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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. LEITE1,2Vii P. S. P. HERRMANN

1,Y. P. MASCARENHAS

2, M. E. ALVES3

1Embrapa Instrumentação Agropecuária, , CP 741, 13560-970, São Carlos, SP, Brazil, 2Instituto de Física de São Carlos – IFSC/USP, CP 369, 13560-970, São Carlos, SP, Brazil, 3Departamento 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

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.