Event
ChBE Seminar: Hongmei Luo
Friday, July 19, 2013
2:00 p.m.-3:00 p.m.
2113A Chem./Nuc. Eng. Bldg. (Conference Room)
Professor Dongxia Liu
liud@umd.edu
Polymer-Assisted Chemical Solution Approach to Epitaxial Thin Films and Nanomaterials
Hongmei Luo
Assistant Professor
Department of Chemical Engineering
New Mexico State University
In this talk I am going to introduce you a chemical solution approach, called polymer-assisted deposition (PAD), for the growth of nanostructured thin films and nanoparticle networks. The use of water soluable polymer as the binding agent for the metal ions has several advantages. First, the formation of covalent complexes between the lone pairs on the nitrogen atoms of the polymer and the metal cations make it possible to prepare almost any metal precursor solutions. Secondly, the precursor solutions are environmentally friendly as metal salts and commercially available polymers are used as the source materials. The unique chemistry and processing design of this technique deliver stable and homogeneous solutions at a molecular level that allows epitaxial growth of high quality thin films and nanomaterials.
First we report the synthesis and characterization of epitaxial superconducting molybdenum nitride films with different crystal structures and chemical compositions grown by PAD. Hexagonal MoN was stabilized on c-cut sapphire but cubic Mo2N on (001) SrTiO3 even though exactly the same precursor solution and the processing parameters (such as the annealing temperature and environment) were used. Both X-ray diffraction and high-resolution transmission electron microscopy confirmed the growth of epitaxial molybdenum nitride films with an epitaxial relationship between the film and the substrate as (0001)MoN||(0001)Al2O3 and [10<10>]MoN||[11<20>]Al2O3 for MoN on c-cut Al2O3 and (001)Mo2N||(001)STO and [111]Mo2N||[111]STO for Mo2N on SrTiO3. Both MoN and Mo2N films were phase pure materials and showed superconducting transition at 12 K and 5 K, respectively.
The second example will be nanostructured oxides for lithium-ion battery application. Cobalt oxide has successfully grown on nickel foam by a facile polymer-assisted chemical solution method. The carbon left from the decomposition of polymers is an effective binder between the metal oxides and nickel foam. As compared to the metal oxide powders prepared in a conventional way by using polymer binder and carbon black, these one-step direct growth electrodes showed much better Li storage properties with high capacities, stable cyclability, and rate capability. The good performances of these electrodes could be attributed to intimate contact between the active material and nickel foam, the porosity of the current collector, and the network structure of the active materials. This general method could also be applied to other transition metal oxides.
About the Speaker
Hongmei Luo is an assistant professor in Chemical Engineering at New Mexico State University (NMSU). She holds a Ph.D. degree in Chemical Engineering from Tulane University in 2006. She was a postdoctoral research associate in Los Alamos National Laboratory from August 2006 to August 2009. Dr. Luo is the Principal Investigator of the Thin Films and Nanomaterials Research Group at NMSU and she is graduate student advisor in department of chemical engineering.
