

the

Perdew−Burke−Ernzerhof (PBE) exchange correlation functional34 was used. The plane-wave cutoff energy was set to 520 eV. For calculation of the equilibrium atomic structures the Brillouin zone sampling according to the Monkhorst−Pack scheme35 with a 5×5×5 k-point convergence grid was employed. The structural relaxation was performed until the force acting on each atom became less than 0.001 eV/Å. Such parameters allowed us to obtain a good correspondence of AlN elastic constants


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(C11 = 376.71 GPa, C33 = 354.23 GPa) with the previous studies.36–40 The maximum number of atoms in the considered atomic structures of AlN NWs was 360 (150 Al, 150 N and 60 passivating H atoms). Experimental observations. SEM was used for the initial characterization of a product. A representative SEM image (Figure 1b) shows that after the synthesis the Al foil is covered with a layer of NWs having diameters of 40-150 nm and a length varying from relatively short scales – 5-10 m to rather long ones, i.e. up to hundreds of micrometres. NWs chemical composition was confirmed by dark-field STEM combined with EDX analysis. Representative electron image and spatially-resolved map of an individual NW are demonstrated in Figures 1c and 1d. Oxygen signal coming from the NW edges is related to a thin layer of surface Al oxide. HRTEM images and corresponding FFT patterns (Figures 1e and 1f) display crystal structures of fabricated AlN NWs. The characteristic interplanar distances, as measured from the FFT, are 𝑑0002 = 0.25 nm and 𝑑1011 = 0.24 nm. These distances correspond well with the (0002) and (1011) interplanar spacings of AlN with a wurtzite structure (space group Р63mс, JCPDS: 25-1133). Fully indexed FFT images are shown in Figure S2 (Supporting Information). HRTEM images further confirmed that fabricated AlN NWs might have different growth directions, e.g. the wires in Figures 1e and 1f have growth axes along the [0002] and [1011] orientations (zone axes [2110] and [1213], respectively). A thin amorphous layer (2 - 3 nm) on the wire surfaces is apparently a layer of Al2O3, this agrees well with the EDX data.

Figure 1. (a) Scheme of in situ TEM setup for tensile and bending tests. (b) SEM image of synthesized AlN NWs. (c) Dark-field STEM image. (d) Corresponding elemental maps from an individual NW. (e,f) HRTEM images of NWs with the growth directions of [0002] and [1011], respectfully. The corresponding insets show FFT patterns with the key spots indexed.


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The Young’s modulus of AlN NWs with the two above mentioned growth directions were determined via in situ TEM bending tests (Supporting Information, Movies S1-S3). For this, the nanostructures were pushed forward by a gold probe against the AFM cantilever. Utilization of a piezoresistive self-sensing AFM probe allows us to perform the direct force measurements during in situ tests.41 Simultaneously, the gold wire displacements were precisely registered and the forcedisplacement curves were recorded. Figure 2 demonstrates the corresponding force-displacement bending curves measured from individual AlN NWs with the different growth axis crystal orientations. The force-displacement curves recorded in these experiments have a similar appearance to the characteristics peculiar to buckling of a macrobeam, which is explained by the Euler’s formula:42

𝑃𝑐𝑟 =

𝜋2 ∙ 𝐸 ∙ 𝐼0 (𝐾𝐿0)2

(1)

where Pcr is the critical load; E – the Young’s modulus, I0 – the minimum area moment of inertia of the cross section of the NW, L0 – the length of the NW, K – the NW effective length factor. Minimum area moment of inertia was calculated assuming that the cross-sectional area of a tested NW has a cylindrical shape: 𝐼0 =

𝜋𝑟4 4 ,

where r is the NW radius. This assumption was verified after

careful analysis of multiple NW SEM images taken at a low (2 kV) accelerating voltage and in the beam deceleration mode. This mode allows us to get clear surface information and to unambiguously determine the cross-sectional shape (Figure S3).


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Figure 2. In situ TEM bending tests on individual AlN NWs. (a,b) Force-displacement curves obtained for NWs with the growth axes along the [1011] and [0002] orientations, respectfully. Corresponding insets show consecutive time-lapse TEM images recorded during bending. The numbers on the insets correspond to the characteristic points marked on the curves. The insets in the upper right corners show SAED patterns taken from the NWs before bending with the key reflections marked.

