Structural and mechanical properties of amorphous Zr-based alloy thin films
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Structural and mechanical properties of amorphous Zr–based alloy thin films 1,3
S.G. Mayr, 2M. Moske and 3K. Samwer Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana–Champaign, 104 S. Goodwin Ave., Urbana, IL 61801, U.S.A. 2 Forschungszentrum caesar, Friedensplatz 16, 53111 Bonn, Germany 3 I. Physikalisches Institut, Bunsenstr. 9, 37073 G¨ottingen, Germany 1
ABSTRACT The evolution of surface structures of coevaporated and sputtered amorphous Zr65Al7.5Cu27.5 films with varying deposition conditions is investigated primarily with scanning tunneling microscopy (STM). While vapor deposited thin films reveal pronounced structure formation, depending on parameters, such as substrate temperature, film composition (variation of the Al versus the Cu content) and the angle of incidence, comparable sputtered films hardly show any structure formation. With the help of a numerical analysis of the STM data, surface diffusion, self–shadowing and energy transfer in the case of sputtering can be identified as the main structure forming mechanisms. Presuming these atomic processes, it is possible to model the main experimentally observed features of amorphous thin film growth by the use of stochastic continuum growth equations, which are numerically solved. Additionally, the connection to intrinsic stress formation during film growth is discussed. INTRODUCTION Structure formation and intrinsic film stress formation during film growth of crystalline materials has been the topic of numerous experimental and theoretical studies during recent years (for an overview see [1, 2]). Particularly, these aspects of film growth are of fundamental interest for technical applications of thin films, as surface and interface morphologies and the growth mode can have a deep impact on mechanical, electrical and magnetic properties in applications (e.g. [3]) and stresses in films can lead to film failure due to diffusional instabilities and crack propagation [4, 5, 6]. In contrast to crystal films, amorphous films can be characterized by in–plane radial isotropic surface processes and mechanical properties, which makes them the ideal model system for film growth studies and the co-occuring mechanical stresses with the surface processes as the only origin. In previous studies [7, 8, 9], the cluster–like surface structure formation of vapor deposited thin films was systematically analyzed using STM growth studies and could be theoretically modelled by using surface diffusion and self–shadowing as the main
P3.33.1
surface processes in continuum growth equations. These equations are stochastic partial differential equations of the Langevin type for the evolution of the surface h(x, y) on a two dimensional coordinate system in plane of the substrate ∂h = F [h] + η ∂t
(1)
with spatially and temporaly uncorrelated Gaussian noise η and F [h] being a functional of spatial derivatives of h with the coefficients describing the importance of each specific term representing a single surface process. Stress formation could be explained in quantitative ag
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