Fluid-Mediated Assembly of Nanocrystalline Silicon

许多电子设备，如彩色显示器和太阳能电池，都是使用半导体纳米晶体制造的，这些纳米晶体由潜在的毒性元素组成。相反，使用硅纳米晶(SiNC)来生产这些和其他设备是可能的。然而，为了使SiNC发挥作用，它们必须形成被称为超晶格的结构，其中晶体之间的距离被仔细地控制以产生所需的材料性能。由于晶体之间的作用力，SiNC往往堆积得太紧密，这降低了由此产生的超晶格的性能。研究人员将探索使用聚合物改变SiNC的堆积方式的可能性，增加晶体之间的距离，而不会使距离太大，从而使材料的独特性能丢失。实验将探索几个参数对超晶格形成的影响，并将使用理论模型和数值模拟来解释数据。该项目有可能证明，可以形成有用的硅基超晶格，这将为电子设备提供一种丰富的、无毒的替代材料。研究团队将作为导师参与大自然，培养美国部落本科生研究和教育，该组织让北达科他州的部落高中生和大学生参与科学和工程项目。该项目的第一个目标是通过蒸发干燥形成SiNCs的超晶格，并通过添加不同分子量的聚合物来控制纳米晶的间距。在蒸发组装中，将已知尺寸的SiNC悬浮在有机溶剂中，悬浮液的液滴沉积在玻璃上并让其干燥。在干燥过程中，纳米晶聚集在液滴的边缘，聚合物可能会从SiNC中分离出来。影响所得结构的参数包括聚合物相对分子质量、加工温度、SINC浓度、几何形状、溶剂蒸气压和剪切速率。然后将研究长程有序对组件发光性能的影响。第二个目标是利用胶体结晶的分子模拟中测试的有效粒间势，发展纳米晶体悬浮液相行为的修正平衡理论。还将生成格子-玻尔兹曼模拟，以帮助分析和控制与缓慢蒸发相关的多相流。

CBET - 1603445PI: Hobbie, Erik K.Many electronic devices such as color displays and solar cells are produced using semiconductor nanocrystals that are composed of elements with potential toxicity. It may be possible instead to produce these and other devices using silicon nanocrystals (SiNCs). However, for SiNCs to be useful they must form structures called superlattices where the distance between the crystals is carefully controlled to yield desired material properties. SiNCs tend to pack too tightly owing to the forces between the crystals, which diminishes the performance of the resulting superlattice. The investigators will explore the possibility of using polymers to alter the packing of SiNCs, increasing the distance between crystals without making the distance so large that the unique properties of the material are lost. Experiments will be conducted to explore effects of several parameters on superlattice formation, and data will be interpreted using theoretical models and numerical simulations. The project has the potential to demonstrate that useful silicon-based superlattices can be formed, which would provide an earth-abundant, non-toxic alternative material for electronic devices. The research team will participate as mentors in NATURE, Nurturing American Tribal Undergraduate Research and Education, which engages tribal high school and college students throughout North Dakota in science and engineering projects. The first objective of the project is to form superlattices of SiNCs by evaporative drying and controlling the spacing of nanocrystals by adding polymers of various molecular weights. In evaporative assembly, SiNCs of known size are suspended in an organic solvent, and droplets of the suspension are deposited on glass and allowed to dry. During drying, nanocrystals accumulate at the edge of the droplet and the polymer may phase separate from the SiNCs. Parameters that influence the resulting structures include polymer molecular weight, processing temperature, SiNC concentration, geometry, solvent vapor pressure and shear rate. The influence of long-range order on the luminescent properties of the assemblies will then be investigated. The second objective is to develop modified equilibrium theories of the phase behavior of nanocrystal suspensions using effective interparticle potentials tested in molecular simulations of colloidal crystallization. Lattice-Boltzmann simulations will also be generated to help analyze and control the multiphase flow associated with slow evaporation.