BRIGE: Thermal Transport in Single-Domain Three-Dimensional Colloidal Nanocrystal Superlattices

BRIGE：单域三维胶体纳米晶超晶格中的热传输

• 批准号: 1227979
• 负责人: Robert Wang
• 金额: $ 17.5万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1227979&HistoricalAwards=false
• 关键词: BRIGE; Thermal; Transport; Single; Domain

Abstract#1227979Wang, RobertColloidal nanocrystals are inorganic nanoparticles with organic ligand molecules bonded to their surface. These nanocrystals can self-assemble into periodic arrays due to the van der Waals interactions between their ligand molecules. In analogy to the atomic lattice of a crystal, these nanocrystal assemblies are termed nanocrystal superlattices. These superlattices are best known for their optical and electronic transport properties, however their thermal transport properties remain unexplored. I hypothesize that these superlattices should have an extremely low thermal conductivity because of: (i) a large interfacial density, (ii) a large acoustic impedance mismatch between the inorganic nanoparticle cores and organic ligand matrix, and (iii) filtering of lattice vibrations (i.e. phonons) resulting from its microstructure. A phonon is a quantum of crystal vibrational energy and is analogous to the photon, which is a quantum of electromagnetic energy. In non-metallic solids, phonons are the dominant mode of heat conduction. Do to the exquisite periodicity of these self-assembled nanocrystals, these superlattices should behave as phononic crystals. Phononic crystals are artificially structured materials with periodic variations in acoustic impedance. This periodicity results in a phononic band gap, which forbids the propagation of phonons in a particular energy range. The phononic crystal is analogous to the well-known photonic crystal, which uses periodic variations in refractive index to create a photonic band gap. Phononic crystals can be used for phonon filters, waveguides, resonators, and superlenses.To investigate these thermal transport hypotheses, I will (1) Synthesize monodisperse nanocrystals and assemble them into single-domain three-dimensional nanocrystal superlattices, (2) Experimentally measure their thermal conductivity as a function of nanocrystal size, (3) Numerically determine their phonon band structure, and thereby identify their potential as phononic crystals, and (4) Create a phonon spectroscopy apparatus to be used in future proposals to experimentally measure the phonon band gap of these superlattices as a function of nanocrystal size.Intellectual Merit: This proposal takes significant steps forward by investigating thermal transport in nanocrystal superlattices, which are an unexplored class of materials. It also numerically explores the phononic crystal properties of these superlattices and motivates future proposals to experimentally study this topic. Due to the small ~10 nm superlattice periodicity, their phononic band gap should be in the 100 GHz ? 1 THz range, which is 100x higher than the best-reported 3-dimensional phononic crystal. Due to their frequency-dependent phonon transport properties, these materials should have drastically different heat conduction properties than conventional solids. Furthermore, this type of phonon transport engineering could lead to significant advances in thermoelectricity and electronics thermal management.Broader Impacts: To enhance diversity as well as integrate research and education, I have developed a comprehensive outreach plan that addresses instruction at all education levels. This plan includes: (1) Engaging K-12 students via interactive presentations on-site in their classrooms that focus on thermal energy and related topics. Included in this presentation will be hands-on demonstrations that integrate research topics on thermal transport and thermoelectricity. (2) Designing a laboratory module on colloidal nanocrystal synthesis and characterization for incorporation into curriculum at the community college level. The integration of research tools such as transmission electron microscopy is included. (3) Recruiting individuals from underrepresented groups into my research and mentoring them toward their respective career goals. My plan for these initiatives includes metrics to gauge their effectiveness. For example, the K-12 initiative will be assessed using concept knowledge questions from the AAAS Science Assessment database. The questions in this database meet rigorous psychometric standards and have a large data set with which to compare the answers of the service recipients.

摘要#1227979Wang，RobertColloidal纳米晶体是无机纳米颗粒，其表面结合有有机配体分子。 由于配体分子之间的货车范德华相互作用，这些纳米晶体可以自组装成周期性阵列。类似于晶体的原子晶格，这些超晶格被称为超晶格。 这些超晶格以其光学和电子输运性质而闻名，但其热输运性质尚未探索。我假设这些超晶格应该具有极低的热导率，因为：（i）大的界面密度，（ii）无机纳米粒子核和有机配体基质之间的大的声阻抗失配，以及（iii）过滤晶格振动（即声子）导致其微观结构。声子是晶体振动能的量子，类似于光子，光子是电磁能的量子。在非金属固体中，声子是热传导的主要模式。由于这些自组装纳米晶体的精细周期性，这些超晶格应该表现为声子晶体。声子晶体是一种具有周期性声阻抗变化的人工结构材料。这种周期性导致声子带隙，其禁止声子在特定能量范围内的传播。声子晶体类似于众所周知的光子晶体，其使用折射率的周期性变化来产生光子带隙。声子晶体可用于声子滤波器、波导、谐振器和超透镜。为了研究这些热传输假设，我将（1）合成单分散纳米晶体并将其组装成单畴三维纳米晶体超晶格，（2）实验测量其热导率作为纳米晶体尺寸的函数，（3）数值确定其声子能带结构，从而确定它们作为声子晶体的潜力，以及（4）建立一个声子光谱装置，用于未来的建议，以实验测量这些超晶格的声子带隙作为晶体尺寸的函数。这项提案通过研究超晶格中的热传输向前迈出了重要的一步，超晶格是一类未开发的材料。它还数值探讨了这些超晶格的声子晶体性质，并激发了未来的建议，实验研究这一主题。由于小的~10 nm的超晶格周期性，它们的声子带隙应在100 GHz？1 THz范围，比最好的三维声子晶体高100倍。由于它们的频率依赖性声子输运性质，这些材料应该具有与传统固体截然不同的热传导性质。此外，这种类型的声子运输工程可能会导致热电和电子热management.Broader影响的重大进步：以提高多样性，以及整合研究和教育，我已经制定了一个全面的推广计划，解决所有教育水平的教学。该计划包括：（1）通过互动演示吸引K-12学生在他们的教室现场，专注于热能和相关主题。包括在这个演示将动手示范，整合热传输和热电的研究课题。(2)设计一个关于胶体晶体合成和表征的实验室模块，以纳入社区学院一级的课程。研究工具，如透射电子显微镜的集成包括在内。(3)从代表性不足的群体中招募个人进入我的研究，并指导他们实现各自的职业目标。我对这些举措的计划包括衡量其有效性的指标。例如，K-12计划将使用AAAS科学评估数据库中的概念知识问题进行评估。这个数据库中的问题符合严格的心理测量标准，并有一个大的数据集，可与服务接受者的答案进行比较。

项目成果

Modifying Thermal Transport in Colloidal Nanocrystal Solids with Surface Chemistry

• DOI: 10.1021/acsnano.5b05085
• 发表时间: 2015-12-01
• 期刊: ACS NANO
• 影响因子: 17.1
• 作者: Liu, Minglu;Ma, Yuanyu;Wang, Robert Y.
• 通讯作者: Wang, Robert Y.

Colloidal nanocrystal superlattices as phononic crystals: plane wave expansion modeling of phonon band structure

作为声子晶体的胶体纳米晶体超晶格：声子能带结构的平面波展开建模

• DOI: 10.1039/c6ra03876j
• 发表时间: 2016
• 期刊: RSC Advances
• 影响因子: 3.9
• 作者: Sadat, Seid M.;Wang, Robert Y.
• 通讯作者: Wang, Robert Y.