Ni / Ti Neutron Multilayer Structure And Interface Control

As an effective method for research the micro-structure and motion state of the materials, neutron scattering technology has been essential and its applications become more wide day by day in modern scientific research. Neutron multilayer is one of the most important neutron optical components in the neutron optical system, such as the neutron scattering. As the inner wall of neutron guides, the neutron supermirror is an important neutron multilayer component, and its neutron reflectivity is mainly influenced by the structure design and the interface of the multilayers. On the international, the neutron supermirror technology has developed much mature, various kinds of neutron supermirrors have been fabricated with large critical angle and high reflectivity by ion beam sputtering or magnetron sputtering method, combining with the optimized and mature process, including the polarizing supermirror^the non-polarizing supermirror the linear parallel supermirror and the elliptical focusing supermirror. Compared with the international level, the neutron supermirror technology remain in the most basic research at home because of all round restricted, which were mainly fabricated by magnetron sputtering. No neutron supermirror was deposited by ion beam sputtering, and no one has intensive understood and optimized the interface state of the supermirror to improve its neutron reflectivity in China. Because of these two start points, a series experiments about Ni/Ti multilayers have been done.The ion beam assisted deposition (IBAD) device was mainly used to fabricate the Ni/Ti multilayers. In order to obtain the optimal technological parameters of fabrication, a series of the Ni/Ti multilayers were deposited on the Si(100) substrate under the conditions of different sputtering power、substrate temperature and sputtering gas pressure. The influences of the ion polishing and reactive sputtering to the Ni/Ti multilayers interface state were researched, which is the important factor affecting the neutron reflectivity of neutron supermirrors. The mechanical property of several Ni/Ti multilayers which were deposited under different conditions were studied by the nanoindentation technology. Because the supermirrors are mainly fabricated by magnetron sputtering in industrial production, several Ni/Ti multilayers were fabricated by ultrahigh vacuum magnetron sputtering device and analyzed which was exploratory.The atom force microscopy (AFM) was used to measure the surface topography and roughness of the Ni/Ti multilayers. The transmission electron microscopy (TEM) was used to study the thickness and crystal structure of the multilayers. The X-ray photoelectron spectroscopy (XPS) and the auger electron spectroscopy (AES) were used to analyze the component vertical distribution and the interface diffusion of the multilayers.After above-mentioned research, several results and conclusions were found and presented, they are as follow:For the ion beam sputtering process, the surface of Ni/Ti multilayers deposited under lower sputtering power were smoother, but the Ni/Ti multilayers had better crystallinity and compactness which deposited under higher sputtering power; Increasing the substrate temperature properly benefit to reduce the interface roughness of multilayers, meanwhile considering the diffusion between Ni layers and Ti layers is necessary; the higher the sputtering gas pressure, the more rough the interfaces of the multilayers were, because of the columnar growth of the films. So appropriate sputtering powers substrate temperature and sputtering gas pressure should be chosen when fabricating the Ni/Ti multilayers by sputtering method. Using lower power ion beam to impact every interface of the Ni/Ti multilayers for the appropriate duration, and embedding the appropriate N. O atoms in Ni layers or mixing the H atoms with Ti layers by reactive sputtering both can obviously reduce interface roughness of the Ni/Ti multilayers, even can suppress the diffusion between Ni element and Ti element to optimize the interface of the Ni/Ti multilayers. After the nanoindentation analyzing, the Ni/Ti multilayers fabricated by reactive sputtering have the higher hardness and elastic modulus because of the formation of interstitial atoms. With the sputtering power adding, the hardness of the multilayers increases, but the elastic modulus changes little. Although the interface state of the Ni/Ti multilayers fabricated by magnetron sputtering was worse than the multilayers’ fabricated by ion beam sputtering, but the multilayers still had good uniformity and crystallinity, which were deposited quickly and effectively.