“…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 ( C 11 = 376.71 GPa, C 33 = 354.23 GPa) with the previous studies. − The maximum number of atoms in the considered atomic structures of AlN NWs was 360 (150 Al, 150 N, and 60 passivating H atoms).…”
mentioning
confidence: 94%
“…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 Xiang: 37 (…”
mentioning
confidence: 99%
“…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 Xiang: C 11 = 372 GPa, C 12 = 151 GPa, C 13 = 121 GPa, C 33 = 398 GPa, and C 44 = 89 GPa for bulk defect-free single crystal of AlN. For the hexagonal crystals, E [0002] is equal to the C 33 elastic constant and E [101̅1] could be calculated using the equation for crystal compliances for a random direction: where S ij are the compliances of the crystal (calculation of compliances located in the Supporting Information) and θ is the angle between the planes (0001) and (101̅1).…”
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.
“…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 ( C 11 = 376.71 GPa, C 33 = 354.23 GPa) with the previous studies. − The maximum number of atoms in the considered atomic structures of AlN NWs was 360 (150 Al, 150 N, and 60 passivating H atoms).…”
mentioning
confidence: 94%
“…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 Xiang: 37 (…”
mentioning
confidence: 99%
“…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 Xiang: C 11 = 372 GPa, C 12 = 151 GPa, C 13 = 121 GPa, C 33 = 398 GPa, and C 44 = 89 GPa for bulk defect-free single crystal of AlN. For the hexagonal crystals, E [0002] is equal to the C 33 elastic constant and E [101̅1] could be calculated using the equation for crystal compliances for a random direction: where S ij are the compliances of the crystal (calculation of compliances located in the Supporting Information) and θ is the angle between the planes (0001) and (101̅1).…”
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.
“…Such thermalized fluxes are analogous to those of a molecular beam epitaxy or a high pressure sputtering process. The three-body Tersoff potential is applied to describe the atomic interactions between atoms, and its reliability and application have already been proved [ 25 , 27 , 29 ]. Figure 1.…”
Heteroepitaxial growth of aluminum nitride (AIN) has been explored by experiments, but the corresponding growth mechanism is still unrevealed. Here, we use molecular dynamics simulations to study effects of temperature and N : Al flux ratio on deposited AlN. When the temperature increases from 1000 K to 2000 K with an N : Al flux ratio of 2.0, the growth rate of the AlN film decreases. The crystallinity of the deposited AlN is distinctly improved as the temperature increases from 1000 K to 1800 K and it becomes saturated between 1800 K and 2000 K. The crystallinity of the deposited film at 1800 K increases with an increase in the N : Al flux ratio from 0.8 to 2.4, and this degraded a little at an N : Al flux ratio of 2.8. In addition, stoichiometry is closely related to crystallinity of deposited films. Film with good crystallinity is connected with a near 50% N fraction. Furthermore, the average mean biaxial stress and mean normal stress at 1800 K with N : Al flux ratios of 2.0, 2.4 and 2.8 are calculated, indicating that the deposited film with lowest stress has the best crystal quality and the defects appear where stresses occur.
“…The choice of interatomic potentials is based on the nature of bonding between the atoms. Higher order interactions (i.e., those involving more than two atoms) can also be included based on the requirements of the system (Xiang et al 2017). For example, in case of metallic systems, EAM (Embedded Atom Model) potentials (Daw and Baskes 1984) are used.…”
Interatomic potentials for complex materials (like ceramic systems) are important for realistic molecular dynamics (MD) simulations. Such simulations are relevant for understanding equilibrium, transport and dynamical properties of materials, especially in the nanoregime. Here we derive a hybrid interatomic potential (based on bond valence (BV) derived Morse and Coulomb terms), for modeling a complex ceramic, barium tantalum oxynitride (BaTaO 2 N). This material has been chosen due to its relevance for capacitive and photoactive applications. However, the material presents processing challenges such as the emergence of non-stoichiometric phases during processing, demonstrating complex processing-property correlations. This makes MD investigations of this material both scientifically and technologically relevant. The BV based hybrid potential presented here has been used for simulating sintering of BaTaO 2 N nanoparticles (~ 2-20 nm) under different conditions (using the relevant canonical ensemble). Notably, we show that sintering of particles of diameter < 10 nm requires no external sintering aids such as the addition of barium sources (since stoichiometry is preserved during heat treatment in this size regime). Also, we observe that sintering of particles > 10 nm in size results in the formation of a cluster of tantalum and oxygen atoms at the interface of the BaTaO 2 N particles. This is in agreement with the experimental reports. The results presented here suggest that the potential proposed can be used to explore dynamical properties of BaTaO 2 N and related systems. This work will also open avenues for development of nanoscience-enabled aid-free sintering approaches to this and related materials.
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