Nanometer calibration particles: what is available and what is needed?

Information on available polystyrene calibration spheres is presented regarding the particle diameter, uncertainty in the size, and the width of the size distribution for particles in a size range between 20 and 100 nm. The use of differential mobility analysis for measuring the single primary calibration standard in this size range, 100 nm NIST Standard Reference Material (R) 1963, is described along with the key factors in the uncertainty assessment. The issues of differences between international standards and traceability to the NIST Standard are presented. The lack of suitable polystyrene spheres in the 20-40 nm size range will be discussed in terms of measurement uncertainty and width of the size distributions. Results on characterizing a new class of 'molecular' particles known as dendrimers will be described and the possibilities of using these as size calibration standards for the size range from 3 to 15 nm will be discussed.