For the first time, researchers have used light to control the shape of nanoparticles and create micron-size hollow shells from crystals of cuprous oxide (copper and oxygen). Such particles could have future applications as a low-cost catalyst to help pull excess carbon dioxide from the air, a way to improve microscopic imaging and more, says Bryce Sadtler, a chemist at Washington University in St. Louis and senior author of a study on the new method, published last October in Chemistry of Materials.