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

联合收割机结合了半导体和磁性的材料有望在信息技术方面实现技术突破。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。最近的科学注意力主要集中在稀磁半导体上，分别是掺杂有顺磁离子的经典半导体。具有内在铁磁特性的半导体，如氧化铕（EuO），研究得少得多，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中的新效应提供了例子。与其他材料如ZnO、TiO 2、Fe 3 O 4等不同，纳米形态（尺寸和形状）如何影响其性质仍然是未知的。因为适合于制备这样的其它金属氧化物的合成方法如溶胶-凝胶或沉淀方法不能用于氧化态+II的Eu，所以目前没有方法来制造特制的EuO纳米结构和特别限定的纳米颗粒。目前的项目的目的是填补这一空白，并研究粒子形态对电子，光学，磁性和磁电性能的影响。在本提案中描述的概念是基于重要的观察，即通过使用来自另一种材料的牺牲模板，间接合成EuO是可能的。我们之前在将ZnO微晶转化为EuO同时保持颗粒形状和尺寸方面的成功为将概念转移到纳米尺度提供了基础。采用元素铕蒸气处理ZnO纳米晶，制备出长径比可调的EuO纳米棒，并考察了Zn 2+还原为Zn 0、Zn去除和Eu取代的最佳条件。对所得到的EuO纳米颗粒的磁性质的研究将为形状-性质相关性提供新的见解。自组装与这些积木将探索旨在制造有序的纳米棒阵列在基板上作为新型粒子为基础的材料具有高度的方向性。重点是研究EuO在居里温度以上、以下和附近的磁电性质。基于颗粒的周期性EuO纳米棒超结构可能成为磁性随机存取存储器（mRAM）的候选者。与传统的晶体管不同，即使没有恒定的能量供应，也可以保持电阻率的状态。

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.