Nakata Shinya, Uesugi Akio, Sugano Koji, Rossi Francesca, Salviati Giancarlo, Lugstein Alois, Isono Yoshitada
Department of Mechanical Engineering, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan.
Nanotechnology. 2019 Jun 28;30(26):265702. doi: 10.1088/1361-6528/ab0d5d. Epub 2019 Mar 6.
This study evaluated the mechanical properties and piezoresistivity of core-shell silicon carbide nanowires (C/S-SiCNWs) synthesized by a vapor-liquid-solid technique, which are a promising material for harsh environmental micro electromechanical systems (MEMS) applications. The C/S-SiCNWs were composed of a crystalline cubic (3C) SiC core wrapped by an amorphous silicon dioxide (SiO ) shell; however, TEM observations of the NWs showed that hexagonal polytypes (2H, 4H , and 6H) were partially induced in the core by a stacking fault owing to a Shockley partial dislocation. The stress-strain relationship of the C/S-SiCNWs and SiC cores without an SiO shell was examined using MEMS-based nanotensile tests. The tensile strengths of the C/S-SiCNWs and SiC cores were 7.0 GPa and 22.4 GPa on average, respectively. The lower strength of the C/S-SiCNWs could be attributed to the SiO shell with the surface roughness as the breaking point. The Young's modulus of the C/S-SiCNWs was 247.2 GPa on average, whereas that of the SiC cores had a large value with scatter data ranging from 450 to 580 GPa. The geometrical model of the SiC core based on the transmission electron microscopy observations rationalized this scatter data by the volume content of the stacking fault in the core. The piezoresistive effects of the C/S-SiCNW and SiC core were also evaluated from the I-V characteristics under uniaxial tensile strain. The gauge factor of -30.7 at 0.008 ε for the C/S-SiCNW was approximately two-times larger than that of -15.8 at 0.01 ε for the SiC core. This could be caused by an increase of the surface state density at the SiO /SiC interface owing to the positive fixed oxide charge of the SiO shell.
本研究评估了通过气-液-固技术合成的核壳结构碳化硅纳米线（C/S-SiCNWs）的力学性能和压阻特性，该材料在恶劣环境微机电系统（MEMS）应用中颇具前景。C/S-SiCNWs由包裹着非晶二氧化硅（SiO₂）壳层的立方晶系（3C）碳化硅晶体核组成；然而，对纳米线的透射电子显微镜观察表明，由于肖克利部分位错导致的层错，在核中部分诱导出了六方多型体（2H、4H和6H）。使用基于MEMS的纳米拉伸试验研究了无SiO₂壳层的C/S-SiCNWs和碳化硅核的应力-应变关系。C/S-SiCNWs和碳化硅核的平均拉伸强度分别为7.0 GPa和22.4 GPa。C/S-SiCNWs较低的强度可归因于以表面粗糙度为断裂点的SiO₂壳层。C/S-SiCNWs的平均杨氏模量为247.2 GPa，而碳化硅核的杨氏模量值较大，散射数据范围为450至580 GPa。基于透射电子显微镜观察结果的碳化硅核几何模型通过核中层错的体积含量使该散射数据合理化。还从单轴拉伸应变下的I-V特性评估了C/S-SiCNW和碳化硅核的压阻效应。C/S-SiCNW在0.008 ε时的应变片系数为-30.7，约为碳化硅核在0.01 ε时-15.8的两倍。这可能是由于SiO₂壳层的正固定氧化物电荷导致SiO₂/SiC界面处表面态密度增加所致。
