The accurate knowledge of the size distribution of the soil clay particles (φ ≤ 2 μm) can improve the understanding of the soil surface chemical processes, which, in their turn, occur mainly in this smallest sized fraction. However, there are few available techniques for particle size evaluation at the nanoscale.

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References
1. J. S. Villarrubia, A. E. Vladár, J. R. Lowney,
and M. T. Postek, “Scanning electron microscope
analog of scatterometry,” Proceedings of the SPIE,
Vol. 4689, pp. 304-312, 2002.
2. J. R. Lowney, “Monte Carlo simulation of
scanning electron microscope signals for lithographic
metrology,” SCANNING, Vol. 18, pp. 301-306, 1996.
3. M. Watanabe, S. Baba, T. Morimoto, and
S. Sekino, “A novel AFM method for sidewall
measurement of high-aspect ratio patterns,”
Proceedings of the SPIE, Vol. 6922, 6922-18, 2008.
4. M. Tanaka, C. Shishido, W. Nagatmomo, and
K. Watanabe, “Application of Model-Based Library
Approach to Si3N4 Hardmask Measurements,”
Proceedings of the SPIE, Vol. 6922, 6922-93, 2008.
Surface morphology characterization of polymer
microspheres containing high explosives
MATTHEW STAYMATES
Chemical Science and Technology Laboratory
National Institute of Standards and Technology
Matthew.staymates@nist.gov 301-975-3913
The United States Department of Homeland
Security has implemented a substantial deployment
of trace explosive detection systems within the
United States and US embassies around the world.
One type of system is described as a walk-through
portal which aerodynamically screens people for
trace explosive particles. Another system is a
benchtop instrument that can detect explosives from
swipes used to collect explosive particles from
surfaces of luggage, clothing, and other articles.
Well characterized test materials are essential for
validating the performance of these systems. Here,
we explain a method for producing monodisperse
polymer microspheres containing high explosives to
be used as test particles and characterize their overall
surface morphology using scanning electron
microscopy.
Particle size, chemical composition, and detector
response are particularly important when considering
standard test particles for trace explosive detection
systems. Furthermore, the surface morphology of the
microspheres can greatly influence their aerodynamic
properties. This is of great importance in walk-
through portal systems which utilize non-contact
aerodynamic sampling as the primary means of
particle liberation, transport, and collection.
Our results indicate that both the polymer/solvent
formulation and the explosive mass fraction play an
important role in the surface morphology of the
resulting microspheres. For more crystalline
polymers, such as poly(lactide-co-glycolide), the
microspheres exhibit a relatively smooth surface
texture but loose their spherical shape and tend to
collapse into themselves as the explosive mass
fraction is increased. For more amorphous polymers,
such as poly(styrene-co-butadiene), the microsphere
begins to fragment into smaller clusters as the
explosive mass fraction in increased. The small
clusters remain in a spherical group until the mass of
explosive is too great to be contained in the polymer
matrix.
Issues such as microsphere size, uniformity, and
levels of explosive composition will be discussed, as
well as how the surface morphology relates to the
microspheres aerodynamic properties.
Acknowledgement
The Department of Homeland Security Science and
Technology Directorate sponsored this work under an
interagency agreement with the National Institute of
Standards and Technology.
Study of Brazilian Latosols by Atomic Force
Microscopy
F. L. LEITE
1,2Vii
P. S. P. HERRMANN
1
,
Y. P. MASCARENHAS
2
, M. E. ALVES
3
1
Embrapa Instrumentação Agropecuária, , CP 741,
13560-970, São Carlos, SP, Brazil,
2
Instituto de Física de São Carlos – IFSC/USP, CP
369, 13560-970, São Carlos, SP, Brazil,
3
Departamento de Ciências Exatas – ESALQ/USP,
CP 09, 13418-900, Piracicaba, São Paulo, Brazil.
after preparing the samples by using deposition
technique named self-assembled (SA).
The accurate knowledge of the size distribution of
the soil clay particles (φ ≤ 2 μm) can improve the
understanding of the soil surface chemical processes,
which, in their turn, occur mainly in this smallest
sized fraction. However, there are few available
techniques for particle size evaluation at the
nanoscale. Among the available methods there are
those like the scanning electron microscopy (SEM)
and the transmission scanning microscopy (TEM);
however, not always they are able to clearly
differentiate among agglomerates, particles and
grains; furthermore, the sample preparation for these
techniques is usually tedious and time-consuming.
One alternative for submicron evaluations of the soil
clay particles consists of using atomic force
microscopy (AFM) to assess their size distributions.
In this work, we evaluated both morphology and size

2. 276 SCANNING VOL. 30, 3 (2008)
8.0μm
(a)
8.0μm
(b)
distribution of Brazilian Latosols (Oxisols) at the
nanoscale by AFM. Both thickness and diameter of
each individual particle deposited on the mica sheets
were measured allowing for the determination of the
global particle size distribution. Quantitative analysis
of the particles size dictated that we gathered many
AFM images for each sample, so that the results are
accurate and statistically valid. The images show that
these objects are not at all regularity shaped and that
their sizes are in the range from 300 to 600 nm. It
was possible to observe distinct particle populations:
larger ones, which are aggregated in the platelets,
smaller spherical and elliptical particles (see Fig. 1).
Keywords: atomic force microscopy; nanoscale;
tropical soils.
Figure 1. AFM images of Oxisol Clays (Hapludox). Parent rock: (a) Sandstone and (b) Shist.
Review of sample preparation methods of
inorganic particles for microanalysis
(invited)
C. J. ZEISSLER (NIST)
This talk will review some of the basic and
classical sample preparation methods for inorganic
particle microanalysis by electron and ion
microscopy. Poor sample preparation can lead to
uncertain, unusable or misleading microanalysis
results. Sometimes the microscopist won't even know
their results are skewed by the preparation methods.
Various techniques for sample preparation including
dispersion, micromanipulation, filtration, particle
washing and density separation will be discussed.
Approaches to address unwanted charging, needle-in-
haystack searches, agglomeration and chemical
alteration will be described along with "preparation
artifact insurance" strategies.
An example of a strategy to reduce analytical
effort, time and maximize data quality is shown in
Figure 1. Grading the particle loading from low to
high on one analytical substrate is an approach used
for automated particle microanalysis by methods
such as SEM (scanning electron microscopy) and
SIMS (secondary ion mass spectrometry). This is
helpful when there is interest in one material of
interest of unknown proportion relative to other
particles in the sample. In such cases, about 10
particles of interest per field of view will optimize
the analysis, yet this is a Catch-22 situation: until
analysis is performed, the most advantageous particle
loading to prepare for the analysis is unknown. The
graded loading method addresses this problem. The
talk will describe strategies such as this and a variety
of specific preparation techniques.
Fig. 1. Example of graded dispersion strategy for automated
particle analysis. Five different loadings are represented on a
25 mm diameter planchet used in SEM and SIMS instruments.