To be, or not to be [crystalline], that is the question

Chris Takacs (Postdoc)
Michael Chabinyc


Organic molecules often assemble in a periodic pattern known as a crystal lattice; however, defects are known to spoil and/or distort the local structure. Here, continuous lines represent the local crystalline lattice and the bending reveals the variability on the atomic scale. (2.5 μm by 1.4 μm)

The material is a small molecule organic semiconductor (material from Gui Bazan) used in organic photovoltaics. Using low-dose imaging techniques developed for these thin-films, 2.4 nm lattice planes are readily visible in the micrographs. A wavelet algorithm was developed to extract the local orientation of the lattice planes: the micrograph is broken into small images (~15 nm per side) and each image is Fourier transformed to give the local diffraction pattern. A peak is considered “real” when the local diffraction intensity is >3 sigma above the electron shot noise background. These data are then used as the local tangent vectors for drawing the continuous lines in the image. By controlling the space between lines, nano-scale structure can be visualized on much larger length-scales.