Measurement of 100 nm monodisperse particles by four Accurate methods: Traceability and uncertainty

Accurate measurements of particle diameter are necessary for quantitative characterization of key aerosol properties including the Cunningham slip correction factor, charging probability, diffusion coefficient, coagulation coefficient, and optical properties. In this study, we use four techniques to measure the diameter of nominal 100 nm reference spheres having a distributional standard deviation of less than 2 nm. The instruments used are a differential mobility analyzer (DMA), atomic force microscopy (AFM), scanning electron microscopy (SEM), and an electrical-gravitational aerosol balance (EAB). All four measurements are traceable to SI units at National Institute of Standards and Technology (NIST) or at National Institute of Advanced Industrial Science and Technology (AIST). This study includes quantitative estimates of the measurement uncertainty for each technique. It finds that the measured average particle diameter is within 3% for all the methods, with at least some overlap in all the estimated uncertainties using a 95% confidence interval. Nevertheless, the difference between the EAB results and the other methods may become significant as they are separately intended to be used in the manner described here for the traceable certification of future nanoscale particle size standards. Possible reasons for the differences are incorrect or inadequate accounting for surface residue for aerosol measurements, adhesion-force distortion for the AFM measurements, e-beam shrinkage for the SEM measurements, slip correction uncertainty for the DMA, and work function variability of the electrodes for the EAB.