Journal of Research of the
National Institute of
Standards and Technology

Cover Explanation:

The cover contains a transmission electron micrograph of 60 nm polystyrene spheres, which have been certified as a new NIST Standard Reference Material (SRM) for the calibration of nano-scale particle sizing instruments. The particle sizing  measurements were made using an electrical mobility instrument for the particles in aerosol form, and the plotted size distribution function, G(Dp), on the cover includes the raw data, data corrected for the presence of doubly charged monomers (cross symbols), and a Gaussian approximation of the
distribution near the peak (solid curve). The 1st paper in this issue (Mulholland et al., pg. 257) presents the particle
size certification measurements and uncertainty analysis for the 60 nm spheres and also for 100 nm spheres, which will be available as a second new SRM. Cover arranged by C. Carey.