Structural, Themal And Mechanical Properties Study Of SiGe Nanotube

Silicon and Germanium are important materials in electronic industry. SiGe nanotubes show excellent thermal and mechanical properties suggesting that they could be used as nanodrillers, nanotweezers, and microscopy tips. The major interest in SiGe is that their properties depend not only on size but also on composition and atomic arrangement. In addition, SiGe nanotubes may display unique structures and properties.However, structural and related properties of SiGe nanotubes cannot be understood purely from experimental data for their small scales and complex structures. Therefore, it is necessary to use molecular simulation and ab-initio simulation methods to understand structure and properties of these materials.In this work, we adopt ab-initio method to study structural detail of SiGe nanotubes and also use Tersoff-based molecular dynamics method to investigate thermal and mechanical properties of SiGe nanotubes. Some important conclusions were addressed in a systematic here as follows: 1. Structures and energetic stability of SiGe nanotubes were studied by using Ab-initio Method. It is found that zigzag SiGe nanotubes exhibit Gearlike configuration and armchair nanotubes show puckering configuration. The simulation results indicate that large-diameter nanotubes are more stable than small-diameter ones. Moreover, the type 1 (alternating atom arrangement type) nanotubes are more energetically favorable than the type 2 (layered atom arrangement type) nanotubes.2. Thermal evolution study of SiGe nanotubes were investigated by using MD simulation. It is found that during the melting process, the initial nanotubes transform into the compact nanowire first, and then chang into agglomerate structures at higher temperature. It was also found that large-diameter nanotubes exhibit higher melting-like temperature than small-diameter nanotubes, which means that the large-diameter nanotubes are more stable. The melting-like temperatures of Ge-substituted silicon nanotubes decrease with increase of the Ge concentration. In addition, the atomic arrangement type, structural character and energetic stability are the primary governing factors in thermal behaviors of SiGe nanotubes.3. Effects of structural, temperature and strain rate on mechanical properties of SiGe nanotubes were investigated by adopting MD simulation. It is found that three structural transformations were taken place during the extending tests, from initial structure, tensile structure, to critical structure deformation. Simulations indicate that Young's modulus is closely dependent on its diameter, chirality and arrangement-structure. Type1 (alternating atom arrangement-type) armchair SiGe nanotube exhibits the largest Young's modulus. The higher temperature and lower strain rate result in the lower critical strain and tensile strength. It is also found that the critical strains of SiGe nanotubes are significantly dependent on the tube diameter and chirality. Furthermore, based on transition state theory (TST) model, we predict that the critical strain of SiGe (6,6) typel nanotube at 300 K, stretched with a strain rate of 5%/h, is about 3.38%.