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。它们的特征尺寸福尔斯落在独特的长度范围内，其中无机半导体表现出可调的分子样性质，同时保持良好的热稳定性和光稳定性。半导体纳米结构的化学合成通常导致各种各样的颗粒形状和尺寸，这对随后的器件性能产生负面影响。为了解决这个问题，该项目旨在探索一种替代的合成策略，用于生长均匀的原子定义的半导体纳米粒子。创新在于采用化学而不是热生长，这得益于颗粒形成中的反应可控的增量步骤。这种策略能够在控制半导体纳米结构的形状和均匀性方面实现前所未有的精度。开发用于生长原子定义的胶体纳米颗粒的合成方法可能会影响依赖于半导体溶液加工的各种新兴技术。预计这将导致用于太阳能燃料发电和固态照明的材料的电气和光学性能的改善。该项目的教育方面计划集中在阐明学生通过研究活动和课程开发。技术摘要：该项目旨在探索一个反应限制的增长胶体半导体纳米晶体，努力实现可控的演变的颗粒形状和大小。纳米晶体合成通常通过前体的热活化来进行，这得益于快速、低缺陷的结晶。然而，作为扩散限制的生长机制，热注入策略使得其固有地难以控制纳米颗粒尺寸分散、配体覆盖率和样品中的阳离子与阴离子比率。结果，单个纳米颗粒的独特光电性质在组装中变得不均匀地变宽。本策略采用顺序沉积完全饱和的阳离子和阴离子单层到小直径的簇，这导致随着直径的增加，粒径的集中。每个离子层通过原子层沉积的胶体类似物生长，以将前体和纳米晶体保持在分离的相中。因此，自限性单层沉积变得非常有效，从而在每个离子生长周期产生化学计量限定的表面。预计通过这种策略可以实现纳米颗粒均匀性的改善，直至原子级精确的结构。对纳米颗粒尺寸分散的改进的控制可能会促进发光器件的发展，而良好限定的表面组合物可能有助于基于膜的纳米应用（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).