Moiré pattern of artificial opal crystals investigated by acoustic scanning microscopy

Anomalous peculiarities in the form of stripes, the space scale of which much exceeds the ultrasonic wavelength, have been first observed in the acoustic images of the artificial opal crystals. The artificial opal crystal constitutes a close-packed lattice of nanospheres of X-ray amorphous silica. The presence of interferometric stripes is linked with distortions of the periodical structure of opal matrices and comprises of moiré effect. It has been found that acoustic microscopy method has high sensitivity to the changes of structure of opal matrices such as a turning of the adjacent layers of nanospheres at the angle about 1-2°.