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

We have performed experimental measurements of the (111) lattice fringe spa cings in 1.5 and 3 nm particles of Pt in random orientations on carbon supp orts. 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 al most 100 particles can reduce the uncertainty to similar to 1.5 %. Image si mulations have been performed to investigate systematic errors associated w ith particle tilt and edge effects. The simulations suggest that errors ass ociated with particle tilt may be reduced by careful inspection of both ima ges and diffractograms. For 1.5 mm particles, edge effects can lead to aver age fringe spacing in the HREM being up to 1% larger than the crystallite l attice 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.