Reaction Limited Synthesis of Atomically-Defined Semiconductor Nanocrystals

非技术摘要：胶体纳米结构正在成为下一代光学和电子材料的低成本加工的有吸引力的候选者。它们的特征尺寸在独特的长度范围内，无机半导体在保持良好的热稳定性和光稳定性的同时，显示出可调的、类似分子的性质。半导体纳米结构的化学合成通常会导致大量不同的颗粒形状和大小，这对随后的器件性能产生了负面影响。为了解决这个问题，该项目旨在探索一种替代的合成策略，以生长出均匀的、原子定义的半导体纳米颗粒。创新之处在于使用化学而不是热生长，这得益于反应可控的、颗粒形成的渐进步骤。这一策略在控制半导体纳米结构的形状和均匀性方面实现了前所未有的精确。开发一种用于生长原子定义的胶体纳米颗粒的合成方法可能会潜在地影响依赖于半导体溶液处理的广泛新兴技术。预计这将改善太阳能燃料发电和固态照明材料的电气和光学性能。这个项目的教育方面计划集中在通过研究活动和课程开发来阐明学生。技术摘要：该项目旨在探索胶体半导体纳米晶体的反应受限生长，以努力实现粒子形状和大小的可控进化。纳米晶体的合成通常是通过前驱体的热激活进行的，这得益于快速、低缺陷的结晶。然而，作为一种扩散受限的生长机制，热注入策略本身就很难控制纳米粒子的尺寸分散、配体覆盖率和整个样品的阳离子/阴离子比。结果，单个纳米粒子的独特光电特性在组装中变得不均匀地加宽。目前的策略采用了连续沉积完全饱和的阳离子和阴离子单分子层到小直径团簇上，这导致了随着直径的增加颗粒尺寸的聚焦。每个离子层通过原子层沉积的胶体模拟来生长，以保持前驱体和纳米晶体处于不同的相。因此，自限单层沉积变得非常有效，导致在每个离子生长周期中形成化学计量比定义的表面。预计通过这一策略可以改善纳米颗粒的均匀性，直到原子上精确的结构。改善对纳米颗粒尺寸分散性的控制可能会推动发光器件的发展，而定义良好的表面成分可能有助于基于薄膜的纳米晶体应用(太阳能电池、晶体管)。

Non-technical Abstract:Colloidal nanostructures are emerging as attractive candidates for low-cost processing of next-generation optical and electronic materials. Their characteristic size falls within the unique length scale where inorganic semiconductors exhibit tunable, molecular-like properties while retaining a good thermal and photo-stability. The chemical synthesis of semiconductor nanostructures typically results in a large variety of particle shapes and sizes, which negatively affects the ensuing device performance. To address this issue, the project aims to explore an alternative synthetic strategy for growing uniform, atomically-defined semiconductor nanoparticles. The innovation lies in employing chemical rather than thermal growth, which benefits from reaction-controllable, incremental steps in the particle formation. This strategy enables an unprecedented precision in controlling both the shape and the uniformity of semiconductor nanostructures. The development of a synthetic methodology for growing atomically-defined colloidal nanoparticles can potentially affect a wide range of emerging technologies relying on solution processing of semiconductors. It is expected to result in improved electrical and optical performance of materials for the solar fuel generation and solid state lighting. The educational aspects of this project are planned to focus on elucidating students through research activities and curriculum development.Technical Abstract:The project aims to explore a reaction-limited growth of colloidal semiconductor nanocrystals in an effort to achieve a controllable evolution of particle shapes and sizes. Nanocrystal synthesis is typically performed via thermal activation of precursors which benefits from a fast, low-defect crystallization. As a diffusion-limited growth mechanism, however, the hot-injection strategy makes it inherently difficult to control the nanoparticle size dispersion, ligand coverage, and the cation-to-anion ratio across the sample. As a result, distinct optoelectronic properties of individual nanoparticles become inhomogenously broadened in assemblies. The present strategy employs the sequential deposition of fully saturated cationic and anionic monolayers onto small-diameter clusters, which leads to focusing of particle sizes with the increasing diameter. Each ionic layer is grown via a colloidal analog of the atomic layer deposition to keep precursors and nanocrystals in separate phases. As a result, a self-limited monolayer deposition becomes very effective leading to stoichiometrically defined surfaces at each ion growth cycle. It is expected that an improvement in nanoparticle uniformity down to atomically precise structures is attainable through this strategy. An improved control over the nanoparticle size dispersion is likely to advance the development of light-emitting devices, whereas a well-defined surface composition could avail film-based nanocrystal applications (solar cells, transistors).