Effects of hydrogenation on solid state reactions in metallic multilayers

本文研究了金属多层膜如Nb/Ni、Nb/Pd和V/Ni体系中氢化对界面固相反应过程和动力学的影响。在这些体系中，当真空退火温度高于1550 ℃时，沿多层膜界面沿着形成Ni_3Nb、Pd_3Nb和Ni_3V等金属间化合物，多层膜变得均匀化。采用Ar离子束溅射法在Si（111）衬底上制备了Nb/Ni、Nb/Pd和V/Ni三种金属双层膜，每层膜厚为100 ~ 300 nm，并在真空和5atm氢气气氛中于200 ~ 600℃退火0.5- 3.0h。利用X射线衍射（XRD）和俄歇电子能谱深度剖面（AESDP）技术分别对不同热处理条件下的双层膜的相结构和成分分布进行了研究，发现加氢处理显著促进了层间反应生成金属间化合物。形成Ni_3Nb、Pd_3Nb和Ni_3V化合物的反应温度从真空退火的550℃显著降低到氢气退火的450℃。这意味着Nb/Ni、Nb/Pd和V/Ni双层或多层通过氢化而热不稳定，而Ti/Ni、Ti/Pd和Ti/Fe多层通过氢化而强烈稳定。氢化失稳的机理是在H_2气氛下退火时Nb和V层中形成的过剩空位增强了双层膜界面的互扩散。这种氢对固相反应的促进作用将有助于材料制备和工艺工程的改进。

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.