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

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 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 [101̅ 1] 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, which 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 a density functional theory simulation, which shows the pronounced effect of growth axis on the AlN NW mechanical behavior. The modeling reveals that with an increasing NW width the Young's modulus tends to approach the elastic constants of a bulk material.

Recent Progress of In Situ Transmission Electron Microscopy for Energy Materials

“…When the electrical biasing is accomplished through piezo‐probing, one can also utilize the probe for introducing solid‐state chemicals and mechanical strain (without the measurement of force value) . In some cases, special microscope types or adaptions to the microscope are required to introduce some variables: to introduce light into the TEM chamber through a port on the column for photovoltaics or photocatalysis, or to supply gas to the specimen by a differential pumping system for catalysis.…”

In Situ TEM Characterization and Modulation for Phase Engineering of Nanomaterials

“…Based on this multifunctional platform, a variety of in situ nanomechanic works have been performed (commercial holders such as Nanofactory). The double tilt function has also been achieved, as shown in Figure b. − , …”

“…The double tilt function has also been achieved, as shown in Figure 12b. [251][252][253][254]256 Tensile tests are among the most frequently conducted mechanical tests. To achieve tensile deformation, in a typical experiment, the bulk sample is first sectioned to produce a clean fracture surface with numerous nanosized tips.…”

Anisotropic crystal orientations dependent mechanical properties and fracture mechanisms in zinc blende ZnTe nanowires

“…These side surfaces can considerably affect the mechanical behavior and fracture process through partial slipping, full slipping, necking, and/or twinning. [25][26][27][28] Recent experimental 22,29 and theoretical studies 8,9 also suggest that different crystal orientations of NWs can exhibit considerable anisotropic mechanical properties with temperature and strain. The competition between global and local deformations, activation variation in different planes, and the inuence disparity of inter-planar distances may change with temperature and strain rate, [30][31][32][33][34][35] leading to this anisotropic behavior.…”