HIGH-PRECISION MEASUREMENT OF SUBMICROMETER PARTICLE-SIZE DISTRIBUTIONS

Submicrometer particles (polystyrene latices, for example) are often u sed as size standards for the calibration of various instruments and s ubstrates. Ideally, the size distribution of such standards should be extremely narrow. However, the current method of choice for such class ification, transmission electron microscopy (TEM), is fraught with pro blems rendering the reported size distributions uncertain. A far more precise and practical method consists of fractionating the particle sa mple prior to measurement by light scattering. A nominal 100 nm diamet er NIST sample has been so-analyzed and yields a full width at half ma ximum of less than 0.5 nm, far below the resolution of TEM. The fracti onation/light scattering protocol for so narrow a standard is confirme d by repeating the measurement using a broader sample fractionated und er identical conditions.