Observation of Long-Range Orientational Ordering in Metal Films Evaporated at Oblique Incidence onto Glass
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Observation of Long-Range Orientational Ordering in Metal Films Evaporated at Oblique Incidence onto Glass David L. Everitt1, X. D. Zhu*1, William J. Miller2, and Nicholas L. Abbott3 * to whom correspondence should be made ([email protected]) 1Department of Physics, University of California at Davis, Davis, California 95616 2Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, California 95616 3Department of Chemical Engineering, University of Wisconsin, Madison, Wisconsin 53706 ABSTRACT We studied long-range orientational ordering in polycrystalline Au films (10 nm - 30 nm) that are evaporated at oblique incidence onto a glass substrate at room temperature. By measuring the averaged optical second-harmonic response from the films over a 6-mm diameter region, we observed a transition from the expected in-plane mirror symmetry at 10 nm to a surprising three-fold in-plane rotational symmetry at 30 nm. X-ray pole figure analysis performed on these films showed the strong fiber texture typical of fcc films, but with a restricted, three-fold symmetric, distribution of crystallite orientations about the fiber axis. INTRODUCTION Thin polycrystalline films are used in a wide range of industrial applications, from magnetic storage and read-head media to anchoring and control of functional molecular overlayers in applications such as flat panel displays [1]. Properties of a film depend–among other things–on the film's texture, that is, the distribution of crystalline grain orientations within the film. Vapor-phase depositions often lead to crystalline grains terminated with Miller-index planes that have the minimum surface energy and that are more or less parallel to the substrate surface. Such films are termed to have out-of-plane textures (fiber texture) [2]. For many metals, the plane parallel to the substrate is the close-packed atomic plane. For example, a {111} plane is usually parallel to the substrate in face-centered cubic (fcc) metals. Note that for consistency of notation we will define this particular {111} plane to be the (111) plane. When the deposition is at an oblique angle or when a thin film is bombarded with ions at an oblique angle during growth, the resultant crystalline grains may also develop a preferred in-plane orientation with respect to the incidence plane of the deposition or bombardment [4,5,6]. Such films are termed to have both out-of-plane and in-plane textures (sheet texture). In-plane textures can be very desirable since they may provide an easy axis of magnetization in the surface plane for magnetic films. They may also cause molecular overlayers to have a preferred orientation with respect to the in-plane texture [1,7]. Recently Gupta and Abbott observed that on an obliquely deposited gold film (on fused silica) covered with an n-alkanethiol self-assembled monolayer (SAM), a liquid crystal overlayer consisting of 5'-pentylcyanobiphenyl (5CB) was aligned either along the in-plane direction of the deposition or perpendicular to it, dependi
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