In Harvard’s Pierce Hall, the surface of a small germanium-coated gold sheet shines vividly in crimson. A centimeter to the right, where the same metallic coating is literally only about 20 atoms thicker, the surface is a dark blue, almost black. The colors form the logo of the Harvard School of Engineering and Applied Sciences (SEAS), where researchers have demonstrated a new way to customize the color of metal surfaces by exploiting a completely overlooked optical phenomenon.
For centuries it was thought that thin-film interference effects, such as those that cause oily pavements to reflect a rainbow of swirling colors, could not occur in opaque materials. Harvard physicists have now discovered that even very “lossy” thin films, if atomically thin, can be tailored to reflect a particular range of dramatic and vivid colors.
Published in the journal Nature Materials (online) on October 14, the finding opens up new possibilities for sophisticated optical devices, as well as consumer products such as jewelry and new techniques in the visual arts.