SEM Image (IMAGE) American Institute of Physics Caption The multi-phase thermoelectric Cu(1.97)Ag(0.03)Se consists of a main crystal structure of Cu(2)Se and an impurity phase with the crystal structure of CuAgSe. In this scanning electron microscope image the impurity phase shows up as light spots. The dark spots are voids in the crystal structure. Credit Tristan Day/Caltech Usage Restrictions This image may be used only with appropriate caption and credit. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.