Aluminium diboride‐type structure in Ethiopian opal‐CT revealed by fast Fourier transform

• Published in: Journal of applied crystallography Vol. 51; no. 1; pp. 27 - 34
• Main Authors: Gauthier, J.-P., Stephant, N., Rondeau, B., Cody, J. A., Fritsch, E.
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01.02.2018; Blackwell Publishing Ltd
• Subjects: Aluminum; bidisperse arrangement; binary systems; Bright spots; Chemical Sciences; Computed tomography; Crystal structure; Crystallography; Deformation; Digital signal processors; Electron beams; Ethiopian opal; fast Fourier transform; Fast Fourier transformations; Fourier transforms; Image reconstruction; opal‐CT; Parameter estimation; Parameter identification; Photonic crystals; Scanning electron microscopy; SEM; vicinal planes
• ISSN: 1600-5767; 0021-8898; 1600-5767
• DOI: 10.1107/S1600576717016387

Invisible on a scanning electron microscope image of the surface of an Ethiopian opal rough fracture, a periodic arrangement was detected by fast Fourier transform. Using a mask to eliminate the continuous background and keeping only the bright spots in the reciprocal space (fast Fourier transform pattern), an image reconstructed by inverse fast Fourier transform (IFFT) emphasizes a very regular bidisperse array. Taken on a vicinal plane, the image of the successive steps of the stacking allows identification of the crystallographic structure and estimation of the parameters of this aluminium diboride‐type photonic crystal. In addition, another more complex IFFT image allowed confirmation of the structure and determination of the crystallographic indexing of the steps, despite image deformation due to the tilt of the vicinal plane under the electron beam. The structure of a natural CT opal from Ethiopia is explored with a new method, using Fourier transformation, applied to scanning electron microscope images.