【学术报告】PHASE FIELD MODELS OF NANOWIRE SYNTHESIS AND DEFORMATION2016-12-08 17:59:30
时间: 11:00-12:00 am, Dec. 12th, 2016
报告人：Dr. Yanming Wang
Yanming Wang is currently a postdoctoral research fellow in Mechanical Engineering at Stanford University. He completed his B.E in Materials Science and Engineering with secondary B.E. in Intelligence Science and Technology at Shanghai Jiaotong University before being admitted to Stanford University, where he received his M.S and PhD in Materials Science and Engineering, with PhD minors in Electrical Engineering and Mechanical Engineering. His research focuses on atomistic simulations and phase field modeling for studying nano-scale materials synthesis and deformation. Closely combining simulations and experiments, he contributed to multiple collaborative projects on broad topics, including nanowire VLS growth, nanowire surface roughening, heterogeneous dislocation nucleation, nano-fin pattern collapse, stretchable polymer mechanics, and etc. Meanwhile, he is the main developer of a parallel multi-physics phase field simulator.
Nanowires (NWs) are considered as promising components for the next-generation nano-scale devices due to their special electronic and optical properties. To realize NW’s potential into real-world applications, it is crucial to understand the growth mechanisms of the NWs and their failure modes. Therefore, a 3D computational model that can both capture the realistic NW morphology and reach the experimental time scale is critically needed. For this purpose, we developed a 3D multi-phase field model. The model captures the NW tapering and sidewall facets in good agreement with experimental observations. The model reports the steady-state NW growth velocity as a linear function of the vapor chemical potential and the inverse of catalyst diameter, providing a confirmation of the Gibbs-Thomson effect in NW growth. With anisotropic interfacial energies, the model shows the NW growth orientation dependence on catalyst diameter and hence it provides an explanation of the NW kinking in the steady-state growth regime. In this model, we introduce a perturbation force to induce the NW structural transition and the free energies are evaluated at different stages during the droplet movement. It enables us to discuss the instability of the catalyst droplet for different pedestal structures, which is important for understanding the onset of the kinking at the NW base. Coupling with elastic field, the model is applied to study the strain-induced surface roughening of the NW under the stress-relaxation condition, linking the phenomenon of NW rupture to the wavelength of surface undulation and NW diameter. Applying the virtual displacement approach, we demonstrate the ability of the model to predict the stability of the nano-fin structure against collapse at various aspect ratios.