The critical load Pcr is a load when a force-displacement curve character is changed from the linear type, once the force became more than critical, and the NW starts to buckle (points 2 on the forcedisplacement curves in Figure 2). In our experiments, video snapshots were used to additionally confirm that bending of NW had indeed been started. Note, that all NWs returned to their original shapes after removing the load; thus, showing a purely elastic deformation character. Pcr in our tests was used to calculate the Young’s modulus of AlN NWs. Because one end of a NW was fixed to the gold wire (held in the position and restrained against the rotation) and the other one was pinned to the AFM cantilever (Figure 2, insets) (was not restrained against the rotation), according to the “Theory of Elastic Stability” (Timoshenko et al.) in case of such boundary conditions, the NW effective length factor needs to be set to 0.743 (Supporting Information, Figure S4). Overall, 8 different individual NWs were studied under bending conditions. As a result, the Young’s modulus of NWs with the growth axis along the [1011] (𝐸1011) orientation was determined to be in a range from 160 (±30) to 260 (±50) GPa; and in a range from 350 (±70) to 440 (±90) GPa for the 7 ACS Paragon Plus Environment

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wires with the growth direction along the [0002] (𝐸0002) orientation. A summarizing table presenting the results for all bending tests is seen in the Supporting Information (Table S1). The tensile strength of AlN NWs with the two regarded orientations was studied via direct in situ TEM tensile tests. For a tensile test, an individual NW was soldered to the cantilever from one end and to the piezo-driven gold wire from the other end by using an electron beam-induced deposition (EBID) technique32,33 (Figures 3a and 3b). Then, the NWs were stretched under the precisely controlled movements of the gold wire (Supporting Information, Movies S4, S5). For all tensile tests the engineering force-displacement curves were recorded. And this data was used for the accurate calculations of the UTS (Figure 3g).

Figure 3. In situ TEM tensile tests on individual AlN NWs. (a,b) TEM images of the initially clamped NWs (before tension) with the growth axes along the [1011] and [0002] orientations, respectfully. (c,d) and (e,f) Corresponding SAED patterns and fractured NWs images after ultimate tensile strains of the samples in (a) and (b), respectfully. (g) A representative engineering stress-displacement curve for a NW.

The UTS can be calculated as: σ = F/(S·cosφ·cosδ), where F is the measured force, S = πd2/4 – the wire’s cross-sectional area, δ is the angle between the NW and the displacement axis of the AFM probe on its projection to the TEM image plane and φ is the angle between the NW and electron beam.22 In our tests, angle δ was measured for each individual NW. However, in TEM experiments it is impossible to precisely determine the angle between the NW and electron beam. This factor could be taken into 8 ACS Paragon Plus Environment

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account by introducing an error (of up to ±30°) for the φ angle, that would result in a ~15% error for tensile strength determination.22 Overall, 14 individual NWs were successfully tested in tension (Supporting Information, Table S2). Finally, the measured tensile strength was found to vary from 1.4 to 4.5 GPa and from 4.3 to 8.2 GPa for NWs grown along the [1011] and [0002] orientations, respectively. The strong influence of NW crystallographic orientation on UTS could be explained by the significant changes of the surface conditions for NWs with different growth directions. As displayed in Figures 3d and 3f, the characteristic “step-like” type defects on the surface are more common for NWs oriented along the [101 1] direction. These defects can act as stress concentrators during loading and become the sites of crack initiation, which then propagates into the NW bodies and reduces the overall NW strength.44 Nevertheless, depending on the orientation, the UTS of NWs was 4-23 times higher than that of a bulk AlN (~350 MPa)45 revealing the pronounced confinement effect that makes AlN NWs a prospective material for the use as reinforcing agents in various composites. In fact, other 1D nanostructures with exceptionally high UTS and Young’s modulus – BN nanotubes, were already successfully utilized as a reinforcing additive in metal-, ceramic- and polymer-based composite materials.46–48 The advantage of AlN NWs compared to BN nanotubes is the simplicity and cost effectiveness of their synthesis and better wettability by molten metals19 . In order to calculate the Young’s modulus in tensile experiments, it is important to check that a NW is exactly normal to the electron beam direction, to be sure that there are no hidden displacements during the deformation which could result in wrong strain calculations; but the NWs can hardly be strictly aligned as such. The angle between a NW and the electron beam cannot be precisely controlled in TEM, particularly because of the relatively large lengths of the tested NWs (5 m and more), i.e. we had to use low magnifications (×10k or less) during each tensile test imaging. And at such conditions the TEM defocus value can reach significant values. Therefore, for the sake of accuracy, in the present work we refrain from using the in situ tensile tests for the Young’s modulus calculation and apply them only for the UTS measurements; the latter are not affected by the regarded NW initial position issues. Figure 4 summarizes the results for all tested NWs with the two tested orientations based on the results of both bending and tensile tests. The diagram clearly demonstrates a strong dependence of the Young’s modulus and tensile strength on the growth axis of AlN NWs. Also, it is worth mentioning that, while we had tested NWs with diameters varied from 70 to 150 nm, no dependence of mechanical properties on the wire diameters was found. This result corresponds well with the theoretical calculations on elastic constants for AlN NWs,49 which show no significant changes for NWs with a diameter more than 10 nm.


