Aging Effects of As-deposited and Passivated Cobalt Slanted Columnar Thin Films
- PDF / 594,513 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 103 Downloads / 176 Views
Aging Effects of As-deposited and Passivated Cobalt Slanted Columnar Thin Films Daniel Schmidt, Eva Schubert and Mathias Schubert Department of Electrical Engineering and Center for Nanohybrid Functional Materials, University of Nebraska-Lincoln, Lincoln, NE 68588, U.S.A. ABSTRACT Aging effects of as-deposited and passivated slanted columnar thin films from cobalt determined by generalized ellipsometry within the visible spectral region are reported. Slanted columnar thin films have been grown by glancing angle electron beam deposition and subsequently coated with Al2O3 by an atomic layer deposition process. An anisotropic Bruggeman effective medium approximation developed for highly ordered three dimensional metal nanostructures is employed to analyze spectroscopic Mueller matrix ellipsometry data. Our model approach allows for determination of biaxial optical and structural properties as well as fractions of multiple film constituents. While the optical properties of the uncoated film change over time, the alumina passivation layer prevents oxidation in air and therefore aging effects; however, it affects the intrinsic bulk-like Co optical properties. INTRODUCTION Sculptured thin films from metal with three-dimensional geometries made by glancing angle deposition (GLAD) resemble an artificial material class with interesting physical properties [1]. In order to exploit the characteristics of such nanostructured thin films for optical and magneto-optical (magnetic) applications, for example, the as-deposited pristine metallic and magnetic properties need to be protected from oxidation [2,3]. Hence, a thin homogeneous and conformal passivation layer is desired to prevent oxidation and thus avoid material properties alteration in normal ambient conditions. It has been shown previously that atomic layer deposition (ALD) is an excellent technique to conformally coat complex nanostructures and sculptured thin films [4,5]. A challenge consists in proper and accurate characterization of material properties and quantification of material fractions of such complex anisotropic thin films. Generalized ellipsometry, a non-invasive and non-destructive optical method, is highly suitable for probing the anisotropic optical response of nanostructures and determining the anisotropic dielectric function tensor. However, ellipsometry is an indirect technique and requires adequate descriptive mathematical model systems to match experimentally acquired data sets and model calculated data by varying relevant model parameters. Typically, anisotropic effective medium approximations are employed to determine optical properties of slanted columnar thin films (SCTFs) in the visible spectral range. However, models were limited to either uniaxial [6] and orthorhombic descriptions, respectively, in the case of SCTFs from absorbing materials [7,8] or an orthorhombic model applied to lossless metal oxide SCTFs [9, 10]. All previous reports have in common that the nanostructured film comprised only two different film constituents. Recently, we have
Data Loading...
