Evolution of high-pressure metastable phase Si-XIII during silicon nanoindentation: A molecular dynamics study
Evolution of high-pressure metastable phase Si-XIII during silicon nanoindentation: A molecular dynamics study
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DOI：
10.1016/j.commatsci.2021.110344
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发表时间：
2021-04
影响因子：
3.3
通讯作者：
Lin Zhang;Jiwang Yan
中科院分区：
文献类型：
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作者：
Lin Zhang;Jiwang Yan
Berkovich压头广泛应用于单晶硅的纳米压痕实验，用于硅纳米压痕的分子动力学模拟，但一般采用球形压头。为了缩小这一差距，本文在(0，0，1)，(1，0，1)和(1，1，1)硅表面上进行了一系列分子动力学模拟，以探索高压相的演化。通过配位数(CN)、径向分布函数(RDF)和角分布函数(ADF)跟踪了几种可能的硅相。结果表明，亚稳相和高压相沿不同的晶向呈现出不同的对称性。在Berkovich压头下首次发现了大量在纳米压痕中罕见的高压相Si-XIII，并通过跟踪标记硅原子的位置跃迁来表征其演化机制。在{1+1+1}[1+1+0]滑移系中发现bct5相作为高压相Si-II和Si-XIII的过渡相，它与滑移的压扁晶格结构有关。与Si-II的相变判据不同，Si-I向Si-XIII的相变伴随着(0，0，1)面的局部弹性变形。三个相邻晶胞中的原子被压缩成均匀的长程有序晶体结构。在拔出压头和快速释放应力后，晶体表面的弹性变形恢复得不完全。Si-XIII部分回复到原始的Si-I相，其余部分转变为非晶相。相变区的局部静水压力和von Mose应力的分布表明，集中静水压力和比应力导致了这种高压硅相的形成。本研究阐明了Si-XIII相生成的演化过程，丰富了对纳米压痕中硅相变机理的基本认识。
Berkovich indenters are widely employed in nanoindentation experiments of single-crystal silicon, in molecular dynamic simulations of silicon nanoindentation, however, spherical indenters are generally employed. To close this gap, in this paper, a series of molecular dynamic simulations are conducted on (0 0 1), (1 0 1), and (1 1 1) silicon surfaces to explore the evolution of high-pressure phases. Several possible silicon phases are tracked by coordination number (CN), radial distribution function (RDF), and angular distribution function (ADF). Results show that the metastable phases and the high-pressure phases present different symmetrical patterns along different crystallographic orientations. A large amount of high-pressure phase Si-XIII, which is seldomly observed in nanoindentation using a spherical indenter, is first discovered under the Berkovich indenter, and the evolution mechanism is characterized by tracking the position transition of labeled silicon atoms. As a transition phase for high-pressure phase Si-II and Si-XIII, bct5 phase is found in the {1 1 1} [1 1 0] slip systems, which is related with slipping flatten lattice structures. Different from the phase transformation criterion for Si-II, the transformation from Si-I to Si-XIII companies with the local elastic deformation of (0 0 1) surface. The atoms in the three neighboring unit cells are compressed into a uniform long-distance ordered crystal structure. Upon indenter extraction and rapid stress releasing, the elastic deformation of the crystal surface resumes incompletely. A part of Si-XIII recovers to pristine Si-I and the rest changes into amorphous phase. The distribution of local hydrostatic pressure and von Mises stress in the phase transformation regions indicates that the concentrated hydrostatic pressure and specific stress induce this high-pressure silicon phase. This research clarifies the evolutionary process of Si-XIII phase generation and enriches fundamental understanding on the mechanisms of silicon phase transformations in nanoindentation.