title: Phenomenological Model of the Growth of Ultrasmooth Silver Thin Films Deposited with a Germanium Nucleation Layer.
abstract: The structural properties of optically thin (15 nm) silver (Ag) films deposited on SiO2/Si(100) substrates with a germanium (Ge) nucleation layer were studied. The morphological and crystallographical characteristics of Ag thin films with different Ge nucleation layer thicknesses were assessed by cross-sectional transmission electron microscopy (XTEM), reflection high-energy electron diffraction (RHEED), X-ray diffractometry (XRD), grazing incidence X-ray diffractometry (GIXRD), X-ray reflection (XRR), and Fourier transform infrared spectroscopy (FTIR). The surface roughness of Ag thin films was found to decrease significantly by inserting a Ge nucleation layer with a thickness in the range of 1 to 2 nm (i.e., smoothing mode). However, as the Ge nucleation layer thickness increased beyond 2 nm, the surface roughness increased concomitantly (i.e., roughing mode). For the smoothing mode, the role of the Ge nucleation layer in the Ag film deposition is discussed by invoking the surface energy of Ge, the bond dissociation energy of Ag-Ge, and the deposition mechanisms of Ag thin films on a given characteristic Ge nucleation layer. Additionally, Ge island formation, the precipitation of Ge from Ag-Ge alloys, and the penetration of Ge into SiO2 are suggested for the roughing mode. This demonstration of ultrasmooth Ag thin films would offer an advantageous material platform with scalability for applications such as optics, plasmonics, and photonics.
authors.affiliation: †Jack Baskin School of Engineering, University of California at Santa Cruz, Santa Cruz, California 95064, United States.|‡Nanostructured Energy Conversion Technology and Research (NECTAR), Advanced Studies Laboratories, NASA Ames Research Center, Moffett Field, California 94035, United States.
authors.forename: Junce
authors.initials: J
authors.lastname: Zhang
authors.affiliation: †Jack Baskin School of Engineering, University of California at Santa Cruz, Santa Cruz, California 95064, United States.|‡Nanostructured Energy Conversion Technology and Research (NECTAR), Advanced Studies Laboratories, NASA Ames Research Center, Moffett Field, California 94035, United States.
authors.forename: David M
authors.initials: DM
authors.lastname: Fryauf
authors.affiliation: †Jack Baskin School of Engineering, University of California at Santa Cruz, Santa Cruz, California 95064, United States.|‡Nanostructured Energy Conversion Technology and Research (NECTAR), Advanced Studies Laboratories, NASA Ames Research Center, Moffett Field, California 94035, United States.
authors.forename: Matthew
authors.initials: M
authors.lastname: Garrett
authors.forename: V J
authors.initials: VJ
authors.lastname: Logeeswaran
authors.affiliation: ∥Department of Electrical Engineering and Electronics, College of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara-shi, Kanagawa 252-5258, Japan.
authors.forename: Atsuhito
authors.initials: A
authors.lastname: Sawabe
authors.forename: M Saif
authors.initials: MS
authors.lastname: Islam
authors.affiliation: †Jack Baskin School of Engineering, University of California at Santa Cruz, Santa Cruz, California 95064, United States.|‡Nanostructured Energy Conversion Technology and Research (NECTAR), Advanced Studies Laboratories, NASA Ames Research Center, Moffett Field, California 94035, United States.
authors.forename: Nobuhiko P
authors.initials: NP
authors.lastname: Kobayashi