Crystalline and noncrystalline effects in electron diffraction patterns from small clusters in an argon cluster beam

We present an electron diffraction study of extremely small clusters of argon atoms formed by homogeneous nucleation in an expansion nozzle system. The clusters, in general comprising less than 1000 atoms, yielded good quality Debye-Scherrer patterns under conditions essentially free from all substrate interactions. The high precision of the diffraction patterns, even at large angles, makes it possible to assign an effective fcc structure to the particles. However, an anomalously large 111 peak is observed consistently and may be interpreted as resulting from vestiges of noncrystalline structure exhibited by the aggregates in the early stages of their growth.