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Examining elemental surface enrichment in ultrafine aerosol particles using analytical scanning transmission electron microscopy.

Authors
Maynard-AD; Ito-I; Arslan-I; Zimmer-AT; Browning-N; Nicholls-A
Source
Aerosol Sci Tech 2004 Apr; 38(4):365-381
NIOSHTIC No.
20026126
Abstract
The surface structure and chemistry of ultrafine aerosol particles (typically particles smaller than 100 nm in diameter) play key roles in determining physical and chemical behavior, and is relevant to fields as diverse as nanotechnology and aerosol toxicity. Analytical scanning transmission electron microscopy (STEM) is one of the few analytical methods available that is potentially capable of characterizing ultrafine particles at subnanometer resolution. We propose a method that enables STEM to characterize and quantify elemental surface enrichment within radially symmetrical particles at a spatial resolution of less than 1 nm when used in conjunction with electron energy loss spectroscopy (EELS) and X-ray energy dispersive spectroscopy (EDS). Although the method relies on a number of assumptions for complete particle characterization, estimation of the depth of an outer layer of elemental enrichment should be possible with relatively few assumptions. A preliminary investigation of the method has been carried out using particles from gas metal arc welding on mild steel. Using the analysis method, we were able to characterize Si and O enrichment in a number of particles. Two particles were investigated extensively using EELS and EDS analysis. Both techniques allowed surface enrichment of Si to be identified and quantified in the particles, although the relatively poor sensitivity of EDS was a limiting factor in the analysis. EELS allowed rapid data collection and enabled surface enrichment of Si and O to be characterized. Using a simple model to describe elemental composition with radial position, it was estimated that Si and O were enriched in an outer layer around the particle approximately 1 nm deep.
Keywords
Aerosols; Aerosol-particles; Surface-properties; Analytical-processes; Microscopy; Analytical-methods; Models; Nanotechnology
CODEN
ASTYDQ
Publication Date
20040401
Document Type
Journal Article
Fiscal Year
2004
NTIS Accession No.
NTIS Price
Issue of Publication
4
ISSN
0278-6826
NIOSH Division
DART
Priority Area
Research Tools and Approaches: Exposure Assessment Methods
Source Name
Aerosol Science and Technology
State
OH; IL
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