Light alters symmetry in quantum dots, enhancing properties

Researchers at the U.S. Department of Energy's Argonne National Laboratory have discovered how to change the properties of tiny crystals called quantum dots using light. Quantum dots are small semiconductor materials known for their unique optical and electronic properties. By manipulating their structure, scientists can create materials with specific features. Typically, quantum dots of lead sulfide form a high-symmetry cubic crystal structure. However, researchers found that the arrangement of lead atoms in these structures was not always precise. This means that the symmetry is sometimes broken, leading to different material properties. Using advanced laser and X-ray techniques, the team studied how exposure to light affected the quantum dots. They used Megaelectronvolt Ultrafast Electron Diffraction to observe changes in these dots at incredibly short timeframes—down to a trillionth of a second. They also employed ultrafast X-ray scattering experiments to analyze these structural changes further. The studies revealed that when quantum dots were hit with short bursts of light, their symmetry could shift. This reorganization enhanced the alignment of atoms and altered the electronic properties of the materials. The researchers noticed a decrease in bandgap energy, which affects how well the crystals conduct electricity. The team also explored how the size of the quantum dots and their surface chemistry impacted these symmetry changes. By changing these properties, scientists can more precisely control how the quantum dots behave and their electronic and optical functions. This research represents a significant advancement in nanoscience, allowing the design of materials with tailored capabilities. The findings can pave the way for future technological innovations, much like how different Lego structures can be built from the same blocks. The results of this study were published in the journal Advanced Materials.