Professor Arunava Gupta of the University of Alabama is receiving an award from the Macromolecular, Supramolecular and Nanochemistry Program to investigate novel low temperature routes, involving solution chemistry and chemical vapor deposition methods, for the synthesis and characterization of a promising class of magnetic Cr-based chalcospinel materials. These materials, synthesized in the form of monodisperse nanocrystals and thin films, will be characterized using advanced analytical techniques and their physical properties studied in detail. The program is motivated by theoretical results obtained by the investigator that suggest the exciting possibility of inducing half-metallicity - i.e., a material in which there is a gap in one spin band at the Fermi level and no gap in the other spin band - in some of the mixed Cu,Cd chalcospinels. The intellectual merit of the research lies in the synthesis and investigation of the novel mixed chalcospinels utilizing innovative synthesis and characterization methods that have the potential for realizing a new class of spintronic materials. Guided by band structure calculations that will be conducted in parallel, the synthesis of other substituted chalcospinel systems will also be attempted. In collaboration with Oak Ridge National Laboratory, ultra high-resolution scanning transmission electron microscopy with atomic number contrast (STEM-Z) characterization technique will be utilized for detailed structural characterization of the nanocrystals and thin films. Project personnel will play a key role in several ongoing education and outreach activities related to the proposed research. These include collaboration with local schools to facilitate participation by high school students in research, public tours and demonstrations.
Professor Arunava Gupta of the University of Alabama is supported by the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry to investigate a class of complex sulfur and selenium-based inorganic materials - referred to as chalcospinels - that display novel magnetic properties. As part of the research, the PI and his students will utilize unique solution chemistry and vapor deposition approaches for the controlled synthesis of nanocrystals and thin films of these materials. Of particular interest are some mixed chalcospinels, which are theoretically predicted to belong to a small class of exotic materials called half-metals. Half-metallic materials are considered one of the "holy grails" of spin electronics research, and continue to be elusive. This research will help maintain and increase the momentum of the young field of spin electronics by realizing the potential of this extremely interesting class of materials that have thus far not been fully exploited. The project requires a multidisciplinary effort that will make significant contributions to scientific knowledge, education, outreach and infrastructure. Project personnel will play a key role in several ongoing education and outreach activities related to the proposed research. These include collaboration with local schools to facilitate participation by high school students in research, public tours and demonstrations.
Spin-based transport in semiconductor systems has been proposed as the foundation of a new class of spintronic devices. For the practical realization of such devices it is important to identify new magnetic systems operating at room temperature that can be readily integrated with standard semiconductors. A promising class of materials for this purpose are the ferromagnetic chromium-based chalcogenides (ACr2X4: A = Cd, Hg, Cu, etc; X=S, Se, Te) that have the spinel structure (chalcospinels). Additionally, they serve as important model systems for the fundamental studies of the interaction between charge carriers and magnetic ions. The goal of the project was to utilize novel low temperature routes, involving solution chemistry and chemical vapor deposition techniques, for the synthesis of both new and existing materials of the Cr-chacospinel series in the form of nanocrystals and thin films. These materials were characterized using advanced analytical techniques and their physical properties studied in detail. The program was motivated by theoretical results that suggest the exciting possibility of inducing half-metallicity in some of the mixed Cu,Cd chalcospinels. The synthesis of related ternary and quaternary chalcogenides with band gap in the visible for solar cell applications was also explored as part of the project. Major accomplishments in the project include: - Colloidal synthesis of magnetic CuCr2S4 nanocrystals and nanoclusters - Synthesis and magnetic properties of Cr2Te3 and CuCr2Te4 nanocrystals - Solution-phase synthesis and magnetic properties of Cu1-xCoxCr2S4 nanocrystals - Growth of wurtzite-phase CuInxGa1-xS2 semiconductor nanocrystals with tunable band gap - Phase-controlled synthesis of novel Cu2FeSnS4, Cu2CoSnS4, and Cu2CdxZn1-xSnS4 nanocrystals - Electronic structure of magnetic semiconductor CdCr2Te4: a possible spin-dependent symmetry filter The results from the project have thus far resulted in nine journal publications, with additional three that have been submitted. Eight invited talks and several contributed talks based on the project have been presented. Two REU students worked on the project. Two international students and a high school student also participated in the project.
