AlN/BN纳米结构多层膜微结构及力学性能

Microstructure and mechanical properties of AlN/BN nanostructured multilayers

用射频磁控溅射法制备了AlN,BN单层膜及AlN/BN纳米多层膜.采用X射线衍射仪、高分辨率透射电子显微镜和纳米压痕仪对薄膜结构进行表征.分析表明:单层膜AlN为w-AlN结构,BN为非晶相.AlN/BN多层膜中BN的结构与BN层厚有关.当BN层厚小于0.55nm时,由于AlN层模板的作用,BN发生了外延生长,BN与AlN的结构相同;当BN层厚大于0.74nm时,BN为非晶.AlN/BN多层膜的硬度也与BN层的厚度有关.当BN层厚为1—2个分子层时,AlN/BN多层膜具有超硬效应;当BN层厚增加到0.74nm时,AlN/BN多层膜的超硬效应消失.计算了多层膜中BN结构转变的临界厚度.讨论了AlN/BN多层膜的硬化机理,晶态BN与AlN层之间的界面协调应力和模量差异是多层膜硬度提高的主要原因.

Monolithic AlN, BN films and AlN/BN multilayers were prepared by reactive magnetic sputtering. The films were characterized by X-ray diffraction, high-resolution transmission electron microscopy and nanoindentation. Results showed that the w-AlN phase and amorphous BN films structure exist in AlN and BN monolithic films. The crystal structure of BN layers in the multilayers depends on the thickness of BN layers. When the thickness of BN is less than 0.55 nm, BN layers grew epitaxially with AlN under the influence of the ＂template effect＂ of w-AlN layers and form the same structure as AlN. When the thickness of BN is larger than 0.74 nm, BN layers are amorphous. The hardness of AlN/BN multilayers also depends on the thickness of BN layers. When the thickness of BN is 1--2 molecular mono-layers, the superhardness enhancement of the multilayer is observed. The superhardness effect disappears when the thickness of BN is larger than 0.74 nm. The critical thickness of BN layers marking the change from the crystalline to the amorphous structure has been calculated. The hardening mechanism of AlN/BN multilayers has been discussed. The main reason of the superhardness enhancement of the multilayer is the stress and modulus difference between the layers of BN and AlN.