Nobel Prize lecture: Louis Brus, Nobel Prize in Chemistry 2023

Professor Lis Bruce, born in Cleveland, Ohio, and a professor at Columbia University, discusses the groundbreaking discovery of creating quantum dots using solution chemistry. He thanks the Nobel Foundation for the honor and acknowledges minor errors in his presentation slides. The lecture delves into the chemistry of quantum dots, specifically cadmium selenide, and contrasts them with carbon nanotubes, illustrating the size comparison with biological nanoscience and nanocrystals. The journey begins with his time as a staff scientist at AT&T Bell Labs in 1982.

This paragraph focuses on the definition and synthesis of semiconductor nanocrystals, which are small particles with a significant proportion of atoms on the surface. The process involves chemical synthesis creating a colloid with stabilizing ligands on the surface for functionality. The apparatus for making quantum dots is described, highlighting the ability to control composition and size. An example of creating core-shell nanocrystals is given, and the evolution of the synthesis process from aqueous precipitation to the use of inverse micelle solutions is detailed.

The narrative discusses the use of inverse micelle solutions in the synthesis of quantum dots, initiated in 1986. The process involves phase separation into water droplets within a heptane solution, allowing for the growth of individual nanocrystals protected from aggregation. The growth of cadmium selenide nanocrystals is described, along with the ability to control the size and surface properties of the particles. The paragraph also touches on the transition of particles from hydrophilic to hydrophobic and the extraction of pure samples from the micelle solution.

This section delves into the advanced synthesis techniques used to create larger and better-quality quantum dots, including the use of lewsite solvents at higher temperatures. The intermittent success and the influence of impurities on the process are acknowledged. The importance of synthesis optimization is emphasized, with examples from the laboratory of Chris Murray demonstrating the production of high-quality nanocrystals. The paragraph also reflects on the long-term vision and support of Bell Labs for such cutting-edge research.

The speaker reflects on the evolution of microelectronics, particularly the miniaturization of transistors, and how it was driven by photolithography. The potential changes in transistor design due to the physical properties of small particles are discussed, leading to the recognition of quantum size effects. The connection between the quantum size effect and the intermediate regime between molecular properties and solid-state properties is explored, along with the accidental discovery of these effects during surface photochemistry experiments.

The paragraph explores the quantum size effect in detail, explaining how it arises from the incomplete band structure of small semiconductor particles. The difference between the bulk material and quantum dots in terms of energy levels and transitions is highlighted. The explanation is provided using both solid-state physics and chemical bonding concepts, illustrating the shift from molecular to bulk properties as the nanocrystal size increases. The implications for optical and electronic properties, such as the discrete molecular orbitals in quantum dots, are discussed.

This section discusses the optical properties of quantum dots, emphasizing their potential as chromophores due to their size-dependent electronic and optical properties. The quantum size effect is related to the discrete energy levels and the resulting optical transitions, which are likened to those of aromatic hydrocarbons. The paragraph also touches on the importance of surface chemistry in achieving good luminescence and the role of quantum dots in various applications, such as lasers, optical fibers, and light-emitting diodes.

The lecture concludes with a discussion on the unique electron behavior in nanostructures, such as quantum dots and carbon nanotubes, and the challenges in their synthesis. The importance of electron correlation and the dimensionality of materials on electron interactions are highlighted. The paragraph emphasizes the need for continuous learning and the interdisciplinary nature of nanoscience, acknowledging the collaborative efforts that led to the advancements in quantum dot research.

In the final paragraph, Professor Lis Bruce expresses his gratitude to the Nobel Foundation, his family, and his collaborators for their support throughout his career. He reflects on the importance of collaboration, the interdisciplinary nature of research, and the challenges in the synthesis of nanomaterials.