"This cover art depicts selected colloidal nanorod heterostructures where lattice symmetry and strain, surface chemistry, and reaction kinetics dictate growth mechanisms, illuminating paths to precise morphologies with prescribed function."
Materials science and engineering professor Moonsub Shim and graduate students Gryphon Drake and Logan Keating have recently published a review paper, “Design Principles of Colloidal Nanorod Heterostructures,” in Chemical Reviews. Their invited review was a part of the Anisotropic Nanomaterials special issue. Drake and Keating’s artwork made the cover of the current issue.
Shim, also the director of graduate studies in the materials science and engineering department, discusses the research presented in the review:
Can you give a brief overview of the area of research presented in this review?
MS: Our review covers the nascent area of anisotropic heterostructures of nanometer dimensions that are achieved through solution chemistry. Anisotropic structures exhibit properties with different values when measured along axes in different directions. We focus on materials that contain two or more different semiconductor nanoparticles that are put together, or grown together, coherently in terms of how their atoms are arranged and form anisotropic shapes, such as rods.
Through such materials, we can not only tune the size and shape of each constituent semiconductor, but also envision new capabilities arising from interfacing them. For example, light upconversion, where low-energy photons are converted to high-energy photons, and multi-functional devices that can emit, detect and harvest light within the same device platform, are being explored with anisotropic nanorod heterostructures.
What made you interested in this field of research?
MS: I have been fascinated by how so many things around us are often governed by how charges are generated and recombined, everything from electronics we interact with every day to lightning during a thunderstorm. Combine that with the fun and excitement of making something new, and I knew this is what I wanted to do.
What are a few of the key points discussed in the review?
MS: The nanoparticles covered in our review are quite complex, consisting of multiple compositions and anisotropic shapes. They are often synthesized serendipitously and the understanding of the underlying mechanisms of growth are not yet well understood. We have taken various advances in this area that are often disparate and provided a coherent picture of the fundamental factors that contribute to regioselectivity and anisotropy- the factors that will allow one to be more predictive in synthesizing new structures.
A large part of the review deals with the underlying chemistry and materials science of how such structures can be grown with precision with intended/controlled shape. There are two main synthetic approaches: one in which atomically coherent growth of the second phase occurs on existing particles (heteroepitaxy) and one where a single composition particle is partially converted to two or more different phases via exchange of some of the atoms (partial ion exchange). In addition, we discuss current and future prospects in applications of these anisotropic nanorod heterostructures.
What are the broader applications and implications of this area of research?
MS: There are numerous potential applications in photonics, optoelectronics and photovoltaics. Light upconversion that is useful for solar cells and biomedical imaging, and multi-functional light harvesting/emitting devices are a couple of examples that are currently being explored. In addition, there may be opportunities in engineering novel photocatalysts and quantum light sources through these types of materials.
How does this review fit in with your own research?
MS: This is really the core of my research group’s efforts, developing new combinations and shapes of materials with nanoscale precision. The review paper includes a significant amount of our work within the context of recent advances in the field.
Closing thoughts?
MS: I would like to acknowledge my graduate students, Gryphon Drake, and Logan Keating, who have pioneered in this area and have coauthored the review paper.