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Figure 4. Statistically proven ranges of the measured Young’s modulus and the ultimate tensile strength values under in situ TEM bending and tensile tests on numerous AlN NWs having two studied growth orientations. Average values are shown by star symbols.

In order to compare the Young’s modulus of a bulk AlN with the values measured in the present work, we used elastic constants which were calculated by Xiang37 – C11 = 372 GPa; C12 = 151 GPa; C13 = 121 GPa; C33 = 398 GPa and C44 = 89 GPa for bulk defect-free single crystal of AlN. For the hexagonal crystals 𝐸[0002] is equal to C33 elastic constant and 𝐸[1011] could be calculated using the equation for crystal compliances for a random direction:50 1 𝐸[1011]

= 𝑆 = 𝑆11(𝑠𝑖𝑛4 𝜃) + 𝑆33(𝑐𝑜𝑠4 𝜃) +(2𝑆13 + 𝑆44)(𝑠𝑖𝑛2 𝜃)(𝑐𝑜𝑠2 𝜃)

(2)

where Sij are the compliances of the crystal (calculation of compliances could be found in the Supporting Information); and θ is the angle between the planes (0001) and (1011). The angle θ for the hexagonal system based on the c/a ratio could be calculated as:50 cos 𝜃 = 0.75 ∙

𝑎 2 𝑐

()

{

∙ 𝑙 ∙ 0.75 ∙

𝑎 2 𝑐

()

(

2

2

∙ ℎ + 𝑘 + ℎ𝑘 + 0.75 ∙

𝑎 2 𝑐

()

)}

―1/2

2

∙𝑙

(3)

For a wurtzite AlN crystal with the space group Р63mс the lattice constants are: a = 0. 3111 nm and c = 0.4979 nm. By putting these values into Eq. (3) the angle θ between planes (0001) and (1011) was determined as 61.58ᵒ. Using this angle in Eq. (2), 𝐸[1011] was calculated to be 256 GPa. Summing up, the calculated Young’s moduli for a bulk single crystal of AlN in different directions are 𝐸[0002] = 398 𝐺𝑃𝑎 and 𝐸[1011] = 256 GPa, these numbers are very close to the average values of 10 ACS Paragon Plus Environment

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experimentally measured moduli of AlN NWs in the present work (the difference is within the experimental error). A strong dependence of Young’s modulus on growth axis orientation for

both AlN single crystals and AlN NWs could be explained by the elastic anisotropy phenomenon, which is common for hexagonal crystals due to the difference in length and strength of interatomic bonds in different crystallographic orientations. On the other hand, the effect of NW growth directions on UTS is more related to changes of the surface conditions for NWs with different orientations. Theoretical verification of experimental results. We then analyzed the difference of the elastic properties of AlN NWs using ab initio DFT calculations. We considered the AlN nanowires with the growth directions close to the experiment, namely ([0001] and [1010]). For a comparison, a [1120]oriented nanowire was additionally computed. The atomic structures of AlN NWs having the regarded orientations are presented in Figure S5 (Supporting Information). The NW surface was fully passivated by hydrogen atoms, so the effect of surface reconstruction on the mechanical properties of AlN-NW could be neglected. The strain energy was calculated for all NWs in a series of longitudinal strains at the increments of ~0.5%. Every energy values set was approximated by the following equation that gives the Young’s modulus: 1 ∂2𝑈

𝐸 = 𝑉 ∂𝜀2

(4)

where V is the volume of the nanowire unit cell, U is the strain energy, and  is the strain. The partial derivatives at a zero strain in other dimensions are vanished; this gives the E value as an analog of the elastic constants C33 and C11 of a bulk AlN. The NW volumes were calculated by multiplication of the unit cell lengths and cross-sectional areas determined by the two ways: (i) as an area bounded by the centers of the outermost H atoms, and (ii) with inclusion of the additional area relevant to hydrogen van der Waals spheres (see the error bar in Figure 5). */ of the NW width leads to increasing of its elastic constant in line with the following formula: 1

