Continuous Phase Diagramming of Epitaxial Films
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Continuous Phase Diagramming of Epitaxial Films Young K.Yoo and Frank Tsui Abstract High-throughput and systematic studies of complex materials systems using the approach of “continuous phase diagramming” (CPD) are described in this article. The discussions focus on the techniques of epitaxial film synthesis of CPD and mapping physical and structural properties, using two different material systems as examples: doped perovskite manganese oxides and magnetic alloys. In doped perovskite manganese oxides, a highly correlated system, mapping the optical, electrical, and magnetic properties, reveals surprising evidence of electronic phase transitions that correlate with the low-temperature magnetic order. In magnetic alloys, application of CPD, particularly using real-time characterization during epitaxial growth, makes it possible to examine structure–property relations systematically. Keywords: combinatorial methods, continuous phase diagramming, magnetic properties, orbital ordering.
Introduction One of the exciting prospects of scientific research is the study of critical phenomena such as phase transitions. In materials science, studies of phase diagrams have led to discoveries of new materials and properties. In the process, structural, mechanical, electronic, and magnetic phase information can be mapped as functions of thermodynamic and kinetic parameters such as temperature and composition. The essence of phase mapping is identifying phase transitions and exploring ordering parameters and structure– property relationships. The abrupt nature of phase boundaries and the generally large parameter space they lie in often make them difficult to study systematically. The conventional method for phase mapping has been to synthesize and characterize a large number of samples one at a time, each prepared and studied with one set of parameters (e.g., one composition and one set of processing conditions).* This approach of using discrete samples can become exceedingly tedious and difficult when one tries to explore both wide * Each sample can certainly be diced up for different experiments or secondary processing procedures, as these are done routinely.
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and narrow regions in the parameter space, such as a complex, multiparameter phase diagram and the proximity of a discontinuous phase boundary. In this article, we describe a different experimental approach, namely, “continuous phase diagramming” (CPD), and its applications in understanding the fundamental physics of complex condensed-matter systems and studying epitaxial thin-film processes. The approach uses parallel synthesis and characterization techniques to survey the entire phase diagram of a complex epitaxial system, while having sufficient resolution (e.g., compositional details) to explore narrow and discontinuous features including phase boundaries. CPD experiments can be designed to target key materials and processing parameters by varying them on a single substrate continuously and studying their effects. In what follows, we first briefly describe the te
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