On a radiant afternoon in May, Dr. Moungi Bawendi, winner of the 2023 Nobel laureate in Chemistry and distinguished physical chemist, returned to his academic roots at the University of Chicago to deliver the prestigious Harkins Lecture.
A former UChicago graduate student who now serves as the Lester Wolf Professor of Chemistry at MIT, Bawendi captivated a packed audience as he recounted his extraordinary journey with quantum dots. Throughout the lecture his enthusiasm was evident as he detailed how these microscopic particles, once a scientific curiosity, have evolved to revolutionize diverse fields from biological imaging to consumer electronics.
He began his lecture by demystifying the "quantum" in quantum dots, illustrating the wave-particle duality of electrons, a concept even now he still finds "mind blowing". He highlighted a Hitachi experiment from the late 1980s, where "a single particle, a single electron" could create "a wave which is actually huge" and exhibit interference.
This wave-like behavior, he explained, is fundamental to how quantum dots work: they essentially act as a "box for that wave," a phenomenon known as the “quantum confinement effect”. To illustrate this, Bawendi used a musical analogy: just as a larger flute produces a deeper sound than a smaller piccolo, a smaller quantum dot leads to a higher energy state for the electron confined within it.
Bawendi then shared the fascinating story of the quantum confinement effect's initial discoveries. He explained that in the 1980’s, Louis Bruce in the US and Alexei Ekimov in Russia, driven purely by scientific curiosity, both independently stumbled upon the very same phenomenon.
Remarkably, both researchers, unaware of each other's work for years, even used the exact phrase -"quantum size effect" - in their separate papers. It was this pioneering work that eventually led to Bruce and Yekimov sharing the 2023 Nobel Prize in Chemistry with Bawendi himself.
Bawendi's pivotal contribution was in revolutionizing how quantum dots are made, developing the "hot injection method" with his students at MIT. This breakthrough allowed scientists to dive deeper into fundamental physics, observing rare phenomena and understanding how quantum dots transition from behaving like individual atoms to exhibiting properties akin to bulk materials.
He fondly recalled the critical moment when electronic microscopy data revealed that the material's properties began to be dictated by its smallest building block, the unit cell. This pivotal development, which unveiled the material's inherent quantum properties, was what ultimately allowed quantum dots to become precisely controllable.
The lecture then shifted to the commercialization of quantum dots, especially their use in displays. The timing was perfect, Bawendi noted, as the invention of the gallium nitride LED in the early 1990s paved the way for quantum dot applications. Initially, they found use in biological imaging, then later in the screens of products like Sony's and Samsung's QD-OLED televisions.
Looking ahead, Bawendi explored the future potential of quantum dots in areas like energy harvesting and night vision. His lecture, overall, was a powerful testament to a career driven by deep scientific curiosity, highlighting the immense impact that persistent research can have as these tiny particles continue to shape our future.
References
Definition of quantum confinement. (2023). Photonics.com. Retrieved from https://www.photonics.com/EDU/quantum_confinement/d8259
Manna, L., & Odom, T. W. (2024). Profile of Alexei I. Ekimov, Louis E. Brus, and Moungi G. Bawendi: 2023 Nobel laureates in chemistry. Proceedings of the National Academy of Sciences of the United States of America, 121(29), e2410357121. https://doi.org/10.1073/pnas.2410357121
Murray, C. B., Norris, D. J., & Bawendi, M. G. (1993). Synthesis and characterization of nearly monodisperse CdE (E = sulfur, selenium, tellurium) semiconductor nanocrystallites. Journal of the American Chemical Society, 115(19), 8706–8715. https://doi.org/10.1021/ja00072a025