Understanding Heterogeneous Nucleation in Nanocrystal Growth with Molecular Probes

纳米晶体是几何上良好有序的固体，直径约为0.00000005英寸。 由两种不同金属物质制成的双金属纳米晶体具有通常优于其单金属对应物的上级性质。两种不同金属在金属间化合物中相对于彼此的排列在确定金属间化合物的性质方面是非常重要的，并且已经做出相当大的努力来将一种金属存款在另一种金属的金属间化合物表面上精确定位。 检测和量化沉积的金属仍然是一个巨大的挑战，特别是当纳米晶体仍然悬浮在生长的反应介质中时。秦东博士通过开发一类分子，异氰化物（含有-NC化学基团的分子）作为探针，通过光谱技术，表面增强拉曼散射（Sers）检测异氰化物，从而解决了这一挑战。最终目标是建立一个科学的基础，使合理的合成纳米晶体的组成和形状得到良好的控制，这有更广泛的社会影响，通过他们的需要在各种应用。该研究项目涵盖多个学科，如材料科学，化学，胶体科学，固态物理学，光子学和表面科学，重点是学生发展的以下组成部分：i）积极学习涉及理解纳米材料的结构和性质关系的跨学科领域; ii）提供Qin实验室纳米材料合成实践经验的培训，以及格鲁吉亚理工学院和国家实验室最先进设施中纳米材料表征的培训;以及iii）让社区和社会，包括高中学生和教师，接触纳米级科学和技术概念。在这项研究中，来自格鲁吉亚理工学院的董勤博士得到了大分子，超分子和纳米化学（MSN）计划的支持，研究了纳米晶体的异相成核和过度生长所涉及的基本原理。具体地说，一类新的异氰化物为基础的分子探针（R-NC）的开发用于原位检测和分析的第二贵金属（M：Pd，Pt，Ir，Rh，或Ru）上的银纳米晶体悬浮在原来的生长溶液中的表面增强拉曼散射（Sers）的过度生长。因为异氰化物基团与金属表面的结合类似于一氧化碳的结合，所以预期当异氰化物基团分别与Ag和M原子结合时，NC键的伸缩频率不同。因此，通过跟踪NC振动的伸缩频率和强度，可以真实的实时监测沉积在Ag纳米晶体上的M原子。另一方面，银纳米晶体上的Sers热点可以被设计成与M原子有利于异质成核的位点相一致，从而实现前所未有的灵敏度，检测限低于一个单层。通过利用它们对金属原子的完美灵敏度，新型Sers探针开辟了新的机会，以阐明在Ag纳米晶体表面上的第二种贵金属的种子过度生长所涉及的机制细节。机制的见解支持合理的设计和基于知识的合成双和多金属纳米晶体的各种应用。该研究项目涵盖多个学科，如材料科学，化学，胶体科学，固态物理学，光子学和表面科学，重点是学生发展的以下组成部分：i）积极学习涉及理解纳米材料的结构和性质关系的跨学科领域; ii）提供Qin实验室纳米材料合成实践经验的培训，以及格鲁吉亚理工学院和国家实验室最先进设施中纳米材料表征的培训;以及iii）让社区和社会，包括高中学生和教师，接触纳米级科学和技术概念。

Nanocrystals are geometrically well-ordered solids with diameters on the order of 0.00000005 inches. Bimetallic nanocrystals, made of two different metal species, have properties that are often superior to their single-metal counterparts. The arrangement of the two different metals relative to each other in the nanocrystal is very important in determining the nanocrystal properties, and considerable effort has been made to deposit one metal atop the nanocrystal surface of another metal with precision in location. It remains a grand challenge to detect and quantify the metal being deposited, particularly when the nanocrystals are still suspended in the reaction medium undergoing growth. Dr. Dong Qin addresses this challenge by developing a class of molecules, the isocyanides (molecules containing the -NC chemical group), as probes for in situ characterization with detection of the isocyanides by a spectroscopic technique, surface-enhanced Raman scattering (SERS). The ultimate goal is to establish a scientific basis for enabling the rational synthesis of bimetallic nanocrystals with well-controlled compositions and shapes, which have broader societal impact through their need in a variety of applications. This research project encompasses multiple disciplines such as materials science, chemistry, colloidal science, solid-state physics, photonics, and surface science, with a focus on the following components for student development: i) active learning in interdisciplinary areas involved in understanding the structure and property relationships of nanomaterials; ii) training that provides hands-on experience in the synthesis of nanomaterials in the Qin laboratory, and on the characterization of nanomaterials in the state-of-the-art facilities at Georgia Tech and national laboratories; and iii) exposing the community and society, including high school students and teachers, to nanoscale science and technology concepts.In this research, Dr. Dong Qin from the Georgia Institute of Technology is supported by the Macromolecular, Supramolecular and Nanochemistry (MSN) Program to study the fundamentals involved in the heterogeneous nucleation and overgrowth of bimetallic nanocrystals. Specifically, a novel class of isocyanide-based molecular probes (R-NC) are developed for in situ detection and analysis of the overgrowth of a second noble metal (M: Pd, Pt, Ir, Rh, or Ru) on Ag nanocrystals suspended in the original growth solution by surface-enhanced Raman scattering (SERS). Because the binding of the isocyanide group to a metal surface is similar to that of carbon monoxide, it is anticipated that the stretching frequency of the NC bond differs when the isocyanide group binds to the Ag and M atoms, respectively. Therefore, it is feasible to monitor the M atoms being deposited onto Ag nanocrystals by following the stretching frequencies and intensities of NC vibration in real time. On the other hand, the SERS hot spots on the Ag nanocrystals can be designed to coincide with the sites favored by M atoms for heterogeneous nucleation, allowing for unprecedented sensitivity with a detection limit below one monolayer. By leveraging their consummate sensitivity toward metal atoms, the novel SERS probes open up new opportunities to elucidate the mechanistic details involved in the seeded overgrowth of a second noble metal on the surface of Ag nanocrystals. The mechanistic insights support the rational design and knowledge-based synthesis of bi- and multi-metallic nanocrystals for a variety of applications. This research project encompasses multiple disciplines such as materials science, chemistry, colloidal science, solid-state physics, photonics, and surface science, with a focus on the following components for student development: i) active learning in interdisciplinary areas involved in understanding the structure and property relationships of nanomaterials; ii) training that provides hands-on experience in the synthesis of nanomaterials in the Qin laboratory, and on the characterization of nanomaterials in the state-of-the-art facilities at Georgia Tech and national laboratories; and iii) exposing the community and society, including high school students and teachers, to nanoscale science and technology concepts.