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

非技术描述：磁性材料广泛用于信息存储，而半导体材料对于信息的高速处理至关重要，因此这两种材料构成了当今绝大多数电子设备的最重要组成部分。在传统的半导体材料中发展铁磁性是非常需要的，以使电子设备更快，更小，更便宜，更节能。该项目研究了如何使用多种方法在氧化物半导体中开发稳定的室温以上铁磁性，最重要的是利用纳米级尺寸范围内制备的氧化物材料的独特和新颖特性。通过吸引研究生参与研究，该项目为博伊西州立大学材料科学与工程和生物分子科学领域的新博士课程提供了重要支持（从2012年秋季开始）。该研究项目的重要方面被整合到材料科学与工程和物理专业的几个现有的和新的跨学科研究生课程中。同时，本项目也为一些本科生、当地高中学生和理科教师提供了研究机会。技术细节：尽管在过去的10年里，在使用3d阳离子（稀磁半导体）的稀释水平掺杂的传统半导体中，在生产稳定、可靠和可重复的室温铁磁性方面缺乏成功，但由于其使电子设备更快、更小、更节能和更便宜的潜力，这一方向的研究仍然更加令人兴奋。迄今为止报道的大多数实验数据表明，过渡金属掺杂氧化物半导体纳米颗粒中存在铁磁性。然而，最近的一些发现，如缺乏磁矩与掺杂浓度的系统依赖性，即使在未掺杂的氧化物半导体中也观察到铁磁性，以及缺乏自旋轨道相互作用所期望的性质，都不能令人信服地支持它作为一个真正的稀磁半导体体系。因此，需要一种新的机制来理解这种新型铁磁性，这是本项目的主要目标之一。一种新颖的方法是在氧化物半导体纳米颗粒上覆盖各种有机分子，以研究纳米颗粒和这些连接分子之间的电荷转移是否会改变电子结构，从而在这些氧化物中产生铁磁性。与普林斯顿大学Steven Bernasek教授合作的x射线吸收近边结构（XANES）研究被用于评估纳米颗粒和有机分子之间的电荷转移。其他表面敏感技术包括x射线光电子能谱和傅里叶变换红外能谱也可用于进一步的研究。最后，基于PI最近观察到异硫氰酸荧光素染料与ZnO纳米级三脚架结构化学结合时荧光发射增加90倍，研究了表面结合有机染料的物理化学性质，特别是荧光发射，这是由于它们与氧化物半导体纳米粒子的相互作用和电荷转移。对研究生、本科生和高中生进行XANES、透射电子显微镜、x射线光电子能谱、超导量子干涉装置磁强计和x射线衍射等前沿研究技术的培训。

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.