Block Copolymer Monolayer Structure Measured with Scanning Force Microscopy Moiré Patterns

We demonstrate that an analytical model can be used to interpret moiré patterns in scanning force microscopy images of spherical domain block copolymer films, yielding grain orientations and a more than 10-fold increase in scan size without requiring a tedious empirical calibration. Moiré patterns are the product of interference between two overlapping regular gratings and are sensitive to the grating periodicity and alignment. We apply this technique to SFM of a monolayer of a spherical domain block copolymer, where the SFM scan lines act as a reference grating, and the close-packed rows of the block copolymer domains form the sample grating. The block copolymer grain orientation and size are calculated from the moiré patterns using an analytical model. The accuracy of the model is confirmed by directly imaging the block copolymer lattice with high-resolution SFM. Furthermore, we investigate the moiré patterns of defects in this two-dimensional array of domains and demonstrate that dislocations can be reliably imaged depending on the pitch of the moiré fringes and the orientation of the Burgers vector of the dislocations.