EAGER/RUI: Defect & Surface Related Novel Phenomena in Oxide Semiconductor Nanoparticles

NON-TECHNICAL DESCRIPTION: Magnetic materials are widely used for information storage while semiconducting materials are essential for high speed processing of information, thus these two materials form the most important components of the vast majority of electronic devices today. Developing ferromagnetism in conventional semiconductor materials is highly desired to make electronic devices faster, smaller, cheaper, and more energy efficient. This project investigates ways to develop stable above-room temperature ferromagnetism in oxide semiconductors using multiple approaches, most importantly using the unique and novel properties of oxide materials when prepared in nanoscale size range. By engaging graduate students in the research, this project provides significant support for the new doctoral programs at Boise State University in the areas of Materials Science and Engineering, and Biomolecular Sciences (starting in Fall 2012). Significant aspects of this research project are integrated into several existing as well as new interdisciplinary graduate courses in the Materials Science and Engineering, and Physics programs. Also, this project provides research opportunities for several undergraduate students, and students and science teachers from local high schools. TECHNICAL DETAILS: In spite of the lack of success in producing stable, reliable and reproducible room temperature ferromagnetism in conventional semiconductors using dilute level doping of 3d cations(dilute magnetic semiconductors) during the past 10 years, research in this direction remains even more exciting due to its potential to make electronic devices faster, smaller, more energy efficient and less expensive. Most of the experimental data reported so far indicate the presence of ferromagnetism in transition-metal doped oxide semiconductor nanoparticles. However, several recent findings such as the lack of a systematic dependence of the magnetic moment with dopant concentration, observation of ferromagnetism even in undoped oxide semiconductors, and absence of properties expected from spin-orbit interaction do not convincingly support it as a true dilute magnetic semiconductor system. Thus, a new mechanism to understand the novel ferromagnetism is needed and this is one of the major goals of this project. A novel approach is being undertaken where the oxide semiconductor nanoparticles are capped with various organic molecules to investigate if charge transfer between nanoparticles and these linked molecules modifies the electronic structure and thereby produces ferromagnetism in these oxides. X-ray absorption near edge structure (XANES) studies in collaboration with Professor Steven Bernasek at Princeton University is being utilized to evaluate the charge transfer between the nanoparticles and the organic molecules. Other surface sensitive techniques including X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy are also available for additional studies. Finally, modification of the physicochemical properties, especially fluorescence emission, of the surface bound organic dyes due to their interaction with oxide semiconductor nanoparticles and charge transfer are also being investigated based on the PI's recent observation of a 90-fold increase in the fluorescence emission of fluorescein isothiocyanate dye when chemically bound to ZnO nanoscale tripod structures. Graduate, undergraduate and high school students are being trained on cutting-edge research techniques such as XANES, transmission electron microscopy, X-ray photoelectron spectroscopy, superconducting quantum interference device magnetometry and X-ray diffraction.