E[abcd] = A[abcd]W + Cbulk ij

(5)

where A[abcd] is the fitting parameter, W is the nanowire width, and Cbulk is the value of the bulk AlN ij elastic constant. The results of elastic constant calculations are presented in Figure 5. With increasing the nanowire width, the E[1010] and E[1120] values (starting from 178.3 ± 35.2 GPa and 209.4 ± 49.3 GPa, respectively) tend to approach the same bulk elastic constant Cbulk 11 (376.71 GPa), whereas E[0001] approaches Cbulk 33 (354.23 GPa) starting from the value of 120.5 ± 29.6 GPa. Such values correspond 11 ACS Paragon Plus Environment

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well with the experimentally derived data. The fitting parameters were estimated as: 𝐴[1120] = 177.9 GPa∙nm, 𝐴[1010] = -260.3 GPa∙nm and 𝐴[0001] = -338.5 GPa∙nm.

Figure 5. Elastic constant of AlN NWs with the different growth directions vs the inverse NW diameter. The curves for NW orientations [0001], [1010] and [1120] are depicted by red, blue and green colors, respectively. The insets present the corresponding atomic structures. The colored frames correspond to the atomic models with various growth orientations. The values of C33 and C11 elastic constants of a bulk AlN are presented by black solid and dashed horizontal lines, respectively.

Thus, herein we have studied crystallography-derived Young’s modulus and the ultimate tensile strength of individual AlN NWs via a combination of direct in situ bending and tensile tests inside HRTEM. Overall, more than 20 NWs have been tested and the strong dependence of Young’s modulus and strength on the AlN NWs growth orientation is documented. The Young’s modulus of NWs with the growth direction along the [1011] (𝐸[1011]) orientation has been found to be in the range from 160 to 260 GPa, whereas in the range from 350 to 440 GPa for NWs with the growth axis along the [0002] (𝐸[0002]) orientations. These values are in a good agreement with the experimental data for single crystals of AlN. In situ tensile tests have demonstrated that UTS values vary from 1.4 to 4.5 GPa, and from 4.3 to 8.2 GPa, for NWs grown along the [1011] and [0002] orientations, correspondingly. The performed DFT calculations of elastic constants for AlN NWs show that with increasing the NW widths the E[1010] and E[1120] tend to approach the same bulk elastic constant Cbulk 11 , whereas E[0001] approaches Cbulk 33 . Theoretical results verified the experimental data. 12 ACS Paragon Plus Environment

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Exceptional AlN NW mechanical properties in combination with their high chemical stability and one-dimensional shape make them a promising nanomaterial for reinforcing applications in metal matrix and other composites. Especially effective would be the applications of NWs grown along the [0002] direction; these exhibit the highest values of the Young’s modulus and tensile strength. In addition, rather low elastic stiffness of the present NWs in comparison with the AlN bulk forms suggests a profound piezoelectric response which may be of interest for future experimental endeavours.

ASSOCIATED CONTENT Supporting Information – figures with descriptions (pdf); Video of buckling test of nanowire with growth axes along the [0002] orientation (avi); Video of buckling test of nanowire with growth axes along the [1011] orientation (avi); Video of buckling test of nanowire with growth axes along the [1011] orientation (avi); Video of tensile test of nanowire with growth axes along the [0002] orientation (avi); Video of tensile test of nanowire with growth axes along the [1011] orientation (avi); AUTOR INFORMATION Corresponding Authors *E-mail: [email protected], Phone: +61431422403; *E-mail: [email protected], Phone: +61731386601. Author Contributions K.LF. and D.G. conceived the idea of the project. K.L.F. synthesized AlN nanowires and performed all in situ TEM mechanical experiments. D.G.K. and P.B.S. carried out DFT calculations. D.G. oversaw the whole project. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Acknowledgements This work was supported by the Australian Research Council (ARC) Laureate Fellowship FL160100089, and Queensland University of Technology (QUT) Projects 322170-0355/51 and 322170-0348/07. K.L.F. and D.G. particularly thank the Central Analytical Research Facility (CARF) of QUT for the experimental support. P.B.S., D.G.K. and D.G. acknowledge the financial support from the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST “MISiS” (No. K2-2017-082). D.G.K. acknowledges the Grant of President of Russian Federation for government support of young Ph.D scientists (MK- 3326.2017.2) and financial support of the RFBR project No. 18-32-00682 mol_a. Notes 13 ACS Paragon Plus Environment

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The authors declare no competing financial interest.


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Crystallography-Derived Young's Modulus and Tensile Strength of AlN

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