Sampling of Sub-micron Particles for Electron Microscopy

• Published in: Nature (London) 1961-01, Vol.189 (4761), p.336-336
• Main Authors: BILLINGS, C. E, MEGAW, W. J, WIFFEN, R. D
• Format: Article
• Language: English
• Subjects: Humanities and Social Sciences; letter; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/189336a0

IN recent work on the attachment of radioactive particles to Aitken nuclei, we have been concerned with the sampling and subsequent examination by electron microscopy of Aitken nuclei in the size-range 0.01–0.1µ diameter. A thermal precipitator was used for sampling, and the nuclei were at first collected on an electron microscope grid covered by a carbon film, instead of on the usual glass coverslip. Doubts arose as to whether the sample was a uniform one or whether there was preferential deposition over the copper bars of the grid by reason of the increased thermal gradient in the neighbourhood of the bars or by sagging of the carbon film between them. This effect has already been reported by Cartwright 1 , who, to obtain uniform samples, used the thermal precipitator with the usual coverslips coated with a ‘Formvar’ film. After collection of the sample the film was scratched into sections of suitable size, floated off the coverslip in distilled water and placed on a grid for subsequent examination by electron microscopy. Cartwright observed preferential deposition on the grid bars of dust particles up to a few microns in diameter by means of an optical microscope, but in the present work the Aitken nuclei were too small for optical microscopy, and nuclei deposited over the grid bars could not be seen with the electron microscope.