Effect of temperature on beam damage of asbestos fibers in the transmission electron microscope (TEM) at 100kV

Our plain-English summary of Effect of temperature on beam damage of asbestos fibers in the transmission electron microscope (TEM) at 100kV, by J. Martin, M. Beauparlant, S. Sauvé, et al (Micron, 2017).

The study

• Authors: J. Martin, M. Beauparlant, S. Sauvé, G. L'Espérance
• Journal: Micron
• Published: 2017;94:26-36
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Damage to asbestos fibers by the transmission electron microscope (TEM) electron beam is a known limitation of this powerful method of analysis. Although it is often considered only in terms of loss of crystallinity, recent studies have shown that the damage may also change the elemental composition of fibers, thus causing significant identification errors. In this study, the main objective was to assess whether temperature is a factor influencing damage to asbestos fibers and, if so, how it can be used to minimize damage. It was found that lowering the temperature to 123K can inhibit, for a given time, the manifestation of the damage. The significant decrease of atom diffusion at low temperature momentarily prevents mass loss, greatly reducing the possibility of misidentification of anthophyllite asbestos fibers. The results obtained in this study strongly suggest that the predominant mechanism damage is probably related to the induced-electric-field model relegating radiolysis to the status of a subsidiary damage mechanism.

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In plain English

This laboratory study tested whether cooling asbestos fibers reduces damage from the electron beam of a transmission electron microscope (TEM). The authors examined anthophyllite asbestos fibers from a UICC standard reference sample from Finland, at 100 kV. They measured damage mainly through the magnesium-to-silicon (Mg/Si) X-ray ratio, used to tell asbestos types apart. Of four temperatures tested, only 123 K consistently slowed damage compared with room temperature (298 K), especially above 100 A/cm2. Results at 173 K and 223 K were much less reproducible, with effects either absent or unpredictable. A fiber area analyzed at 123 K was re-analyzed after several days at room temperature, and much of its magnesium was gone. The authors could not tell whether it left during warming or re-illumination. In the authors' view, cooling held back the loss, not the damage itself. Cooling did not change how fast the crystal pattern faded. The authors concluded that, while samples stay at 123 K, misidentification of anthophyllite fibers from altered X-ray ratios can be avoided. They also concluded that radiolysis is probably not the main damage mechanism under their conditions.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory experiment using transmission electron microscopy, testing the effect of sample temperature on electron-beam damage to asbestos fibers (the journal labels the article a 'Tutorial')
• Who was studied: Individual fibers of anthophyllite asbestos from a UICC standard reference sample from the Paakkila mine, Tuusniemi, Finland. Five fibers were used in the current-density tests and three fibers in each of the dose tests and the diffraction tests.
• Exposure: Electron-beam illumination in a TEM operated at 100 kV, at sample temperatures of 123 K, 173 K, 223 K and 298 K (room temperature). The beam current was roughly constant and the beam diameter was varied to change current density; in other tests, illumination time was varied at a constant current density.
• Main results:
  • Cooling to 123 K reduced the rate of damage (measured by the Mg/Si ratio) compared with 298 K, especially at current densities greater than 100 A/cm2.
  • Results at 173 K and 223 K were much less reproducible, with effects on damage rate either absent or unpredictable.
  • In preliminary tests, the mean Mg/Si ratio of undamaged anthophyllite fiber was about 0.6, plus or minus 0.03.
  • At room temperature (298 K), on three fibers at constant current density, damage began immediately and increased with total dose, and no dose threshold was seen.
  • For one fiber analyzed at 123 K at 39 A/cm2, increasing the total dose did not influence the damage.
  • A fiber area first analyzed at 123 K was re-analyzed at 123 K after the sample had been at room temperature for several days. Its Mg/Si ratio was then much lower. The authors interpreted this as magnesium having left the previously illuminated area. They stated that further tests are needed to tell whether the loss happened during the return to room temperature or very quickly during the second illumination.
  • On three fibers at 30 A/cm2, cooling did not change the average time for complete fading of the diffraction pattern: about 25 s at 123 K and about 23.3 s at 298 K. A significant drop in the Mg/Si ratio took about 135 s at 123 K and about 70 s at 298 K. The 123 K value is the mean of only two fibers, because one of the three fibers showed no significant drop.
  • Profiles across a damaged area showed three changes. The magnesium signal dropped sharply in the damaged area and rose slightly at its edge. The oxygen signal decreased. The silicon signal increased slightly.
• The authors' conclusion: The authors concluded that at 123 K, mass loss does not happen as long as the sample stays at that temperature, so misidentification of anthophyllite asbestos fibers from changed X-ray intensity ratios can be avoided. They noted that cooling reduced only the diffusion caused by the damage, not the damage itself. They also concluded that the rise in silicon suggests an induced-electric-field damage mechanism, so radiolysis is not the predominant mechanism under their conditions.
• Limitations the authors state:
  • Fiber thickness was not measured; it was estimated from the fiber diameter on the image.
  • No damage threshold was identified, so the authors could not say whether temperature affects such a threshold.
  • Further tests are needed to determine when the magnesium loss occurs: during the return to room temperature or during the second illumination.
  • The methods used could not follow the loss of crystal structure precisely, because it happens very rapidly.
  • The idea that oxygen leaves the sample as gas bubbles was not directly supported by evidence in this study.
  • More data are needed to quantify the identification uncertainty caused by beam damage.

Topics

Medical terms in this study, explained in our Lexicon: Anthophyllite.

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