Uniform Microcrystals of Platinum and Gold

Theories describing bulk properties of solids are simplified by neglecting the presence of a boundary; i.e., one usually assumes a crystal of infinite size. There are situations, however, in which it is not permissible to neglect the effects that crystal boundaries have on electronic and vibrational properties. Order-of-magnitude calculations show that for most properties, particles must be less than 1000 Å before size effects become manifest. To study physical properties which are crystal-size dependent it is often desirable to have a sample containing many distinct particles of a well-defined size distribution confined to a small volume. Hydrosols of platinum and gold have been prepared using various procedures in order to determine the optimum conditions required to produce a given crystal size with a uniform size distribution. Crystal size and morphology were analyzed by electron microscopy and electron diffraction. Uniform microcrystals were obtained with sizes ranging from 40 to 500 Å. Methods for dialyzing and dehydrating the hydrosols are also discussed.