Qi Chengzhu, Striemer Christopher C, Gaborski Thomas R, McGrath James L, Fauchet Philippe M
Materials Science Program, University of Rochester, Rochester, NY 14627, USA. Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, TN 37235, USA.
Nanotechnology. 2015 Feb 6;26(5):055706. doi: 10.1088/0957-4484/26/5/055706. Epub 2015 Jan 15.
Porous nanocrystalline silicon (pnc-Si) membranes are a new class of membrane material with promising applications in biological separations. Pores are formed in a silicon film sandwiched between nm thick silicon dioxide layers during rapid thermal annealing. Controlling pore size is critical in the size-dependent separation applications. In this work, we systematically studied the influence of the silicon dioxide capping layers on pnc-Si membranes. Even a single nm thick top oxide layer is enough to switch from agglomeration to pore formation after annealing. Both the pore size and porosity increase with the thickness of the top oxide, but quickly reach a plateau after 10 nm of oxide. The bottom oxide layer acts as a barrier layer to prevent the a-Si film from undergoing homo-epitaxial growth during annealing. Both the pore size and porosity decrease as the thickness of the bottom oxide layer increases to 100 nm. The decrease of the pore size and porosity is correlated with the increased roughness of the bottom oxide layer, which hinders nanocrystal nucleation and nanopore formation.
多孔纳米晶硅（pnc-Si）膜是一类新型膜材料，在生物分离领域有着广阔的应用前景。在快速热退火过程中，夹在纳米厚二氧化硅层之间的硅膜中会形成孔隙。在尺寸依赖型分离应用中，控制孔径至关重要。在这项工作中，我们系统地研究了二氧化硅覆盖层对pnc-Si膜的影响。即使是单个纳米厚的顶部氧化层，在退火后也足以从团聚转变为形成孔隙。孔径和孔隙率均随顶部氧化层厚度的增加而增大，但在氧化层厚度达到10纳米后迅速趋于平稳。底部氧化层起到阻挡层的作用，防止非晶硅膜在退火过程中发生同质外延生长。随着底部氧化层厚度增加到100纳米，孔径和孔隙率均减小。孔径和孔隙率的减小与底部氧化层粗糙度的增加相关，这阻碍了纳米晶成核和纳米孔形成。
