Localized Texture Formation and its Detection in Polycrystalline Thin Films of Gold
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KAREN E. HARRIS and ALEXANDER H. KING Department of Materials Science & Engineering, State University of New York at Stony Brook, Stony Brook, NY 11794-2275. ABSTRACT
We have developed a technique for detecting microscopic variations in texture in thin film TEM specimens using conical dark field imaging. This technique has been used to identify texture variations in 25nm thick gold films which were deposited on rock salt and annealed at 150°C. After annealing, the films were mostly (111) textured with one micrometer wide bands of contrast in which the grain remained randomly oriented. When the contrast due to the variation in texture was first observed, the films were columnar-structured and the grain sizes in both the textured and untextured regions were uniform, with a mean equivalent diameter of 54nm; no abnormal grains were observed. After additional annealing, abnormal (11)1 oriented grains appeared in some untextured regions of the film. The evolution of texture during grain growth and the influence of substrate morphology on texture formation will be discussed. INTRODUCTION
Both experimental studies and computer simulations indicate that texture formation and grain growth are strongly correlated. Studies of grain growth kinetics during texture changes reveal that grain growth takes place in several stages which have different values of the grain growth exponent associated with variations in the shape of the grain size distribution [1,2,3]. Such behavior is attributed to the dependence of grain boundary energy and mobility on the orientation difference between neighboring grains; grains of different orientations will grow at different rates. During the development of texture, the grain growth rate slows as neighboring grains approach the texture ori-
entation, forming small angle grain boundaries with low mobility [4]. Incomplete texture development provides a driving force for abnormal grain growth; grains which do not have the preferred orientation may have grain boundaries with higher mobility and, therefore, an advantage for growth [1]. In this manner, a minor texture component can become the major component if the grain growth in the initially major component is retarded by a high frequency of low mobility boundaries. Grains of the growing texture component are larger and those of the disappearing component are smaller than the mean grain size [5], so during a texture transition, an originally unimodal grain size distribution can become bimodal, developing two distinct peaks as the growing component consumes the disappearing component [2]. Texture in thin films can develop as a result of nucleation at preferred sites and/or growth of grains with a preferred orientation. The condition of the substrate strongly influences the texture of the deposited film. The topography and crystallographic orientation of the substrate provide preferred sites and orientations for adatoms forming nuclei, and contaminants adsorbed on the surfaces of the substrate influence this oriented nucleation [6,7]. During grain gro
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