离子注入合成In纳米颗粒在Al薄膜中超导性质的研究

In recent years, an increasing level of research interests has been concentrated on nanocomposite materials. This results from the simple premise that using building blocks of heterogeneous chemical species, multi-phases in nanoscale range makes it possible to design and create new materials with the unprecedented flexibility in tuning their physical properties according to the characteristics of nanostructures. For a film having superconducting nanoparticles inside, its superconductivity is dependent on many factors such as the chemical species of particles and film, particle size, etc. Thus the superconducting properties of such nanocomposite film are not yet well investigated. In this research, In nanoparticles will be synthesized by using ion implantation in an epitaxial Al film. In order to control the growth of embedded In nanoparticles, We will investigate the influences of implantation dose, annealing temperature and duration on the final size of In nanoparticles. Afterwards, the superconductivity of the Al/In nanocomposite film consisted of zero dimensional In nanoparticles and two-dimensional Al film will be studied. We will focus on the tuning of the superconducting transition temperature, critical current density, critical filed by varying the particle size and the volume ratio between the In nanoparticles and Al film. The theory of superconducting proximity effects will be employed to explain the experimental observations. Ultimately, our research should lead to a better understanding of the superconducting properties in such a nanocomposite film, which is important for the possible application in the future.

根据纳米结构的特点，把异质、异相的材料在纳米尺度下进行合成获得性能可调的纳米复合材料是近年来纳米材料研究领域一个新的发展方向。对于含有超导纳米颗粒的复合薄膜，其超导性质不但与纳米颗粒的种类、大小有关，还与薄膜的材料有关。因受多种因素的影响，目前对纳米颗粒复合薄膜超导性质的研究并不完善。本项目中，我们利用离子注入的方法在Al的外延薄膜中合成In的纳米颗粒。研究在注入和退火过程中注入剂量、退火温度和时间对纳米颗粒尺寸的影响，实现In纳米颗粒的可控生长。在此基础上，对由零维In纳米颗粒和二维Al薄膜构成的Al/In纳米复合薄膜的超导性质进行研究，注重纳米颗粒大小及其在Al薄膜中的体积分数对超导转变温度、临界电流密度、临界磁场的调制。结合超导的近邻效应理论对其调制机理进行解释, 并为该纳米复合体系超导性质的调控及应用打下基础。

利用离子注入及后退火的方式，在Al衬底中合成了In的纳米颗粒。研究了退火过程中，In纳米颗粒在Al衬底中的生长动力学。研究结果表明，随着纳米颗粒尺寸的增加，其在Al衬底中的取向由初始的In（200）<002>//Al(200)<002>转变为In（111）<110>//Al(002)<110>。该结构转变的特征尺寸（半径）大约在2.3~2.6 nm。通过分析纳米颗粒的平均尺寸与退火温度、退火时间的关系，研究了In纳米颗粒在退火过程中的生长机制并给出相应的理论解释；获得了In原子在Al衬底中的扩散系数D。对Al/In纳米复合薄膜的超导性质进行了详细的研究，回答了In纳米颗粒的尺寸及其在Al薄膜中的体积分数对于系统超导转变温度的影响，利用超导的近邻效应给出了对实验结果的理论解释。