A team of researchers led by the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has developed a new way to directly observe how electrons interact with defects in two-dimensional (2D) semiconductors. These materials, which consist of just one or a few layers of atoms, have unique electronic properties that differ from traditional silicon-based semiconductors. The study, published in the journal Nature, used advanced simulations to interpret experimental data and uncovered how defects in these materials influence electron behavior. Scientists from institutions including the University of California, the Flatiron Institute, and Japan's National Institute for Materials Science also contributed to the research. In 2D semiconductors, electrons can behave differently under certain conditions. For example, they can form a Wigner solid, a state where electrons become immobile and arrange themselves into a highly ordered structure. This is unlike the typical behavior of electrons in conventional materials, where they move more freely. However, directly observing these interactions has been challenging. Previously, scientists relied on measuring electrical conductivity rather than visually capturing electron movements. To address this, the team used a scanning tunneling microscope, which allows for high-resolution imaging of surfaces at the atomic level. The researchers imaged a 2D semiconductor called molybdenum diselenide, which was placed between layers of graphite, silicon, and boron nitride to enhance the clarity of the images. Their findings revealed that the number of defects in the material had a significant impact on electron behavior. When there were many defects, electrons formed a surprisingly stable Wigner solid with irregular patterns. With fewer defects, electrons organized into more uniform, triangular patterns that transitioned more easily into a state known as the Fermi liquid, where electrons move more freely. To ensure the accuracy of their observations, the researchers used a Quantum Monte Carlo simulation, a computational method that models complex quantum interactions. The simulation results closely matched the experimental images, confirming the validity of both the imaging technique and the theoretical model. This research highlights the importance of controlling defects in 2D materials as electronic devices continue to shrink in size. The team is now expanding their work to study how electron behavior changes in confined spaces and in materials with fewer defects. Their methodology could also be applied to understand the electronic properties of other 2D semiconductors with strongly interacting electrons.