Synthesis of Europium-Based Magnetic Semiconductor Nanocrystals and Studies of Their Electronic Properties
Asuigui, Dane Romar Camcam
Stoll, Sarah L.
The divalent europium monochalcogenides (EuQ, Q = O, S, Se, and Te) are model magnetic semiconductors, exhibiting strong coupled magnetic, optical, and electronic properties. With rising interests in the synthesis of nanocrystals that exhibit size-dependent effects concurrent with the development of miniaturized electronic devices, our research looks to developing novel ways to synthesize divalent europium nanocrystals and study how their properties may be affected as a function of their size and composition. With our experience in synthesizing and characterizing the EuS nanocrystals (NC), we pursued the study of related systems: the EuSe nanocrystals and the alloyed EuSxSe1-x systems. The alloyed system could be prepared by both solid-state and nanocrystal growth techniques; and a set of characterization techniques were employed, and described in detail, showing the importance of nanocrystal analysis. In our pursuit to synthesize EuSe nanocrystals, a thorough search for alternative precursors led us to a report suggesting new methods to prepare europium diseleno- and dithiophosphinate complexes as single-source precursors (SSPs). This allowed our group to develop a family of lanthanide diselenophosphinate SSPs to prepare Ln-Se nanomaterials. As a result, purer EuSe NCs were prepared using a new Europium-diselenophosphiante SSP, and size-control was demonstrated to produce crystals with dimensions from 3 to 100 nm. The EuQ materials also exhibit a unique phenomenon due to magnetic exchange interactions that lead to their conduction band splitting. We employed magnetic circular dichroism (MCD) to measure the temperature and field dependent effects on the band splitting in the EuS and EuSe nanocrystal systems, which we found to be much greater than even those found in DMS materials. We also pursued the preparation of new structures of divalent europium materials and targeted the robust and compositionally flexible halide perovskites (ABX3, A/B = cation, X = halides). Evidence of bulk europium-based halide perovskites prepared by solid-state techniques suggested that novel perovskite materials could be stabilized. This led to our development of a new synthetic method to prepare CsEuX3 nanocrystals, exhibiting interesting shapes that could perhaps be controlled in future studies.
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