Factors affecting the accuracy of lattice spacing determination by HREM in nanometre-sized Pt particles

We have performed experimental measurements of the (111) lattice fringe spacings in 1.5 and 3 nm particles of Pt in random orientations on carbon supports. We obtain a spread in the values of the (111) spacing of at least 8% which we attribute to the low signal-to-noise ratio associated with images of small supported particles. For 3 nm particles, making measurements on almost 100 particles can reduce the uncertainty to ~ 1.5%. Image simulations have been performed to investigate systematic errors associated with particle tilt and edge effects. The simulations suggest that errors associated with particle tilt may be reduced by careful inspection of both images and diffractograms. For 1.5 nm particles, edge effects can lead to average fringe spacing in the HREM being up to 1% larger than the crystallite lattice spacing. Such effects must be taken into account if accurate lattice measurements are to be performed on particles in the 1-2 nm size range.