On the threshold conditions for electron beam damage of asbestos amosite fibers in the transmission electron microscope (TEM)

ABSTRACT

Asbestos amosite fibers were investigated to evaluate the damage caused by a transmission electron microscope (TEM) electron beam. Since elemental x-ray intensity ratios obtained by energy dispersive x-ray spectroscopy (EDS) are commonly used for asbestos identification, the impact of beam damage on these ratios was evaluated. It was determined that the magnesium/silicon ratio best represented the damage caused to the fiber. Various tests showed that most fibers have a current density threshold above which the chemical composition of the fiber is modified. The value of this threshold current density varied depending on the fiber, regardless of fiber diameter, and in some cases could not be determined. The existence of a threshold electron dose was also demonstrated. This value was dependent on the current density used and can be increased by providing a recovery period between exposures to the electron beam. This study also established that the electron beam current is directly related to the damage rate above a current density of 165 A/cm². The large number of different results obtained suggest, that in order to ensure that the amosite fibers are not damaged, analysis should be conducted below a current density of 100 A/cm².

KEYWORDS:

• Current density
• damage mechanism
• electron dose

Acknowledgments

The authors wish to thank Jean-Philippe Masse, Philippe Plamondon, both from the Center for Characterization and Microscopy of Materials, the (CM)², Annie Ouellet and Jacques Lesage from the IRSST, and the staff from JEOL for technical support and useful discussion.

Funding

Professor L'Espérance wishes to thank the IRSST for its financial support.