Triangular Au and disk-shaped Au-Cu alloy nanocrystals have been generated in thin SiO2 film matrixes, by sol-gel spin-coating followed by annealing at 800 degreesC in 10%H-2-90%Ar. Transmission electron microscope images confirm the shapes of the embedded nanocrystals. X-ray diffraction patterns reveal that the Au and Au-Cu nanocrystals have a (111) orientation. The disk-shaped alloy nanocrystals exhibit surface plasmon absorption at wavelengths intermediate between those of Au and Cu.