CAREER: Anisotropy-Directed Synthesis of Optically Active 1D van der Waals Nanocrystals and Development of Multiscale Solid State Chemistry Educational Activities

【非技术摘要】下一代更快、更高效、更致密的功能器件需要尺寸接近原子尺度的固态构建块。无机一维（1D）固体结晶成纤维状束，承载单链，厚度小于一纳米，由于其高导电性和强吸收特性，使其适合于节能电子和光子器件，最近受到了关注。然而，尽管前景光明，但人们对控制这些一维固体的纳米级形态、尺寸和物理性质的合成方法知之甚少。该奖项由美国国家科学基金会材料研究部固态和材料化学项目支持，首席研究员和他的研究小组将阐明精确指导和影响这些一维无机纤维结晶成各种尺寸和维度的纳米级晶体的化学线索。由此产生的尺寸分辨纳米结构阵列用于系统地建立光学性质如何从体到超薄纳米结构的演变。预计这些策略可转化为显示一维纤维状基序的几种固体，作为量子计算、微电子、能源和传感技术的超薄构建块。这些材料的独特性质连接了大块和纳米级固体，为培养崭露头角的科学家提供了理想的平台。通过补充的动手演示、夏季训练营和指导活动，向不同层次的学生介绍合成和表征技术，以及涉及固态材料的实际应用。技术摘要：固体中复杂现象和强相关行为的发现依赖于将固体精确雕刻成接近原子极限的稳定低维晶体。虽然二维范德华固体（vdW）已经得到了很好的研究，但对于更受限制的一维/准一维（q-1D） vdW的化学和物理性质知之甚少。在这些长度尺度和维度中，可以实现由有限尺寸效应引起的独特物理特性，如弹道电输运、尺寸相关的光学共振模式、长载流子寿命和一维激子。该奖项由美国国家科学基金会材料研究部固态和材料化学项目支持，首席研究员和他的研究小组通过阐明化学线索来解决化学知识差距，首先，指导1D/q-1D vdW链亚基组装成定义良好的纳米结构（如纳米线、纳米带或纳米片），其次，控制和改变电子带结构和光物理性质的所得纳米晶体。总体假设是，控制各向异性链间vdW相互作用的程度可以实现精确的纳米晶体尺寸分辨率，从而可以改善自下而上生长的1D/q-1D vdW纳米结构的光电性能。具体目标，涉及到pnic原和chgen -based 1D/q-1D vdW晶体，包括：(1)建立控制各向异性键、结构和气相前驱体纳米级生长习惯的内在化学相互作用；(2)在化学气相沉积系统中，通过工程成核、通量控制和催化生长途径，确定外部定向生长途径来控制1D/q-1D vdW纳米结构的形貌和尺寸；(3)通过分层组装和异质结构，从机理上阐明气相链内和链间生长途径，从而获得具有可调光物理性质的一维/q-1D vdW纳米晶体。这些低维固体的独特结构和性质促进了教育活动的发展，向不同层次的学生介绍了大块和纳米级固体材料的化学、性质和应用，包括固态和纳米化学训练营和指导计划。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL ABSTRACTThe next generation of faster, more efficient, and densified functional devices require solid state building blocks that have sizes that approach the atomic scale. Inorganic one-dimensional (1D) solids that crystallize as fiber-like bundles bearing single chains with thicknesses less than a nanometer gained recent attention due to their high degrees of conductivity and strong absorption characteristics that make them suitable for energy-efficient electronic and photonic devices. However, while promising, there is meager understanding of the synthetic methodologies to control the nanoscale morphology, size, and physical properties of these 1D solids. With this CAREER award, supported by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, the principal investigator and his research group will elucidate the chemical cues that precisely direct and influence the crystallization of these 1D inorganic fibers into nanoscale crystals with various sizes and dimensionalities. The resulting array of dimensionally resolved nanostructures is used to systematically establish how the optical properties evolve from the bulk down to ultrathin nanostructures. It is anticipated that these strategies are translatable to several classes solids that display 1D fiber-like motif, poised as ultrathin building blocks in quantum computing, microelectronics, energy, and sensing technologies. The unique nature of these materials which bridge bulk and nanoscale solids presents an ideal platform to train budding scientists. Students across multiple levels are introduced to synthetic and characterization techniques, as well as the practical applications, which involve solid state materials through complementary hands-on demonstration, summer bootcamp, and mentorship activities.TECHNICAL ABSTRACTThe discovery of complex phenomena and strongly correlated behavior in the solid state has relied on the precise sculpting of solids into stable low-dimensional crystals approaching the atomic limit. Whereas 2D van der Waals (vdW) solids are well studied, little is known about the chemistry and physics of the more confined 1D/quasi-1D (q-1D) vdW counterparts. In these length scales and dimensionalities, unique physical properties arising from finite size effects like ballistic electrical transport, size-dependent optical resonance modes, long carrier lifetimes, and 1D excitonics become realizable. With this CAREER award, supported by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, the principal investigator and his research group addresses the chemical knowledge gap by elucidating the chemical cues that, first, direct the assembly of 1D/q-1D vdW chain sub-units into well-defined nanostructures (as nanowire, nanoribbon, or nanosheet) and, second, control and alter the electronic band structures and photophysical properties of the resulting nanocrystals. The overarching hypothesis is that the control over the degree of anisotropic inter-chain vdW interactions enables the precise nanocrystalline dimensional resolution which, in turn, could improve the optoelectronic properties of bottom-up grown 1D/q-1D vdW nanostructures. The specific objectives, which involve pnictogen- and chalcogen-based 1D/q-1D vdW crystals, are: (1) establish the intrinsic chemical interactions governing anisotropic bonding, structure, and nanoscale growth habits from vapor phase precursors; (2) identify extrinsically directed growth pathways to control morphologies and sizes in 1D/q-1D vdW nanostructures through engineered nucleation, flux control, and catalyzed growth routes in a chemical vapor deposition system; and (3) mechanistically elucidate vapor phase intra- and inter-chain growth pathways that lead to dimensionally resolved 1D/q-1D vdW nanocrystals with modulable photophysical properties via hierarchical assembly and heterostructuring. The unique structure and properties of these low-dimensional solids facilitate the development of educational activities introduce the chemistry, properties, and applications of both bulk and nanoscale solid state materials to students across various levels, including a solid state and nano-chemistry bootcamp and mentoring program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.