Scale-dependent diffusion anisotropy in nanoporous silicon.
Scale-dependent diffusion anisotropy in nanoporous silicon.
复制标题
纳米多孔硅中的比例依赖性扩散各向异性。
DOI：
10.1038/srep40207
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发表时间：
2017-01-20
影响因子：
4.6
通讯作者：
Valiullin R
中科院分区：
文献类型：
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作者：
Kondrashova D;Lauerer A;Mehlhorn D;Jobic H;Feldhoff A;Thommes M;Chakraborty D;Gommes C;Zecevic J;de Jongh P;Bunde A;Kärger J;Valiullin R
通过电化学蚀刻高掺B的p型硅晶片产生的纳米多孔硅可以制备成具有嵌入硅基质中的管状孔。这种材料已经发现了许多技术应用，并提供了一个有用的模型系统，用于研究限制下的相变。本文报道了一个联合实验和模拟研究扩散在这样的材料，覆盖位移从分子尺寸高达几十微米，精心挑选的探针分子。除了通过通道的质量传递之外，还发现在垂直于通道的方向上发生扩散（以小得多的速率），从而提供了连通性的明确证据。随着位移的增加，在轴向和横向方向上的传播逐渐延迟，这表明了一个规模依赖的，分层分布的运输阻力（“收缩”的渠道）和相邻渠道之间的捷径（连接“桥梁”）。从这些研究的实验证据证实了分子动力学（MD）模拟的原子位移的范围内，合理化与一个简单的模型的统计分布的“收缩”和“桥梁”的位移在微米范围内，通过动态蒙特卡罗（DMC）模拟。这两个范围被证明是相互转移的DMC模拟的基础上，由电子断层扫描确定的孔隙空间拓扑结构。
Nanoporous silicon produced by electrochemical etching of highly B-doped p-type silicon wafers can be prepared with tubular pores imbedded in a silicon matrix. Such materials have found many technological applications and provide a useful model system for studying phase transitions under confinement. This paper reports a joint experimental and simulation study of diffusion in such materials, covering displacements from molecular dimensions up to tens of micrometers with carefully selected probe molecules. In addition to mass transfer through the channels, diffusion (at much smaller rates) is also found to occur in directions perpendicular to the channels, thus providing clear evidence of connectivity. With increasing displacements, propagation in both axial and transversal directions is progressively retarded, suggesting a scale-dependent, hierarchical distribution of transport resistances (“constrictions” in the channels) and of shortcuts (connecting “bridges”) between adjacent channels. The experimental evidence from these studies is confirmed by molecular dynamics (MD) simulation in the range of atomistic displacements and rationalized with a simple model of statistically distributed “constrictions” and “bridges” for displacements in the micrometer range via dynamic Monte Carlo (DMC) simulation. Both ranges are demonstrated to be mutually transferrable by DMC simulations based on the pore space topology determined by electron tomography.