Calibration Particles Relevant to the Measurement of Nanosize Particles.
Calibration Particles Relevant to the Measurement of
Nanosize Particles.
(72 K)
Mulholland, G. W.
Annual Meeting. Proceedings. American Association of
Aerosol Research. Book of ABSTRACTS. October 11-15,
1999, Tacoma, WA, 1-1 pp, 1999.
Keywords:
particles
Abstract:
The development of technologies associated with
nanometer size particles, such as automated wafer
inspection systems, requires several monosize
calibration particlcs with diameters in the range from 1
nm to 100 nm. The one relevant calibration standard from
NIST is the 100 nm Standard Reference Material 1963. The
characteristics of these particles will be described
along with the methodology for characterizing the sizing
uncertainty, which is based on ISO's "Guide to the
Expression of Uncertainty." The issues of discrepancies
among various accepted standards will be discussed along
with the need for traceability to an accurate reference
standard. A summary of other sources of nanometer size
calibration particles will be given along with
information on nominal size, width of size distribution,
and traceability. One limitation of existing polystyrene
calibration particles is that the width of the size
distribution increases dramatically with decreasing
particle size. For example, the coefficient of variation
for 100 nm spheres is about 0.02, while the value for 30
nm spheres it is about 0.2. Another challenge for
particle sizes less than 100 nm is the generation of an
aerosol with the same characteristics as the particles
in suspension. Typically the aerosol is formed by
pneumatically atomizing a suspension of the monosize
spheres. The contaminant in the water leaves a residue
on the dried spheres. The thickness of this layer
relative to the particle diameter increases as the
particle size decreases. Also, for particles with
diameters less than about 50 nm, the formation of
multiplet particle can become an issue. The potential
effectiveness of electrospray systems to reduce these
effects will be discussed. For very small particle sizes
there are exciting new calibration possibilities based
on "molecular" particles. These include dendrimers and
macromolecules. The results of sizing studies carried
out at NTST on dendrimers ranging in size from 2 nm to
15 nm will be presented.
