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NMSU's professor researching chemical solutions to creating metal oxide films

Ongoing research at New Mexico State University, led by assistant professor Hongmei Luo, could lead to new ways to create metal oxide films.



Hongmei Luo, assistant professor of chemical engineering at New Mexico State University, is researching ways to create metal oxide films via chemical solutions (NMSU photo by Darren Phillips)

Metal oxides are chemical compounds containing at least one oxygen atom as well as at least one metal element. They exhibit an amazing range of electronic, magnetic, optical and thermal properties that conventional metallic elements and semiconductors do not possess, such as colossal magnetoresistance (the ability to dramatically change their electrical resistance in the presence of a magnetic field), ferroelectricity (the ability to store a permanent electric field), high temperature superconductors (having exactly zero electrical resistance at temperatures greater than -405.4°F), and multiferroicity (exhibiting any type of long-range magnetic ordering, spontaneous electric polarization and/or ferroelasticity).

Oxide films are chemical compounds containing oxygen, which when exposed to air, forms a thin layer on metal surfaces. The film increases the metal's resistance to chemical attack.

These films envelope even the purest elements; aluminum foil, for example, has an oxide coating that protects the foil from corrosion. Most metal surfaces consist of oxides and hydroxides in the presence of air. Thin film technology is the process of depositing and characterizing functional material layers on a substrate, defined as the supporting material on which a circuit is formed or fabricated. The film provides properties unattainable in the substrates alone and can reduce both material cost and weight. Solar cells, wearable computers, field-effect-transistors and computer monitors all benefit from metal oxide films.

Epitaxial thin films - single-crystal-like films on single-crystal substrates, are routinely used as active layers to build high-performance electronic and optical devices as they usually exhibit improved physical properties over polycrystalline films.

Among a variety of techniques available to prepare epitaxial thin films, chemical solution deposition is a beneficial way to create films due to the low cost of the procedure, easy setup and the ability to coat large areas of irregular surfaces. This would allow the coating to be applied via spinning, dipping, printing or painting from chemical solutions. Luo, an assistant professor of chemical engineering at NMSU, and a team of student researchers, are developing a polymer-assisted chemical solution approach to create functional metal oxide nanostructures. The polymer-assisted deposition is unique since the solutions are very stable for years, where polymers in the solutions actually bind with metal ions, which prevent the metals from undergoing hydrolysis. Therefore, it is a very straightforward process that synthesizes the complex oxides and allows precise control of the stoichiometry.

Luo has been conducting her research at NMSU for two years, but has about 10 years experience total in nanomaterial research, including work at Los Alamos National Laboratory. She developed and taught a new elective materials course, Nanoscience and Nanotechnology, last spring, and the class had 22 undergraduate and graduate students from the physics, chemistry, electrical engineering and chemical engineering departments.

Luo's thin films and nanomaterial laboratory graduated two Master of Science students in fall 2010: Stacy Baber won an Alumni Outstanding Graduate Award as the only M.S. student in NMSU Graduate School that semester. She now is working in a United States Air Force research laboratory in California. The other graduate, Qianglu Lin, earned a Graduate Assistantship Award and carried a 4.0 GPA; he currently is pursuing his doctorate at NMSU. The Luo laboratory currently consists of three doctorate candidates: Lin, Yun Xu and Joshua Hill; a master's student, Ling Fei; and four undergraduate students: Yingxi Chen, Jose Urquijo, Marco Dunwell and Baraka Lwoya.

Due to the research connection, the graduate and undergraduate students have opportunities to work at Los Alamos as summer students. Baber and Lin joined LANL in summer 2010, while Hill and Dunwell were there this summer.

The group is working on a variety of research projects supported by NMSU Start-up, NMSU IRG, New Mexico Consortium, and the U.S. Air Force, including radiation tolerance of oxide nanocrystals, semiconductor and hybrid nanostructures, catalysts for algal biofuels, multifunctional ceramic oxide thin films for fuel cells, photovoltaic solar cells, water-splitting, lithium-ion batteries and transparent conductors. Recently, Luo's proposal on oxide nanocomposites was recommended by the National Science Foundation, and her group is expected to receive three years of funding from NSF beginning in October. In addition, Luo co-authored a paper, in collaboration with colleagues at LANL, North Carolina State University, University of Cambridge in Great Britain, and China.

For more information visit Luo's research page on the NMSU website at http://chemeng.nmsu.edu/HL/research.html.