title: Ultrasmooth and thermally stable silver-based thin films with subnanometer roughness by aluminum doping.
abstract: Rough surface and poor stability of ultrathin Ag films limit their applications in nanophotonic and optoelectronic devices. Here, we report an approach for fabricating ultrasmooth and thermally stable Ag-based thin films on SiO2/Si substrates by Al-doping. The effect of Al-doping on the surface morphology and stability of ultrathin Ag films at room temperature and elevated temperature was investigated. The 15 nm Al-doped Ag films with an Al atomic concentration of 4% have a root-mean-square roughness as low as 0.4 nm. The smooth surface morphology is maintained even after 300 °C annealing in N2. Al-doping enhances the nuclei density of films. Moreover, a capping layer spontaneously formed over the Al-doped Ag films restrains the surface diffusion and mass transportation of Ag atoms. Therefore, Al-doping induces ultrathin Ag films with highly stable and ultrasmooth surface morphology.
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Michigan , Ann Arbor, Michigan 48109, United States .
authors.forename: Deen
authors.initials: D
authors.lastname: Gu
authors.forename: Cheng
authors.initials: C
authors.lastname: Zhang
authors.forename: Yi-Kuei
authors.initials: YK
authors.lastname: Wu
authors.forename: L Jay
authors.initials: LJ
authors.lastname: Guo
keywords: Ag films; Al-doping; RMS roughness; capping layer; thermal stability; ultrasmoothness