Development of Amorphous Metals Using High Throughput Experiments
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Development of Amorphous Metals Using High Throughput Experiments C. Eric Ramberg, Y. Wang, Q. Fan, E. McDermott, J. Wang, K. Kenyon, M. Hornbostel, S. Guan, S. Nguyen Symyx Technologies, Inc., 3100 Central Expressway, Santa Clara, CA 95051. ABSTRACT High throughput, thin film synthesis and screening methods have been developed to investigate potential bulk metallic glass (BMG) compositions. Physical vapor deposition (PVD) was used for sample synthesis. A novel screening tool was developed to measure changes in resistance vs. temperature of these thin film samples. Example data for 34 compositions in the Mg-rich region of the Mg-Cu-Y ternary system are presented. INTRODUCTION “Combinatorial” or “High Throughput” methods have been applied in a variety of fields for the discovery of new materials. These methods are based on a hierarchy of information quality. Coarse, but rapid measurements are typically used to differentiate between good and bad samples. More detailed, (expensive) measurements are subsequently performed on only the better samples. Thus, experimental efficiency is maximized. A workflow for the discovery and development of novel amorphous metals has been developed at Symyx. This workflow includes thin film synthesis and screening methods, bulk synthesis capabilities, and bulk characterization capabilities. This paper describes thin film screening using the temperature dependence of sample resistance. High throughput synthesis has been carried out using a proprietary combinatorial physical vapor deposition (PVD) system [1]. As described in a companion paper [2], samples are typically synthesized in “library” format, in which a plurality of discrete samples is made on a single substrate for ease of synthesis and measurement. This system can automatically create libraries of metals from up to 40 different PVD target choices. Samples are made by the sequential deposition of different metals. The stoichiometry of each sample is determined by the relative thickness of each metal deposited. To ensure mixing, the metals are deposited periodically, such that the continuous thickness of any given metal is always less than 3-4nm. Each “period” is repeated as many times as required to achieve the desired thickness. Typical thicknesses used in this study were approximately 200 nm. EXPERIMENTAL RESULTS Samples in the present study were made by depositing thin films onto pre-electroded silica wafers, such that each sample had its own set of 4 point probe electrodes (electrodes were TiN). The samples were capped in-situ, with ~100nm of nominally SiN (amorphous, nitrogen deficient Si3N4), deposited by reactive sputtering of Si in nitrogen.
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For testing, the samples were sequentially heated in vacuum, using an infra-red laser, and resistance was monitored as a function of temperature (measured by pyrometer). The experimental setup and procedure is described in [2, 3]. Samples were heated at 10 K/sec to 500 C, after which the heating laser was turned off. Initial cooling rates were of the order 100K/s
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