Hierarchical Superstructures of Ferromagnetic Semiconductor Nanoparticles: Synthesis an Exploration of Magnetoresistive Phenomena.

将半导体和磁性结合在一起的材料有望成为信息技术的突破口。所谓的自旋电子学需要能够产生和处理自旋极化电流的化合物。近年来的科学研究主要集中在稀磁半导体上，即经顺磁离子掺杂的经典半导体。具有固有铁磁特性的半导体，如氧化铕（EuO），研究得很少，尽管这些材料是探索和理解磁响应特性等基本现象的有价值的模型。这类特殊的功能固体为自旋电子学、一般磁电学和磁光学的新效应提供了例子。与其他材料如ZnO， TiO2， Fe3O4等不同，纳米形态（尺寸和形状）如何影响其性能在很大程度上仍然未知。由于适用于制备这类其他金属氧化物的溶胶-凝胶或沉淀法等合成方法对于氧化态为+II的Eu都不适用，因此目前还没有方法来制造定制的EuO纳米结构，特别是定义的纳米颗粒。当前项目的目的是填补这一空白，并研究粒子形态对电子、光学、磁性和磁电性质的影响。当前提案中描述的概念是基于一个重要的观察，即通过使用来自另一种材料的牺牲模板可以间接合成EuO。我们之前成功地将ZnO微晶转化为EuO，同时保持颗粒的形状和尺寸，为将这一概念转移到纳米尺度提供了基础。以ZnO纳米晶为原料，经单质铕蒸气处理，制备出宽高比可调的EuO纳米棒，并考察了Zn2+还原为Zn0、去除Zn和取代Eu的最佳条件。对所得到的EuO纳米颗粒的磁性能的研究将为形状-性能相关性提供新的见解。这些构建块的自组装将被探索，目标是在基板上制造有序的纳米棒阵列，作为具有高度定向特性的新型颗粒基材料。重点研究EuO在居里温度以上、以下和附近的磁电特性。基于粒子的周期性铕纳米棒超结构可能成为磁性随机存取存储器（mram）的候选材料。与传统的晶体管不同，即使没有持续的能量供应，电阻率状态也能保持。

Materials that combine semiconductor and magnetic properties are expected to enable a technological breakthrough in information technology. So-called spin-based electronics re-quire compounds capable of generating and processing spin-polarized currents. The recent scientific attention was largely focused on dilute magnetic semiconductors, respectively classical semiconductors doped with paramagnetic ions. Semiconductors with intrinsic ferromagnetic properties such as europium(II) oxide (EuO) have been studied much less, although such materials are valuable models for exploring and understanding fundamental phenomena such as magnetoresponsive properties. This special class of functional solids deliver examples for new effects in spintronics, magneto-electricity in general and also magneto-optics. Unlike other materials such as ZnO, TiO2, Fe3O4, etc., it is still largely un-known how the nanomorphology (size and shape) affects its properties. Because synthesis methods like sol-gel or precipitation methods suitable for the preparation of such other metal oxides fail for Eu in oxidation state +II, there is currently no method to fabricate tai-lored EuO nanostructures and especially defined nanoparticles. The aim of the current project is to fill this gap and to investigate the effects of particle morphology on electronic, optical, magnetic and magneto-electric properties. The concept described in the current proposal is based on the important observation that the indirect synthesis of EuO is possible by using sacrificial templates from another material. Our previous success in converting ZnO microcrystals to EuO while maintaining particle shape and size provides the base for transferring the concept to the nano-scale. EuO nanorods with adjustable aspect ratio will be prepared from ZnO nanocrystals by treatment with elemental europium vapor, and the optimal conditions for the reduction of Zn2+ to Zn0, the removal of Zn and the substitution by Eu will be examined. The investigation of the magnetic properties of the resulting EuO nanoparticles will provide new insights into shape-property correlations. Self-assembly with these building blocks will be explored aiming at the fabrication of ordered nanorod arrays on a substrate as novel particle-based materials with highly directional properties. The focus will be on studying the magneto-electric properties above, below and near the Curie temperature of EuO. The particle-based, periodic EuO nanorod superstructures may become candidates for magnetic random access memories (mRAMs). Other than conventional transistors, the state of resistivity could be maintained even without the constant supply of energy.