Cold Injection Synthesis of Nanoheterostructures based on Cluster Decomposition

纳米晶体吸引了相当大的兴趣，因为它们承诺功能材料的巨大潜力，并具有取决于其尺寸的物理性质。它们通过湿化学方法合成，具有越来越复杂的结构。复杂性通过制造具有各向异性形状的颗粒（例如纳米棒）或在不同材料的复杂异质结构中（例如具有多个壳的颗粒）或两者来实现。将新材料沉积到纳米结构上通常需要两种前体分子的反应，所述前体分子在非均质成核反应中在种子颗粒的表面处反应。因此，前体反应性需要匹配。此外，晶格失配和表面配体的影响需要考虑。因此，纳米颗粒的制造通常在高温下进行。如果复杂的形态暴露于热，它们会迅速降解。各向异性形状熔化成球形颗粒，而异质结构中的界面形成材料梯度。因此，高温限制了通过湿化学方法可获得的纳米结构的复杂性。温和的反应条件、低温和不存在前体分解反应将避免这些限制，并允许合成更广泛的纳米材料。在这个项目中，我们的目标是建立一个新的合成路线，形成纳米晶体异质结的基础上“冷注入”的方法。在这里，化学触发器，而不是物理参数启动的生长反应的一个bismuth。我们打算采用超小型半导体集群作为种子生长的材料来源。这些团簇可以非原位产生并充当靶材料的储存器。由于它们的分子结构，它们可以在明确定义的条件下分解。通过将半导体化合物的形成与生长反应分离，一般方法将适用于宽范围的晶种材料。使用化学触发剂来引发反应允许在非常温和的条件和热力学控制下工作，这对于热不稳定的形态至关重要。因此，以大大降低的能量成本制造限定的异质结构将是可能的。我们将适用于两个半导体模型系统的原则，形成“硬”的潜在步骤在核/壳粒子和区域选择性生长的各向异性粒子在一个方向。这两个系统的高度兴趣的纳米异质结构的基本理解和未来的应用胶体纳米晶体在复杂的材料和电子器件。然而，所提出的反应将是非常有益的超出本项目的范围，例如，对于掺杂掺杂的纳米晶体的改性，其中掺杂剂扩散必须被抑制，或者对于已经组装成更大的超结构的纳米晶体。

Nanocrystals have attracted considerable interest, because they promise large potential for miniaturisation of functional materials and have physical properties that depend on their size. They have been synthesised by wet-chemical means with more and more complex architectures. Complexity is either achieved by making particles with anisotropic shape (e.g. nanorods) or in complex heterostructures of different materials (e.g. particles with multiple shells), or both. The deposition of a new material onto a nanostructure requires the reaction of usually two precursor molecules that react at the surface of a seed particle in a heterogeneous nucleation reaction. Therefore precursor reactivities need to be matched. In addition, lattice mismatch and effects of surface ligands need to be taken into account. Therefore, the fabrication of nanoparticles usually occurs at high temperatures. If complex morphologies are exposed to heat they quickly degrade. Anisotropic shapes melt into spherical particles, while interfaces in heterostructures form a material gradient. High temperature thus poses a limit to the complexity of nanostructures that are accessible by wet-chemical methods. Mild reaction conditions, low temperature, and the absence of precursor decomposition reactions would evade these restrictions and allow the synthesis of a much wider range of nanomaterials. In this project, we aim to establish a new synthetic route to form nanocrystalline heterostructures based on a "cold injection" approach. Here, chemical triggers rather than physical parameters initiate the growth reaction of a nanocrystal.We intend to employ ultrasmall semiconductor clusters as source of material for seeded growth. These clusters can be produced ex-situ and act as a reservoir of the target material. Due to their molecular structure they can be decomposed under well-defined conditions. By separating the formation of the semiconductor compound from the growth reaction the general approach will be applicable to a broad spectrum of seed materials. The use of a chemical trigger to initiate the reaction allows working under very mild conditions and thermodynamic control, which is crucial for thermally unstable morphologies. Fabrication of defined heterostructures will thus be possible at much reduced energy costs. We will apply the principle to two semiconductor model systems, the formation of "hard" potential steps in core/shell particles and regio-selective growth of anisotropic particles in only one direction. Both systems are of high interest for both a fundamental understanding of nanoheterostructures and future application of colloidal nanocrystals in complex materials and electronic devices. However, the proposed reaction will be highly beneficial beyond the scope of this project, e.g. for modification of nanocrystals with impurity doping, in which dopant diffusion must be suppressed, or for nanocrystals that have been assembled into a larger superstructure.