Stress, Substrate and Size Effects on Nanomechanical Properties of Materials

• Main Authors: Yi-Chung Huang, 黃奕中
• Other Authors: 張守一
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/84kjhc

博士 === 國立中興大學 === 材料科學與工程學系所 === 99 === Recently, the rapid development of nanotechnology leads to the reduction in product size and the enhancement of device performance in MEMS, optoelectronics, semiconductors, and biotechnology. Because of high surface-to-volume ratio, quantum confinement effect and dielectric restriction, nanomaterials show significantly different optical, electrical, thermal, magnetic, mechanical and chemical properties from those of coventional materials,and have great application potential. In material preparations and practical applications, mechanical properties play a very important and fundamental role, and need to be verified before applications. For nanotechnology, to understand the mechanical properties of nanomaterials and to clarify the influence factors will promote the development of nanomaterials. Thus in this study, the effects of residual stress, substrate and size on the mechanical properties of nanofilms and nanoparticles were investigated. In the study of residual stress effect, it was found that compressive residual stress retarded crack propagation, whereas tensile stress lowered the mechanical strength and interface adhesion of thin films.The modification models about different types of residual stress caused measurement variations need to be corrected. In the aspect of substrate effect, the hardness and modulus of different film/substrate systems, nanoindentation tests, showed different variation trends. A hard film/soft substrate system at very small indentation depths, the measured hardness deviated from film hardness, and the typical rule (no substrate effect at 0.1t) did not work. Easy plastic deformation of soft substrate lowered interface shear stress accumulation and interface delamination. In the research of size effect, it was found that, as nanoparticle size decreased, the modulus and hardness substantially increased because of perfect structure, dislocation starvation and surface effect. In ultra-small silver nanoballs, no dislocation formation or lattice distortion was observed during in-situ TEM/Nanoindentation analyses, confirming the aforementioned dislocation starvation.