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Surface oxidation state of combustion-synthesized gamma-Fe2O3 nanoparticles determined by electron energy loss spectroscopy in the transmission electron microscope.

Authors
Jasinski-J; Pinkerton-KE; Kennedy-IM; Leppert-VJ
Source
Sens Actuators B Chem 2005 Aug; 109(1):19-23
NIOSHTIC No.
20032820
Abstract
Electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM) was used to compare the iron oxidation state at the surface and interior of gamma-Fe2O3 nanoparticles produced by the combustion process under fuel conditions leading to low and high soot concentrations. These experiments were performed in the nanoprobe mode, which allowed for very high spatial resolution (the probe size was 1.4 nm). Here, low soot concentrations were obtained in a laminar ethylene-air diffusion flame seeded with iron pentacarbonyl, while high soot concentrations were achieved with the addition of acetylene to this fuel mixture. The studies showed that the surface oxidation state of iron was lowered with the addition of acetylene, although the core composition remained the same. This was indicated by changes in both the iron L23- and the oxygen K-edges at the surface of the particles. These highly spatially-resolved measurements showed a chemical shift of both the L3 and L2 iron lines, accompanied by significant reduction of the L3:L2-intensity ratio, indicating Fe2+ at the particle surface. Reduction in the pre-edge peak of the oxygen K-edge at the particle surface also indicated iron reduction at the surface. These results suggest that the surface oxidation state, and therefore gas-sensing properties, of combustion-synthesized iron oxide nanoparticles is highly dependent on flame conditions. Furthermore, this study shows that EELS is an important research tool for the investigation of nanoscale gas-sensors, allowing differentiation of composition and oxidation state at the interior and surface of individual nanostructures in these materials.
Keywords
Spectrographic-analysis; Spectroscopes; Microscopic-analysis; Microscopy; Iron-compounds; Iron-oxides; Nanotechnology
Contact
V. J. Leppert, School of Engineering, University of California, P.O. Box 2039, Merced, CA 95344, USA
CODEN
SABCEB
Publication Date
20050801
Document Type
Journal Article
Email Address
vleppert@ucmerced.edu
Funding Amount
1055222
Funding Type
Cooperative Agreement; Agriculture
Fiscal Year
2005
NTIS Accession No.
NTIS Price
Identifying No.
Cooperative-Agreement-Number-U07-CCU-906162
Issue of Publication
1
ISSN
0925-4005
Source Name
Sensors and Actuators B: Chemical
State
CA
Performing Organization
University of California - Davis
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