Si_3N_4在h-AlN上的晶体化与AlN/Si_3N_4纳米多层膜的超硬效应

Crystallization of Si_3N_4 on h-AlN and superhardness effect of AlN/Si_3N_4 nanomultilayers

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.

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.