Understanding Heterogeneous Nucleation in Nanocrystal Growth with Molecular Probes

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

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.