纳米Ag颗粒复合薄膜的制备及其吸收特性

利用磁控溅射分层制备Ag和SiO₂薄膜,通过快速热处理,使Ag颗粒富集在复合薄膜的表面.研究了Ag膜层厚度、退火时间、退火温度和退火方式对Ag颗粒形貌的影响,以及Ag颗粒致密度对其共振吸收的影响.结果表明:通过控制每层Ag膜的厚度,可有效控制Ag颗粒形貌.当每层金属为2 nm、退火温度为500 ℃时,形成的颗粒粒径大小均匀且致密度较高.通过间断退火可有效降低Ag颗粒的粒径.发现Ag颗粒表面等离子共振吸收并没有随颗粒粒径的减小而明显降低,甚至提高.这和以往的报道不同.通过深入研究金属颗粒表面等离子体产生机理,发现其表面等离子共振吸收增强的原因是致密度较高的颗粒表面能级与费米能级差值较大,Ag颗粒内部的电子向颗粒表面迁移越多,形成新的费米能级E'_F的电子数就越多,表面等离子共振吸收就越强.最终得出了金属颗粒共振吸收不单纯依赖于金属粒径、和颗粒的致密度也有很大关系的结论.

Ag Nano Particle Composite Film Preparation and Surface Absorption Characteristics

Ag and SiO₂ films were prepared by RF magnetron sputtering layer by layer. Ag nanoparticles diffused towards and mostly assembled near the surfaces of composite films via ripid thermal treatment. The effects of the thickness of each Ag film, the thermal treatment time, temperature and process on the Ag particle morphology were investigated. The relationship of Ag particles density with the resonance absorption was researched, too. It is found that different Ag particle shapes can be obtained by changing the thickness of each Ag film. The smaller Ag particles can be obtained by intermittent thermal treatment. The Ag particle density and particle uniformity can be improved by annealing at 500 ℃. The result in this paper is different from previous reports. Namely, the surface plasmon resonance absorption of Ag particles does not significantly decrease with the decreasing of particle size, even improves. It is found that the higher the density of the Ag particles is, the larger of the difference between the particle surface energy level and Fermi level is. With the migrating of the electrons from the particle interior to the surface, the electron number to form new Fermi level E'_F increases, so the surface plasmon resonance absorption becomes stronger. Finally, we draw a conclusion that the metal particle resonance absorption not only relies on the metal particle size, but also greatly relies on the particle density.