Yoo Yongmin, Kim Young-Joo, Kim Do-Nyun, Lee Joo-Hyoung
School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Republic of Korea.
Department of Mechanical and Aerospace Engineering, Seoul National University, Republic of Korea.
Phys Chem Chem Phys. 2016 Aug 3;18(31):21949-53. doi: 10.1039/c6cp03248f.
The Poisson's ratio νij = -ε/ε, where ε and ε (i,j = x, y, z) are applied and resulting strain, respectively, are computed from first-principles for Si with an array of cylindrical, nanometer-sized pores aligned in the z direction (nanoporous Si, or np-Si). Through density functional theory calculations, it is demonstrated that the periodic arrangement of pores introduces strong anisotropy in the Poisson's ratio of np-Si: while νyz remains close to the Poisson's ratio of the bulk, νzx and νxy exhibit an increase and a sharp decrease from the bulk value, respectively, as the volume fraction of pores (ϕ) becomes large. It is shown that the characteristic dependence of the Poisson's ratio on ϕ originates from the difference in the actual stress on np-Si, which is caused by the dissimilar surface geometry. Unlike random porous materials, this finding signifies the importance of structural details in determining the mechanical response of ordered systems at a nanoscale.
泊松比νij = -ε/ε，其中ε和ε（i, j = x, y, z）分别是施加的应变和产生的应变，是通过第一性原理计算得到的，针对的是具有沿z方向排列的圆柱形纳米尺寸孔阵列的硅（纳米多孔硅，或np-Si）。通过密度泛函理论计算表明，孔的周期性排列在np-Si的泊松比中引入了很强的各向异性：当孔隙体积分数（ϕ）变大时，虽然νyz仍接近块体的泊松比，但νzx和νxy分别相对于块体值呈现增加和急剧下降。结果表明，泊松比对ϕ的特征依赖性源于np-Si上实际应力的差异，这是由不同的表面几何形状引起的。与随机多孔材料不同，这一发现表明了结构细节在确定纳米尺度有序系统的力学响应中的重要性。
