Preparation of Advanced Nanomaterials from Single Source Designer Precursors

William Marsh Rice University, Houston TX

Investigators

Abstract

With this award, the Macromolecular, Supramolecular and Nanochemistry program is funding the research of Kenton H. Whitmire of Rice University to develop new ways to make advanced metallic substances with potentially useful magnetic properties. The work is focusing on materials made from metals such as iron or manganese. When these metals are combined with a substance such as phosphorus, the two can come together in many different forms. Iron combined with phosphorus, for example, can form in at least five ways. All of these resulting substances are different, but they all are semiconductors, some of which display unusual behavior. One of these is called "magnetocaloric". This means their magnetic state varies with temperature. Substances like this could be used to produce an electronic refrigerator, in other words, a solid-state device that does not require the use of refrigerant gases. This work is, thus, having a broad impact: on the production of new and potentially important materials that will find a wide variety of uses in industry, and through the training of the next generation of scientists in advanced techniques for preparing specialized materials. This research is developing new ways to prepare advanced materials that are difficult or impossible to synthesize by conventional means. In order to achieve this goal, new molecular precursors combining one or more transition metals (M) with the group 15 elements (E) are being prepared. The resulting E-M compositions have important magnetic, electronic and/or superconducting properties. This project is geared to overcoming the synthetic challenges of preparing advanced materials of binary, ternary and higher transition metal/main group element compositions. The approach considers single source precursors based on transition metal carbonyl compounds containing one or more transition metals as well as phosphorus and/or arsenic. The molecular precursors are prepared using sophisticated organometallic techniques to achieve the desired E/M compositions. These compounds are characterized by a variety of methods including single crystal X-ray diffraction, multinuclear and variable temperature nuclear magnetic resonance spectroscopy, infrared spectroscopy and mass spectrometry among others. The conversion of these precursors to the desired materials is examined by thermal decomposition methods. The resulting materials, prepared either as nanoparticles or thin films, are analyzed by scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy, powder and film X-ray diffraction, energy dispersive X-ray spectroscopy, and other electronic and magnetic measurement techniques.