Effects of hydrogenation on solid state reactions in metallic multilayers

研究了氢化对Nb/Ni、Nb/Pd、V/Ni等金属多层膜界面固相反应过程和动力学的影响。在这些系统中，当多层膜在真空中于~550℃以上的温度下进行热处理时，沿多层膜的界面形成了Ni3Nb、Pd3Nb和Ni3V等金属间化合物，多层膜变得均匀。用Ar离子束溅射技术在Si衬底上制备了Nb/Ni、Nb/Pd和V/Ni系金属双层膜，膜厚分别为10 0~30 0 nm，并在2 0 0~6 0 0℃的真空和5atm的氢气气氛中进行了0.5~3.0h的热处理。用X射线衍射仪(X射线衍射仪)和俄歇电子能谱深度剖析(AESDP)技术分别测量了不同热处理条件下各双层膜的相结构和成分沿厚度的分布，发现氢化处理显著促进了形成金属间化合物的层间反应。形成Ni3Nb、Pd3Nb和Ni3V化合物的反应温度由真空退火的~550℃显著降低到氢退火的~450℃。这意味着Nb/Ni、Nb/Pd和V/Ni双层或多层膜的热失稳是由氢化引起的，而Ti/Ni、Ti/Pd和Ti/Fe多层膜则是通过氢化强烈稳定的。前者氢化失稳的一个机制是在H_2气氛下退火时Nb和V层中形成的过量空位增强了双层界面上的互扩散。这种固相反应的氢增强效应将有助于材料制备和加工工程的改进。

We studied effects of hydrogenation on the process and kinetics of solid-state reactions across the interfaces in metallic multilayers such as Nb/Ni, Nb/Pd and V/Ni systems. In these systems, intermetallic compounds such as Ni_3Nb, Pd_3Nb and Ni_3V are formed along the interfaces of the multilayers when they are annealed at temperatures above 〜550℃ in vacuum, and the multiplayers become homogenized. The objective of this study is to examine whether the dissolved hydrogen influences the reaction processes and kinetics and to reveal their mechanisms.Metallic bilayers of the Nb/Ni, Nb/Pd and V/Ni systems, each layer thickness being 100 to 300 nm, were prepared on Si (111) substrates with Ar ion-beam sputtering at room temperature, and were annealed at temperatures between 200 to 600℃ for 0.5-3.0 h in vacuum and H_2 atmosphere of 5 atm. The phase structure and composition distribution along the thickness of each bilayer subjected to different heat treatments were measured by X-ray diffraction (XRD) and Auger Electron Spectroscopy Depth Profiling (AESDP) techniques, respectively.It was found that the interlayer reactions forming the intermetallic compounds were significantly enhanced by the hydrogenation in all the systems. The reaction temperatures forming the Ni_3Nb, Pd_3Nb and Ni_3V compounds were remarkably reduced from 〜550℃ (vacuum annealing) to 〜450℃ (hydrogen annealing). This means that the Nb/Ni, Nb/Pd and V/Ni bilayers or multilayers are thermally destabilized by hydrogenation, in contrast to Ti/Ni, Ti/Pd and Ti/Fe multilayers which are strongly stabilized by hydrogenation. A mechanism for the destabilization by hydrogenation in the former systems is enhancement of interdiffusion across the interface of the bilayers caused by superabundant vacancies formed in the Nb and V layers during annealing under H_2 atmosphere. This hydrogen enhancement of solid-state reactions will be useful for improvements of materials fabrication and processing engineering.