Variation of Lattice Spacing with Thickness of Thin Gold Platelets
Variation of lattice parameters with crystal size in very small crystals (generally less than 500 Å in size) has been the subject of many research papers over a long period of time. In principle this method should provide a direct experimental measurement of surface tension but in many cases the reported results are contradictory. This fact has been noted in recent reviews, and the abnormal spacings are now generally regarded with considerable reserve. The many reported contradictions arise from a variety of experimental factors which cannot be discussed here. This paper, however, reports new experiments using a different approach which we believe has eliminated the previous experimental difficulties, and conclusively demonstrates lattice parameter variations associated with surface energy. These experiments consist of the preparation of thin, parallel, clean and nearly perfect platelets of Au and the subsequent measurement of the lattice spacings of these platelets as a function of thickness.The Au platelets were chemically grown by the reduction of chloroauric acid with salicylic acid. Reproducibly clean crystals from 1-5 µ in diameter and ranging in thickness from 80-300 Å were produced.