Comparison of 100 nm Monodisperse Particle Size Measured by Four Accurate Methods

Kaleb Duelge, GEORGE MULHOLLAND, Vince Hackley, Natalia Farkas, John Kramar, Michael Zachariah, Keiji Takahata, Hiromu Sakurai, Kensei Ehara, National Institute of Standards and Technology

     Abstract Number: 23
     Working Group: Instrumentation and Methods

Abstract
Measurement results for the number mean diameter of 100 nm monodisperse polystyrene spheres (JSR SC-010-S, SRM1963) by four independent methods will be presented. These methods are differential mobility analysis (DMA), atomic force microscopy (AFM), scanning electron microscopy (SEM), and electro-gravitational aerosol balance (EAB). The first three of the methods are traceable to the wavelength of light with the two microscopies traceable via NIST’s Calibrated Atomic Force Microscope. The fourth method, with the lowest uncertainty of the four measurements, is based on a direct relationship between the particle diameter and the voltage, electrode spacing, particle density, and fundamental constants. The total range in the number average diameters is slightly less than 3% of the mean of the means. For many applications, the use of standards based on these measurements would enhance the accuracy of size measurements for aerosols and colloids.

The 95% confidence intervals for some of the measurements barely overlap, raising the concern that some uncertainty components may have been underestimated or some measurement biases may have been overlooked. Possible reasons for the differences will be discussed including the slip correction for DMA, the work function of the EAB electrodes, determination of the physical edge of the particle for SEM, and the particle-substrate adhesion-force distortion for AFM. Another concern is the differences in the particle environments for the different measurements – two are aerosol measurements and two are based on the deposition of particles onto a surface. Improvements in these methods or the development of new techniques are important for progress in fundamental aerosol and colloidal research.