TEM study of InSbTe crystal morphology as a function of crystallization conditions
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TEM study of InSbTe crystal morphology as a function of crystallization conditions Marcel A. Verheijen1, Andrei Mijiritskii2, Bart J. Kooi3 1 Philips Centre for Industrial Technology, Eindhoven, the Netherlands 2 Philips Research, Eindhoven, the Netherlands 3 University of Groningen, Groningen, the Netherlands ABSTRACT In this work crystallization of an InSbTe alloy in Blu-ray Disc rewritable (BD-RE) media is studied using Transmission Electron Microscopy (TEM). Two different crystalline states can be formed in a thin InSbTe layer depending on crystallization conditions. These two states give rise to different reflectivity levels of the recording stack as well as a different level of normalized media noise. It is shown that the two states correspond to the same phase (R 3 m), but that they show clear differences in morphology as well as in texture. INTRODUCTION Apart from an amorphous phase, most phase-change materials suitable for rewritable optical media possess two crystalline states. If simultaneously present in the recording layer, these different crystalline states give rise to variations in optical properties and crystallization behavior and, therefore, affect data recording and retrieval performance of phase-change storage media. The difference in the two crystalline states is generally assigned to different crystallographic phases: cubic and trigonal [1,2]. In this work crystallization of an InSbTe alloy is studied. It has been found that the two different crystalline states appear to consist of the same crystallographic phase. However, differences in morphology as well as in texture have been observed. These differences will be discussed in detail below. EXPERIMENTAL Initialization The Blu-ray Disc rewritable (BD-RE) media used in the present study consist of the following stack of layers: pc-C-M-C-I-P-I-cover, where pc is the polycarbonate substrate, M = Ag, I is a dielectric layer (composition 80% ZnS, 20% SiO2), and P is the phase change layer; In5Sb20Te75 in this case. The Ag layer is sandwiched between capping layers (C) to protect it against corrosion. Upon sputter deposition the P-layer is amorphous. Initialization (i.e. crystallization of the P-layer) has been performed using a commercial Hitachi initializer. During initialization a laser beam (810 nm wavelength) is focused onto the recording stack of the rotating disc. The laser spot formed on the disc has dimensions of about 100 µm by 1 µm and is oriented with its longer axis along the radial direction of the disc. Such geometry leads to an almost two-dimensional temperature distribution. In the experiments several initialization parameters have been varied: speed (i.e. the linear velocity of the rotating disc), pitch (i.e. the radial displacement of the 100µm broad laser spot upon a single rotation of the disc), and the laser power. An overview of all experiments is displayed in table I. TEM sample preparation In order to image the crystalline morphology of the P-layer in plan-view, this layer should be the only crystalline layer presen
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