Si3N4在h-AlN上的晶体化与AlN/Si3N4纳米多层膜的超硬效应

采用反应磁控溅射法制备了一系列具有不同Si₃N₄层厚度的AlN/Si₃N₄纳米多层膜，利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能.研究了Si₃N₄层在AlN/Si₃N₄纳米多层膜中的晶化现象及其对多层膜生长结构与力学性能的影响.结果表明，在六方纤锌矿结构的晶体AlN调制层的模板作用下，通常溅射条件下以非晶态存在的Si₃N₄层在其厚度小于约1nm时被强制晶化为结构与AlN相同的赝形晶体，AlN/Si₃N₄纳米多层膜形成共格外延生长的结构，相应地，多层膜产生硬度升高的超硬效应.Si₃N₄随层厚的进一步增加又转变为非晶态，多层膜的共格生长结构因而受到破坏，其硬度也随之降低.分析认为，AlN/Si₃N₄纳米多层膜超硬效应的产生与多层膜共格外延生长所形成的拉压交变应力场导致的两调制层模量差的增大有关. 关键词： 3N₄纳米多层膜')" href="#">AlN/Si₃N₄纳米多层膜 外延生长 赝晶体 超硬效应

Crystallization of Si3N4 on h-AlN and superhardness effect of AlN/Si3N4 nanomultilayers

A series of AlN/Si₃N₄ multilayers with different Si₃N₄ thickness were synthesized by reactive magnetic sputtering. The microsructure of the multilayers was characterized with X ray diffraction and high resolution transmission electron microscopy, and nanoindentation was employed to measure their mechanical properties. The crystallization behavior of Si₃N₄ modulation layer in the multilayers and its influences on the microstructure and mechanical properties of AlN/Si₃N₄ multilayers were studied. The results show that when Si₃N₄ thickness is less than about 1 nm, Si₃N₄, normally amorphous in deposition state, could form a wurtzite type pseduocrystal structure, same as the structure of h AlN, due to the template effect of AlN crystal layer. Crystallized Si₃N₄ layers and AlN template layers grow coherently into columnar crystals. Correspondingly, the hardness of the films is enhanced, showing a superhardness effect. Further increasing the thickness of Si₃N₄ layers, the coherent interfaces of the multilayers are damaged and Si₃N₄ layers become amorphous, accompanied by the decline in hardness of the films. The discussion indicates that the superhardness effect in AlN/Si₃N₄ nanomultilayers is related to the enhancement of modulus difference between the two different module layers caused by the alternating stress field in the coherent growth structure.